Auxin pathway-mediated enhancement of root architecture and osmotic stress tolerance by OsZFP350 improves rice yield

• OsZFP350 is localized in the nucleus. • OsZFP350 promotes rice biomass via enhanced root architecture. • OsZFP350 regulates auxin levels in rice roots by controlling auxin signal transduction. • IAA partially rescues drought-induced root inhibition in oszfp350 . • OsZFP350 overexpression enhances grain yield components. C2H2-type zinc finger proteins represent a major class of transcription factors that play pivotal roles in coordinating plant growth processes and mediating adaptive responses to abiotic stresses. Currently, the functional characterization of C2H2 zinc finger proteins in modulating root system architecture in rice remains limited. Here, we demonstrate that the nuclear-localized OsZFP350 functions as a key positive regulator of root development in rice. Overexpression of OsZFP350 significantly promotes the elongation of primary and adventitious roots, increases the number of lateral and adventitious roots, enhances the density of lateral roots and root hairs, and thereby improves the spatiotemporal distribution of the root system architecture. In contrast, the oszfp350 loss-of-function mutant exhibits opposite phenotypes. Further studies indicate that OsZFP350 influences root morphogenesis by regulating auxin biosynthesis, transport, and signal transduction. Overexpression lines of OsZFP350 show significantly increased endogenous auxin levels and greater sensitivity to auxin inhibitors. Exogenous application of IAA can partially rescue the root developmental defects caused by the oszfp350 loss-of-function mutation. Moreover, OsZFP350 overexpression enhances root development in rice seedlings under osmotic stress, whereas exogenous IAA treatment significantly improves the osmotic stress tolerance of oszfp350 mutant seedlings. Additionally, OsZFP350 overexpression increases grain length and width, alters grain shape, and consequently improves rice yield. In conclusion, we propose that OsZFP350 synergistically enhances root development and osmotic stress adaptation through the auxin pathway, ultimately increasing rice yield.