KSEF R&D Excellence: Identification of Signal (s) Modulating Cross Talk Between Defense Signaling Pathways

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 specific interactions 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. However, the mechanism of cross talk among these pathways is still unclear. ssi2 mutant, which is constitutively activated in SA mediated responses and repressed in JA mediated defense signaling, provides us with an ideal system to understand cross talk among these pathways. 55/2 encodes stearoyl- ACP desaturase (S-ACP-DES), which plays an important role in regulating the levels of fatty acid (FA) desaturation. Although S-ACP-DES catalyzes the initial desaturation step required for biosynthesis of JA precursor linolenic acid, a mutation in ssi2 does not alter the levels of linolenic acid or the induced endogenous levels of JA. This has led us to postulate that S-ACP-DES possibly generates a FA signal, which is required for activation of certain JA mediated responses and repression of the SA signaling pathway. This has now been confirmed by identifying a suppressor gene, which upregulates 18:1 levels in ssi2 plants and rescues defective cross talk in these plants. However, it is not clear how 18:1 modulates the cross talk between SA- and JA-pathways and in the proposed study we will attempt to understand biochemical basis of the cross talk and identify signal(s), which modulate cross talk. The proposed work is likely to reveal novel information about role of FA signal molecules and how they participate in regulation of defense pathways.