Antisense-mediated depletion of potato leaf omega 3 fatty acid desaturase lowers linolenic acid content and reduces gene activation in response to wounding

Fatty acid omega 3 desaturases act on membrane lipids to catalyse the forma tion of trienoic fatty acids, the most abundant in plant tissues being alph a-linolenic acid. This fatty acid is a precursor of jasmonic acid, a plant growth regulator involved in the control of wound-induced gene activation i n plants and in the induction of tuberization in potato. We isolated a pota to omega 3 desaturase cDNA, possibly encoding a plastidial isoform, and use d it to investigate its expression pattern throughout plant development and in response to wounding. Plastidial omega 3 desaturase gene transcripts ac cumulate rapidly upon wounding, preceding the jasmonate-dependent induction of the wound-responsive proteinase inhibitor II gene. We generated transge nic potato plants constitutively expressing an antisense RNA to this plasti dial omega 3 desaturase. Selected transgenic lines in which the cognate ome ga 3 desaturase mRNA is largely depleted show a marked reduction, of up to 60%, in trienoic acids in leaves and tubers. In these lines, a correspondin g reduction in jasmonate content and proteinase inhibitor II expression is observed upon wounding. Our results indicate that a reduction in omega 3 de saturase mRNA levels compromises the wound-induced activation of proteinase inhibitor II, suggesting that wound-induced synthesis of linolenic acid is required for jasmonic acid production. The antisense-mediated depletion of fatty acid omega 3 desaturases is a viable alternative for reducing trieno ic fatty acid content in plant species in which a mutant screening approach is not applicable.