The OsSPL-SNB complex orchestrates the reproductive transition through tillering suppression in rice

Optimization of plant architecture has been a key objective in cereal domestication and breeding, achieved by suppressing tiller and bract formation during the vegetative-to-reproductive transition to increase panicle branching and grain yield. The SQUAMOSA PROMOTER BINDING PROTEIN LIKE (SPL) and APETALA2 (AP2) transcription factor families are known to regulate such age-dependent developmental transitions, but their specific roles in rice reproductive tillering remain unclear. Here, we show that OsSPL12 and OsSPL13 form a regulatory complex with the AP2-family protein SUPERNUMERARY BRACT (SNB) and inhibit tiller outgrowth during the reproductive stage. The Osspl12 Osspl13 double mutant exhibits elongated axillary buds in the upper phytomers and reduced panicle branching, whereas the Osspl12 Osspl13 snb triple mutant undergoes a reversion to vegetative tillering, producing ectopic shoots and smaller panicles. Mechanistically, OsSPL12 and OsSPL13 physically interact with SNB and synergistically activate the expression of the bract suppressors NECK LEAF1 (NL1) and PLASTOCHRON1 (PLA1), promoting the switch from vegetative to reproductive branching. These results expand the known SPL regulatory network for tiller control and offer strategies for engineering developmental transitions in crops.