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Accumulation of eicosapolyenoic acids enhances sensitivity to abscisic acid and mitigates the effects of drought in transgenic Arabidopsis thaliana

Yuan, Xiaowei, Li, Yaxiao, Liu, Shiyang, Xia, Fei, Li, Xinzheng, Qi, Baoxiu
Journal of experimental botany 2014 v.65 no.6 pp. 1637-1649
Arabidopsis thaliana, Isochrysis galbana, abscisic acid, alpha-linolenic acid, arachidonic acid, biochemical pathways, biomass, biosynthesis, docosahexaenoic acid, drought, drought tolerance, eicosapentaenoic acid, gene expression regulation, genes, genetically modified organisms, leaf area, leaves, linoleic acid, mannitol, metabolites, microalgae, osmotic stress, seed germination, seedlings, stomata
IgASE1, a C18 Δ9-specific polyunsaturated fatty acid elongase from the marine microalga Isochrysis galbana, is able to convert linoleic acid and α-linolenic acid to eicosadienoic acid and eicosatrienoic acid in Arabidopsis. Eicosadienoic acid and eicosatrienoic acid are precursors of arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid, which are synthesized via the Δ8 desaturation biosynthetic pathways. This study shows that the IgASE1-expressing transgenic Arabidopsis exhibited altered morphology (decreased leaf area and biomass) and enhanced drought resistance compared to wild-type plants. The transgenic Arabidopsis were hypersensitive to abscisic acid (ABA) during seed germination, post-germination growth, and seedling development. They had elevated leaf ABA levels under well-watered and dehydrated conditions and their stomata were more sensitive to ABA. Exogenous application of eicosadienoic acid and eicosatrienoic acid can mimic ABA and drought responses in the wild type plants, similar to that found in the transgenic ones. The transcript levels of genes involved in the biosynthesis of ABA (NCED3, ABA1, AAO3) as well as other stress-related genes were upregulated in this transgenic line upon osmotic stress (300mM mannitol). Taken together, these results indicate that these two eicosapolyenoic acids or their derived metabolites can mitigate the effects of drought in transgenic Arabidopsis, at least in part, through the action of ABA.