Journal articles: 'Variegation'

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Lloyd, Vett K., David Dyment, Donald A. R. Sinclair, and Thomas A. Grigliatti. "Different patterns of gene silencing in position-effect variegation." Genome 46, no. 6 (December 1, 2003): 1104–17. http://dx.doi.org/10.1139/g03-070.

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Position-effect variegation (PEV) results when a fully functional gene is moved from its normal position to a position near to a broken heterochromatic-euchromatic boundary. In this new position, the gene, while remaining unaltered at the DNA level, is transcriptionally silenced in some cells but active in others, producing a diagnostic mosaic phenotype. Many variegating stocks show phenotypic instability, in that the level of variegation is dramatically different in different isolates or when out crossed. To test if this phenotypic instability was due to segregation of spontaneously accumulated mutations that suppress variegation, four different and well-characterized strains showing PEV for the white+ gene (wm4, wmMc, wm51b, and wmJ) and representing both large and small spot variegators were repeatedly out crossed to a strain free of modifiers, and the phenotypes of these variegators were monitored for 30 generations. Once free of modifiers, these variegating strains were then allowed to reaccumulate modifiers. The spontaneous suppressors of variegation were found to include both dominant and recessive, autosomal and X-linked alleles selected to reduce the detrimental effects of silencing white+ and adjacent genes. The time of peak sensitivity to temperature during development was also determined for these four variegators. Although large and small spot variegators have previously been attributed to early and late silencing events, respectively, the variegators we examined all shared a common early period of peak sensitivity to temperature. Once free of their variegation suppressors, the different variegating strains showed considerable differences in the frequency of inactivation at a cellular level (the number of cells showing silencing of a given gene) and the extent of variegation within the cell (the number of silenced genes). These results suggest that large and small spot variegation may be a superficial consequence of spontaneous variegation suppressors. The nature and number of these spontaneous variegation suppressors depends on the number of genes silenced in a given variegating rearrangement. These results are interpreted in the context of a model that proposes that the different underlying patterns of gene silencing seen in PEV can be attributed directly to the formation of heterochromatin domains possessing different properties of propagation during cell division.Key words: Drosophila melanogaster, position-effect variegation, spontaneous suppressors of variegation.

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Dorer, Douglas R., and Steven Henikoff. "Transgene Repeat Arrays Interact With Distant Heterochromatin and Cause Silencing in cis and trans." Genetics 147, no. 3 (November 1, 1997): 1181–90. http://dx.doi.org/10.1093/genetics/147.3.1181.

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Tandem repeats of Drosophila transgenes can cause heterochromatic variegation for transgene expression in a copy-number and orientation-dependent manner. Here, we demonstrate different ways in which these transgene repeat arrays interact with other sequences at a distance, displaying properties identical to those of a naturally occurring block of interstitial heterochromatin. Arrays consisting of tandemly repeated white transgenes are strongly affected by proximity to constitutive heterochromatin. Moving an array closer to heterochromatin enhanced variegation, and enhancement was reverted by recombination of the array onto a normal sequence chromosome. Rearrangements that lack the array enhanced variegation of white on a homologue bearing the array. Therefore, silencing of white genes within a repeat array depends on its distance from heterochromatin of the same chromosome or of its paired homologue. In addition, white transgene arrays cause variegation of a nearby gene in cis, a hallmark of classical position-effect variegation. Such spreading of heterochromatic silencing correlates with array size. Finally, white transgene arrays cause pairing-dependent silencing of a non-variegating white insertion at the homologous position.

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Talbert, P. B., C. D. LeCiel, and S. Henikoff. "Modification of the Drosophila heterochromatic mutation brownDominant by linkage alterations." Genetics 136, no. 2 (February 1, 1994): 559–71. http://dx.doi.org/10.1093/genetics/136.2.559.

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Abstract The variegating mutation brownDominant (bwD) of Drosophila melanogaster is associated with an insertion of heterochromatin into chromosome arm 2R at 59E, the site of the bw gene. Mutagenesis produced 150 dominant suppressors of bwD variegation. These fall into two classes: unlinked suppressors, which also suppress other variegating mutations; and linked chromosome rearrangements, which suppress only bwD. Some rearrangements are broken at 59E, and so might directly interfere with variegation caused by the heterochromatic insertion at that site. However, most rearrangements are translocations broken proximal to bw within the 52D-57D region of 2R. Translocation breakpoints on the X chromosome are scattered throughout the X euchromatin, while those on chromosome 3 are confined to the tips. This suggests that a special property of the X chromosome suppresses bwD variegation, as does a distal autosomal location. Conversely, two enhancers of bwD are caused by translocations from the same part of 2R to proximal heterochromatin, bringing the bwD heterochromatic insertion close to the chromocenter with which it strongly associates. These results support the notion that heterochromatin formation at a genetic locus depends on its location within the nucleus.

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Locke, J., M. A. Kotarski, and K. D. Tartof. "Dosage-dependent modifiers of position effect variegation in Drosophila and a mass action model that explains their effect." Genetics 120, no. 1 (September 1, 1988): 181–98. http://dx.doi.org/10.1093/genetics/120.1.181.

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Abstract Twelve dominant enhancers of position effect variegation, representing four loci on the second and third chromosomes of Drosophila melanogaster, have been induced by P-element mutagenesis. Instead of simple transposon insertions, seven of these mutations are cytologically visible duplications and three are deficiencies. The duplications define two distinct regions, each coinciding with a locus that also behaves as a dominant haplo-dependent suppressor of variegation. Conversely, two of the deficiencies overlap with a region that contains a haplo-dependent enhancer of variegation while duplications of this same region act to suppress variegation. The third deficiency defines another haplo-dependent enhancer. These data indicate that loci capable of modifying variegation do so in an antipodal fashion through changes in the wild-type gene copy number and may be divided into two reciprocally acting classes. Class I modifiers enhance variegation when duplicated or suppress variegation when deficient. Class II modifiers enhance when deficient but suppress when duplicated. From our data, and those of others, we propose that in Drosophila there are about 20 to 30 dominant loci that modify variegation. Most appear to be of the class I type whereas only two class II modifiers have been identified so far. From these observations we put forth a model, based on the law of mass action, for understanding how such suppressor-enhancer loci function. We propose that each class I modifier codes for a structural protein component of heterochromatin and their effects on variegation are a consequence of their dosage dependent influence on the extent of the assembly of heterochromatin at the chromosomal site of the position effect. It is further proposed that class II modifiers may inhibit the class I products directly, bind to hypothetical termination sites that define heterochromatin boundaries or promote euchromatin formation. Consistent with our mass action model we find that combining two enhancers together produce additive and not epistatic effects. Also, since different enhancers have different relative strengths on different variegating mutants, we suggest that heterochromatic domains are constructed by a combinatorial association of proteins. The mass action model proposed here is of general significance for any assembly driven reaction and has implications for understanding a wide variety of biological phenomena.(ABSTRACT TRUNCATED AT 400 WORDS)

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Eissenberg, J. C., G. D. Morris, G. Reuter, and T. Hartnett. "The heterochromatin-associated protein HP-1 is an essential protein in Drosophila with dosage-dependent effects on position-effect variegation." Genetics 131, no. 2 (June 1, 1992): 345–52. http://dx.doi.org/10.1093/genetics/131.2.345.

