OsMADS25 regulates root system development via auxin signalling in rice

The phytohormone auxin is essential for root development in plants. OsMADS25 is a homologue of the AGL17-clade MADS-box genes in rice. Despite recent progress, the molecular mechanisms underlying the regulation of root development by OsMADS25 are not well known. It is unclear whether OsMADS25 regulates root development via auxin signalling. In this study, we examined the role of OsMADS25 in root development and characterized the signalling pathway through which OsMADS25 regulates root system development in rice. OsMADS25 overexpression significantly increased, but RNAi gene silencing repressed primary root (PR) length and lateral root (LR) density. Moreover, OsMADS25 promoted LR development in response to NO3-. Further study showed that OsMADS25 increased auxin accumulation in the root system by enhancing auxin biosynthesis and transport, while also reducing auxin degradation, therefore stimulating root development. More importantly, OsMADS25 was found to regulate OsIAA14 expression directly by binding to the CArG-box in the promoter region of OsIAA14, which encodes an Aux/indole acetic acid (IAA) transcriptional repressor of auxin signalling. Elevated auxin levels and decreased OsIAA14 expression might lead to reduced OsIAA14 protein accumulation, as a mechanism to regulate auxin signalling. Therefore, our findings reveal a molecular mechanism by which OsMADS25 modulates root system growth and development in rice, at least partilly, via Aux/IAA-based auxin signalling.