Academic literature on the topic '7B chromosome'

A TC/AG-repeat microsatellite sequence derived from the rice blast fungus (Magnaporthe grisea) hybridized to all of the centromeres of Hordeum vulgare chromosomes, but hybridized faintly or not at all to the chromosomes of Hordeum bulbosum. Using this H. vulgare centromere-specific probe, the chromosomes of four F1 hybrids between H. vulgare and H. bulbosum were analyzed. The chromosome constitution in the root tips of the hybrids was mosaic, i.e., 7 (7v, H. vulgare) and 14 (7v + 7b H. bulbosum), or 14 (7v + 7b) and 27 (14v + 13b), or 7 (7v), 14 (7v + 7b), and 27 (14v + 13b). The 27-chromosome tetraploid hybrid cells were revealed to have the NOR (nucleolus organizer region) bearing chromosome of H. bulbosum in a hemizygous state, which might indicate some role for this chromosome in the chromosome instability of the hybrid condition. The chromosomal distribution showed that the chromosomes of H. vulgare were concentric and chromosomes of H. bulbosum were peripheral in the mitotic squash. This non-random chromosome distribution and the centromere-specific repeated DNA differences in the two species were discussed in relation to H. bulbosum chromosome elimination. Meiotic chromosome analyses revealed a high frequency of homoeologous chromosome pairing in early prophase. However, this chromosome pairing did not persist until later meiotic stages and many univalents and chromosome fragments resulted. These were revealed to be H. bulbosum by fluorescence in situ hybridization (FISH) analysis with the H. vulgare centromere-specific probe. Because the chromosome segregation of H. vulgare and H. bulbosum chromosomes at anaphase I of meiosis was random, the possibility for obtaining chromosome substitution lines in diploid barley from the diploid hybrid was discussed.Key words: Hordeum vulgare, Hordeum bulbosum, centromere-specific repeated DNA, FISH, chromosome instability.

The durum wheat (Triticum turgidum L. var. durum) cultivar 'Vic' was treated with the chemical mutagen N-methyl-N′-nitrosourea and among the M2 progeny a mutant with "chocolate chaff" (designated cc) was identified. Genetic analyses indicated that chocolate chaff is due to a single recessive gene mutation. The penetrance of the gene for chocolate chaff was environmentally influenced and varied from dark blotches on the glumes to complete coloration of culms as well as spikes. To determine the chromosomal location of the gene, the mutant was crossed with a set of 'Langdon' durum disomic substitution lines in which each of the 14 A- and B-genome chromosomes of durum wheat were replaced by their respective D-genome homoeologues. The segregation of cc was normal in all of the crosses except for those with the 7D(7A) and 7D(7B) lines. Cytogenetic analysis indicated that the gene was located on chromosome 7B, and that chromosome 7D has a gene that prevents the expression of cc when present in one or more copies. It was shown that the 'Langdon' D-genome disomic substitution lines can be used to determine the chromosomal location of genes in tetraploid wheat.Key words: Triticum turgidum, aneuploid, chromosome substitution, monosomic, cytogenetics.

The objective of this study was to investigate the effect of individual durum wheat (Triticum turgidum L.) chromosomes on crossability with maize (Zea mays L.) and to cytologically characterize the haploids recovered. Fourteen 'Langdon' (LDN) D-genome disomic substitution lines, a LDN Ph mutant (Ph1b ph1b), and normal 'Langdon' were pollinated with maize pollen. After pollination, hormonal treatment was given daily for up to 14 days. Haploid embryos were obtained from all lines and were aseptically cultured. From a total of 55 358 pollinated florets, 895 embryos were obtained. Only 14 of the embryos germinated and developed into healthy plants. Different substitution lines showed varying degrees of success. The most successful was the substitution 5D(5B) for both embryo formation and haploid plantlet production. These results indicate that the substitution of 5D for 5B confers on durum wheat a greater ability to produce haploids. Fluorescent genomic in situ hybridization (GISH) showed that the substitution haploids consisted of 7 A-genome chromosomes, 6 B-genome chromosomes, and 1 D-genome chromosome. Triticum urartu Tum. genomic DNA was efficient in probing the 7 A-genome chromosomes, although the D-genome chromosome also showed intermediate hybridization. This shows a close affinity between the A genome and D genome. We also elucidated the evolutionary translocation involving the chromosomes 4A and 7B that occurred at the time of evolution of durum wheat. We found that the distal segment translocated from chromosome 7B constitutes about 24% of the long arm of 4A.Key words: cyclic translocation 4A·5A·7B, crossability, disomic substitution, fluorescent genomic in situ hybridization (GISH), Triticum turgidum.