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Abstract Chromosome rearrangements which place euchromatic genes adjacent to a heterochromatic breakpoint frequently result in gene repression (position-effect variegation). This repression is thought to reflect the spreading of a heterochromatic structure into neighboring euchromatin. Two allelic dominant suppressors of position-effect variegation were found to contain mutations within the gene encoding the heterochromatin-specific chromosomal protein HP-1. The site of mutation for each allele is given: one converts Lys169 into a nonsense (ochre) codon, while the other is a frameshift after Ser10. In flies heterozygous for one of the mutant alleles (Su(var)2-504), a truncated HP-1 protein was detectable by Western blot analysis. An HP-1 minigene, consisting of HP-1 cDNA under the control of an Hsp70 heat-inducible promoter, was transduced into flies by P element-mediated germ line transformation. Heat-shock driven expression of this minigene results in elevated HP-1 protein level and enhancement of position-effect variegation. Levels of variegating gene expression thus appear to depend upon the level of expression of a heterochromatin-specific protein. The implications of these observations for mechanism of heterochromatic position effects and heterochromatin function are discussed.

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Lloyd, Vett K., Donald A. Sinclair, and Thomas A. Grigliatti. "Competition Between Different Variegating Rearrangements for Limited Heterochromatic Factors in Drosophila melanogaster." Genetics 145, no. 4 (April 1, 1997): 945–59. http://dx.doi.org/10.1093/genetics/145.4.945.

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Position effect variegation (PEV) results from the juxtaposition of a euchromatic gene to heterochromatin. In its new position the gene is inactivated in some cells and not in others. This mosaic expression is consistent with variability in the spread of heterochromatin from cell to cell. As many components of heterochromatin are likely to be produced in limited amounts, the spread of heterochromatin into a normally euchromatic region should be accompanied by a concomitant loss or redistribution of the protein components from other heterochromatic regions. We have shown that this is the case by simultaneously monitoring variegation of a euchromatic and a heterochromatic gene associated with a single chromosome rearrangement. Secondly, if several heterochromatic regions of the genome share limited components of heterochromatin, then some variegating rearrangements should compete for these components. We have examined this hypothesis by testing flies with combinations of two or more different variegating rearrangements. Of the nine combinations of pairs of variegating rearrangements we studied, seven showed nonreciprocal interactions. These results imply that many components of heterochromatin are both shared and present in limited amounts and that they can transfer between chromosomal sites. Consequently, even nonvariegation portions of the genome will be disrupted by re-allocation of heterochromatic proteins associated with PEV. These results have implications for models of PEV.

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Michailidis, John, Neil D. Murray, and Jennifer A. Marshall Graves. "A correlation between development time and variegated position effect in Drosophila melanogaster." Genetical Research 52, no. 2 (October 1988): 119–23. http://dx.doi.org/10.1017/s0016672300027488.

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SummaryPosition-effect variegation is a phenomenon in which cell-autonomous genes, normally expressed in all cells of a tissue, are expressed in some cells but not in others, leading to a mosaic tissue. Variegation occurs when a normally euchromatic gene is re-positioned close to heterochromatin by chromosome rearrangement. The extent of variegation is known to be influenced by a number of environmental and genetic factors. In the courss of investigations of the influence of the pH of larval medium on the extent of eye-colour variegation in In(1)ωm4 Drosophila melanogaster, we have found that the extent of variegation depends on development time. Flies reared at pH 2·6 develop slowly and show more extreme variegation than those reared at higher pH. This effect, as well as variations within the pH treatments, can be accounted for by differences in development time. The observed regression relationship between variegation and development time also appears to accommodate the influences of temperature on both variables. We suggest that development time may account causally for the reported influences of a number of environmental agents (temperature, crowding, chemicals) on variegation. Ways in which this might occur are discussed in the context of models of the molecular basis of differential gene activity.

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Hearn, M. G., A. Hedrick, T. A. Grigliatti, and B. T. Wakimoto. "The effect of modifiers of position-effect variegation on the variegation of heterochromatic genes of Drosophila melanogaster." Genetics 128, no. 4 (August 1, 1991): 785–97. http://dx.doi.org/10.1093/genetics/128.4.785.

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Abstract Dominant modifiers of position-effect variegation of Drosophila melanogaster were tested for their effects on the variegation of genes normally located in heterochromatin. These modifiers were previously isolated as strong suppressors of the variegation of euchromatic genes and have been postulated to encode structural components of heterochromatin or other products that influence chromosome condensation. While eight of the modifiers had weak or no detectable effects, six acted as enhancers of light (lt) variegation. The two modifiers with the strongest effects on lt were shown to also enhance the variegation of neighboring heterochromatic genes. These results suggest that the wild-type gene products of some modifiers of position-effect variegation are required for proper expression of genes normally located within or near the heterochromatin of chromosome 2. We conclude that these heterochromatic genes have fundamentally different regulatory requirements compared to those typical of euchromatic genes.

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9

Marcotrigiano, Michael, and Grant Hackett. "Quantifying Leaf Variegation." HortScience 28, no. 4 (April 1993): 344. http://dx.doi.org/10.21273/hortsci.28.4.344.

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Rodermel, Steven. "Arabidopsis Variegation Mutants." Arabidopsis Book 1 (January 2002): e0079. http://dx.doi.org/10.1199/tab.0079.

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Qi, Yafei, Xiaomin Wang, Pei Lei, Huimin Li, Liru Yan, Jun Zhao, Jingjing Meng, et al. "The chloroplast metalloproteases VAR2 and EGY1 act synergistically to regulate chloroplast development in Arabidopsis." Journal of Biological Chemistry 295, no. 4 (December 13, 2019): 1036–46. http://dx.doi.org/10.1074/jbc.ra119.011853.

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Chloroplast development and photosynthesis require the proper assembly and turnover of photosynthetic protein complexes. Chloroplasts harbor a repertoire of proteases to facilitate proteostasis and development. We have previously used an Arabidopsis leaf variegation mutant, yellow variegated2 (var2), defective in thylakoid FtsH protease complexes, as a tool to dissect the genetic regulation of chloroplast development. Here, we report a new genetic enhancer mutant of var2, enhancer of variegation3–1 (evr3–1). We confirm that EVR3 encodes a chloroplast metalloprotease, reported previously as ethylene-dependent gravitropism-deficient and yellow-green1 (EGY1)/ammonium overly sensitive1 (AMOS1). We observed that mutations in EVR3/EGY1/AMOS1 cause more severe leaf variegation in var2–5 and synthetic lethality in var2–4. Using a modified blue-native PAGE system, we reveal abnormal accumulations of photosystem I, photosystem II, and light-harvesting antenna complexes in EVR3/EGY1/AMOS1 mutants. Moreover, we discover distinct roles of VAR2 and EVR3/EGY1/AMOS1 in the turnover of photosystem II reaction center under high light stress. In summary, our findings indicate that two chloroplast metalloproteases, VAR2/AtFtsH2 and EVR3/EGY1/AMOS1, function coordinately to regulate chloroplast development and reveal new roles of EVR3/EGY1/AMOS1 in regulating chloroplast proteostasis in Arabidopsis.

