PROG1 acts upstream of LAZY1 to regulate rice tiller angle as a repressor

Rice tiller angle, as a component of plant architecture, affects rice grain yield via plant density. However, the molecular mechanism underlying rice tiller angle remains elusive. We report that the key domestication gene PROSTRATE GROWTH 1 ( PROG1 ) controls rice tiller angle by regulating shoot gravitropism and LAZY1 ( LA1 )-mediated asymmetric distribution of auxin. Acting as a transcriptional repressor, PROG1 negatively regulates the expression of LA1 in light-grown rice seedlings. Overexpression of LA1 partially rescued the larger tiller angle of the PROG1 complementation transgenic plant ( prog1-D ). Double-mutant analysis showed that PROG1 acts upstream of LA1 to regulate shoot gravitropism and tiller angle. Mutation of Suppressors of lazy1 ( SOL1 ), encoding DWARF3 (D3) acting in the strigolactone signal pathway, suppressed the large tiller angle of prog1-D by rescuing the transcription of LA1. The discovery of a light-sensitive PROG1-LA1 transcription regulatory module controlling rice shoot gravitropism and tiller angle sheds light on the genetic control of rice tiller angle.