Mining of <i>CtOPR2</i> as an essential gene regulating jasmonic acid mediated insect tolerance in <i>camellia tachangensis</i> through genome-wide association studies

Abstract Jasmonic acid (JA), a pivotal lipid-derived phytohormone, serves as a critical regulator in plant growth and defense mechanisms. However, the genetic mechanisms of OPR2 gene in JA-dependent biotic defenses of Camellia tachangensis have rarely been investigated. In this study, we performed a genome-wide association study (GWAS) to analyze 100 720 high-quality single nucleotide polymorphisms (SNPs) among 350 tea accessions from Guizhou province to identify genetic variations associated with JA. Analysis showed C. tachangensis displayed higher levels of JA content, further analysis identified 60 high-quality SNPs and 9 candidate genes related to JA. Among them, CtOPR2 encoding 12-oxophytodienoic acid reductase 2 is responsible for catalyzing the conversion of 4,5-didehydro-JA (4,5-ddh-JA) to JA. The expression level of CtOPR2 in three tea accessions with different JA content was consistent with the dynamic changes of JA content. The expression level of synthetic (AOS, AOC and ACX) and responsive (WRKY18 and MYC2) genes were significantly decreased and increased in asODN-CtOPR2-treated shoot tips and transgenic tobacco lines overexpressing CtOPR2, respectively, which were consistent with the JA content. These results further revealed that CtOPR2 gene played essential roles in promoting JA biosynthesis. A significant reduction in insect bite area was observed on transgenic tobacco leaves compared to wild-type (WT) leaves in feeding experiments with Spodoptera litura, highlighting that the positive regulatory function of CtOPR2 gene in JA-mediated immune responses. This study provides a robust theoretical foundation for marker-assisted selection (MAS) breeding in tea, aimed at developing high-JA germplasm with potentially enhanced pest resistance for cultivation in Guizhou.