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Marcotrigiano, Michael, Thomas H. Boyle, Pamela A. Morgan, and Karen L. Ambach. "Leaf Color Variants from Coleus Shoot Cultures." Journal of the American Society for Horticultural Science 115, no. 4 (July 1990): 681–86. http://dx.doi.org/10.21273/jashs.115.4.681.

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Nuclear-controlled leaf variegation was studied among Coleus × hybridus Voss (formerly C. blumei Benth.) cultivars propagated by seed and as shoot cultures on Murashige and Skoog (MS) medium + 1 to 3 mg BA/liter. Cultivars tested possessed pattern chlorophyll variegation and either pattern or nonpattern anthocyanin variegation. The gene controlling an albino midrib region appears to be fairly stable, with only 2% of the micropropagated plantlets having a solid-green leaf characteristic, a characteristic that was always inherited following selfing. Pattern anthocyanin variegation (PAV) was fairly stable, while nonpattern anthocyanin variegation (NAV) was very unstable. In addition, variants from pattern-variegated phenotypes produced offspring identical to their parent following selfing. In contrast, variants of nonpattern cultivars, when selfed, yielded offspring identical to the original cultivar, identical to the variant, or novel phenotypes. When variants were returned to culture, those derived from cultivars with PAV were more stable than those derived from nonpattern cultivars. In Coleus, micropropagation may induce epigenetic and/or heritable changes in leaf variegation. Cultivars with NAV are less stable than cultivars with PAV. Chemical names used; N-(phenylmethyl)-lH-purine-6-amine [benzyladenine (BA)].

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Zhang, Qiang, Jing Huang, Peng Zhou, Mingzhuo Hao, and Min Zhang. "Cytological and Transcriptomic Analysis Provide Insights into the Formation of Variegated Leaves in Ilex × altaclerensis ‘Belgica Aurea’." Plants 10, no. 3 (March 15, 2021): 552. http://dx.doi.org/10.3390/plants10030552.

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Ilex × altaclerensis ‘Belgica Aurea’ is an attractive ornamental plant bearing yellow-green variegated leaves. However, the mechanisms underlying the formation of leaf variegation in this species are still unclear. Here, the juvenile yellow leaves and mature variegated leaves of I. altaclerensis ‘Belgica Aurea’ were compared in terms of leaf structure, pigment content and transcriptomics. The results showed that no obvious differences in histology were noticed between yellow and variegated leaves, however, ruptured thylakoid membranes and altered ultrastructure of chloroplasts were found in yellow leaves (yellow) and yellow sectors of the variegated leaves (variegation). Moreover, the yellow leaves and the yellow sectors of variegated leaves had significantly lower chlorophyll compared to green sectors of the variegated leaves (green). In addition, transcriptomic sequencing identified 1675 differentially expressed genes (DEGs) among the three pairwise comparisons (yellow vs. green, variegation vs. green, yellow vs. variegation). Expression of magnesium-protoporphyrin IX monomethyl ester (MgPME) [oxidative] cyclase, monogalactosyldiacylglycerol (MGDG) synthase and digalactosyldiacylglycerol (DGDG) synthase were decreased in the yellow leaves. Altogether, chlorophyll deficiency might be the main factors driving the formation of leaf variegation in I.altaclerensis ‘Belgica Aurea’.

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Campitelli, Brandon E., Ivana Stehlik, and John R. Stinchcombe. "Leaf variegation is associated with reduced herbivore damage in Hydrophyllum virginianum." Botany 86, no. 3 (March 2008): 306–13. http://dx.doi.org/10.1139/b07-139.

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Leaf variegation refers to local regions of the upper surface of a leaf having reduced or obstructed chlorophyll, which results in whitish spots. These lighter spots may compromise the photosynthetic efficiency of a leaf, and many competing hypotheses have been put forward to explain why this patterning may be adaptive. It has been suggested that variegation is either an adaptive response to environmental conditions or a defence mechanism against herbivore damage. To test whether leaf variegation reduces herbivore damage, we first assessed the frequency of variegated and nonvariegated leaves in natural populations of the plant Hydrophyllum virginianum L., and second, measured herbivore damage to both variegated and nonvariegated leaves. We found that variegated leaves were present at high frequencies within natural populations (6%–31%) and that nonvariegated leaves sustained nearly twice the amount of damage by comparison with variegated leaves. Therefore, leaf variegation appears to be beneficial by reducing herbivore damage to leaves. These data are consistent with the fundamental prediction of the herbivory hypothesis for the benefits of leaf variegation.

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Bishop, C. P. "Evidence for intrinsic differences in the formation of chromatin domains in Drosophila melanogaster." Genetics 132, no. 4 (December 1, 1992): 1063–69. http://dx.doi.org/10.1093/genetics/132.4.1063.

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Abstract The results of an investigation into intrinsic differences in the formation of two different heterochromatic domains are presented. The study utilized two different position effect variegation mutants in Drosophila melanogaster for investigating the process of compacting different stretches of DNA into heterochromatin. Each stretch of DNA encodes for a gene that affects different aspects of bristle morphology. The expression of each gene is prevented when it is compacted into heterochromatin thus the genes serve as effective reporter systems to monitor the spread of heterochromatin. Both variegating mutants are scored in the same cell such that environmental and genetic background differences are unambiguously eliminated. Any differences observed in the repression of the two genes must therefore be the result of intrinsic differences in the heterochromatic compaction process for the two stretches of DNA. Studies of the effects different enhancers of variegation have upon the compaction of the two genes indicate each compaction event occurs independently of the other, and that different components are involved in the two processes. These results are discussed with regard to spreading heterochromatin and the role this process may play in regulating gene expression.

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Zhang, Zhilu, Zhonghua Liu, Haina Song, Minghui Chen, and Shiping Cheng. "Protective Role of Leaf Variegation in Pittosporum tobira under Low Temperature: Insights into the Physio-Biochemical and Molecular Mechanisms." International Journal of Molecular Sciences 20, no. 19 (September 30, 2019): 4857. http://dx.doi.org/10.3390/ijms20194857.