Individual substitution lines have been produced with Hordeum chilense chromosome A substituted in turn for chromosome 7A, 7B, or 7D of Triticum aestivum. Telocentric substitutions with the α arm, substituted for chromosome 7A or 7D, or the β arm substituted for chromosome 7B have also been produced. The substitutions have been confirmed by the presence of a purple straw marker, by gel isoelectric focusing of α-amylase isozymes, and cytologically using telocentric chromosome markers. Chromosome A has consequently been designated 7Hch.Key words: Hordeum chilense, wheat, chromosome substitution, homoeology, α-amylase.

Amelogenin is the major enamel matrix component in developing teeth. In eutherian mammals, amelogenin is expressed from the X chromosome only, or from both the X and Y chromosomes. Two classes of porcine amelogenin cDNA clones have been characterized, but the chromosomal localization of the gene(s) encoding them is unknown. To determine if there are sex-based differences in the expression of porcine amelogenin, we paired PCR primers for exons 1a, 1b, 7a, and 7b, and amplified enamel organ-derived cDNA separately from porcine males and females. The results show that exons 1a/2a and 7a are always together and can be amplified from both males (XY) and females (XX). Exons 1b/2b and 7b are also always paired, but can be amplified only from females. We conclude that porcine amelogenin is expressed from separate genes on the X and Y chromosomes, and not, as previously proposed, from a single gene with two promoters.

Increased chromosome instability was induced by a rye (Secale cereale L.) monosomic 2R chromosome into wheat (Triticum aestivum L.). Centromere breakage and telomere dysfunction result in high rates of chromosome aberrations, including breakages, fissions, fusions, deletions, and translocations. Plants with target traits were sequentially selected to produce a breeding population, from which 3 translocation lines with target traits have been selected. In these lines, wheat chromosomes 2A, 2B, and 7B recombined with segments of the rye chromosome arm 2RL. This was detected by FISH analysis using repeat sequences pSc119.2, pAs1 and genomic DNA of rye together as probes. The translocation chromosomes in these lines were named as 2ASMR, 2BSMR, and 7BSMR. The small segments that were transferred into wheat consisted of pSc119.2 repeats and other chromatin regions that conferred resistance to stripe rust and expressed target traits. These translocation lines were highly resistant to stripe rust, and expressed several typical traits that were associated with chromosome arm 2RL, which are better than those of its wheat parent, disomic addition, and substitution lines that show agronomic characteristics. The integration of molecular methods and conventional techniques to improve wheat breeding schemes are discussed.

The aim of this study was to investigate the possibilities of applying molecular markers-microsatellites in breeding boron tolerant wheat. The study comprised the investigation of allelic variability of sixty bread wheat accessions in two microsatellite loci (Xgwm46-7B and Xgwm577-7B) for which was assumed that are placed near the 7B chromosome locus involved in the expression of boron tolerance in wheat. Phenotypic variability concerning boron tolerance was assessed via root length reduction of wheat seedlings grown in the presence of high external boron, applied as boric acid solution (concentrations 50, 100 and 150 mg/l, boron treatments B50, B100 and B150). The indication of marker-trait associations was determined by comparing the allelic variability in the two microsatellite loci with the phenotypic variability in boron tolerance. Nonparametric Kruskal-Wallis test was used for the comparisons. The indication of marker-trait association was found for both Xgwm46-7B and Xgwm577-7B; on B150 and B50 treatments, respectively. Allelic forms identified in Xgwm577-7B locus may be related to tolerance, medium tolerance and sensitivity to high boron. This was not the case for Xgwm46-7B, where the identified alleles were related only to boron tolerance and sensitivity. Therefore, Xgwm577-7B may be preferred over Xgwm46-7B when studying boron tolerance in wheat. However, a considerable portion of boron tolerant accessions carried different alleles in the investigated loci, implying boron tolerance as a quantitative trait with more than one chromosomal region involved in its expression. Therefore, the allelic variability of more than the analyzed two loci should be investigated.

