Mutation of Short Panicle Gene 3 Caused Shorter Panicle Through Auxin and Cytokinin Pathway in Rice

Panicle size is an important agronomic trait in rice, greatly influences the grain yield of rice (Oryza sativa L.). Although many panicle size genes have been reported, new panicle size controlling genes still need to be discovered. Here, we isolated two rice mutants, named Oryza sativa short panicle gene 3 (Osspg3), which displayed a semi-dwarf phenotype, shorter panicle, and smaller grain, thus, the number of grains per spike decreased. Inhibition of cell expansion of the Osspg3 mutants resulted in smaller grain size. We cloned Osspg3 by using map-based cloning combined with resequencing technique. OsSPG3 is highly expressed in the leaf sheath and panicle, and OsSPG3 protein is localized in the nucleus. Transcriptional analysis revealed antenna proteins photosynthesis, plant hormone signal transduction, plant mitogen-activated protein kinase (MAPK) signaling pathway, glycosaminoglycan degradation, glycosphingolipid biosynthesis and starch and sucrose metabolism were affected in the Osspg3 mutant. Moreover, the content of endogenous IAAs is significant decrease, but the content of endogenous cytokinin is significant increase. Our results indicating OsSPG3 is a key crosstalk factor of auxin and cytokinin pathway and providing a new potential gene resource for the improvement of rice panicle size.