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Leaf variegation has been demonstrated to have adaptive functions such as cold tolerance. Pittosporum tobira is an ornamental plant with natural leaf variegated cultivars grown in temperate regions. Herein, we investigated the role of leaf variegation in low temperature responses by comparing variegated “Variegatum” and non-variegated “Green Pittosporum” cultivars. We found that leaf variegation is associated with impaired chloroplast development in the yellow sector, reduced chlorophyll content, strong accumulation of carotenoids and high levels of ROS. However, the photosynthetic efficiency was not obviously impaired in the variegated leaves. Also, leaf variegation plays low temperature protective function since “Variegatum” displayed strong and efficient ROS-scavenging enzymatic systems to buffer cold (10 °C)-induced damages. Transcriptome analysis under cold conditions revealed 309 differentially expressed genes between both cultivars. Distinctly, the strong cold response observed in “Variegatum” was essentially attributed to the up-regulation of HSP70/90 genes involved in cellular homeostasis; up-regulation of POD genes responsible for cell detoxification and up-regulation of FAD2 genes and subsequent down-regulation of GDSL genes leading to high accumulation of polyunsaturated fatty acids for cell membrane fluidity. Overall, our results indicated that leaf variegation is associated with changes in physiological, biochemical and molecular components playing low temperature protective function in P. tobira.

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Ramírez, Angel, Eric Milot, Immaculada Ponsa, Camelia Marcos-Gutiérrez, Angustias Page, Mirentxu Santos, José Jorcano, and Miguel Vidal. "Sequence and Chromosomal Context Effects on Variegated Expression of Keratin 5/lacZ Constructs in Stratified Epithelia of Transgenic Mice." Genetics 158, no. 1 (May 1, 2001): 341–50. http://dx.doi.org/10.1093/genetics/158.1.341.

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Abstract The expression of transgene loci in mammals often occurs in a heterocellular fashion resulting in variegated patterns of expression. We have examined the effect of chromosomal integration site, copy number, and transcriptionally activating sequences on the variegation of a keratin 5-lacZ (K5Z) construct in the stratified epithelia of transgenic mice. lacZ expression in these mice is always mosaic, and the β-gal activity per cell is usually higher in the lines with a higher proportion of expressing cells. Similar constructs, in which cDNAs were exchanged by lacZ sequences, showed no variegation. Also, when a strongly active, nonvariegating construct was coinjected with K5Z, most transgenic lines showed an almost homogeneous lacZ expression. The comparison of transgene arrays of different copies inserted at the same locus (obtained by using a lox/Cre system) showed that the reduction of copy number does not lead to an increase in the proportion of cells that express the transgene. Finally, in most of the variegating or nonexpressing lines the transgenes were located both at intermediate positions and at peritelomeric regions in the long chromosome arms. These findings suggest that the probability and efficiency of expression of K5Z genes depend on both long range chromosomal influences and on sequences in the transgene array.

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McCracken, Allen, and John Locke. "Mutations in ash1 and trx enhance P-element-dependent silencing in Drosophila melanogaster." Genome 59, no. 8 (August 2016): 527–40. http://dx.doi.org/10.1139/gen-2014-0127.

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In Drosophila melanogaster, the mini-w+ transgene in Pci is normally expressed throughout the adult eye; however, when other P or KP elements are present, a variegated-eye phenotype results, indicating random w+ silencing during development called P-element-dependent silencing (PDS). Mutant Su(var)205 and Su(var)3-7 alleles act as haplo-suppressors/triplo-enhancers of this variegated phenotype, indicating that these heterochromatic modifiers act dose dependently in PDS. Previously, we recovered a spontaneous mutation of P{lacW}ciDplac called P{lacW}ciDplacE1 (E1) that variegated in the absence of P elements, presumably due to the insertion of an adjacent gypsy element. From a screen for genetic modifiers of E1 variegation, we describe here the isolation of five mutations in ash1 and three in trx that enhance the E1 variegated phenotype in a dose-dependent and cumulative manner. These mutant alleles enhance PDS at E1, and in E1/P{lacW}ciDplac, but suppress position effect variegation (PEV) at In(1)wm4. This opposite action is consistent with a model where ASH1 and TRX mark transcriptionally active chromatin domains. If ASH1 or TRX function is lost or reduced, heterochromatin can spread into these domains creating a sink that diverts heterochromatic proteins from other variegating locations, which then may express a suppressed phenotype.

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Balasov, M. L. "Genetic factors controlling white gene expression of the transposon AR4-24 at a telomere in Drosophila melanogaster." Genome 45, no. 6 (December 1, 2002): 1025–34. http://dx.doi.org/10.1139/g02-074.

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The position effect of the AR 4-24 P[white, rosy] transposon was studied at cytological position 60F. Three copies of the transposon (within ~50-kb region) resulted in a spatially restricted pattern of white variegation. This pattern was modified by temperature and by removal of the Y chromosome, suggesting that it was due to classical heterochromatin-induced position effect variegation (PEV). In contrast with classical PEV, extra dose of the heterochromatin protein 1 (HP1) suppressed white variegation and one dose enhanced it. The effect of Pc-G, trx-G, and other PEV suppressors was also tested. It was found that E(Pc)1, TrlR85, and mutations of Su(z)2C relieve AR 4-24- silencing and z1 enhances it. To explain the results obtained with these modifiers, it is proposed that PEV and telomeric position effect can counteract each other at this particular cytological site.Key words: position effect variegation, heterochromatin protein 1, Drosophila melanogaster.

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Hudson, J. J., R. G. Nelson, and B. K. Behe. "CONSUMER PREFERENCES FOR GERANIUM FLOWER COLOR AND LEAF VARIEGATION." HortScience 30, no. 3 (June 1995): 440a—440. http://dx.doi.org/10.21273/hortsci.30.3.440a.

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Some consumer preference studies show that red is the most popular flower color. Most data analyses were univariate. Conjoint analysis allows simultaneous determination of attribute preferences without all alternatives being shown. Our purpose was to determine consumer preferences for geranium flower color, leaf variegation, and price simultaneously using conjoint analysis. Two-hundred and four consumers shopping at two Montgomery, Ala., garden centers in Apr. 1993 rated 25 composite geranium photographs. A lavender geranium, `Danielle', with green and white leaf variegation priced at $1.39 was most preferred. Flower color was most important in the purchase decision, followed by price. Leaf variegation was a minor consideration in the purchase decision.

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Li, Qiansheng, Jianjun Chen, Dennis B. McConnell, and Richard J. Henny. "A Simple and Effective Method for Quantifying Leaf Variegation." HortTechnology 17, no. 3 (January 2007): 285–88. http://dx.doi.org/10.21273/horttech.17.3.285.

