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Dissecting Defense Signaling Pathways in Soybean and Arabidopsis
Department of Plant Pathology
Despite the economic importance of the soybean crop and the devastating losses incurred by its diseases very little is known about the molecular mechanisms underlying host defense against pathogens infecting soybean. The purpose of this study is to understand the molecular mechanisms governing soybean defense against two of its major pathogens, Phtophthtora sojae and soybean mosiac virus.
2009 Project Description
Research pertaining to objectives 1a, 1b, 1d, and 2 was conducted. Results obtained have improved our understanding of resistance gene-mediated signaling and the roles of defense-related phytohormones in soybean defense to microbial pathogens as well as to the identification of components mediating low oleic acid-derived signaling in Arabidopsis. These research findings were presented as five-oral and six-poster presentations at annual society (International Society of Molecular Plant-Microbe Interactions, American Phytopathological Society, American Society of Plant Biologists, American Society for Virology) conferences (2009). The project has resulted in the training of one high school, four undergraduate and two graduate students, as well as two postdoctoral researchers.
Research related to this project identified the following
1. Similar to Arabidopsis, soybean also induces constitutive defense signaling when oleic acid levels are reduced in the plant. The induced defense responses include, increased expression of pathogenesis-related genes, accumulation of salicylic acid and enhanced basal resistance to Pseudomonas syringae and Phytophthora sojae. Reduction in oleic acid levels in soybean can be achieved by silencing the expression of genes encoding the oleic acid synthesizing stearoyl-acyl carrier protein-desaturases or by exogenous glycerol application on healthy plants.
2. Soybean orthologs of genes involved in the biosynthesis of the defense-related hormones salicylic acid and jasmonic acid were identified, and functionally characterized. Our studies have shown that both salicylic acid and jasmonic acid are important for soybean defense to oomycete, bacterial and viral pathogens. These findings are being prepared for publication in a peer-reviewed journal.
3. Identified several molecular components mediating Rsv1-mediated resistance to soybean mosaic virus and Rpg1-B-mediated resistance to P. syringae. Of these studies related to RAR1, SGT1 and Hsp90 have been published, while results related to several other downstream components are being prepared for publication in peer-reviewed journals.
4. Identified two transcription factors that mediate low oleic acid-derived jasmonate responses in Arabidopsis. A role for these transcription factors in defense against Botrytis cinerea was also identified. These data are being prepared for publication in a peer-reviewed journal.
5. Demonstrated a role for glycerol-3-phosphate in mediating Arabidopsis defense to the anthracnose fungus Colletotrichum higginsianum. The data were published in a peer-reviewed journal.
6. The plant cuticle was identified as a major factor in signal perception during the induction of systemic immunity in Arabidopsis. The data were published in a peer-reviewed journal.
Kachroo A, Ghabrial SA (2009) Virus-induced gene silencing in soybean. In Methods in Molecular Biology. Ed. J.M. Walker. Humana Press Inc. (in press)
Venugopal SC, Chanda B, Vaillancourt L, Kachroo A, Kachroo P. (2009) The common metabolite glycerol-3-phosphate is a novel regulator of plant defense signaling. Plant Signaling and Behaviour 4:746-749
Venugopal SC, Jeong R-D, Mandal MK, Zhu S, Chandra-Shekara AC, Xia Y, Hersh M, Stromberg AJ, Navarre D, Kachroo A, Kachroo P. (2009) Enhanced Disease Susceptibility 1 and salicylic acid act redundantly to regulate resistance gene expression and low OLEATE-induced defense signaling. PLoS Genetics 5:e1000545
Xia Y, Gao Q-M, Yu K, Lapchyk L, Navarre DA, Hildebrand D, Kachroo A, Kachroo P. (2009) An intact cuticle in distal tissues is essential for the induction of systemic acquired resistance in plants. Cell Host & Microbe 5:151-165