Identification and Symbiotic Phenotype Characterization of an OPDA Reductase Gene AsOPR1 in Chinese Milk Vetch

Abstract

In higher plants, the 12-oxo-phytodienoic acid reductase (OPR) family mainly consists of two subgroups. OPR3-like enzymes belong to subgroup II, and they were proved to be key functional enzymes participating in jasmonic acid (JA) biosynthesis, while functions of OPR1-like enzymes classified into subgroup I remain largely unclear, particularly in symbiosis. This study identified and functionally characterized a gene encoding 12-oxophytodienoate reductase in Astragalus sinicus. Sequence homology analysis indicated that this gene encodes an OPR1-like enzyme. It was found that the gene expression of AsOPR1 was upregulated after inoculation with Mesorhizobium huakuii 7653R. Subcellular localization showed that in uninfected host plant cells, AsOPR1 was localized in the amyloplast, a differentiated form of plastid; while in the infected cells, AsOPR1 co-localized with rhizobia. Knockdown of the AsOPR1 gene decreased the nodule number to 34.6% that of the control roots, and significantly reduced the JA level in both transgenic roots and nodules, while overexpression of the AsOPR1 gene resulted in enlarged nodule meristem, but caused no changes in nodule number. Taken together, these results indicate that AsOPR1 may participate in the regulation of nodule formation and development, as well as affect endogenous JA metabolism.