The involvement of auxin response factor OsARF7 in positively regulating root development by mediating the expression of OsCRL1 in rice (Oryza sativa L.).

The root is one of the most important organs that determines the final grain yield in rice. Auxin is essential for root development in plants. Rice auxin response factor7 (OsARF7), belonging to the ARF family, is a key regulator of root development. Here, we show that OsARF7 positively regulates root development via auxin signaling. The osarf7 mutants display a significant decrease in the root number, adventitious root (AR) number and length, and primary root (PR) length, compared with the wild-type. Exogenous NAA treatment significantly suppresses PR length in osarf7 mutants, OsARF7-OE lines, and its wild-type, does not affect the root number of osarf7 mutants, but suppresses the biomass of osarf7 mutants. At the molecular level, OsARF7 is preferentially expressed in the culm, root, and leaf, especially highly expressed in the tips of the PR, AR, root pericycle, and lateral root (LR) primordia; meanwhile, OsARF7 expression is significantly enhanced by exogenous NAA treatment, suggesting that the positive regulatory role of OsARF7 on root development is based on auxin signaling. A series of biochemical and genetic analyses demonstrate that OsARF7 functions upstream of OsCRL1 and acts downstream of OsMADS25 to regulate root development via auxin signaling. To conclude, OsARF7 is a key positive regulatory factor that regulates root development by activating the expression of OsCRL1 via auxin signaling, by which, OsMADS25 positively mediates OsARF7 expression in rice. This work provides valuable insight into the regulatory mechanism controlling root development and a genetic resource for the molecular improvement of root architecture.