Academic literature on the topic 'RNAi-INDUCED TRANSCRIPTIONAL SILENCING'
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Journal articles on the topic "RNAi-INDUCED TRANSCRIPTIONAL SILENCING"
1
Swaminathan, Sanjay, Chantelle L. Hood, Kazuo Suzuki, and Anthony D. Kelleher. "RNA duplexes in transcriptional regulation." BioMolecular Concepts 1, no. 3-4 (October 1, 2010): 285–96. http://dx.doi.org/10.1515/bmc.2010.021.
Full textAbstract:
AbstractTranscriptional regulation by small RNA molecules, including small interfering RNA and microRNA, has emerged as an important gene expression modulator. The regulatory pathways controlling gene expression, post-transcriptional gene silencing and transcriptional gene silencing (TGS) have been demonstrated in yeast, plants and more recently in human cells. In this review, we discuss the currents models of transcriptional regulation and the main components of the RNA-induced silencing complex and RNA-induced transcriptional silencing complex machinery, as well as confounding off-target effects and gene activation. We also discuss RNA-mediated TGS within the NF-κB motif of the human immunodeficiency virus type 1 5′ long tandem repeat promoter region and the associated epigenetic modifications. Finally, we outline the current RNA interference (RNAi) delivery methods and describe the current status of human trials investigating potential RNAi therapeutics for several human diseases.
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Abdellatef, Eltayb, Nasrein Mohamed Kamal, and Hisashi Tsujimoto. "Tuning Beforehand: A Foresight on RNA Interference (RNAi) and In Vitro-Derived dsRNAs to Enhance Crop Resilience to Biotic and Abiotic Stresses." International Journal of Molecular Sciences 22, no. 14 (July 19, 2021): 7687. http://dx.doi.org/10.3390/ijms22147687.
Full textAbstract:
Crop yield is severely affected by biotic and abiotic stresses. Plants adapt to these stresses mainly through gene expression reprogramming at the transcriptional and post-transcriptional levels. Recently, the exogenous application of double-stranded RNAs (dsRNAs) and RNA interference (RNAi) technology has emerged as a sustainable and publicly acceptable alternative to genetic transformation, hence, small RNAs (micro-RNAs and small interfering RNAs) have an important role in combating biotic and abiotic stresses in plants. RNAi limits the transcript level by either suppressing transcription (transcriptional gene silencing) or activating sequence-specific RNA degradation (post-transcriptional gene silencing). Using RNAi tools and their respective targets in abiotic stress responses in many crops is well documented. Many miRNAs families are reported in plant tolerance response or adaptation to drought, salinity, and temperature stresses. In biotic stress, the spray-induced gene silencing (SIGS) provides an intelligent method of using dsRNA as a trigger to silence target genes in pests and pathogens without producing side effects such as those caused by chemical pesticides. In this review, we focus on the potential of SIGS as the most recent application of RNAi in agriculture and point out the trends, challenges, and risks of production technologies. Additionally, we provide insights into the potential applications of exogenous RNAi against biotic stresses. We also review the current status of RNAi/miRNA tools and their respective targets on abiotic stress and the most common responsive miRNA families triggered by stress conditions in different crop species.
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Zhang, Junlong. "Special delivery: Small RNAs silencing gene expression." Biochemist 26, no. 5 (October 1, 2004): 20–23. http://dx.doi.org/10.1042/bio02605020.
Full textAbstract:
RNA interference (RNAi), which refers to RNA-induced transcriptional gene silencing, is a natural phenomenon that exists widely in living organisms. Recent advances in RNAi research indicate that RNAi technology is a powerful tool in studying gene function and has a great potential in gene therapy. Although many methods, including viral and non-viral vectors, have been used to deliver small interference RNA molecules into cells and animals, development of better delivery methods is still crucial for the application of RNAi technology in both basic research and gene therapy.
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Das, Panchashree, and Satyabrata Nanda. "Host-delivered-RNAi-mediated resistance in bananas against biotic stresses." Journal of Experimental Biology and Agricultural Sciences 10, no. 5 (October 31, 2022): 953–59. http://dx.doi.org/10.18006/2022.10(5).953.959.
