An Insight of Quinclorac Resistance Mechanism in Early Watergrass ( Echinochloa oryzoides )

Abstract Background Quinclorac- main herbicide targeting to barnyard grass, has been used for decades in rice fields. Echinochloa species have been reported evolving into quinclorac resistance.Objective: Quinclorac resistance and its mechanism remain undisclosed in Echinochloa oryzoides (Ard.) Fritsch that needs to be uncovered. Methods Dose-response assays were performed, followed by ethylene synthesis, and related enzyme activities along with gene transcription were studied. β-CAS activity and its molecular docking were investigated. Results E. oryzoides evolved into 21 times resistance to quinclorac from Jiangsu province of China. The increment in ethylene levels in this biotype was correlated negatively with the level of resistance and positively with quinclorac-induced growth inhibition. Ethylene response pathway determination showed that resistant biotype decreased 1-aminocyclopropane-1-carboxylic acid (ACC) contents, related enzyme activities, and transcription of ACS and ACO genes. These results indicated that ethylene biosynthesis inhibition and quinclorac resistance possessed a positive correlation. Resistant biotype exhibited ~ 2-fold more β-CAS activity than susceptible ones. Resistant EcCAS gene depicted nucleotide changes as compared to susceptible ones, which resulted in two amino acid substitutions (Met-287-Lys and Thr-352-Ala). Consequently, resistant β-CAS enzyme exhibited an increase in binding residue in active site (simulation modelling); that can be the probable reason for higher enzyme activity in the resistant biotype. Conclusions The study concludes that variation in response pathway of auxin and potentially improved cyanide degradation were plausible mechanisms endowing quinclorac resistance in E. oryzoides .