A CHLOROPLAST LIPOXYGENASE IS REQUIRED FOR WOUND-INDUCED JASMONIC ACID ACCUMULATION IN ARABIDOPSIS

Plant lipoxygenases are thought to be involved in the biosynthesis of lipid-derived signaling molecules, The potential involvement of a spec ific Arabidopsis thaliana lipoxygenase isozyme, LOX2, in the biosynthe sis of the plant growth regulators jasmonic acid (JA) and abscisic aci d was investigated. Our characterization of LOX2 indicates that the pr otein is targeted to chloroplasts. The physiological role of this chlo roplast lipoxygenase;was analyzed in transgenic plants where cosuppres sion reduced LOX2 accumulation. The reduction in LOX2 levels caused no obvious changes in plant growth or in the accumulation of abscisic ac id. However, the wound-induced accumulation of JA observed in control plants was absent in leaves of transgenic plants that lacked LOX2. Thu s, LOXZ is required for the wound-induced synthesis of the plant growt h regulator JA in leaves. We also examined the expression of a wound- and JA-inducible Arabidopsis gene, vsp, in transgenic and control plan ts. Leaves of transgenic plants lacking LOX2 accumulated less vsp mRNA than did control leaves in response to wounding, This result suggests that wound-induced JA (or some other LOX2-requiring component of the wound response pathway) is involved in the wound-induced regulation of this gene.