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A simple and effective method for quantification of leaf variegation was developed. Using a digital camera or a scanner, the image of a variegated leaf was imported into a computer and saved to a file. Total pixels of the entire leaf area and total pixels of each color within the leaf were determined using an Adobe Photoshop graphics editor. Thus, the percentage of each color's total pixel count in relation to the total pixel count of the entire leaf was obtained. Total leaf area was measured through a leaf area meter; the exact area of this color was calculated in reference to the pixel percentage obtained from Photoshop. Using this method, variegated leaves of ‘Mary Ann’ aglaonema (Aglaonema x), ‘Ornate’ calathea (Calathea ornate), ‘Yellow Petra’ codiaeum (Codiaeum variegatum), ‘Florida Beauty’ dracaena (Dracaena surculosa), ‘Camille’ dieffenbachia (Dieffenbachia maculata), and ‘Triostar’ stromanthe (Stromanthe sanguinea) were quantified. After a brief training period, this method was used by five randomly selected individuals to quantify the variegation of the same set of leaves. The results were highly reproducible no matter who performed the quantification. This method, which the authors have chosen to call the quantification of leaf variegation (QLV) method, can be used for monitoring changes in colors and variegation patterns incited by abiotic and biotic stresses as well as quantifying differences in variegation patterns of plants developed in breeding programs.

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Tartof, Kenneth D., and Marilyn Bremer. "Mechanisms for the construction and developmental control of heterochromatin formation and imprinted chromosome domains." Development 108, Supplement (April 1, 1990): 35–45. http://dx.doi.org/10.1242/dev.108.supplement.35.

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The study of variegating position effects in Drosophila provides a model system to explore the mechanism and material basis for the construction and developmental control of heterochromatin domains and the imprinted genomic structures that they may create. The results of our experiments in this regard have implications for a diverse assortment of long-range chromosome phenomena related to gene and chromosome inactivation. Specifically, as a consequence of our studies on position effect variegation, we propose a simple mechanism of X-chromosome inactivation, suggest a purpose for genomic imprinting, and postulate a general means for regulating the time in development at which certain genes become heterochromatically repressed.

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Eberl, Daniel F., Lori J. Lorenz, Michael B. Melnick, Vanita Sood, Paul Lasko, and Norbert Perrimon. "A New Enhancer of Position-Effect Variegation in Drosophila melanogaster Encodes a Putative RNA Helicase That Binds Chromosomes and Is Regulated by the Cell Cycle." Genetics 146, no. 3 (July 1, 1997): 951–63. http://dx.doi.org/10.1093/genetics/146.3.951.

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In Drosophila melanogaster, position-effect variegation of the white gene has been a useful phenomenon by which to study chromosome structure and the genes that modify it. We have identified a new enhancer of variegation locus, Dmrnahel (hel). Deletion or mutation of hel enhances white variegation, and this can be reversed by a transformed copy of her +. In the presence of two endogenous copies, the transformed her + behaves as a suppressor of variegation. hel is an essential gene and functions both maternally and zygotically. The HEL protein is similar to known RNA helicases, but contains an unusual variant (DECD) of the DEAD motif common to these proteins. Potential HEL homologues have been found in mammals, yeast and worms. HEL protein associates with salivary gland chromosomes and locates to nuclei of embryos and ovaries, but disappears in mitotic domains of embryos as chromosomes condense. We propose that the HEL protein promotes an open chromatin structure that favors transcription during development by regulating the spread of heterochromatin, and that HEL is regulated by, and may have a role in, the mitotic cell cycle during embryogenesis.

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Pennisi, Svoboda V., and Dennis McConnell. "The Use of a Variegated Plant to Determine Adaptations to Altered Light Levels." HortScience 32, no. 4 (July 1997): 594B—594. http://dx.doi.org/10.21273/hortsci.32.4.594b.

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Variegated Dracaena sanderana plants were grown under 47%, 63%, 80%, and 91% shade cloth. Prior to that, plants were grown under uniform light levels in a greenhouse. Morphological changes which manifested the adaptation to different light levels were not evident until all four leaves present in the apical whorl had expanded. Changes first appeared in a leaf which was 5-15 mm long when plants were placed under the different shade levels. The changes were recognized as alteration in the amount of leaf variegation which gradually changed as new leaves unfolded. After development of four leaves no further morphological changes were apparent. The first `transition' leaf had variegation similar to the preceding leaf and the last `transition' leaf had variegation comparable to the next successive leaf. The amount of variegation was quantified and the changes under different light levels determined. The use of a variegated plant enabled us to readily observe the morphological changes related to light adaptation and showed that a plant is an integrated system which adapts to altered environment over an extended period of time.

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25

Bingham, E. T., and W. M. Clement. "Alfalfa transposable elements and variegation." Developmental Genetics 10, no. 6 (1989): 552–60. http://dx.doi.org/10.1002/dvg.1020100614.

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26

Tartof, Kenneth D. "Position effect variegation in yeast." BioEssays 16, no. 10 (October 1994): 713–14. http://dx.doi.org/10.1002/bies.950161004.

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27

Abadie, Cyril, Marlène Lamothe, Caroline Mauve, Françoise Gilard, and Guillaume Tcherkez. "Leaf green-white variegation is advantageous under N deprivation in Pelargonium×hortorum." Functional Plant Biology 42, no. 6 (2015): 543. http://dx.doi.org/10.1071/fp14250.

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Variegation (patchy surface area with different colours) is a common trait of plant leaves. In green-white variegated leaves, two tissues with contrasted primary carbon metabolisms (autotrophic in green and heterotrophic in white tissues) are juxtaposed. It is generally believed that variegation is detrimental to growth due to the lower photosynthetic surface area. However, the common occurrence of leaf variegation in nature raises the question of a possible advantage under certain circumstances. Here, we examined growth and metabolism of variegated Pelargonium × hortorum L.H.Bailey using metabolomics techniques under N deprivation. Our results showed that variegated plants tolerate N deficiency much better, i.e. do not stop leaf biomass production after 9 weeks of N deprivation, even though the growth of green plants is eventually arrested and leaf senescence is triggered. Metabolic analysis indicates that white areas are naturally enriched in arginine, which decreases a lot upon N deprivation, probably to feed green areas. This process may compensate for the lower proteolysis enhancement in green areas and thus contribute to maintaining photosynthetic activity. We conclude that under our experimental conditions, leaf variegation was advantageous under prolonged N deprivation.

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28

Martin-Morris, Linda E., Amy K. Csink, Douglas R. Darer, Paul B. Talbert, and Steven Henikoff. "Heterochromatic trans-Inactivation of Drosophila white Transgenes." Genetics 147, no. 2 (October 1, 1997): 671–77. http://dx.doi.org/10.1093/genetics/147.2.671.

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Position effect variegation of most Drosophila melanogaster genes, including the white eye pigment gene, is recessive. We find that this is not always the case for white transgenes. Three examples are described in which a lesion causing variegation is capable of silencing the white transgene on the paired homologue (trans-inactivation). These examples include two different transgene constructs inserted at three distinct genomic locations. The lesions that cause variegation of white minimally disrupt the linear order of genes on the chromosomes, permitting close homologous pairing. At one of these sites, trans-inactivation has also been extended to include a vital gene in the vicinity of the white transgene insertion. These findings suggest that many Drosophila genes, in many positions in the genome, can sense the heterochromatic state of a paired homologue.

