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.