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Both the biotic and abiotic stressors restrict the yield potential of many crops, including bananas. Bananas belong to the genus Musa and are the world’s most popular and widely produced fruit for their nutritional and industrial importance. The demand for bananas is growing each day worldwide. However, different pest infestations are hampering the production of bananas, making it a matter of concern for global food security. Several biotechnological tools and applications including RNA interference (RNAi) have been employed to enhance the biotic stress resistance in plants. The capacity to silence targeted genes at transcriptional and post-transcriptional levels makes the RNAi technique a popular choice for gene knock-down and functional genomics studies in crops. Silencing of different suppressor molecule coding genes through RNAi helps crops to combat the detrimental effects of plant pathogens. The host-induced gene silencing (HIGS) technology, also known as the host-delivered RNAi (HD-RNAi), is nowadays gaining popularity due to its ability to target an array of pathogens, comprising bacteria, nematodes, fungi, viruses, and insects. This methodology is employed to manage disease pest outbreaks in a diverse range of crop species, including bananas. Besides HIGS, virus-induced and spray-induced gene silencing (VIGS and SIGS, respectively) are the potential approaches where RNAi technology is exploited to control plant-pathogenic diseases. The current review emphasizes the different kinds of diseases of bananas and the potential of HD-RNAi, a new-age and promising technology to build a barrier against significant crop and economic loss.
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Kajitani, Takuya, Hiroaki Kato, Yuji Chikashige, Chihiro Tsutsumi, Yasushi Hiraoka, Hiroshi Kimura, Yasuyuki Ohkawa, Chikashi Obuse, Damien Hermand, and Yota Murakami. "Ser7 of RNAPII-CTD facilitates heterochromatin formation by linking ncRNA to RNAi." Proceedings of the National Academy of Sciences 114, no. 52 (December 13, 2017): E11208—E11217. http://dx.doi.org/10.1073/pnas.1714579115.
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Some long noncoding RNAs (ncRNAs) transcribed by RNA polymerase II (RNAPII) are retained on chromatin, where they regulate RNAi and chromatin structure. The molecular basis of this retention remains unknown. We show that in fission yeast serine 7 (Ser7) of the C-terminal domain (CTD) of RNAPII is required for efficient siRNA generation for RNAi-dependent heterochromatin formation. Surprisingly, Ser7 facilitates chromatin retention of nascent heterochromatic RNAs (hRNAs). Chromatin retention of hRNAs and siRNA generation requires both Ser7 and an RNA-binding activity of the chromodomain of Chp1, a subunit of the RNA-induced transcriptional silencing (RITS) complex. Furthermore, RITS associates with RNAPII in a Ser7-dependent manner. We propose that Ser7 promotes cotranscriptional chromatin retention of hRNA by recruiting the RNA-chromatin connector protein Chp1, which facilitates RNAi-dependent heterochromatin formation. Our findings reveal a function of the CTD code: linking ncRNA transcription to RNAi for heterochromatin formation.
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Suprun, Andrey R., Konstantin V. Kiselev, and Alexandra S. Dubrovina. "Exogenously Induced Silencing of Four MYB Transcription Repressor Genes and Activation of Anthocyanin Accumulation in Solanum lycopersicum." International Journal of Molecular Sciences 24, no. 11 (May 26, 2023): 9344. http://dx.doi.org/10.3390/ijms24119344.
Full textAbstract:
RNA interference (RNAi) is a natural post-transcriptional regulatory mechanism that can be artificially induced by exogenous application of double-stranded RNAs (dsRNAs) to the plant surfaces. Recent studies show that it is possible to silence plant genes and change plant properties using plant RNA spraying and other approaches for dsRNA delivery. In this study, we investigated the effect of exogenous gene-specific dsRNAs on the silencing of four tomato genes encoding MYB-family transcription repressors of anthocyanin biosynthesis in the leaves of tomato Solanum lycopersicum L. We found that the exogenous application of dsRNAs encoding for the SlMYBATV1, SlMYB32, SlMYB76, and SlTRY genes downregulated mRNA levels of these endogenous repressors of anthocyanin production, upregulated the expression of anthocyanin biosynthesis-related genes, and enhanced anthocyanin content in the leaves of S. lycopersicum. The data demonstrated that exogenous gene-specific dsRNAs can induce post-transcriptional gene silencing in tomato leaves by direct foliar application of dsRNAs. This approach may be used for plant secondary metabolism induction and as a silencing tool for gene function studies without the need to produce genetically modified plants.