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29

Morcillo, Patrick, and Ross J. MacIntyre. "Genetic and molecular characterization of a variegating hsp70-lacZ fusion gene in the euchromatic 31B region of Drosophila melanogaster." Genome 44, no. 4 (August 1, 2001): 698–707. http://dx.doi.org/10.1139/g01-038.

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A hsp70lacZ fusion gene introduced into Drosophila melanogaster at the euchromatic 31B region by P-element transformation displayed a variegated expression with respect to the lacZ fusion protein in the salivary gland cells under heat-shock conditions. The variegation is also reflected by the chromosome puffing pattern. Subsequent transposition of the 31B P element to other euchromatic positions restored wild-type activity, that is, a nonvariegated phenotype. A lower developmental temperature reduced the amount of expression under heat-shock conditions, similar to genes undergoing position-effect variegation (PEV). However, other modifiers of PEV did not affect the expression pattern of the gene. These results show a novel euchromatic tissue-specific variegation that is not associated with classical heterochromatic PEV.Key words: Drosophila, euchromatic position effect, heat shock construct.

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30

Kim, Jongyun, Seung Won Kang, Chun Ho Pak, and Mi Seon Kim. "Changes in Leaf Variegation and Coloration of English Ivy and Polka Dot Plant under Various Indoor Light Intensities." HortTechnology 22, no. 1 (February 2012): 49–55. http://dx.doi.org/10.21273/horttech.22.1.49.

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Variegated foliage plants are often used in interiorscaping in low light environments. The changes in leaf morphology and coloration of two variegated foliage plants, english ivy (Hedera helix ‘Golden Ingot’) and polka dot plant (Hypoestes phyllostachya), under various light intensities [photosynthetic photon flux (PPF) at 2.7, 6.75, 13.5, 67.5, and 135 μmol·m−2·s−1] were investigated to elucidate their optimum indoor light environment. Digital image analysis was used to quantify the changes in variegation area and color in CIELAB color space. The changes in leaf morphology (thickness, length:width) and coloration were different between the two species. In general, growth of both species increased with increasing PPF. English ivy showed no significant changes in leaf variegation under different PPF. Under low PPF (≤13.5 μmol·m−2·s−1), newly developed leaves of polka dot plant had reduced leaf variegation (44%, 72%, and 85% variegation loss under 13.5, 6.75, and 2.7 μmol·m−2·s−1, respectively). Anthocyanin content in leaves of polka dot plant also decreased with decreasing PPF, which reduced plants’ aesthetic quality. English ivy leaves under high PPF (≥67.5 μmol·m−2·s−1) displayed high brightness (L*) and yellowish green color (hue angle < 108°), which diminished its aesthetic value. Smaller leaf size and narrower shape of polka dot plant leaves under high PPF (≥67.5 μmol·m−2·s−1) also diminished its aesthetic value. Overall, english ivy performed well in a PPF range from 2.7 to 13.5 μmol·m−2·s−1, and polka dot plant required a PPF of at least 13.5 μmol·m−2·s−1 to maintain its red-purple variegation in the indoor environment.

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Provvidenti, R. "Inheritance of a Partial Chlorophyll Deficiency in Watermelon Activated by Low Temperatures at the Seedling Stage." HortScience 29, no. 9 (September 1994): 1062–63. http://dx.doi.org/10.21273/hortsci.29.9.1062.

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Seedlings of watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] are commonly affected by a partial chlorophyll deficiency that is activated by low temperatures (<20C), causing foliar symptoms and growth retardation. Cotyledons appear whitish-green, whereas the first leaves display a mosaic-like variegation consisting of scattered white flecks and patches. While this disorder is common in commercial watermelon cultivars, some land races from Zimbabwe appeared to be unaffected. From cross and backcross populations of the cold-sensitive cultivar New Hampshire Midget with the cold-resistant line PP261-1 (from PI 482261), the leaf variegation was determined to be conferred by a single recessive gene. The symbol slv (seedling leaf variegation) is assigned to this factor. The dominant allele at this same locus can be exploited for the development of new “cold-resistant” cultivars and F1 hybrids, thus providing economic gain due to earlier planting.

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32

Chakrabarti, Dalia, Somnath Mukhopadhyay, and Ashish K. Duttagupta. "A novel genetic interaction between daughterless and a variegating rearrangement strain of Drosophila melanogaster." Genome 38, no. 1 (February 1, 1995): 105–11. http://dx.doi.org/10.1139/g95-013.

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The effect of the maternal-effect mutation daughterless (da) on the reinverted In(1)BM2 strain of Drosophila melanogaster has been evaluated cytogenetically. Results show that while the variegated nature of the single X chromosome of In(1)BM2(rv) males born to ♂ da/da × ♀ +/+ parents is suppressed, their female sibs, homozygous for the In(1)BM2(rv) chromosome, survive the lethal effect of the absence of da+ product in their zygotes.Key words: Drosophila, variegation, modifier of variegation, position effect.

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33

Behe, Bridget, Robert Nelson, Susan Barton, Charles Hall, Charles D. Safley, and Steven Turner. "Consumer Preferences for Geranium Flower Color, Leaf Variegation, and Price." HortScience 34, no. 4 (July 1999): 740–42. http://dx.doi.org/10.21273/hortsci.34.4.740.

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Researchers often investigate consumer preferences by examining variables consecutively, rather than simultaneously. Conjoint analysis facilitates simultaneous investigation of multiple variables. Cluster analysis facilitates development of actionable market segments. Our objective was to identify relative importance and consumer preferences for flower color, leaf variegation, and price of geraniums (Pelargonium ×hortorum L.H. Bail.) and to identify several actionable market segments. We also evaluated the desirability of a hypothetical blue geranium. Photographic images were digitized and manipulated to produce plants similar in flower area, but varying in flower color (red, lavender, pink, white, and blue), leaf variegation (plain green, dark green zone, and white zone), and price ($1.39 to $2.79). Conjoint analysis revealed that flower color was the primary consideration in the purchase decision, followed by leaf variegation and price. A cluster analysis that excluded blue geraniums yielded four actionable consumer segments. When preferences for the blue geranium were included, six consumer segments were identified.

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34

Dorn, R., V. Krauss, G. Reuter, and H. Saumweber. "The enhancer of position-effect variegation of Drosophila, E(var)3-93D, codes for a chromatin protein containing a conserved domain common to several transcriptional regulators." Proceedings of the National Academy of Sciences 90, no. 23 (December 1, 1993): 11376–80. http://dx.doi.org/10.1073/pnas.90.23.11376.

