The Rice Receptor-Like Kinases DWARF AND RUNTISH SPIKELET1 and 2 Repress Cell Death and Affect Sugar Utilization during Reproductive Development

Cell-to-cell communication precisely controls the creation of new organs during reproductive growth. However, the sensor molecules that mediate developmental signals in monocot plants are poorly understood. Here, we report that DWARF AND RUNTISH SPIKELET1 (DRUS1) and DRUS2, two closely related receptor-like kinases (RLKs), redundantly control reproductive growth and development in rice (Oryza sativa). A drus1-1 drus2 double knockout mutant, but not either single mutant, showed extreme dwarfism and barren inflorescences that harbored sterile spikelets. The gibberellin pathway was not impaired in this mutant. A phenotypic comparison of mutants expressing different amounts of DRUS1 and 2 revealed that reproductive growth requires a threshold level of DRUS1/2 proteins. DRUS1 and 2 maintain cell viability by repressing protease-mediated cell degradation and likely by affecting sugar utilization or conversion. In the later stages of anther development, survival of the endothecium requires DRUS1/2, which may stimulate expression of the UDP-glucose pyrophosphorylase gene UGP2 and starch biosynthesis in pollen. Unlike their Arabidopsis thaliana ortholog FERONIA, DRUS1 and 2 mediate a fundamental signaling process that is essential for cell survival and represents a novel biological function for the CrRLK1L RLK subfamily.