Intronic microRNA-directed regulation of mitochondrial reactive oxygen species enhances plant stress tolerance in Arabidopsis

• MicroRNAs (miRNAs) play crucial roles in regulating plant development and stress responses. However, the functions and mechanism of intronic miRNAs in plants are poorly understood.
• This study reports a stress-responsive RNA splicing mechanism for intronic miR400 production, whereby miR400 modulates reactive oxygen species (ROS) accumulation and improves plant tolerance by downregulating its target expression.
• To monitor the intron splicing events, we used an intronic miR400 splicing-dependent luciferase transgenic line. Luciferase activity was observed to decrease after high cadmium concentration treatment due to the retention of the miR400-containing intron, which inhibited the production of mature miR400. Furthermore, we demonstrated that under Cd treatments, Pentatricopeptide Repeat Protein 1 (PPR1), the target of miR400, acts as a positive regulator by inducing ROS accumulation. Ppr1 mutation affected the Complex III activity in the electron transport chain and RNA editing of the mitochondrial gene ccmB.
• This study illustrates intron splicing as a key step in intronic miR400 production and highlights the function of intronic miRNAs as a ‘signal transducer’ in enhancing plant stress tolerance.