Barnyardgrass EcPIP2;4 and EcPIP2;5 are associated with altered quinclorac redistribution in Arabidopsis.

Barnyardgrass (Echinochloa crus-galli var. zelayensis) is a major weed in rice fields, and reduced sensitivity to the auxin-type herbicide quinclorac has been increasingly reported. Our previous work found two plasma membrane intrinsic protein genes, EcPIP2;4 and EcPIP2;5, that showed differential quinclorac-induced expression between susceptible and resistant barnyardgrass populations, suggesting their possible involvement in quinclorac translocation. Here, quinclorac-related phenotypes in Arabidopsis lines carrying EcPIP2;4 or population-derived EcPIP2;5 constructs were evaluated. Full-length coding sequences of EcPIP2;4 and EcPIP2;5 were obtained from the previously characterized resistant and susceptible source populations. The coding sequence of EcPIP2;5 was identical among individuals within each population and the R- and S-population-derived variants differed at six amino acid positions. Arabidopsis lines carrying CaMV 35S-driven EcPIP2 constructs were generated to evaluate quinclorac accumulation, leaf-to-root translocation, and growth responses. Among the tested transgenic lines, the 35S::EcPIP2;5-R line showed the lowest foliar quinclorac concentration, the highest root concentration and translocation factor, and the highest GR₅₀. Molecular docking further suggested a slightly more favorable interaction between EcPIP2;5-R and quinclorac. Together, these findings show that Arabidopsis lines carrying barnyardgrass EcPIP2 constructs exhibit distinct quinclorac redistribution and response phenotypes, with the 35S::EcPIP2;5-R line showing the strongest leaf-to-root translocation among the tested lines. These results support an association between the introduced EcPIP2 constructs and altered quinclorac redistribution in Arabidopsis and provide a transport-based perspective for interpreting differential quinclorac responses in barnyardgrass.