After transition to the reproductive phase, normal shoot apical meristems (SAMs) converted to inflorescence meristem (IM) to produce panicle. Then, the IM starts to initiate branch meristems (BMs). Among the meristems that are generated from the BMs, early ones acquire BM identity and grow as next order branches while later ones are specified as determinate spikelet meristems (SMs). The pattern of branching is determined by the timing of the meristem phase shift from the BM to the SM. Delays in SM specification lead to reiterations of branching, resulting in larger inflorescences that could potentially produce more grain. Conversely, the acceleration of SM specification results in smaller inflorescences with fewer spikelets (Kyozuka et al., 2014). Many genes have been identified as regulators of phase change in rice. Various microRNAs e.g., miR156, miR172, miR159, miR396, miR529 and their target genes regulate rice tiller and panicle branching. At early vegetative stage, miR156 promotes tillering by inhibiting SPL genes. After reproductive transition, SPL genes reach the highest levels at the early panicle stage. miR156 and miR529 at reproductive stage would maintain the SPL expression to the more optimal levels, thus promoting panicle branching. At the downstream, the miR172/AP2 pathway is used in regulating panicle, but not tiller, branching. Therefore, the activities of the miR156/miR529/SPL and miR172/AP2 pathways harmoniously coordinate vegetative and reproductive branching by shifting gene networks in different developmental stages (Wang et al., 2015).
