Reproductive transition of grasses is characterized by switching the pattern of lateral branches. Two of the most striking features of reproductive branching are the suppression of outgrowth of the subtending leaves (bracts), and the rapid formation of higher-order branches, compared to the vegetative branching. However, the underlying molecular mechanisms of such changes are largely unknown. We showed that the intrinsic time ruler microRNA156/529-targeted SQUAMOSA PROMOTER BINDING PROTEIN LIKE (SPL) genes determine the pattern switch between vegetative and reproductive branching by regulating Neck leaf1 (NL1) in rice. SPLs and NL1 co-regulate the expression of another heterochronic gene Plastochron1 (PLA1) by binding to its promoter and controlling its chromatin accessibility. Furthermore, the reprogramming of transcriptome and chromatin accessibility following the reproductive transition are globally dysregulated in the mutants of SPLs and NL1. The heterochronic-vegetative branches are slowly initiated with outgrown bracts in the mutants of SPLs, PLA1 and NL1; however, these genes are specifically expressed in the bract primordia, suggesting that the defects of reproductive branching are the consequences of bract outgrowth. Collectively, our results propose that the leaf outgrowth or not determines the lateral branching pattern, bract suppression has critical roles in regulating the formation of high-branch type inflorescence in grasses, hence determines the crop yield.