Determining the distribution and correspondence of genome-scale homologous genes in wheat are effective ways to uncover chromosome rearrangement that has occurred during crop evolution and domestication, which can contribute to improvements in crop breeding. High-resolution and comprehensive analysis of the wheat genome by the International Wheat Genome Sequencing Consortium (IWGSC) revealed a total of 88,733 high-confidence homologous genes of four major types (1:1:1, 1:1:0, 0:1:1 and 1:0:1) among the A, B and D subgenomes of wheat. This data was used to compare homologous gene densities among chromosomes, clarify their distribution and correspondence relationship, and compare their functional enrichment. The average density of 1:1:1 homologous genes was about 10 times more than the density of the other three types of homologous genes, although the homologous gene densities of the various chromosomes were similar within each homologous type. Three regions of exceptional density were detected in 1:1:1 homologous genes, the isolate peak on the tail of chromosome 4A, and the desert regions at the start of chromosome 7A and 7D. The correspondence between homologous genes of the wheat subgenomes demonstrated translocation between the tail segments of chromosome 4A and 5A, and the inversion of the segment of original 5A and 7B into the tail of 4A. The homologous genes on the inserting segments of 5A and 7B to 4A were highly enriched in nitrogen, primary metabolite and small molecular metabolism processes, compared with genes on other regions of the original 4A chromosome. This study provides a refined genome-scale reference of homologous genes for wheat molecular research and breeding, which will help to broaden the application of the wheat genome and can be used as a template for research on other polyploid plants.

Tetraploid triticale, (A/B)(A/B)RR (2n = 28), is a botanical novelty, an amphiploid composed of a diploid rye and a 14 chromosome wheat genome made up of chromosomes of the A and B genomes of tetraploid wheat. Restriction fragment length polymorphism (RFLP) markers were used to elucidate the chromosome composition of the mixed wheat genome of 35 different tetraploid triticale lines. Of 128 possible A/B chromosome pair combinations, only 6 were found among these lines, with a prevalence of the 1A, 2A, 3B, 4B, 5B, 6B, and 7B karyotype. In most triticale lines stable wheat genomes made up of only homologous A or B genome chromosome pairs were identified, however, in some lines homoeologous chromosome pairs were found. In this paper we demonstrate that RFLPs can be used successfully as an alternative to C-banding for the identification of the chromosome composition of tetraploid triticale and discuss the possible selective advantage of specific chromosome composition.Key words: tetraploid triticale, mixed wheat genome, RFLR

Barley yellow dwarf virus (BYDV) resistance in soft red winter wheat (SRWW) cultivars has been achieved by substituting a group 7 chromosome from Thinopyrum intermedium for chromosome 7D. To localize BYDV resistance, a detailed molecular genetic analysis was done on the alien group 7 Th. intermedium chromosome to determine its structural organization. Triticeae group 7 RFLP markers and rye specific repetitive sequences used in the analysis showed that the alien chromosome in the P29 substitution line has distinguishing features. The 350–480 bp rye telomeric sequence family was present on the long arm as determined by Southern and fluorescence in situ hybridization. However, further analysis using a rye dispersed repetitive sequence indicated that this alien chromosome does not contain introgressed segments from the rye genome. The alien chromosome is homoeologous to wheat chromosomes 7A and 7D as determined by RFLP analysis. Presence of the waxy gene on chromosomes 7A, 7B, and 7D but its absence on the alien chromosome in P29 suggests some internal structural differences on the short arm between Th. intermedium and wheat group 7 chromosomes. The identification of rye telomeric sequences on the alien Thinopyrum chromosome and the homoeology to wheat chromosomes 7A and 7D provide the necessary information and tools to analyze smaller segments of the Thinopyrum chromosome and to localize BYDV resistance in SRWW cultivars.Key words: barley yellow dwarf virus, Thinopyrum intermedium, rye repetitive sequences, RFLP, homoeologous group 7.

