Glycerolipid Metabolism and its Role in Plant Defense

The salicylic acid (SA)-, jasmonic acid (JA)- and ethylene-mediated plant defense pathways act independently, synergistically as well as antagonistically, thus undergoing extensive cross talk. We have recently shown that a fatty acid (FA) regulated pathway is involved in modulating both the SAand JA-related responses in Arabidopsis. We identified three genes, all of which participate in the prokaryotic FA pathway and modulate SA and JA pathways in the Arabidopsis desaturase deficient (ssi2) mutant. Loss-of-function mutations in the genes encoding for glycerol-3-phosphate (G3P) acyltransferase, G3P dehydrogenase and a membrane associated w6 desaturase restore wild-type like phenotypes in the ssi2 plants. Our work with these mutants has demonstrated that complementation of the ssi2-triggered phenotypes involves restoration of oleic acid (18:1) levels in ssi2 plants. Our work also shows that a reduction in 18:1 levels caused by the glycerol application coverts wild-type plants into ssi2-mimics. Furthermore, sensitivity of wild-type plants to glycerol application was enhanced by overexpression of the ACT1 gene, which acylates G3P and 18: 1. These results suggest that 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 SA- and JA-mediated signaling pathways. In the proposed work, we aim to isolate mutants that render plants tolerant to glycerol and study their role in plant defense. In addition, we will attempt to identify 18:1 binding proteins and study their role in plant defense. Our work will help investigate and better understand the emerging role of FAs and glycerolipid metabolism in the plant defense.