RAPID, TRANSIENT, AND HIGHLY LOCALIZED INDUCTION OF PLASTIDIAL OMEGA-3-FATTY-ACID DESATURASE MESSENGER-RNA AT FUNGAL INFECTION SITES IN PETROSELINUM-CRISPUM

Parsley (Petroselinum crispum) plants and suspension-cultured cells ha ve been used extensively for studies of non-host-resistance mechanisms in plant/pathogen interactions, We now show that treatment of culture d parsley cells with a defined peptide elicitor of fungal origin cause s rapid and large changes in the levels of various unsaturated fatty a cids, While linoleic acid decreased and linolenic acid increased stead ily for several hours, comparatively sharp increases in oleic acid fol lowed a biphasic time course, In contrast, the overall level of steari c acid remained unaffected, Using a PCR-based approach, a parsley cDNA was isolated sharing high sequence similarity with omega-3 fatty acid desaturases. Subsequent isolation and characterization of a full-leng th cDNA enabled its functional identification as a plastid-localized o mega-3 fatty acid desaturase by complementation of the Arabidopsis tha liana fad7/8 double mutant which is low in trienoic fatty acids, omega -3 Fatty acid desaturase mRNA accumulated rapidly and transiently in e licitor-treated cultured parsley cells, protoplasts, and leaves, as we ll as highly localized around fungal infection sites in parsley leaf b uds. These results indicate that unsaturated fatty acid metabolism is yet another component of the highly complex, transcriptionally regulat ed pathogen defense response in plants.