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In Drosophila modifying mutations of position-effect variegation have been successfully used to genetically dissect chromatin components. The enhancer of position-effect variegation E(var)3-93D [formerly E-var(3)3] encodes proteins containing a domain common to the transcriptional regulators tramtrack and the products of the Broad complex. It interacts with a number of chromatin genes that suppress position-effect variegation. Mutations in E(var)3-93D exhibit an imprinting-like effect on the Y chromosome. This effect is transmitted paternally over several generations. Homeotic transformations in E(var)3-93D mutants indicate an involvement of the gene products in regulation of homeotic gene complexes. An antiserum raised against E(var)3-93D protein detects this chromosomal protein in a large subset of sites in polytene chromosomes. Our genetic and molecular data suggest that the proteins of E(var)3-93D are generally involved in establishing and/or maintaining an open chromatin conformation.

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35

Terada, K., H. Katayama, and C. Uematsu. "Plant virus causing variegation in camellia." Acta Horticulturae, no. 1331 (December 2021): 319–24. http://dx.doi.org/10.17660/actahortic.2021.1331.42.

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36

Marcotrigiano, Michael. "Chimeras and Variegation: Patterns of Deceit." HortScience 32, no. 5 (August 1997): 773–84. http://dx.doi.org/10.21273/hortsci.32.5.773.

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37

McINTYRE, S., and G. W. BARRETT. "Habitat Variegation, An Alternative to Fragmentation." Conservation Biology 6, no. 1 (March 1992): 146–47. http://dx.doi.org/10.1046/j.1523-1739.1992.610146.x.

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38

Lebowltz, Robert J., and Reiner H. Kloth. "Genetics of foliar variegation in coleus." Journal of Heredity 77, no. 2 (March 1986): 125–26. http://dx.doi.org/10.1093/oxfordjournals.jhered.a110184.

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39

Spradling, A. C. "Position Effect Variegation and Genomic Instability." Cold Spring Harbor Symposia on Quantitative Biology 58 (January 1, 1993): 585–96. http://dx.doi.org/10.1101/sqb.1993.058.01.065.

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40

Henikoff, Steven. "Position-effect variegation after 60 years." Trends in Genetics 6 (1990): 422–26. http://dx.doi.org/10.1016/0168-9525(90)90304-o.

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41

Reute, Gunter, and Pierre Spierer. "Position effect variegation and chromatin proteins." BioEssays 14, no. 9 (September 1992): 605–12. http://dx.doi.org/10.1002/bies.950140907.

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42

Kristensen, L. Kahl. "Consequences of surface variegation of asteroids." Planetary and Space Science 42, no. 4 (April 1994): 315–21. http://dx.doi.org/10.1016/0032-0633(94)90103-1.

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43

Kellum, R., and B. M. Alberts. "Heterochromatin protein 1 is required for correct chromosome segregation in Drosophila embryos." Journal of Cell Science 108, no. 4 (April 1, 1995): 1419–31. http://dx.doi.org/10.1242/jcs.108.4.1419.

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Heterochromatin protein 1 is associated with centromeric heterochromatin in Drosophila, mice, and humans. Loss of function mutations in the gene encoding heterochromatin protein 1 in Drosophila, Suppressor of variegation2-5, decrease the mosaic repression observed for euchromatic genes that have been juxtaposed to centromeric heterochromatin. These heterochromatin protein 1 mutations not only suppress this position-effect variegation, but also cause recessive embryonic lethality. In this study, we analyze the latter phenotype in the hope of gaining insight into heterochromatin function. In our analyses of four alleles of Suppressor of variegation2-5, the lethality was found to be associated with defects in chromosome morphology and segregation. While some of these defects are seen throughout embryonic development, both the frequency and severity of the defects are greatest between cycles 10 and 14 when zygotic transcription of the Suppressor of variegation2-5 gene apparently begins. By this time in development, heterochromatin protein 1 levels are diminished by four-fold in a quarter of the embryos produced by parents that are both heterozygous for a null allele (Suppressor of variegation2-5(05)). In a live analysis of the phenotype, we find prophase to be lengthened by more than two-fold in Suppressor of variegation2-5(05) mutant embryos with subsequent defects in chromosome segregation. The elongated prophase suggests that the segregation phenotype is a consequence of defects in events that occur during prophase, either in chromosome condensation or kinetochore assembly or function. Immunostaining with an antibody against a centromerespecific antigen indicates that the kinetochores of most chromosomes are functional. The immunostaining results are more consistent with defects in chromosome condensation being responsible for the segregation phenotype.

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44

Delattre, M., A. Spierer, C. H. Tonka, and P. Spierer. "The genomic silencing of position-effect variegation in Drosophila melanogaster: interaction between the heterochromatin-associated proteins Su(var)3-7 and HP1." Journal of Cell Science 113, no. 23 (December 1, 2000): 4253–61. http://dx.doi.org/10.1242/jcs.113.23.4253.

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Position-effect variegation results from mosaic silencing by chromosomal rearrangements juxtaposing euchromatin genes next to pericentric heterochromatin. An increase in the amounts of the heterochromatin-associated Su(var)3-7 and HP1 proteins augments silencing. Using the yeast two-hybrid protein interaction trap system, we have isolated HP1 using Su(var)3-7 as a bait. We have then delimited three binding sites on Su(var)3-7 for HP1. On HP1, the C-terminal moiety, including the chromo shadow domain, is required for interaction. In vivo, both proteins co-localise not only in heterochromatin, but also in a limited set of sites in euchromatin and at telomeres. When delocalised to the sites bound by the protein Polycomb in euchromatin, HP1 recruits Su(var)3-7. Finally, and in contrast with euchromatin genes, a decrease in the amounts of both proteins enhances variegation of the light gene, one of the few genetic loci mapped within pericentric heterochromatin. This body of data supports a direct link between Su(var)3-7 and HP1 in the genomic silencing of position-effect variegation.

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45

Jaquet, Yannis, Marion Delattre, Anne Spierer, and Pierre Spierer. "Functional dissection of theDrosophilamodifier of variegationSu(var)3-7." Development 129, no. 17 (September 1, 2002): 3975–82. http://dx.doi.org/10.1242/dev.129.17.3975.

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An increase in the dose of the heterochromatin-associated Su(var)3-7 protein of Drosophila augments the genomic silencing of position-effect variegation. We have expressed a number of fragments of the protein in flies to assign functions to the different domains. Specific binding to pericentric heterochromatin depends on the C-terminal half of the protein. The N terminus, containing six of the seven widely spaced zinc fingers, is required for binding to bands on euchromatic arms, with no preference for pericentric heterochromatin. In contrast to the enhancing properties of the full-length protein, the N terminus half has no effect on heterochromatin-dependent position-effect variegation. In contrast, the C terminus moiety suppresses variegation. This dominant negative effect on variegation could result from association of the fragment with the wild type endogenous protein. Indeed, we have found and mapped a domain of self-association in this C-terminal half. Furthermore, a small fragment of the C-terminal region actually depletes pericentric heterochromatin from endogenous Su(var)3-7 and has a very strong suppressor effect. This depletion is not followed by a depletion of HP1, a companion of Su(var)3-7. This indicates that Su(var)3-7 does not recruit HP1 to heterochromatin. We propose in conclusion that the association of Su(var)3-7 to heterochromatin depends on protein-protein interaction mediated by the C-terminal half of the sequence, while the silencing function requires also the N-terminal half containing the zinc fingers.

