Study on the Mechanism of Pyrimoxsulam Resistance in Highland Barley

Highland barley (Hordeum vulgare var. nudum), a member of the genus Hordeum in the family Poaceae, represents a unique cultivated crop adapted to the Qinghai–Tibet Plateau. Weed infestation has long posed a serious threat to the yield and quality of highland barley, and the lack of effective weed management strategies has become a major constraint in its production. Pyroxsulam is an acetolactate synthase (ALS)-inhibiting herbicide widely used for weed control in highland barley fields. This study investigated the molecular mechanisms underlying the response of highland barley to pyroxsulam by integrating physiological, biochemical, and transcriptomic analyses. ALS activity assays showed that the resistant variety ‘Qing0306’ exhibited a significant increase in relative ALS activity within 1–4 days after pyroxsulam treatment. qRT-PCR analysis revealed a rapid induction of HvnALS expression, which was significantly higher in ‘Qing0306’ than in ‘Qing0160’ on the first day after treatment (p < 0.01), indicating that resistance is primarily associated with target-enzyme overexpression rather than target-site mutations. Moreover, transgenic Arabidopsis lines overexpressing HvnP450 and HvnGSTs displayed enhanced tolerance to pyroxsulam, as evidenced by an increased root length and fresh weight compared with wild-type plants. This study provides mechanistic insights that support the genetic improvement of pyroxsulam-resistant highland barley.