circGDSL-induced OPR3 expression regulates jasmonate signaling and copper tolerance in rice (Oryza sativa)

This study investigates the regulatory function of circular RNA (circRNA) as a competing endogenous RNA (ceRNA) in rice (Oryza sativa L.) under toxic levels of copper (Cu) stress. Physiological parameters and differences in Cu accumulation were analyzed through a hydroponic experiment. RNA sequencing (RNA-seq) identified 1051 circRNAs, of which 26 were differentially expressed (FDR <0.05, |log₂FC| > 1) under Cu stress. A Cu-responsive ceRNA network mediated by circRNAs was constructed, comprising 16 circRNAs, 34 miRNAs, and 126 mRNAs. Topological analysis identified the circGDSL/miR1850.1/OPR3 triplet as a key regulatory hub, which was experimentally validated by RT-qPCR. Overexpression of circGDSL conferred significant resistance to Cu stress, characterized by enhanced antioxidant enzyme activity, reduced reactive oxygen species (ROS) levels, and alleviated Cu-induced growth suppression. Functional studies indicated that circGDSL upregulates the expression of the key jasmonic acid (JA) synthesis gene OPR3 by sponging miR1850.1, thereby activating the JA signaling pathway. The increased endogenous JA concentration represses the expression of genes (IRT1, Nramp5, and HMA2) that promote Cu uptake and translocation, resulting in decreased Cu concentration in rice. Conversely, overexpression of miR1850.1 reduces endogenous JA concentration and increases sensitivity to Cu, a phenotype that can be rescued by exogenous methyl jasmonate (MeJA). In conclusion, we identified a Cu-responsive circRNA in rice and confirmed its role in activating JA synthesis pathway as miRNA sponge, thereby enhancing rice tolerance to Cu stress.