Parsley (Petroselinum crispum) plants and suspension-cultured cells have been used extensively for studies of non-host-resistance mechanisms in plant͞pathogen interactions. We now show that treatment of cultured parsley cells with a defined peptide elicitor of fungal origin causes rapid and large changes in the levels of various unsaturated fatty acids. While linoleic acid decreased and linolenic acid increased steadily for several hours, comparatively sharp increases in oleic acid followed a biphasic time course. In contrast, the overall level of stearic acid remained unaffected. Using a PCR-based approach, a parsley cDNA was isolated sharing high sequence similarity with -3 fatty acid desaturases. Subsequent isolation and characterization of a fulllength cDNA enabled its functional identification as a plastidlocalized -3 fatty acid desaturase by complementation of the Arabidopsis thaliana fad7͞8 double mutant which is low in trienoic fatty acids. -3 Fatty acid desaturase mRNA accumulated rapidly and transiently in elicitor-treated cultured parsley cells, protoplasts, and leaves, as well as highly localized around fungal infection sites in parsley leaf buds. These results indicate that unsaturated fatty acid metabolism is yet another component of the highly complex, transcriptionally regulated pathogen defense response in plants.

In parsley (Petroselinum crispum), members of the ELI7 gene family were rapidly transcriptionally activated following treatment with an elicitor derived from the phytopathogen Phytophthora sojae. Several cDNA and genomic ELI7 clones were isolated. The deduced amino acid sequences revealed close similarity to fatty acid desaturases/hydroxylases, however, the precise functions are still unknown. Analysis of the promoters of two strongly elicitor-induced family members, ELI7.1 and ELI7.2, allowed us to functionally pinpoint a novel, independently acting regulatory region (S box), the only major sequence similarity between the two gene promoters. In situ RNA/RNA hybridization using an ELI7.1 gene-specific probe demonstrated that expression of this gene is rapidly and locally induced around infection sites in planta as well.