Poster: Late and Moved Abstracts

Abs # 1399: Fatty acid signaling modulates cross talk between salicylic acid- and jasmonic acid-dependent defense signaling pathways in the ssi2 mutant of Arabidopsis

Presenter:	Kachroo, Aardra , apkach2@uky.edu
Authors	Kachroo, Aardra  (A)   Hirotada, Fukushigae  (B)   David, Hildebrand  (B)   Daniel, Klessig F (C)   Pradeep, Kachroo  (A)
Affiliations:	(A): Department of Plant Pathology, University of Kentucky (B): Department of Agronomy, University of Kentucky (C): Boyce Thompson Institue, Cornell University

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 remains to be elucidated. The ssi2 mutant, constitutively activated in SA-mediated responses and repressed in JA-mediated signaling, provides us with an ideal system to understand cross talk among SA and JA pathways. SSI2 encodes stearoyl-ACP desaturase (S-ACP-DES), which along with other soluble fatty acid (FA) desaturases, plays an important role in regulating levels of FA desaturation 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 linolenic acid (18:3), perception of JA or the induced endogenous levels of JA. This has led us to postulate that the S-ACP-DES derived FA oleic acid (18:1) or its derivative is required for activation of certain JA-mediated responses and repression of the SA signaling pathway. We have identified several genes involved in the FA pathway, which when mutated can restore ssi2 phenotypes either partially or completely. Our studies indicate that increase in the levels of 18:1 in specific compartments of the cell leads to restoration of wt phenotypes in ssi2 plants. Furthermore, reversion of JA responsiveness involves a step upstream of the COI1 gene in the JA pathway. These results suggest that FA signaling regulates cross talk between SA and JA pathways.