Different -Regulatory Elements Control the Tissue-Specific Contribution of Plastid ω-3 Desaturases to Wounding and Hormone Responses.

Trienoic fatty acids are essential constituents of biomembranes and precursors of jasmonates involved in plant defense responses. Two ω-3 desaturases, FAD7 and FAD8, synthetize trienoic fatty acids in the plastid. Promoter:GUS and mutagenesis analysis was used to identify -elements controlling and basal expression and their response to hormones or wounding. promoter GUS activity was much higher than that of in leaves, with specific expression in the flower stamen and pistil and root meristem and vasculature. This specific tissue and organ expression of was controlled by different -elements. Thus, promoter deletion and mutagenesis analysis indicated that WRKY proteins might be essential for basal expression of in leaves. Two MYB target sequences present in the promoter might be responsible for its expression in the flower stamen and stigma of the pistil and in the root meristem, and for the wound-specific response. Two MYB target sequences detected in the distal region of the gene promoter seemed to negatively control expression, particularly in true leaves and flowers, suggesting that MYB transcription factors act as repressors of gene basal expression, modulating the different relative abundance of both plastid ω-3 desaturases at the transcriptional level. Our data showed that the two ABA repression sequences detected in the promoter were functional, suggesting an ABA-dependent mechanism involved in the different regulation of both ω-3 plastid desaturases. These results reveal the implication of different signaling pathways for the concerted regulation of trienoic fatty acid content in Arabidopsis.