The group I GH3 family genes encoding JA-Ile synthetase act as positive regulator in the resistance of rice to Xanthomonas oryzae pv. oryzae.

Plant GH3 genes are key components of the hormonal mechanism regulating growth and development, responding to biotic and abiotic stress. GH3 proteins are involved in hormonal homeostasis through conjugation to amino acids of the free form of salicylic acid, jasmonic acid (JA) or indole-3-acetic acid (IAA). Our previous work has uncovered that two GH3 genes encoding IAA-amido synthetase play important roles in the resistance to bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo) in rice, however, whether other rice GH3 genes play roles in resistance to Xoo is unclear. Here, we validated that GH3.3, GH3.5, GH3.6 and GH3.12, four members of group I GH3 family, are the functional JA-Ile synthetases by catalyzing the conversion of free JA into active form of JA-Ile in vitro and in vivo. The overexpressing plants of four genes individually accumulated less JA but more JA-Ile than the wild type plants. Conversely, the corresponding suppressing plants of four genes contained comparable JA and JA-Ile concentrations, but the triple and quadruple suppressing plants had lower level of JA-Ile compared with wild type plants, suggesting functional redundancy of the same clade of GH3 family. Furthermore, the group I GH3 family genes positively mediated rice resistance to bacterial pathogen Xoo through modulating JA homeostasis and regulating transcription pattern of JA-responsive genes.

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