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Mao, Kai, Peter Breen, and Gary Ruvkun. "Mitochondrial dysfunction induces RNA interference in C. elegans through a pathway homologous to the mammalian RIG-I antiviral response." PLOS Biology 18, no. 12 (December 2, 2020): e3000996. http://dx.doi.org/10.1371/journal.pbio.3000996.
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RNA interference (RNAi) is an antiviral pathway common to many eukaryotes that detects and cleaves foreign nucleic acids. In mammals, mitochondrially localized proteins such as mitochondrial antiviral signaling (MAVS), retinoic acid-inducible gene I (RIG-I), and melanoma differentiation-associated protein 5 (MDA5) mediate antiviral responses. Here, we report that mitochondrial dysfunction in Caenorhabditis elegans activates RNAi-directed silencing via induction of a pathway homologous to the mammalian RIG-I helicase viral response pathway. The induction of RNAi also requires the conserved RNA decapping enzyme EOL-1/DXO. The transcriptional induction of eol-1 requires DRH-1 as well as the mitochondrial unfolded protein response (UPRmt). Upon mitochondrial dysfunction, EOL-1 is concentrated into foci that depend on the transcription of mitochondrial RNAs that may form double-stranded RNA (dsRNA), as has been observed in mammalian antiviral responses. Enhanced RNAi triggered by mitochondrial dysfunction is necessary for the increase in longevity that is induced by mitochondrial dysfunction.
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Buck, Amy H., and Mark Blaxter. "Functional diversification of Argonautes in nematodes: an expanding universe." Biochemical Society Transactions 41, no. 4 (July 18, 2013): 881–86. http://dx.doi.org/10.1042/bst20130086.
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In the last decade, many diverse RNAi (RNA interference) pathways have been discovered that mediate gene silencing at epigenetic, transcriptional and post-transcriptional levels. The diversity of RNAi pathways is inherently linked to the evolution of Ago (Argonaute) proteins, the central protein component of RISCs (RNA-induced silencing complexes). An increasing number of diverse Agos have been identified in different species. The functions of most of these proteins are not yet known, but they are generally assumed to play roles in development, genome stability and/or protection against viruses. Recent research in the nematode Caenorhabditis elegans has expanded the breadth of RNAi functions to include transgenerational epigenetic memory and, possibly, environmental sensing. These functions are inherently linked to the production of secondary siRNAs (small interfering RNAs) that bind to members of a clade of WAGOs (worm-specific Agos). In the present article, we review briefly what is known about the evolution and function of Ago proteins in eukaryotes, including the expansion of WAGOs in nematodes. We postulate that the rapid evolution of WAGOs enables the exceptional functional plasticity of nematodes, including their capacity for parasitism.
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Andika, Ida Bagus, Hideki Kondo, and Nobuhiro Suzuki. "Dicer functions transcriptionally and posttranscriptionally in a multilayer antiviral defense." Proceedings of the National Academy of Sciences 116, no. 6 (January 23, 2019): 2274–81. http://dx.doi.org/10.1073/pnas.1812407116.
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In antiviral RNA interference (RNAi), Dicer plays a primary role in processing double-stranded RNA (dsRNA) molecules into small-interfering RNAs (siRNAs) that guide Argonaute effectors to posttranscriptional suppression of target viral genes. Here, we show a distinct role for Dicer in the siRNA-independent transcriptional induction of certain host genes upon viral infection in a filamentous fungus. Previous studies have shown that the two key players, dicer-like 2 (dcl2) and argonaute-like 2 (agl2), of antiviral RNAi in a phytopathogenic ascomycete,Cryphonectria parasitica, are highly transcriptionally induced upon infection with certain RNA mycoviruses, including the positive-stranded RNA hypovirus mutant lacking the RNAi suppressor (Cryphonectriahypovirus 1-Δp69, CHV1-Δp69). This induction is regulated by the Spt–Ada–Gcn5 acetyltransferase (SAGA) complex, a well-known transcriptional coactivator. The present study shows that diverse host genes, in addition todcl2andagl2, were up-regulated more than 10-fold by SAGA upon infection with CHV1-Δp69. Interestingly, DCL2, but not AGL2, was essential for SAGA-mediated global gene up-regulation. Moreover, deletion of certain virus-induced genes enhanced a CHV1-Δp69 symptom (growth rate) but not its accumulation. Constitutive, modest levels ofdcl2expression drastically reduced viral siRNA accumulation but were sufficient for full-scale up-regulation of host genes, suggesting that high induction ofdcl2and siRNA production are not essential for the transcriptional up-regulation function of DCL2. These data clearly demonstrate the dual functionality of DCL2: as a dsRNA-specific nuclease in posttranscriptional antiviral RNA silencing and as a key player in SAGA-mediated host gene induction, which independently represses viral replication and alleviates virus-induced symptom expression.
