OsMADS5 interacts with OsSPL14/17 to inhibit rice root elongation by restricting cell proliferation of root meristem under ammonium supply.

Nitrogen (N) is a vital major nutrient for rice (Oryza sativa). Rice responds to different applications of N by altering its root morphology, including root elongation. Although ammonium (NH ) is the primary source of N for rice, NH is toxic to rice roots and inhibits root elongation. However, the precise molecular mechanism that NH -inhibited root elongation of rice is not well understood. Here, we identified a rice T-DNA insert mutant of OsMADS5 with a longer seminal root (SR) under sufficient N conditions. RT-qPCR analysis revealed that the expression level of OsMADS5 was increased under NH compared with NO supply. Under NH conditions, knocking out OsMADS5 (cas9) produced a longer SR, phenocopying osmads5, while there was no significant difference in SR length between wild-type (WT) and cas9 under NO supply. Moreover, OsMADS5-overexpression (OE) plants displayed the opposite SR phenotype. Further study demonstrated that enhancement of OsMADS5 by NH supply inhibited rice SR elongation, likely by reducing root meristem activity of root tip, with the involvement of OsCYCB1;1. We also found that OsMADS5 interacted with OsSPL14 and OsSPL17 (OsSPL14/17) to repress their transcriptional activation by attenuating DNA binding ability. Moreover, loss of OsSPL14/17 function in osmads5 eliminated its stimulative effect on SR elongation under NH conditions, implying OsSPL14/17 may function downstream of OsMADS5 to mediate rice SR elongation under NH supply. Overall, our results indicate the existence of a novel modulatory pathway in which enhancement of OsMADS5 by NH supply represses the transcriptional activities of OsSPL14/17 to restrict SR elongation of rice.