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Henny, R. J., C. A. Conover, and R. T. Poole. "‘Triumph’ Dieffenbachia." HortScience 22, no. 5 (October 1987): 965–66. http://dx.doi.org/10.21273/hortsci.22.5.965.

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Abstract Dieffenbachia species and cultivars are important tropical ornamental foliage plants due to their attractive foliar variegation, ease of production, and adaptability to interior environments. About 20 cultivars have been produced commercially in Florida. Previously, most new cultivars were obtained from private plant collections or as mutations of established cultivars. Because dieffenbachia occur naturally in a variety of sizes, growth habits, and variegation patterns, they were included as part of the foliage plant breeding program at the Central Florida Research and Education Center–Apopka. The hybrid Dieffenbachia cultivar Triumph was developed and selected as part of that program.

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Sinclair, Donald A. R., Nigel J. Clegg, Jennifer Antonchuk, Thomas A. Milne, Kryn Stankunas, Chris Ruse, Thomas A. Grigliatti, Judith A. Kassis, and Hugh W. Brock. "Enhancer of Polycomb Is a Suppressor of Position-Effect Variegation in Drosophila melanogaster." Genetics 148, no. 1 (January 1, 1998): 211–20. http://dx.doi.org/10.1093/genetics/148.1.211.

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Abstract Polycomb group (PcG) genes of Drosophila are negative regulators of homeotic gene expression required for maintenance of determination. Sequence similarity between Polycomb and Su(var)205 led to the suggestion that PcG genes and modifiers of position-effect variegation (PEV) might function analogously in the establishment of chromatin structure. If PcG proteins participate directly in the same process that leads to PEV, PcG mutations should suppress PEV. We show that mutations in E(Pc), an unusual member of the PcG, suppress PEV of four variegating rearrangements: In(l)wm4, BSV, T(2;3)SbV, and In(2R)bwVDe2. Using reversion of a P element insertion, deficiency mapping, and recombination mapping as criteria, homeotic effects and suppression of PEV associated with E(Pc) co-map. Asx is an enhancer of PEV, whereas nine other PcG loci do not affect PEV. These results support the conclusion that there are fewer similarities between PcG genes and modifiers of PEV than previously supposed. However, E(Pc) appears to be an important link between the two groups. We discuss why Asx might act as an enhancer of PEV.

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Dimitri, P., and C. Pisano. "Position effect variegation in Drosophila melanogaster: relationship between suppression effect and the amount of Y chromosome." Genetics 122, no. 4 (August 1, 1989): 793–800. http://dx.doi.org/10.1093/genetics/122.4.793.

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Abstract Position effect variegation results from chromosome rearrangements which translocate euchromatic genes close to the heterochromatin. The euchromatin-heterochromatin association is responsible for the inactivation of these genes in some cell clones. In Drosophila melanogaster the Y chromosome, which is entirely heterochromatic, is known to suppress variegation of euchromatic genes. In the present work we have investigated the genetic nature of the variegation suppressing property of the D. melanogaster Y chromosome. We have determined the extent to which different cytologically characterized Y chromosome deficiencies and Y fragments suppress three V-type position effects: the Y-suppressed lethality, the white mottled and the brown dominant variegated phenotypes. We find that: (1) chromosomes which are cytologically different and yet retain similar amounts of heterochromatin are equally effective suppressors, and (2) suppression effect is positively related to the size of the Y chromosome deficiencies and fragments that we tested. It increases with increasing amounts of Y heterochromatin up to 60-80% of the entire Y, after which the effect reaches a plateau. These findings suggest suppression is a function of the amount of Y heterochromatin present in the genome and is not attributable to any discrete Y region.

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Vladimirov, Svoboda V., and Dennis B. McConnell. "Anatomical and Morphological Modifications of the Periclinal Chimera Dracaena sanderana `Ribbon' in Response to Four Light Intensities." HortScience 31, no. 4 (August 1996): 581d—581. http://dx.doi.org/10.21273/hortsci.31.4.581d.

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Effects of four shade levels (47%, 63%, 80%, and 91%) on growth of D. sanderana `Ribbon' were evaluated. D. sanderana exhibited morphological and anatomical plasticity manifested in differences in all growth parameters examined. Plant growth rate was significantly influenced by the light levels. Under 63% and 80% shade plants grew faster and achieved greater biomass than plants grown under 475% and 91% shade. Leaf variegation was affected by the shade level. Plants grown in 47% and 63% shade had less total variegation than plants grown in 80% and 91% shade. Leaf thickness was greater in plants grown under higher light levels. Marginal leaf growth was suppressed in plants grown in 47% and 63% shade, thus reducing the width of the achlorophyllous margins. The reverse occurred in leaves of plants grown in 80% and 91% shade. The change in variegation pattern occurred very early in leaf ontogeny—during lamina formation and expansion. This change was attributed to differences in relative contribution of the three shoot apical layers under different light conditions. Thus, Dracaena sanderana `Ribbon' when grown in the southeastern United States is shade obligate, with an optimum light intensity level of less than 53% of full sunlight.

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Hu, Meimei, Mengdi Li, and Jianbo Wang. "Comprehensive Analysis of the SUV Gene Family in Allopolyploid Brassica napus and Its Diploid Ancestors." Genes 12, no. 12 (November 23, 2021): 1848. http://dx.doi.org/10.3390/genes12121848.

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SUV (the Suppressor of variegation [Su(var)] homologs and related) gene family is a subgroup of the SET gene family. According to the SRA domain and WIYLD domain distributions, it can be divided into two categories, namely SUVH (the Suppressor of variegation [Su(var)] homologs) and SUVR (the Suppressor of variegation [Su(var)] related). In this study, 139 SUV genes were identified in allopolyploid Brassica napus and its diploid ancestors, and their evolutionary relationships, protein properties, gene structures, motif distributions, transposable elements, cis-acting elements and gene expression patterns were analyzed. Our results showed that the SUV gene family of B. napus was amplified during allopolyploidization, in which the segmental duplication and TRD played critical roles. After the separation of Brassica and Arabidopsis lineages, orthologous gene analysis showed that many SUV genes were lost during the evolutionary process in B. rapa, B. oleracea and B. napus. The analysis of the gene and protein structures and expression patterns of 30 orthologous gene pairs which may have evolutionary relationships showed that most of them were conserved in gene structures and protein motifs, but only four gene pairs had the same expression patterns.

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Journal articles on the topic 'Variegation'

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