A novel OsIAA3-OsARF16-OsBUL1 module regulates grain size in rice

Abstract

Auxin plays an important role in almost every aspect of plant growth and development. However, the molecular mechanism underlying the control of grain size via auxin signaling pathways is still obscure. Here, we reported that the rice Aux/IAA gene OsIAA3 positively regulates grain size by promoting the cell expansion and proliferation of spikelet hulls. OsIAA3 interacted with 11 OsARFs, among which the interaction with OsARF16 was the strongest. Knockout of osarf16 led to smaller grain with decreased grain length, grain width, grain thickness and 1,000-grain weight. Meanwhile, transgenic plants overexpressing OsARF16 produced apparently bigger grain with increased grain length and 1,000-grain weight. Additionally, OsBUL1, which positive regulates grain size by promoting cell expansion is a direct target gene of OsARF16. Results demonstrated that the interaction between OsIAA3 and OsARF16 repressed the transcriptional activation of OsARF16 on OsBUL1. Taken together, our study revealed a novel OsIAA3-OsARF16-OsBUL1 module which regulates grain size, enriching the molecular mechanism of auxin signaling pathway involved in regulating grain size.