Molecular biology of jasmonic acid biosynthesis in plants

Jasmonic acid, a linolenic acid-derived cyclopentanone, plays regulatory ro les in plant development and responses to environmental stresses, such as m echanical wounding or pathogen attack. The action of JA in regulating plant growth and stress responses often requires the elevation of endogenous lev els by de novo synthesis. An especially well studied case has been the synt hesis of JA in response to wounding. Jasmonates are synthesised through the octadecanoid pathway, in which linolenic acid is converted into JA by a pr ocess that is likely to begin in chloroplasts and end in peroxisomes. Conve rsion of linolenic acid to 12-oxo-phytodienoic acid in chloroplasts is acco mplished through a multi-step enzymatic process involving lipoxygenase, all ene oxide synthase and allene oxide cyclase. JA synthesis proceeds with the action of a cytoplasmic 12-oxo-phytodienoic acid reductase and three round s of beta-oxidation that take place in peroxisomes. Most of the enzymes and the corresponding coding genes involved have been isolated and characteris ed in different plant species. The majority of these genes are transcriptio nally activated by wounding and some of them are also activated by JA, allo wing feed-back regulation of the biosynthetic pathway. (C) Elsevier, Paris.