Roles of plastid omega-3 fatty acid desaturases in defense response of higher plants

In higher plants, the membrane lipids contain a high proportion of trienoic fatty acids, it has been suggested that these fatty acids, especially lino lenic acid, play an important role as a precursor to a defense-related sign al molecule, jasmonate, In Arabidopsis, three genes encoding the omega-3 fa tty acid desaturase, namely, FAD3, FAD7 and FADE, are responsible for the p roduction of trienoic fatty acids. The FAD3 enzyme is localized in microsom es, while the FAD7 and the FAD8 enzymes are localized in plastid membranes. Environmental stimuli, such as wounding, salt stress and pathogen invasion , which lead to a rapid increase in jasmonate production, significantly ind uce expression of the FAD7 and FAD8 genes. Recent findings have supported t he view that plastids are involved in jasmonate production. We have been ab le to clarify the regulatory mechanism of a plastid w-3 desaturase gene by analyzing the Arabidopsis FAD7 promoter with respect to tissue-specific, li ght-responsive and wound-induced expression. In particular, this promoter p rovides a unique model for studying the mechanism of transcriptional activa tion through wound signal transduction pathways.