Jasmonic Acid: Genetic Pathway, Signal Transduction and Action in Plant Development and Defence

Jasmonic acid (JA) is one of the most signaling phytohormones which play an essential role in plant development and response to biotic and abiotic stresses. It plays a key regulatory role in root elongation, pollen production, germination, fruit ripening, plant senescence. Additionally, it activates plant defenses against pests, pathogens and abiotic stress. Jasmonic acid and its derivative methyl jasmonate are abundant in plant cellsand have a physiological signaling mechanism. Recently, jasmonates have been reported to be the active forms precursors comprising certain amino acid conjugates. Jasmonates are generally synthesized and accumulated upon environmental or developmental stimuli. Jasmonate signal transduction process is regulated by a signaling mechanism embracing certain repressor proteins which control different transcription factors regulating the expression of jasmonate responsive genes.

The first step of JA synthesis takes place in chloroplasts membranes, where a phospholipase generates both of α-linolenic acid and hexadecatrienoic acid from membrane phospholipids. JAs synthesisoccurs generally from the α-linolenic acid precursor through the octadecanoidpathway. Chloroplastic 13-lipoxygenase oxidizes αLA forming the 13-hydroperoxy derivative of linolenic acid. The Arabidopsis genome comprises six genes encoding lipoxygenases. Three of such genes (LOX2, LOX3 and LOX4) regulate JA production. The next steps of JA synthesis occur in the peroxisome.