Colour is an important determinant of quality and customer appeal for Asian noodles that are made from bread wheat (Triticum aestivum L.). The Asian noodle market represents approximately one third of wheat exports from Australia and as a consequence maintaining and improving colour for noodles is an important research and breeding objective. The focus of this project is yellow alkaline noodles (YAN) prepared using wheat flour and alkaline salts, sodium and potassium carbonate, and for which a bright yellow colour is desired. Xanthophylls, primarily lutein, and apigenin di-Cglycosides (ACGs) have been shown to be important components of this yellow colour. ACGs were of particular interest since, in contrast to lutein, the content in flour could be increased without adverse effects on colour of other end-products. There was little information either on the genetic variation for ACG content or the mechanism and genetic control of biosynthesis which was surprising in view of their putative role in a wide range of plant processes, food colour and flavour, and possibly human health. The aims of this project were to provide new information on the role of ACGs in YAN colour and genetic regulation of their biosynthesis. To achieve this aims: genetic variation in grain ACG traits in bread wheat and related species was surveyed, the quantitative contribution of ACG to the yellow colour of YAN was determined and compared to lutein, QTL for ACG content and composition were located, and candidate genes associated with variation in ACG composition identified. Substantial variation in both grain ACG content and the ratio, ACG1/ACG2, were identified within bread wheat cultivars and related species. Genotype controlled the major portion of the variation. ACG content appeared to be a multigenic trait whereas variation in ACG1/ACG2 was associated with a limited number of chromosomes, in particular chromosomes 1B, 7B and 7D. In the absence of chromosome 7B (Chinese Spring 7B nullisomics) there was a substantial increase in ACG1/ACG2, i.e. a relative increase in the glucose-containing isomer, possibly indicating the presence of a Cglycosyltransferase on 7B with specificity for UDP-galactose. A similar phenotype observed in some wheat cultivars could be explained by a deletion or mutation of a gene controlling this enzyme. The results suggest that it should be possible to manipulate both ACG content and composition through breeding. Only 30% of ACG (means 19.3 µg/g) is recovered in flour, which contributed to 1 to 3 CIE b* units to the part of the yellow colour of yellow alkaline noodles (YAN) that develops specifically in the presence of alkali. The relatively low recovery of ACG in flour contrasts with the high recovery of lutein (90%, with means 1.011 µg/g). Since the difference between white salted noodles (WSN) and YAN is approximately 6 b* units, this would indicate that another unidentified compound(s) is responsible for the difference. Potential for ACG0-based improvement of bread wheat cultivars for YAN yellowness is likely to be limited by the range of genetic variation, the location of ACG in grain tissues that are largely discarded during milling and the lack of correlation between grain and flour ACG content. Moreover, the observed variation in ACG recovery in small scale milling was not reflected in larger scale milling anticipated to better represent commercial practice. The improvement in flour recovery and the amount of ACG recovered in the flour were not significant and not enough to achieve the yellowness of commercial noodles. Selection that requires larger scale milling is costly, time consuming and not applicable to early generation screening. In this context, further work on QTL associated with variation in ACG content and development of marker-assisted-selection would be very useful. Addition of thirteen new markers to the QTL region for ACG trait on chromosome 7BS in a Sunco/Tasman doubled haploid population reduced the size of the QTL interval from 28.8cM to approximately 5.5cM. In this revised 7BS map, the major QTL for ACG1 and ACG2 content as well as ACG1/ACG2 ratio were detected within 4.7cM of SSR marker Xwmc76. The QTL region linked to Xwmc76 was shown to be syntenic with a region in rice chromosome 6S between AP005387 and AP005761 and a region on Brachypodium chromosome 1. Based on these comparisons, the most likely candidate gene associated with variation in ACG composition appeared to be a glycosyltransferase. Alternate alleles at the 7BS QTL may be associated with amino acid changes within the C glycosyltransferase that shift the substrate specificity from galactose (ACG2, Tasman) to glucose (ACG1, Sunco). Alternatively, based on a comparison of Chinese Spring nullisomic-tetrasomic lines where nullisomic 7B was associated with a phenotype similar to Sunco, it is possible that Sunco contains a null allele. Other candidate genes located on the same chromosome that could potentially be involved in ACG biosynthesis were identified and included a sugar transporter, which could determine the relative sizes of the available pools of UDP-glucose and UDPgalactose, an epimerase required for inter-conversion of these sugars, other glycosyltransferases and a flavone-2-hydroxylase (F2H) involved in the first committed step in the pathway to ACG. Research approaches that could be used to validate the role of the candidate gene are discussed along with other options for improving the colour of wheat cultivars for the YAN market. Options for utilizing ACG as yellow pigment of noodles might include incorporating the embryo or seed coat materials (pollard and bran) into the flour after milling and genetic modification of bread wheat to achieve ACG expression in the starchy endosperm.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2012