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

Abstract

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.

Cytochrome P450 CYP94B3 mediates catabolism and inactivation of the plant hormone jasmonoyl-L-isoleucine

“…Overproduction of JA-Ile in wounded cyp94b3 leaves indicates that this pathway operates as a negative feedback loop to effectively restrain JA-Ile accumulation. The time lag (∼30 min) in wound-induced 12OH-JA-Ile accumulation relative to JA-Ile, which accumulates immediately upon leaf damage (8,11,25), is consistent with our in vivo and in vitro data showing that JA-Ile is a substrate for CYP94B3. The absence of 12OH-JA-Ile in undamaged WT and CYP94B3-OE leaves presumably reflects the lack of CYP94B3 substrate (JA-Ile) in these tissues.…”

Role of NINJA in root jasmonate signaling

“…It has been shown previously that JAR1 activity is not strictly required for the wound-induced expression of JA-responsive genes in rosette leaves, where other JA-amino synthetases may exist to account for the remaining JAIle levels in null jar1 mutants (8,18,30). Other reports indirectly support a primary role for JAR1 in the roots.…”

“…We found that jar1-1 and jar1-13 displayed an intermediate susceptibility to S. littoralis between that of the WT and coi1-1. This could be attributed to delayed or decreased JA-Ile accumulation that activates slower or reduced downstream defense responses (8,30). In contrast, cotyledon wounding in jar1-1 and jar1-13 failed to activate JGP and JAZ10 expression in roots.…”

“…Other reports indirectly support a primary role for JAR1 in the roots. First, JAR1 mRNA levels are highest in seedling roots (30). Second, jar1-1 displayed a root-specific impairment in the activation of a wound-induced FAD7p-LUC reporter (16).…”

Spatially selective hormonal control of RAP2.6L and ANAC071 transcription factors involved in tissue reunion in Arabidopsis

“…LOX2 [encoding lipoxygenase 2 (At3g45140), a JA biosynthesis enzyme] was selected because this gene was exclusively expressed in wounded tissue (Fig. 5A) and is known to be wound-inducible (26). LOX2 expression peaked 1 d after stem cutting, with higher expression in the lower cut region (Fig.…”