Abstract
RGB1, a subunit of heterotrimeric G protein, plays important roles in
regulating grain size and weight of rice. However, the molecular
mechanisms underlying controlling grain filling process by G protein are
still largely unclear. In the present study, we show that, RGB1 controls
not only the grain size, but the grain filling process. Knock-down ofRGB1 significantly delayed grain development and reduced starch
accumulation and grain weight, which was closely related to the delayed
and lower expression of genes encoding sucrose metabolism and starch
biosynthesis related enzymes during grain filling stage. Suppression ofRGB1 expression also resulted in the lower auxin content in
grains, which was correlated with the lower expression ofOsNF-YB1 and OsYUC11 during grain filling stage. Further
biochemical evidence showed that OsYUC11 expression was under
control of OsNF-YB1 by its interaction with promoter of OsYUC11 .
Taken together, we propose that RGB1 controls rice grain development and
grain filling process by changing auxin homeostasis in endosperm cells,
and OsNF-YB1, which acts as a key downstream effector of RGB1,
interacts directly with the promoter of OsYUC11 and promotes the
transactivation of OsYUC11 , thereby regulating auxin biosynthesis
and starch accumulation and grain size.
Keywords: auxin, grain filling, OsNF-YB1, OsYUC11, RGB1,
rice, starch biosynthesis