The Discovery Of A Rare Site Mutation Of GW2 And Its Mechanism Of Regulating Grain Size And Grain Weight In Rice

Rice is an important cereal crop in the world.Rice yield is determined by the number of effective panicles,the number of grains per panicle and the grain weight.In previous study,our group developed an advanced backcross population by crossing large grain line JF42 and small grain variety Huazhan(HZ),the recurrent parent,and fine-mapped a major QTL controlling grain shape and grain weight.On this basis,our research was carried out around the function of this major QTL,and the main results were as the follows:1.Main gene GW2 of grain shape and grain weight was determined.By using BC3F1 as the female parent and HZ as the recurrent parent for further backcrossing,and using SSR molecular marker-assisted selection technology for target gene selection and genetic background selection,the backcrossing progeny of higher generation was constructed and the near isogenic line was screened.The 1000-grain weight and grain size of NIL-GW2 were significantly increased compared with the recurrent parent HZ.According to the previous mapping results,sequencing comparison of candidate genes and expression level analysis,it was found that compared with GW2HZ,there was a rare site mutation in the coding sequence of GW2JF42,which caused the missense mutation of GW2 protein.Combined with the phenotype,smaller grain size and decreased 1000grain weight of the complementary plants,the major gene controlling grain shape and grain weight in JF42 was identified as GW2 allele.2.The enlargement of NIL-GW2 glume is mainly due to the increase of cell number,and GW2 may be involved in regulating glume cell proliferation.The number and size of cells on the surface and inside of the glume were observed and statistically analyzed by scanning electron microscopy and paraffin section respectively.Combined with the results of cell proliferation and elongation related gene expression,it was found that the number of glume cells in NIL-GW2 was significantly increased.And there was no significant difference in the cell size between HZ and NIL-GW2.It is suggested that GW2 may be involved in the biological process of regulating cell proliferation.3.GW2 is localized in cytoplasm and nucleus and may interact with CHB705,the subunit of the chromatin remodeling complex SWI/SNF.GW2 was found distributed in cytoplasm and nucleus by transient expression of the fusion protein in tobacco leaves and rice protoplasts.Based on the studies of GW2 homologous proteins in Arabidopsis and wheat and the prediction of protein interaction,we identified a positive interaction between GW2 and the chromatin remodeling complex subunit CHB705 in yeast twohybrid system,suggesting that GW2 may interact directly with CHB705.In conclusion,this study enriches the functions of the grain shape and grain weight gene GW2 in a different genetic background by a different mutated way,and preliminarily clarifies the physiological mechanism of GW2 influences the glume size by regulating the number of cells,thereby influencing the grain weight.The results of subcellular localization of GW2 protein were supplemented and a new potential interaction protein CHB705 was identified.This study enriches the theoretical foundation for further studying on the molecular mechanism of the major genes of grain shape and grain weight.In addition,NIL-GW2,the near isogenic line based on cultivated rice,can be directly used for field planting to further investigate the yield,providing a reference for the cultivation of high-yield rice varieties.