RGB1 positively regulates both grain size and grain filling
Previous studies have showed that RGB1 play important roles in regulating growth and development of rice plants (Utsunomiya et al., 2011; Sun et al ., 2018). However, it remains largely unknown how the grain development and grain filling is regulated by RGB1 . To investigate the molecular mechanisms of RGB1 regulation on grain development and grain filling, we used Wuyujing 8 (hereafterWYJ8 ) as background, to generate two RGB1 RNA-interfered transgenic lines (hereafter RGB1Ri-5 and RGB1Ri-6 ). Compared with WYJ8 , the grain RGB1 protein levels were significantly lower in RGB1Ri-5 and RGB1Ri-6 lines, measured by western blot assay using a RGB1-specific antibody (Figure 1a). The final grain size, including the length, width, and thickness of grains, of two transgenic rice lines with suppressed expression ofRGB1 were markedly reduced, and consequently, the final grain weight reduced significantly, as compared with WYJ8 (Figure 1b-1f), which was very similar to the phenotype observed in several other reports (Utsunomiya et al., 2011; Sun et al., 2018). Furthermore, the grain starch content of RGB1Ri lines was also lower than that of WYJ8 (Figure 1g). We further tracked the caryopsis development and dry matter accumulation after flowering, and the caryopsis size and grain weight of WYJ8 increased rapidly and maximal values were reached at 25 DAF. However, the increase of caryopsis size was obviously delayed and the dry matter accumulation of grains much slowly during the early stage of grain filling of RGB1Ri lines (Figure 1h and 1i). These results implied that RGB1 might also be involved in regulating the grain filling processes as well as the grain size.