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Betti, Federico, Maria José Ladera-Carmona, Pierdomenico Perata, and Elena Loreti. "RNAi Mediated Hypoxia Stress Tolerance in Plants." International Journal of Molecular Sciences 21, no. 24 (December 10, 2020): 9394. http://dx.doi.org/10.3390/ijms21249394.
Full textAbstract:
Small RNAs regulate various biological process involved in genome stability, development, and adaptive responses to biotic or abiotic stresses. Small RNAs include microRNAs (miRNAs) and small interfering RNAs (siRNAs). MicroRNAs (miRNAs) are regulators of gene expression that affect the transcriptional and post-transcriptional regulation in plants and animals through RNA interference (RNAi). miRNAs are endogenous small RNAs that originate from the processing of non-coding primary miRNA transcripts folding into hairpin-like structures. The mature miRNAs are incorporated into the RNA-induced silencing complex (RISC) and drive the Argonaute (AGO) proteins towards their mRNA targets. siRNAs are generated from a double-stranded RNA (dsRNA) of cellular or exogenous origin. siRNAs are also involved in the adaptive response to biotic or abiotic stresses. The response of plants to hypoxia includes a genome-wide transcription reprogramming. However, little is known about the involvement of RNA signaling in gene regulation under low oxygen availability. Interestingly, miRNAs have been shown to play a role in the responses to hypoxia in animals, and recent evidence suggests that hypoxia modulates the expression of various miRNAs in plant systems. In this review, we describe recent discoveries on the impact of RNAi on plant responses to hypoxic stress in plants.
Dissertations / Theses on the topic "RNAi-INDUCED TRANSCRIPTIONAL SILENCING"
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PUNJABI, MANSI. "RNAi-INDUCED TRANSCRIPTIONAL SILENCING OF INOSITOL POLYPHOSPHATE 6-/3-/5-KINASE (IPK2) GENE IN SOYBEAN SEEDS TO GENERATE LOW PHYTATE LINES." Thesis, 2019. http://dspace.dtu.ac.in:8080/jspui/handle/repository/16676.
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Soybean is one of the leading oilseed crops in the world and is showing a
remarkable surge in its utilization in formulating animal feeds and supplements. Its
dietary consumption, however, is incongruent with its existing industrial demand due
to the presence of anti-nutritional factors in sufficiently large amounts. Phytic acid, in
particular, raises concern as it causes a concomitant loss of indigestible complexed
minerals and charged proteins in the waste and results in reduced mineral
bioavailability in both livestock and humans. Reducing the seed phytate level thus
seems indispensable to overcome the nutritional menace associated with soy grain
consumption.
To conceive our objective, we designed and expressed an inositol poly
phosphate 6-/3-/5-kinase gene-specific intron-containing self-complementary hairpin
RNAi construct in the seeds of Pusa-16 soybean cultivar. Inositol polyphosphate 6-/3
/5-kinase is a multifunctional kinase which catalyzes the formation of inositol
pentakisphosphate, the immediate substrate of PA biosynthesis. Due to a broad range
of substrate specificity, it plays a pivotal role in regulating the cellular phytic acid
turnover and is therefore conceived to be the most appropriate target for effective seed
phytate reduction.
