Novel mutations in acetolactate synthase confer high levels of resistance to tribenuron-methyl in Fagopyrum tataricum

Abstract

Tartary buckwheat (Fagopyrum tataricum) field weeds are rich in species, with many weeds causing reduced quality, yield, and crop failure. The selection of herbicide-resistant Tartary buckwheat varieties, while applying low-toxicity and efficient herbicides as a complementary weed control system, is one way to improve Tartary buckwheat yield and quality. Therefore, the development of herbicide-resistant varieties is important for the breeding of Tartary buckwheat. In this experiment, 50 mM ethyl methyl sulfonate solution was used to treat Tartary buckwheat seeds (M₁) and then planted in the field. Harvested seeds (M₂) were planted in the experiment field of Guizhou University, and when seedlings had 5–7 leaves, the seedlings were sprayed with 166 mg/L tribenuron-methyl (TBM). A total of 15 resistant plants were obtained, of which three were highly resistant. Using the homologous cloning method, an acetolactate synthase (ALS) gene encoding 547 amino acids was identified in Tartary buckwheat. A GTG (valine) to GGA (glycine) mutation (V409G) occurred at position 409 of the ALS gene in the high tribenuron-methyl resistant mutant sm113. The dm36 mutant harbored a double mutation, a deletion mutation at position 405, and a GTG (valine) to GGA (glycine) mutation (V411G) at position 411. The dm110 mutant underwent a double mutation: an ATG (methionine) to AGG (arginine) mutation (M333R) at position 333 and an insertion mutation at position 372. The synthesis of Chl a, Chl b, total Chl, and Car was significantly inhibited by TBM treatment. TBM was more efficient at suppressing the growth of wild-type plants than that of mutant plants. Antioxidant enzyme activities such as ascorbate peroxidase, peroxidase, and superoxide dismutase were significantly higher in resistant plants than in wild-type after spraying with TBM; malondialdehyde content was significantly lower than in wild-type plants after spraying with TBM. Plants with a single-site mutation in the ALS gene could survive, but their growth was affected by herbicide application. In contrast, plants with dual-site mutations in the ALS gene were not affected, indicating that plants with dual-site mutations in the ALS gene showed higher levels of resistance than plants with a single-site mutation in the ALS gene.