Rice(Oryza sativa L.)inflorescence(panicle)architecture is an important agronomic trait,serving as one of the determinants of rice yield.A number of genes related to panicle development have been cloned and functionally characterized so far.However,more information is needed for fully understanding of the mechanism underlying the panicle development.In the present study,we identified a clustered spikelets 4(cl4)mutant in the 93-11 genetic background.Compared to its wild-type 93-11,cl4 mutant has a typical clustered spikelets phenotype with all primary branches clustered on the base of the main rachis and 2–3abnormal spikelets clustered on the primary branches.Moreover,cl4 mutant also shows shorter plant height than that of the wild type.Map-based cloning strategy is performed to clone the CL4 gene.As a result,CL4 is demonstrated to encode a putative cytochrome P450 protein CYP724B1,which is involved in brassinosteroid biosynthesis.To confirm our mapping result,the CL4 RNAi transgenic plants are generated.And the transgenic plants also show similar phenotype as the cl4 mutant.These results provide strong evidence that CL4 plays an important role in rice panicle development as well as plant height regulation. A number of genes related to panicle development have been cloned and functionally characterized so far. needed for fully understanding of the mechanism underlying the panicle development. In the present study, we identified a clustered spikelets 4 (cl4) mutant in the 93-11 genetic background.Compared to its wild-type 93-11, cl4 mutant has a typical clustered spikelets phenotype with all primary branches clustered on the base of the main rachis and 2-3 normal spikelets clustered on the primary branches. Moreover, cl4 mutant also shows shorter plant height than that of the wild type. Map-based cloning strategy is performed to clone the CL4 gene.As a result, CL4 is demonstrated to encode a putative cytochrome P450 protein CYP724B1, which is involved in brassinosteroid biosynthesis.To confirm our mapping result, the CL4 RNAi transgenic plants are generated. And the transgenic plants also show similar phenotype as the cl4 mutant.These results provide strong evidence that CL4 plays an important role in rice panicle development as well as plant height regulation.