Loss of function of OsMADS34 leads to large sterile lemma and low grain yield in rice (Oryza sativa L.)

Rice (Oryza sativa L.) is one of the most important food crops, especially in Asia. The spikelet is a characteristic structure of grass inflorescences that determines crop output. However, the molecular mechanism that controls spikelet development and grain yield in rice remains unclear. In this study, we isolated a new osmads34 allelic mutant (i.e., osmads34-t). The osmads34-t mutant showed more primary branch numbers, short panicles, and long sterile lemmas. The sterile lemmas were transformed into the lemmas and had the lemma identity in the osmads34-t mutant, suggesting that the sterile lemma and lemma are homologous organs. Additionally, osmads34-t displayed smaller grains on its secondary branches of panicles and a lower seed-setting rate. These results suggest that OsMADS34 plays an important role in determination of grain size and yield in rice. OsMADS34 was expressed in tested organs and tissues, and its green fluorescent protein (GFP) signal was located in the nucleus. The result of this study will be used to understand the identity of unique organs in grass spikelets and may improve grain yield in breeding practice.