We subsequently conducted a genotypic, phenotypic, and biochemical
analysis of the developed putative transgenic populations and found low phytic acid
levels, moderate accumulation of inorganic phosphate and elevated mineral content in
some lines. These low phytic acid lines did not show any reduction in seedling
emergence and displayed an overall good agronomic performance, thus, proving to be
a successful attempt.
2
Odokonyero, Denis 1984. "Identification of ARGONAUTES Involved in Antiviral RNA Silencing in Nicotiana benthamiana." Thesis, 2012. http://hdl.handle.net/1969.1/148228.
Full textAbstract:
ARGONAUTE proteins (AGOs) are generally accepted as key components of the post transcriptional gene silencing mechanism, also involved in plant antiviral defense. Except for reports on the antiviral roles of AGO1, AGO2 and AGO7 in Arabidopsis, the exact roles played by the individual AGOs in other plant species are largely unknown. This research focused on the identification and characterization of AGOs involved in antiviral RNAi response to various viruses in N. benthamiana. Based on the temporal and spatial distribution of AGO transcripts in 3 and 8-week old plant root, stem and leaf tissues, expressions of NbAGO mRNAs were found to vary with age and tissue specificity. Plant endogenous AGO mRNAs were knocked down through virus induced gene silencing techniques using the Tobacco rattle virus vector system and posteriorly challenged with a GFP-chimeric virus construct deficient of a silencing suppressor. Unlike in control non-silenced plants, the Tomato bushy stunt virus construct deficient of its P19 silencing suppressor was consistently seen to exhibit a strong fluorescence on N. benthamiana plants silenced for NbAGOs 2 and X. Similar results were also obtained upon silencing of NbAGO2 using hairpin vector techniques. Comparable observations were also made when Tobacco mosaic virus GFP constructs were agroinfiltrated on NbAGO2 silenced plants further hinting the antiviral defense roles played by these AGOs. Agroinfiltration of Foxtailmosaic virus, Sunnhemp mosaic virus, and Turnip crinkle virus GFP chimeric constructs on NbAGO2 silenced N. benthamiana plants, however did not result in accumulation of GFP indicating the AGO antiviral defense specificity to TBSV and TMV. The results also hinted at a role for AGO7. Collectively my findings suggest that the expression of AGOs in N. benthamiana is tissue and age dependent, and that unlike in the model plant Arabidopsis where the main antiviral AGO is thought to be AtAGO1; in N. benthamiana, NbAGOs 2 and X seem to be involved in an antiviral defense role against TBSV and TMV with other AGOs perhaps contributing.
Book chapters on the topic "RNAi-INDUCED TRANSCRIPTIONAL SILENCING"
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Ricci, Angela, Silvia Sabbadini, Laura Miozzi, Bruno Mezzetti, and Emanuela Noris. "Host-induced gene silencing and spray-induced gene silencing for crop protection against viruses." In RNAi for plant improvement and protection, 72–85. Wallingford: CABI, 2021. http://dx.doi.org/10.1079/9781789248890.0008.
Full textAbstract:
Abstract Since the beginning of agriculture, plant virus diseases have been a strong challenge for farming. Following its discovery at the very beginning of the 1990s, the RNA interference (RNAi) mechanism has been widely studied and exploited as an integrative tool to obtain resistance to viruses in several plant species, with high target-sequence specificity. In this chapter, we describe and review the major aspects of host-induced gene silencing (HIGS), as one of the possible plant defence methods, using genetic engineering techniques. In particular, we focus our attention on the use of RNAi-based gene constructs to introduce stable resistance in host plants against viral diseases, by triggering post-transcriptional gene silencing (PTGS). Recently, spray-induced gene silencing (SIGS), consisting of the topical application of small RNA molecules to plants, has been explored as an alternative tool to the stable integration of RNAi-based gene constructs in plants. SIGS has great and innovative potential for crop defence against different plant pathogens and pests and is expected to raise less public and political concern, as it does not alter the genetic structure of the plant.
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Ricci, Angela, Silvia Sabbadini, Laura Miozzi, Bruno Mezzetti, and Emanuela Noris. "Host-induced gene silencing and spray-induced gene silencing for crop protection against viruses." In RNAi for plant improvement and protection, 72–85. Wallingford: CABI, 2021. http://dx.doi.org/10.1079/9781789248890.0072.
