The Role Of OsU496A In Grain Filling Of Rice

OsU496A is an integral membrane protein with unknown function in Oryza sativa. Our preliminary results showed that OsU496A was highly expressed in the endosperm of rice. So the role of OsU496A in the grain filling of rice was researched in OsU496A overexpression and RNA interference (RNAi) knockdown transgenic rice lines. The research included the following: OsU496A gene expression analysis in rice plants; the identification of OsU496A transgenic rice lines; phenotypic analysis of OsU496A transgenic rice; physiological, biochemistrical and molecular biological analysis of grain during the grain filling of rice. The main results were as follows:1. The relative expression levels of OsU496A in various tissues during different development stages, especially in rice grain during germination and grain filling were researched by real time RT-PCR. The expression level of OsU496A gradually increased in roots, while decreased in leaves with the development of rice seedlings. In the mature period of rice, the expression levels of OsU496A in the grain and roots were higher than other tissues. There was not obvious change in the relative expression levels of OsU496A during the rice seed germination.But the expression levels of OsU496A continuously increased during the grain filling and reached the maximum at the 20DAF and then decreased slightly.2. The OsU496A overexpression and RNA interference (RNAi) knockdown transgenic rice lines were confirmed by PCR analysis of hygromycin resistance gene, GUS staining and real time RT-PCR, and the results showed that the expression of OsU496A was upregulated in overexpression transgenic rice lines while downregulated in RNAi knockdown transgenic rice lines.3. Phenotypic analysis of OsU496A transgenic rice showed that, no significantly difference in a series of agronomic traits was observed between OsU496A overexpression transgenic rice lines and wild-type plants, but OsU496A RNAi knockdown transgenic rice lines had shorter plant height, fewer effective tillers, shorter panicle length, shorter grain length, and lighter grain weight than wild-type plants.4. Further research on the expression levels of OsU496A in transgenic rice grain during the grain filling also showed that the expression of OsU496A was upregulated in overexpression transgenic rice lines while downregulated in RNAi knockdown transgenic rice lines. Meanwhile, during the grain filling, OsU496A RNAi knockdown transgenic rice lines had smaller caryopsis, lighter caryopsis weight than wild-type plants. These results were basically consistent with the grain phenotypes of transgenic rice. But there were no obvious difference in soluble sugar and starch contents during grain filling among OsU496A RNAi knockdown and overexpression transgenic rice lines, and wild-type plants. Further analyses showed that the activities of enzymes and expression levels of AGPL and SSS were increased while the activities of enzymes and expression levels of BE was decreased slightly in OsU496A RNAi knockdown transgenic rice lines, but there was no obvious difference between OsU496A overexpression transgenic rice line and wild-type plants.Above all, OsU496A may be involved respectively in the rice grain filling, and play an important role in the regulation of grain filling. Those results laid a foundation for better understand the function of OsU496A protein and the molecular mechanism of grain filling of rice, and also provided a basis for further improving the yield and quality of rice.