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

Abstract

Flixweed [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, two ALS genes were identified in tribenuron-methyl-susceptible (TS) or -resistant (TR) D. sophia. Resistance mutations of Asp-376-Glu and Pro-197-Ala were identified on ALS1 and ALS2 isozymes in TR D. sophia, respectively. The TR D. sophia evolved 10836.3-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 ALS1 gene was 2.2- and 1.6-fold higher than ALS2 genes in TR D. sophia on the 1st and 7th days after tribenuron-methyl treatment (DAT), respectively. In contrast, the relative expression level of ALS1 and ALS2 in TS D. sophia is 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.

Characterization of target-site resistance to ALS-inhibiting herbicides in Ammannia multiflora populations

“…For instance, Wang et al (2019) reported a resistant a C. bursa-pastoris population with the Pro-197-Ser mutation in ALS1 and the Pro-197-His mutation in ALS2. Xu et al (2021) found that a combination of two ALS mutations (Asp-376-Glu in ALS1 and Pro-197-Ala in ALS2) in D. sophia showed more than 10,000-fold resistance to tribenuron-methyl. Tanigaki et al (2021) reported a relatively rare resistant case in which the Pro-197-Ser and Asp-376-Glu mutations had occurred in a single ALS gene.…”

Synthesis of Novel Pyrimidinylselenium Compounds as Acetolactate Synthase‐Inhibiting Herbicides

“…There are now five classes of herbicides available on the market targeting the ALS enzyme, triazolopyrimidines (TP), [5] sulfonylureas (SU), [6] pyrimidinylthiobenzoates (PTB), [7] sulfonylaminocarbonyl triazolinones (SCT), [8] and imidazolinone (IMI), [9] collectively called ALS‐inhibiting herbicides [10] . These herbicides have been widely used for weed control in rice and cotton fields and exhibit high specificity to weeds, low toxicity to animals and humans, and high herbicidal activity [11] .…”