Wound response in passion fruit (Passiflora f. edulis flavicarpa) plants: gene characterization of a novel chloroplast-targeted allene oxide synthase up-regulated by mechanical injury and methyl jasmonate.

The induction of a chloroplast-localized 13-lipoxygenase (13-LOX) in passion fruit leaves in response to methyl jasmonate (MeJa) was previously reported. Since allene oxide synthase (AOS) is a key cytochrome P450 enzyme in the oxylipin pathway leading to AOS-derived jasmonates, the results above led in turn to an investigation of AOS in our model plant. Spectrophotometric assays showed that 24 h exposure of MeJa caused a high increase in 13-hydroperoxy linolenic acid (13-HPOT) metabolizing activity in leaf tissue. Western analysis using polyclonal antibodies against tomato AOS strongly indicate that, at least a part of the 13-HPOT metabolizing capacity can be attributed to AOS activity. We cloned the cDNA from a novel AOS encoding gene from passion fruit, named PfAOS. The 1,512 bp open reading frame of the AOS-cDNA codes a putative protein of 504 amino acid residues containing a chloroplast target sequence. Database comparisons of the deduced amino acid sequence showed highest similarity with dicot AOSs. Immunocytochemistry analysis showed the compartmentalization of AOS in chloroplasts of MeJa treated leaves, corroborating the predicted subcellular localization. Northern analysis showed that AOS gene expression is induced in leaf tissue in response to mechanical wounding and exposure to MeJa. In addition, such treatments caused an increase in papain inhibitor(s) in leaf tissue. Taken together, these results indicate that PfAOS may play an important role in systemic wound response against chewing insect attack. Furthermore, it can be useful as a tool for understanding the regulation of jasmonates biosynthesis in passion fruit.