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Characterization of Resistance Gene-mediated Signaling and Role of Oleic Acid and Glycerol 3-Phosphate in Plant Defense
Department of Plant Pathology
Plant diseases have a devastating impact on agricultural production every year and annual worldwide crop losses due to disease have been estimated in excess of $100 billion. The use of resistant varieties, pesticide use, and cultural practices such as crop rotation, are often unsuccessful in providing sustained protection against microbial pathogens. Strategies involving the induction of the host's intrinsic defenses could provide growers with an efficient and cost-effective alternative to combat plant diseases. Such an approach would require a thorough understanding of the molecular mechanism(s) underlying pathogen perception and resistance.
2009 Project Description
Study of fatty acid metabolism and defense signaling has resulted in novel findings that have improved our understanding of Arabidopsis and soybean defense signaling pathways. These research findings were presented in three oral and four poster presentations at Annual Society (American Phytopathological Society, American Society of Plant Biology). Work related to this project has also resulted in the training of two undergraduate, four graduate and two postdoctoral researchers.
1. Resistance (R) protein-associated pathways are well known to participate in defense against a variety of microbial pathogens. Salicylic acid (SA) and its associated proteinaceous signaling components, including enhanced disease susceptibility 1 (EDS1), non-race-specific disease resistance 1 (NDR1), phytoalexin deficient 4 (PAD4), senescence associated gene 101 (SAG101) and EDS5, have been identified as components of resistance derived from many R proteins. We showed that EDS1 and SA fulfill redundant functions in defense signaling mediated by R proteins, which were thought to function independent of EDS1 and/or SA. Simultaneous mutations in EDS1 and the SA-synthesizing enzyme SID2 compromised hypersensitive response and/or resistance mediated by R proteins that contain coiled coil domains at their N-terminal ends.
Furthermore, the expression of R genes and the associated defense signaling induced in response to a reduction in the level of oleic acid (18:1) was also suppressed by compromising SA biosynthesis in the eds1 mutant background. The functional redundancy with SA was specific to EDS1. These results redefine our understanding of the roles of EDS1 and SA in plant defense.
2. We have also established a novel link between glycerol-3-phosphate metabolism and plant defense. The G3P levels in plants are associated with defense to a hemibiotrophic fungal pathogen Colletotrichum higginsianum as well as to R protein-mediated resistance.
3. We showed that a defect in cuticle, which forms the outermost structure of the leaf, impairs the plants ability to perceive the mobile systemic acquired resistance (SAR) signal in distal tissues. Several components required for normal development of cuticle have been identified and these were evaluated for their role in plant defense to pathogens.
4. We have evaluated role of photoreceptors in plant defense to pathogens. Our results demonstrate that photoreceptors are required for stability and/or signaling mediated by R proteins. These data have been submitted for publication in a peer-review journal.
Kachroo A, Kachroo P. (2009) Fatty acid derived signals in plant defense. Annual Review of Phytopathology 47:153-176
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
Chanda B, Venugopal SC, Kulshrestha S, Navarre DA, Downie B, Vaillancourt L, Kachroo A, Kachroo P. (2008) Glycerol-3-phosphate levels are associated with basal resistance to the hemibiotrophic fungus Colletotrichum higginsianum in Arabidopsis. Plant Physiology 147:2017-2029