Effects of a novel combination of two mutated acetolactate synthase (ALS) isozymes on resistance to ALS-inhibiting herbicides in flixweed (Descurainia sophia)

Yufang Xu,Mingqi Zheng,Xuefeng Li,Lina Xu,Jing Shen

doi:10.1017/wsc.2021.26

Abstract

AbstractFlixweed [Descurainia sophia(L.) Webb ex Prantl] is a notorious broadleaf weed that is widely distributed in winter wheat–growing areas of China and has evolved resistance to tribenuron-methyl mainly due to target-site resistance (TSR) mutations in acetolactate synthase (ALS). In the current research, twoALSgenes were identified in tribenuron-methyl–susceptible (TS) or tribenuron-methyl–resistant (TR)D. sophia. Resistance mutations of Asp-376-Glu and Pro-197-Ala were identified on ALS1 and ALS2 isozymes in TRD. sophia, respectively. The TRD. sophiaevolved 10,836.3-fold resistance to tribenuron-methyl and displayed cross-resistance to multiple ALS-inhibiting herbicides with different chemical structures. Dose response experiments and ALS activity assay indicated that two mutated ALS isozymes contributed differentially in resistance to tribenuron-methyl, flucetosulfuron, and pyribenzoxim. In addition, the relative expression level of theALS1gene was 2.2- and 1.6-fold higher thanALS2genes in TRD. sophiaat 1 and 7 d after tribenuron-methyl treatment, respectively. In contrast, the relative expression level ofALS1andALS2in TSD. sophiais similar. This is the first research that explored different roles of ALS isozymes in resistance to ALS-inhibiting herbicides, which might provide a new perspective for the weed resistance management.

Highlights

Acetolactate synthase (ALS) (EC 2.2.1.6), recognized as acetohydroxyacid synthase (AHAS; EC 4.1.3.18), catalyzes the formation of 2-acetolactate or 2-aceto-2-hydroxybutyrate in the biosynthesis of branched-chain amino acids (Duggleby et al 2008)
Fifty TS or TR D. sophia plants were sequenced, and the ALS1 or ALS2 of each plant was the same in each D. sophia population, which indicated that the genetic backgrounds of the different plants were very similar or the same
Two resistance mutations on ALS in a single plant were reported in kochia [Bassia scoparia (L.) A.J

Summary

Introduction

Acetolactate synthase (ALS) (EC 2.2.1.6), recognized as acetohydroxyacid synthase (AHAS; EC 4.1.3.18), catalyzes the formation of 2-acetolactate or 2-aceto-2-hydroxybutyrate in the biosynthesis of branched-chain amino acids (Duggleby et al 2008). Whole-plant dose response experiments were used to determine the resistance or cross-resistance levels of TR and TS D. sophia populations to different ALS-inhibiting herbicides, including tribenuronmethyl (SU), flucetosulfuron (SU), pyribenzoxim (PTB), flucarbazone-sodium (SCT), flumetsulam (TP), and imazethapyr (IMI).

Results

Conclusion