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Jasmonic acid (JA) regulates plant growth, development, and stress responses. Coronatine insensitive 1 (COI1) and jasmonate ZIM-domain (JAZ) proteins form a receptor complex for jasmonoyl-l-isoleucine (JA-Ile), 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, 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.

When wounding or grafting interrupts the original connection of plant tissue, cell proliferation is induced and the divided tissue is reunited. Previous studies suggested that gibberellin derived from the cotyledon is required for tissue reunion in cucumber and tomato incised hypocotyls, and tissue reunion of Arabidopsis incised flowering stems is controlled by auxin. Differences in the hormone requirements of the tissue reunion process between Arabidopsis and cucumber might be due to differences in organs or species. In this study, we performed morphological and gene expression analyses of graft union in Arabidopsis hypocotyl. We found that removal of the cotyledon and treatment of the cotyledon with the auxin transport inhibitor triiodobenzoic acid (TIBA) suppressed cell proliferation of vascular tissue during graft union formation. These treatments also suppressed expression of IAA5, ANAC071, ANAC096 and CYCB1;1. ANAC071 is involved in the tissue reunion process. The anac071 anac096 double mutant suppressed cell proliferation more so than either of the single mutants. On the other hand, paclobutrazol treatment or deficiency of gibberellin biosynthesis genes suppressed expansion of cortex cells, and exogenous gibberellin treatment or rga/gai mutations that lack the negative regulator of gibberellin reversed this inhibition. The up-regulation of the key gibberellin biosynthesis gene GA20ox1 during graft union formation was prevented by cotyledon removal or TIBA treatment. These data suggest that auxin regulates cell proliferation of vascular tissue and expansion of cortex cells by promoting gibberellin biosynthesis during graft attachment. We hypothesize that the cotyledon-derived phytohormones are essential for graft reunion of the hypocotyl, processed in a cell type-specific manner, in Arabidopsis.