Genome Editing Reveals Both the Crucial Role of OsCOI2 in Jasmonate Signaling and the Functional Diversity of COI1 Homologs in Rice

Jasmonic acid (JA) regulates plant growth, development and stress responses. Coronatine insensitive 1 (COI1) and jasmonate zinc-finger inflorescence meristem-domain (JAZ) proteins form a receptor complex for jasmonoyl-l-isoleucine, a biologically active form of JA. Three COIs (OsCOI1a, OsCOI1b and OsCOI2) are encoded in the rice genome. In the present study, we generated mutants for each rice COI gene using genome editing to reveal the physiological functions of the three rice COIs. The oscoi2 mutants, but not the oscoi1a and oscoi1b mutants, exhibited severely low fertility, indicating the crucial role of OsCOI2 in rice fertility. Transcriptomic analysis revealed that the transcriptional changes after methyl jasmonate (MeJA) treatment were moderate in the leaves of oscoi2 mutants compared to those in the wild type or oscoi1a and oscoi1b mutants. MeJA-induced chlorophyll degradation and accumulation of antimicrobial secondary metabolites were suppressed in oscoi2 mutants. These results indicate that OsCOI2 plays a central role in JA response in rice leaves. In contrast, the assessment of growth inhibition upon exogenous application of JA to seedlings of each mutant revealed that rice COIs are redundantly involved in shoot growth, whereas OsCOI2 plays a primary role in root growth. In addition, a co-immunoprecipitation assay showed that OsJAZ2 and OsJAZ5 containing divergent Jas motifs physically interacted only with OsCOI2, whereas OsJAZ4 with a canonical Jas motif interacts with all three rice COIs. The present study demonstrated the functional diversity of rice COIs, thereby providing clues to the mechanisms regulating the various physiological functions of JA.