OrMKK3 Influences Morphology and Grain Size in Rice

Although morphology and grain size are important to rice growth and yield, the identity of abundant natural allelic variations that determine agronomically important differences in crops is unknown. Here, we characterized the function of mitogen-activated protein kinase 3 from Oryza officinalis Wall. ex Watt encoded by OrMKK3 . Different alternative splicing variants occurred in OrMKK3 . Green fluorescent protein (GFP)– OrMKK3 fusion proteins localized to the cell membrane and nuclei of rice protoplasts. Overexpression of OrMKK3 influenced the expression levels of the grain size-related genes SMG1 , GW8 , GL3 , GW2 , and DEP3. Phylogenetic analysis showed that OrMKK3 is well conserved in plants while showing large amounts of variation between indica , japonica , and wild rice. In addition, OrMKK3 slightly influenced brassinosteroid (BR) responses and the expression levels of BR-related genes. Our findings thus identify a new gene, OrMKK3 , influencing morphology and grain size and that represents a possible link between mitogen-activated protein kinase and BR response pathways in grain growth.