Characterization of acetolactate synthase from sulfonylurea herbicide‐resistant Schoenoplectus juncoides

Abstract

Ten accessions of sulfonylurea‐resistant Schoenoplectus juncoides were collected from paddy fields in Japan. In order to characterize acetolactate synthase from sulfonylurea‐resistant S. juncoides, acetolactate synthase amino acid substitutions, whole‐plant growth inhibition and acetolactate synthase enzyme inhibition were examined. Schoenoplectus juncoides has two acetolactate synthase genes (ALS1 and ALS2). The sulfonylurea‐resistant accessions harbored amino acid substitutions at Pro197 or Trp574 in either ALS1 or ALS2 (the amino acid number is standardized to the Arabidopsis thaliana sequence). The whole plants of all the sulfonylurea‐resistant accessions showed resistance to imazosulfuron. The resistance level depended on the altered amino acid residues in acetolactate synthase. The acetolactate synthase enzyme that was partially purified from all the sulfonylurea‐resistant accessions was less sensitive to imazosulfuron, compared to the susceptible accession, suggesting that the resistance is related to the altered acetolactate synthase enzyme. In addition, the concentration–response inhibition of acetolactate synthase activity by imazosulfuron in the sulfonylurea‐resistant accessions was remarkably different with the presence of an amino acid substitution in either ALS1 or ALS2. Furthermore, the concentration–response inhibition of acetolactate synthase activity in the sulfonylurea‐resistant accessions with a P197S, P197T or W574L mutation showed a double‐sigmoid curve. The regression analysis of enzyme inhibition suggested that the abundance ratio of ALS1 to ALS2 enzymes was approximately 70:30%, with a range of ±15%. Taken together, these results suggest that the resistance of sulfonylurea‐resistant accessions of S. juncoides is related to altered acetolactate synthase in either ALS1 or ALS2, although the abundance of the altered acetolactate synthase in the plants is different among the sulfonylurea‐resistant accessions.

Resistance mutations of Pro197, Asp376 and Trp574 in the acetohydroxyacid synthase (AHAS) affect pigments, growths, and competitiveness of Descurainia sophia L

“…The data of whole-plant response experiments was converted into the percentage of control and subjected to a non-linear regression analysis using GraphPad Software (v.5.0) 31 , 32 . In this study, two AHAS isozymes with different sensitivities to tribenuron-methyl were confirmed to coexist in all R (pHB8, pHB22, pHB23, pHB24, pHB25 and pHB42) subpopulations.…”

Effects of resistance mutations of Pro197, Asp376 and Trp574 on the characteristics of acetohydroxyacid synthase (AHAS) isozymes

“…The data obtained from whole-plant response experiments and the in vitro AHAS assay were converted into percentages of the control and subjected to a nonlinear regression analysis using GraphPad Software (v.5.0) 31,32 . In this study, two AHAS isozymes with different sensitivities to tribenuron-methyl were confirmed to coexist in all R (pHB8, pHB22, pHB23, pHB24, pHB25 and pHB42) subpopulations.…”

Biology and mechanisms of sulfonylurea resistance in Schoenoplectiella juncoides, a noxious sedge in the rice paddy fields of Japan

“…But, there was little information about how the enzymatic resistance profiles relate to specific ALS mutations. Recently Yamato et al () investigated the in vitro dose–response of ALS to imazosulfuron, using ALS enzymes that were extracted from various SU‐resistant S. juncoides accessions (all homozygous) (Table ).…”

“…Data are the results of regression analyses using the formula, y = s × f ( x ) + (1 − s ) × g ( x ). See the text for details and Yamato et al ().…”

“…Dose–responses to imazosulfuron of acetolactate synthase (ALS) extracts from sulfonylurea (SU) ‐resistant Schoenoplectiella juncoides with P ro 197 S er mutations (Yamato et al ). (□), Susceptible K yo ; (♦), ALS2 ‐mutated Tai ; (◊), ALS2 ‐mutated Yok ; (○), ALS1 ‐mutated Ich ; (●), ALS 1‐mutated Sei (see Table ).…”