COI1-mediated perception of jasmonate is critical for plant development and responses to environmental stresses. Monocots such as rice have two groups of COI genes due to gene duplication: OsCOI1a and OsCOI1b that are functionally equivalent to the dicotyledons COI1 and OsCOI2 whose function remains unclear. In order to assess the function of OsCOI2 and its functional redundancy with COI1 genes, we developed a series of rice mutants in the 3 genes OsCOI1a, OsCOI1b and OsCOI2 by CRISPR Cas9-mediated editing and characterized their phenotype and responses to jasmonate. Characterization of OsCOI2 uncovered its important roles in root, leaf and flower development. In particular, we show that crown root growth inhibition by jasmonate relies on OsCOI2 and not on OsCOI1a nor on OsCOI1b, revealing a major function for the non-canonical OsCOI2 in jasmonate-dependent control of rice root growth. Collectively, these results point to a specialized function of OsCOI2 in the regulation of plant development in rice and indicate that sub-functionalisation of jasmonate receptors has occurred in the monocot phylum.
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