Transcriptomics and trans-organellar complementation reveal a limited signaling capacity of 12-cis-oxo-phytodienoic acid in wounded Arabidopsis

Abstract

12-cis-Oxo-phytodienoic acid (OPDA), the main precursor of the key plant growth and defense hormone jasmonoyl-isoleucine (JA-Ile), is believed to have distinct signaling roles in plants responses to stress. In Arabidopsis, insights into OPDA functions have been gained from studying a mutant, which is affected in the conversion of OPDA by missing OPDA REDUCTASE3 (OPR3). opr3 mutants, however, accumulate JA-Ile through a cytosolic bypass mediated by OPR2. Therefore, wound-induced transcriptome of opr2opr3 in comparison to wild-type and allene oxide synthase mutant was analyzed to unravel OPDA signaling. Results showed that OPDA lacked a distinct transcriptional signature, whereas known OPDA-response genes were wound-induced independently of OPDA. The application of OPDA to opr2opr3 resulted in a distinct transcriptional response compared to the endogenous rise of OPDA in the same mutant, with the activation of the sulfur assimilation pathway genes occurring only with the external application of the compound. These findings suggested a compartmentalization of endogenously produced OPDA, investigated further through trans-organellar complementation. OPR3 complemented opr2opr3 mutants in fertility and wound-induced JA-Ile production regardless of its localization. Since in vitro enzymatic studies revealed OPR3s activity on both OPDA and 4,5-ddh-JA, conclusions on translocation of OPDA were not unequivocal. Dissecting the conversion of either OPDA or 4,5-ddh-JA by OPR2 and OPR1 organelle variants pointed, however, to a strong OPDA compartmentalization supporting its lacking signaling function.