Full textAbstract:
Abstract Since the beginning of agriculture, plant virus diseases have been a strong challenge for farming. Following its discovery at the very beginning of the 1990s, the RNA interference (RNAi) mechanism has been widely studied and exploited as an integrative tool to obtain resistance to viruses in several plant species, with high target-sequence specificity. In this chapter, we describe and review the major aspects of host-induced gene silencing (HIGS), as one of the possible plant defence methods, using genetic engineering techniques. In particular, we focus our attention on the use of RNAi-based gene constructs to introduce stable resistance in host plants against viral diseases, by triggering post-transcriptional gene silencing (PTGS). Recently, spray-induced gene silencing (SIGS), consisting of the topical application of small RNA molecules to plants, has been explored as an alternative tool to the stable integration of RNAi-based gene constructs in plants. SIGS has great and innovative potential for crop defence against different plant pathogens and pests and is expected to raise less public and political concern, as it does not alter the genetic structure of the plant.
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Saxena, Shipra, Sneha Yogindran, Manmohan Arya, Yogita Sharma, and Chandra Pal Singh. "RNAi-Mediated Control of Lepidopteran Pests of Important Crop Plants." In Moths and Caterpillars. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.96429.
Full textAbstract:
Insects as pests destroy annually an estimated 18–20% of the crop production worldwide. Caterpillars, the larval stage of moths, are the major pests of agricultural products owing to their voracious feeding habits. In the past few decades, the potent methods of insect control, such as insecticides and Bt toxins, have been constrained as a result of health hazards, environmental issues, and development of resistance, after their prolonged application. Thus, there is need to find alternative options to improve plant protection strategies. Recently, RNA interference (RNAi), the post-transcriptional gene-silencing mechanism, has emerged as one of such a novel, sustainable, and environment friendly approaches for insect management and crop protection. RNAi technology relies on selection of a vital insect pest target gene and its expression as a double stranded RNA or stem-loop RNA molecule, which is recognized by the host RNAi machinery and processed into small interfering RNAs (siRNAs) or microRNAs (miRNAs). The siRNA/miRNA along with the RNA-induced silencing complex (RISC) binds to the complimentary mRNA and induce gene silencing at post-transcriptional level. With effective target-gene selection and transgenic plants expressing these precursor RNA molecules, insect pests of various crops have been efficiently managed. In this chapter, we discuss the basic mechanism of RNAi and its application in controlling lepidopteran pests of important crop plants.
Reports on the topic "RNAi-INDUCED TRANSCRIPTIONAL SILENCING"
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Gal-On, Amit, Shou-Wei Ding, Victor P. Gaba, and Harry S. Paris. role of RNA-dependent RNA polymerase 1 in plant virus defense. United States Department of Agriculture, January 2012. http://dx.doi.org/10.32747/2012.7597919.bard.
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Objectives: Our BARD proposal on the impact of RNA-dependent RNA polymerase 1 (RDR1) in plant defense against viruses was divided into four original objectives. 1. To examine whether a high level of dsRNA expression can stimulate RDR1 transcription independent of salicylic acid (SA) concentration. 2. To determine whether the high or low level of RDR1 transcript accumulation observed in virus resistant and susceptible cultivars is associated with viral resistance and susceptibility. 3. To define the biogenesis and function of RDR1-dependent endogenous siRNAs. 4. To understand why Cucumber mosaic virus (CMV) can overcome RDR1-dependent resistance. The objectives were slightly changed due to the unique finding that cucumber has four different RDR1 genes. Background to the topic: RDR1 is a key plant defense against viruses. RDR1 is induced by virus infection and produces viral and plant dsRNAs which are processed by DICERs to siRNAs. siRNAs guide specific viral and plant RNA cleavage or serve as primers for secondary amplification of viral-dsRNA by RDR. The proposal is based on our preliminary results that a. the association of siRNA and RDR1 accumulation with multiple virus resistance, and b. that virus infection induced the RDR1-dependent production of a new class of endogenous siRNAs. However, the precise mechanisms underlying RDR1 induction and siRNA biogenesis due to virus infection remain to be discovered in plants. Major conclusions, solutions and achievements: We found that in the cucurbit family (cucumber, melon, squash, watermelon) there are 3-4 RDR1 genes not documented in other plant families. This important finding required a change in the emphasis of our objectives. We characterized 4 RDR1s in cucumber and 3 in melon. We demonstrated that in cucumber RDR1b is apparently a new broad spectrum virus resistance gene, independent of SA. In melon RDR1b is truncated, and therefore is assumed to be the reason that melon is highly susceptible to many viruses. RDR1c is dramatically induced due to DNA and RNA virus infection, and inhibition of RDR1c expression led to increased virus accumulation which suggested its important on gene silencing/defense mechanism. We show that induction of antiviral RNAi in Arabidopsis is associated with production of a genetically