Pro‐197‐Ser mutation combinations in acetolactate synthase (ALS) homoeologous genes affect ALS inhibitor herbicide resistance levels in Monochoria korsakowii

BACKGROUND: Monochoria korsakowii is a common broadleaf weed found in rice (Oryza sativa) fields. Acetolactate synthase (ALS) inhibitor herbicides are commonly used to control broadleaf weeds in rice fields. However, prolonged herbicide use has exacerbated resistance issues. In this study, we evaluated the resistance to ALS inhibitors in populations where the same mutation occurred separately and simultaneously in the two ALS homoeologous genes (ALS1 and ALS2) and investigated the resistance mechanisms in M. korsakowii. RESULTS: Monochoria korsakowii exhibited high resistance to bensulfuron-methyl, low resistance to penoxsulam, and sensitivity to imazethapyr. Three resistant populations were identified: M-1 and M-2, which independently evolved the Pro-197-Ser mutation in ALS1 and ALS2, respectively, and M-3, which harbored this mutation in both ALS1 and ALS2. The sensitivity of ALS isolated from these populations to herbicide inhibition corresponded to the whole-plant resistance levels. Subsequently, we cloned and transformed Pro-197-Ser-mutated ALS1 and ALS2 into Arabidopsis thaliana. The resistance of homozygous A. thaliana to bensulfuron-methyl and penoxsulam aligned with bioassay trends. Furthermore, we measured the ploidy, relative expression, and copy number of ALS1 and ALS2, and found no significant differences, suggesting that the evolution of resistance was primarily attributed to the Pro-197-Ser mutation. Finally, we developed a derived cleaved amplified polymorphic sequence marker for detecting Pro-197-Ser mutation in ALS. CONCLUSION: The same mutation occurring separately in homoeologous genes resulted in similar resistance levels, whereas simultaneous mutations in homoeologous genes led to increased resistance levels. © 2024 Society of Chemical Industry.