Characterization of the ‘Oat-Like Rice’ Caused by a Novel Allele OsMADS1Olr Reveals Vital Importance of OsMADS1 in Regulating Grain Shape in Oryza sativa L.

Abstract

Abstract Background Grain shape is a critical agronomic trait affecting grain yield and quality. Exploration and functional characterization of grain shape-related genes will facilitate rice breeding for higher quality and yield. Results Here, we characterized a recessive mutant named Oat-like rice for its unique grain shape which highly resembles oat grains. The Oat-like rice displayed abnormal floral organs, an open hull formed by remarkably elongated leafy lemmas and paleae, occasionally formed conjugated twin brown rice, an aberrant grain shape and a low seed setting rate . By map-based cloning, we discovered that Oat-like rice harbors a novel allele of OsMADS1 gene ( OsMADS1 Olr ), which has a spontaneous point mutation that causes the substitution of an amino acid that is highly conserved in the MADS-box domain of the MADS-box family. Further linkage analysis indicated that the point mutation in the OsMADS1 Olr is associated with Oat-like rice phenotype, and expression analysis of the OsMADS1 by qRT-PCR and GUS staining also indicated that it is highly expressed in flower organs as well as in the early stages of grain development. Furthermore, OsMADS1 Olr -overexpressing plants showed similar phenotypes of Oat-like rice in grain shape, possibly due to the dominant negative effect. And OsMADS1 -RNAi plants also displayed grain phenotypes like Oat-like rice. These results suggested that OsMADS1 Olr is responsible for the Oat-like rice phenotype including aberrant grain shape. Moreover, the expression levels of representative genes related to grain shape regulation were apparently altered in Oat-like rice, OsMADS1 Olr -overexpressing and OsMADS1 -RNAi transgenic plants. Finally, compared with Oat-like rice, OsMADS1 Olr -overexpressing and OsMADS1 -RNAi plants, mild phenotype of seed-specific OsMADS1 -RNAi transgenic plants indicated that OsMADS1 may has has a direct regulation role in grain development and the grain phenotypes of Oat-like rice, OsMADS1 Olr -overexpressing and OsMADS1 -RNAi plants are majorly caused by the abnormal lemma and palea development. Conclusions Altogether, our results showed that grain shape and a low seed setting rate of the notable ‘Oat-like rice’ are caused by a spontaneous point mutation in the novel allele OsMADS1 Olr . Furthermore, our findings suggested that OsMADS1 mediates grain shape possibly by affecting the expression of representative genes related to grain shape regulation. Thus, this study not only revealed that OsMADS1 plays a vital role in regulating grain shape of rice but also highlighted the importance and value of OsMADS1 to improve the quality and yield of rice by molecular breeding.