distinct class of virus-activated siRNAs (vasiRNAs) by RNA dependent RNA polymerase-1 targeting hundreds of host genes for RNA silencing by Argonaute-2. Production of vasiRNAs is induced by viruses from two different super groups of RNA virus families, targeted for inhibition by CMV, and correlated with virus resistance independently of viral siRNAs. We propose that antiviral RNAi activate broad-spectrum antiviral activity via widespread silencing of host genes directed by vasiRNAs, in addition to specific antiviral defense Implications both scientific and agricultural: The RDR1b (resistance) gene can now be used as a transcription marker for broad virus resistance. The discovery of vasiRNAs expands the repertoire of siRNAs and suggests that the siRNA-processing activity of Dicer proteins may play a more important role in the regulation of plant and animal gene expression than is currently known. We assume that precise screening of the vasiRNA host targets will lead in the near future for identification of plant genes associate with virus diseases and perhaps other pathogens.
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Meir, Shimon, Michael S. Reid, Cai-Zhong Jiang, Amnon Lers, and Sonia Philosoph-Hadas. Molecular Studies of Postharvest Leaf and Flower Senescence. United States Department of Agriculture, January 2011. http://dx.doi.org/10.32747/2011.7592657.bard.
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Original objectives: To understand the regulation of abscission by exploring the nature of changes of auxin-related gene expression in tomato (Lycopersicon esculatumMill) abscission zones (AZs) following organ removal, and by analyzing the function of these genes. Our specific goals were: 1) To complete the microarray analyses in tomato flower and leaf AZs, for identifying genes whose expression changes early in response to auxin depletion; 2) To examine, using virus-induced gene silencing (VIGS), the effect of silencing target genes on ethylene sensitivity and abscission competence of the leaf and flower AZs; 3) To isolate and characterize promoters from AZ-specific genes to be used in functional analysis; 4) To generate stable transgenic tomato plants with selected genes silenced with RNAi, under the control of an AZ-specific promoter, for further characterization of their abscission phenotypes. Background: Abscission, the separation of organs from the parent plant, results in postharvest quality loss in many ornamentals and other fresh produce. The process is initiated by changes in the auxin gradient across the AZ, and is triggered by ethylene. Although changes in gene expression have been correlated with the ethylene-mediated execution of abscission, there is almost no information on the initiation of the abscission process, as the AZ becomes sensitized to ethylene. The present project was focused on elucidating these early molecular regulatory events, in order to gain a better control of the abscission process for agricultural manipulations. Major conclusions, solutions, achievements: Microarray analyses, using the Affymetrix Tomato GeneChip®, revealed changes in expression, occurring early in abscission, of many genes with possible regulatory functions. These included a range of auxin- and ethylene-related transcription factors (TFs), other TFs that are transiently induced just after flower removal, and a set of novel AZ-specific genes. We also identified four different defense-related genes, including: Cysteine-type endopeptidase, α- DOX1, WIN2, and SDF2, that are newly-associated with the late stage of the abscission process. This supports the activation of different defense responses and strategies at the late abscission stages, which may enable efficient protection of the exposed tissue toward different environmental stresses. To facilitate functional studies we implemented an efficient VIGS system in tomato, and isolated two abscission-specific promoters (pTAPG1 and pTAPG4) for gene silencing in stable transformation. Using the VIGS system we could demonstrate the importance of TAPGs in abscission of tomato leaf petioles, and evaluated the importance of more than 45 genes in abscission. Among them we identified few critical genes involved in leaf and flower abscission. These included: PTRP-F1, PRP, TKN4, KNOTTED-like homeobox TF, KD1, and KNOX-like homeodomain protein genes, the silencing of which caused a striking retardation of pedicel abscission, and ERF1, ERF4, Clavata-like3 protein, Sucrose transporter protein, and IAA10 genes, the silencing of which delayed petiole abscission. The importance of PRPand KD1 genes in abscission was confirmed also by antisense–silencing using pTAPG4. Experiments testing the effects of RNAi silencing of few other genes are still in progress, The analysis of the microarray results of flower and leaf AZs allowed us to establish a clear sequence of events occurring during acquisition of tissue sensitivity to ethylene, and to confirm our hypothesis that acquisition of ethylene sensitivity in the AZ is associated with altered expression of auxin-regulated genes in both AZs. Implication, both scientific and agricultural: Our studies had provided new insights into the regulation of the abscission process, and shaded light on the molecular mechanisms that drive the acquisition of abscission competence in the AZ. We pointed out some critical genes involved in regulation of abscission, and further expanded our knowledge of auxin-ethylene cross talk during the abscission process. This permits the development of novel techniques for manipulating abscission, and thereby improving the postharvest performance of ornamentals and other crops.
