REU: Molecular, genetic, and biochemical characterization of oleate-regulated defense geneexpression in plants

The undergraduate intern, Mr. Jared Gabbert, for whom funds are requested will perform independent research projects that work towards the completion of a portion of the NSF-funded project (IOS 1051909) related to elucidating the role of oleic acid regulated metabolism in plant defense. The objectives of their research will be to characterize promoter domains that respond to 18:1 levels and responsible for upregulation of resistance (R) genes. Project outline Stearoyl-acyl carrier protein desaturase (SACPD) is one of the conserved enzymes among plants, which catalyzes the first desaturation step in fatty acid biosynthesis (conversion of stearate to oleate). In plants, changes in the levels of oleic acid (18:1), a major monounsaturated fatty acid (FA), results in the alteration of salicylic acid (SA)- and jasmonic acid (JA)-mediated defense responses. This is evident in the Arabidopsis ssi2/fab2 mutant, which owing to its defect in SACPD accumulates high levels of stearic acid (18:0) and reduced levels of 18:1. Consequently, replenishing 18:1 levels results in the restoration of wild-type (wt)-like signaling in the ssi2 mutant. We have identified several genes, loss-of-function of which, restore the altered defense signaling in ssi2 plants. The 18:1 content in wt plants can be lowered by glycerol application to produce ssi2-like phenotypes. The Arabidopsis mutants impaired in glycerol catabolism or generation of glycerol-3-phosphate (G3P) do not induce the SA pathway and fail to reduce their 18:1 levels after glycerol application. The plants overexpressing the ACT1 gene (encodes G3P acyltransferase) metabolize G3P rapidly and are more sensitive to glycerol application. Conversely, a mutation in act1 rescues hypersensitivity to glycerol. The 18:1 levels in plastids are regulated via acylation with G3P and a balance between G3P and 18:1 is critical for the regulation of defense signaling pathways. Moreover, loss of activity of SACPD, and thereby the reduced levels of 18:1 induce the expression of a variety of resistance (R) genes, which in turn confer broad-spectrum disease resistance to multiple pathogens.