Molecular characterization of acetolactate synthase genes in lentil (Lens culinaris Medik.): A key target enzyme of imazethapyr herbicide resistance

Weed infestation severely affects the productivity of lentils. Imazethapyr, a Group 2 herbicide controls prominent broadleaf weeds and grasses in the field. Imazethapyr blocks the first step of branched-chain amino acids (BCAA) biosynthesis by inhibiting the activity of acetolactate synthase (ALS) activity. The present study aims to explore the effect of herbicide stress on the ALS gene expression and enzyme activity in lentil genotypes on different days after spray. The study revealed the presence of two homologous genes in the lentil genome, LcALS2 and LcALS3, present on chromosomes 2 and 3, respectively. qRT-PCR of the LcALS2 gene in the selected herbicide-tolerant (LL1397 and LL1612) and susceptible (FLIP 2004-7 L and PL07) genotypes indicated a significant decrease of the ALS gene expression in the susceptible genotypes. The results were also supported by the in vitro ALS enzyme activity assay, indicating significant inhibition of ALS activity in FLIP 2004-7 L (17.33% and 49.21%) followed by PL07 (33.11% and 19.7%) at 4 and 7 days after spray (DAS), respectively compared to the control. This is the first-ever report on the effect of herbicide stress on ALS gene expression and its correlation with ALS enzyme activity on different days after spraying in lentil crop. It is important from an agronomic perspective to understand herbicide tolerance mechanism at the genetic level for selecting an efficient variety and improving crop productivity.