Abstract: The Mediator complex serves as a critical bridge linking transcription factors (TFs) to RNA polymerase II during mRNA synthesis. Among its subunits, MED25 plays a pivotal role in jasmonate (JA) signaling by directly interacting with the master TF of the JA pathway. However, the biological functions of MED25 in monocotyledonous plants, particularly its contribution to JA-mediated responses in rice, remain largely unexplored. Here, we mutated OsMED25 in rice using CRISPR/Cas9-based genome editing and evaluated JA-mediated developmental and defense phenotypes in these osmed25 mutants, JA-deficient allene oxide cyclase (osaoc) mutants, and wild-type plants. We found that osmed25 mutants exhibited defective anther dehiscence and open husks but normal spikelet morphology, whereas osaoc displayed severe spikelet developmental defects, including non-dehiscent anthers. Notably, OsMED25 is essential for rice resistance against the brown planthopper (BPH). While osaoc mutants completely lost JA responsiveness, osmed25 mutants displayed only partial impairment of BPH-induced JA-responsive gene expression, accompanied by a selective reduction in the accumulation of defensive specialized metabolites (e.g., phenolamides and volatile terpenes). Furthermore, OsMED25 participates in a feedback loop modulating JA biosynthesis during BPH infestation. Collectively, our study uncovers the role of OsMED25 in regulating a subset of JA-dependent spikelet development and herbivore resistance in rice.

Key words: rice, jasmonate, MED25, spikelet development, brown planthopper, specialized metabolites