The role of JAR1 in Jasmonoyl-L-isoleucine production during Arabidopsis wound response

The Arabidopsis thaliana (L.) Heynh. JASMONATE RESISTANT 1( JAR1) locus is essential for pathogen defense, but its role in wound response has not been investigated. JAR1 encodes an enzyme that conjugates jasmonic acid (JA) to isoleucine, which was recently shown to function directly in CORONATINE INSENSITIVE 1 (COI1)-mediated signal transduction. Leaf wounding rapidly increased the level of JA-Ile by about 60-fold to a peak of 279 pmole/g FW at 40 min after wounding. Conjugates with Leu, Val and Phe remained near basal level or were not detected. Kinetic analysis showed that JAR1 had a K (m) of 0.03 mM for Ile, which was 60-80-fold lower than for Leu, Val and Phe. JA-Ile accumulated mostly near the wound site with a minor increase in unwounded portions of wounded leaves. JAR1 transcript also increased dramatically in wounded tissue, reaching a maximum after about 1 h. In the jar1-1 mutant JA-Ile was only about 10% of the WT level at 40 min after leaf wounding, and reached a maximum of 47 pmole/g FW at 2 h. However, the reduced accumulation of JA-Ile had little or no effect on several jasmonate-dependent wound-induced genes. Wound induction of the VSP2 transcript was only slightly delayed while transcripts for LOX2, PDF1.2, WRKY33, TAT3 and CORI3 were unaffected. These results suggest that the rapid increase in JA-Ile mediated by the JAR1 enzyme plays only a minor role in transcriptional modulation of genes induced by mechanical wounding.