The slow wound-response of γVPE is regulated by endogenous salicylic acid in Arabidopsis

Vacuolar processing enzyme (VPE) is a cysteine protease responsible for the maturation of various vacuolar proteins in higher plants. The Arabidopsis thaliana (L.) Heynh. gammaVPE gene, encoding a VPE homologue, is slowly up-regulated in both local and systemic leaves in response to wounding. To clarify the activation mechanism of gammaVPE, we examined the accumulation of gammaVPE mRNA after hormone treatments or after wounding in wild-type and various mutant plants of Arabidopsis. Both ethylene and jasmonic acid (JA) are known as signal molecules that activate the wound-responsive genes. However, treatment with exogenous JA had little effect on the gammaVPE response, although JA activated the vegetative storage protein (VSP) gene, a typical wound-responsive gene. Wounding activated gammaVPE even in two ethylene-insensitive plants (etr1-1 and ein2-1). Thus, the wound-induced expression of gammaVPE was independent of ethylene and JA. We found that the wound-induced expression of gammaVPE was reduced in two SA-deficient plants (pad4-1 and NahG), while the wound-induced expression of VSP increased in these mutants. Appreciable accumulation of SA was not observed in either the local or systemic leaves after wounding. These results suggest that endogenous SA enhances the wound-induced expression of gammaVPE and attenuates the wound-induced expression of VSP, although SA is not a wound-signal that directly activates these genes.