SCOPE A: Fatty Acid Signaling Pathway and its Role in Plant Defense

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Plant diseases have a devastating impact on agricultural production and food supply every year. The outcome of the interaction of plants with a given pathogen is governed by several factors, including the genotype, the physiological state of the plant, environmental signals and, any specific interactions that might occur between the activated signaling pathways. Among various signaling molecules proposed to modulate defense responses, salicylic acid (SA) and jasmonic acid (JA) elicit distinct responses and undergo extensive cross talk, which is likely to influence the amplitude and magnitude of various signals leading to a resistance response. However, the mechanism of cross talk between these pathways remains to be elucidated. In an effort to decipher molecular components underlying SA and JA signaling, we undertook a study of the ssi2 mutant, which is altered in both SA and JA signaling pathways. SSI2 encodes stearoyl-ACP desaturase (S-ACP-DES), which along with other soluble fatty acid (FA) desaturases, regulates the levels of unsaturated FA in the cell. Although S-ACP-DES catalyzes the initial desaturation step required for JA biosynthesis, a mutation in ssi2 does not alter the levels of the JA precursor or the endogenous levels of JA. Therefore repression of JA responses in the ssi2 mutant is not due to defects in the JA biosynthesis pathway. This led us to postulate that S-ACP-DES possibly generates a FA signal, which is required for the activation of certain JA mediated responses and repression of the SA signaling pathway. We have now been able to identify or clone three genes, which participate in the prokaryotic pathway of FA biosynthesis, and a loss-of-function of which restores the various phenotypes in ssi2 plants. This is particularly exciting because our studies suggest that FA intermediates are likely to modulate defense-signaling pathways. The genes identified thus far include glycerol-3-phosphate (G3P) dehydrogenase ( GLY1), G3P acyltransferase ( ACT1) and w6 oleic acid desaturase ( FAD6). Functional analysis of these genes indicates that oleic acid (18:1) levels regulated by glycerolipid metabolism play an important role in the regulation of defense signaling pathways. In the proposed study, we will take several different approaches to determine the role of FA signaling pathway in defense. Our first objective is to carry out oxylipin signature determination and to further characterize molecular and biochemical basis underlying restoration of various ssi2 phenotypes by mutations in the act1 and gly1 genes. Second, we have isolated several suppressors and these will be characterized followed by cloning of the mutant gene. In addition, we propose to identify other components of SSI2-mediated signaling by carrying out epistatic analysis with mutants altered in FA signaling and by initiating a screen to identify defense related glycerol-tolerant mutants. Intellectual merit of the proposed activity: Characterization of the FA signaling pathway and deciphering its role in defense would provide critical information about how various pathways interact with each other. This would have enormous implications, as it would permit us to manipulate multiple defense signaling pathways at the same time and engineer crops that are resistant to a wide variety of bacterial, fungal and viral pathogens. Broader impacts resulting from the proposed activity: The proposed research has a number of broader impacts outside of its scientific merits. Plant diseases are a significant problem in world agriculture and currently up to 30% of crop yield is lost to pests and pathogens. Previous work from the PI’s lab has shown that FA signaling pathway plays a significant role in plant defense. In addition to providing a basic understanding of the plant defense responses, our research will also help elucidate part of the very complex FA signaling pathway. The proposed research will facilitate training of undergraduate, graduate and postdoctoral students and enhance the infrastructure of research through sharing of ideas and materials generated by the proposed work. Our aim is to foster a community of undergraduate students and provide minority students with progressively sophisticated scientific experiences. We also plan to integrate our research with the extension services available at UK to enhance awareness of the recent advances in crop resistance and improve attitude towards genetically modified crops among farmers and agribusiness representatives.
Effective start/end date9/1/048/31/09


  • National Science Foundation


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