Expression of Echinochloa oryzoides CYP71A1 and GSTU23 catalyzes the metabolism of thiobencarb, thereby conferring resistance.

Echinochloa oryzoides (Ard.) Fritsch. is a notorious and prevalent weed in paddy fields. Thiobencarb (TB), a thiocarbamate herbicide, is widely applied in paddy fields for the control of pre-emergence weeds. However, owing to the prolonged and large-scale usage of TB, certain Echinochloa oryzoides populations have evolved resistance to it. In this study, a population of Echinochloa oryzoides from a paddy field was suspected of being resistant to the TB herbicide. Notably, this population also displayed multiple resistance and cross-resistance to Acetolactate synthase (ALS), Acetyl-CoA carboxylase (ACCase), and hormone-based herbicides. The resistance to TB was partially reversed by 50.8 % and 44.7 % upon treatment with a glutathione S-transferase (GST) inhibitor (NBD-Cl) and a cytochrome P450 inhibitor (malathion), respectively. This confirmed that metabolic resistance was the predominant mechanism underlying the observed resistance. RNA-seq analysis uncovered the overexpression of CYP71A1 and GSTU23 in the resistant (R) population. This study is the first to screen and validate metabolic enzymes capable of effectively metabolizing TB in an Echinochloa oryzoides. Functional verification was conducted using a yeast in vitro expression system, which confirmed the metabolic capabilities of both CYP71A1 and GSTU23 genes towards TB. Collectively, these findings demonstrate that the overexpression of CYP71A1 and GSTU23 in the R population endows Echinochloa oryzoides with the evolutionary capacity to develop resistance to thiobencarb. This study has shed light on the resistance mechanisms of Echinochloa oryzoides to TB, thereby enhancing our understanding of its herbicide tolerance. Moreover, these results highlight the necessity for targeted strategies to control resistant populations, ultimately contributing to more effective and sustainable herbicide resistance management in agriculture.