Increased expression of OsSAUR23 and OsRR9 regulates rice plant and organ size

Plant height and grain size are the most important factors determining rice yield. Here, in the rice mutant small plant and organ size1 ( spos1 ) with reduced plant height and small grain, T-DNA insertion revealed that the mutant phenotype was caused by increased expression of of OsSAUR23 and OsRR9 , which participate in auxin and cytokinin signal transduction, respectively. Knock out of OsSAUR23 increased rice grain size but did not change plant height. Double knock out of OsRR9 and its replicated gene OsRR10 also brought similar effects on rice as that of OsSAUR23 knock-out. Genetic analysis suggested that OsSAUR23 was a major recessive gene and OsRR9 was a minor dominant gene, which co-regulated the phenotype of spos1 . Compared with wild type, auxin synthesis and signaling, cytokinin homeostasis and signaling, as well as GA, ABA and BR metabolism and signaling were regulated in seedlings of spos1 . The increased concentrations of IAA and cytokinins in the mutant suggest hormonal co-regulation of rice organ size.