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Tucker, Mark L., Shimon Meir, Amnon Lers, Sonia Philosoph-Hadas, and Cai-Zhong Jiang. Elucidation of signaling pathways that regulate ethylene-induced leaf and flower abscission of agriculturally important plants. United States Department of Agriculture, January 2012. http://dx.doi.org/10.32747/2012.7597929.bard.
Full textAbstract:
The Problem: Abscission is a highly regulated process, occurring as a natural terminal stage of development, in which various organs are separated from the parent plant. In most plant species, the process is initiated by a decrease in active auxin in the abscission zone (AZ) and an increase in ethylene, and may be accelerated by postharvest or environmental stresses. Another potential key regulator in abscission is IDA (Inflorescence Deficient in Abscission), which was identified as an essential peptide signal for floral organ abscission in Arabidopsis. However, information is still lacking regarding the molecular mechanisms integrating all these regulators. In our previous BARD funded research we made substantial progress towards understanding these molecular events in tomato, and the study is still in progress. We established a powerful platform for analysis of genes for regulatory proteins expressed in AZ. We identified changes in gene expression for several transcription factors (TFs) directly linked to ethylene and auxin signaling and several additional regulatory proteins not so obviously linked to these hormones. Moreover, we demonstrated using a virus-induced gene silencing (VIGS) assay that several play a functional role in the onset of abscission. Based on these results we have selected 14 genes for further analysis in stably transformed tomato plants. All 14 genes were suppressed by RNA interference (RNAi) using a constitutive promoter, and 5 of them were also suppressed using an abscission-specific promoter. Transformations are currently at different stages of progress including some lines that already display an abscission phenotype. Objectives: We propose here to (1) complete the functional analysis of the stably transformed tomato plants with T2 lines and perform transcriptome analysis using custom abscission-specific microarrays; (2) conduct an indepth analysis of the role of IDA signaling in tomato leaf and flower abscission; (3) perform transcriptome and proteome analyses to extend the earlier gene expression studies to identify transcripts and proteins that are highly specific to the separation layer (i.e., target cells for cell separation) prior to the onset of abscission; (4) extend and compliment the work in tomato using a winnowed set of genes in soybean. Methodology: Next Generation Sequencing (NGS) of mRNA will be used to further increase the list of abscission-associated genes, and for preparation of a custom tomato abscission microarray to test altered gene expression in transgenic plants. Tandem mass spectrometry (LC-MS/MS) of protein extracts from leaf petiole, flower pedicel and their AZ tissues will be used to identify the proteome of the AZ before and during abscission. AZ-specific gene promoters will be used in stably transformed tomato plants to reduce non-target phenotypes. The bean pod mottle virus (BPMV) plasmid vectors will be used for VIGS analysis in soybean. Expected Contribution: Our study will provide new insights into the regulation of ethylene-induced abscission by further revealing the role of key regulators in the process. This will permit development of novel techniques for manipulating leaf and flower abscission, thereby improving the postharvest performance of agriculturally important crops.