Unravelling the effect of two herbicide resistance mutations on acetolactate synthase kinetics and growth traits

Abstract

Gene mutations conferring herbicide resistance are hypothesized to have negative pleiotropic effects on plant growth and fitness, which may in turn determine the evolutionary dynamics of herbicide resistance alleles. We used the widespread, annual, diploid grass weed Alopecurus aequalis as a model species to investigate the effect of two resistance mutations—the rare Pro-197-Tyr mutation and the most common mutation, Trp-574-Leu—on acetolactate synthase (ALS) functionality and plant growth. We characterized the enzyme kinetics of ALS from two purified A. aequalis populations, each homozygous for the resistance mutation 197-Tyr or 574-Leu, and assessed the pleiotropic effects of these mutations on plant growth. Both mutations reduced sensitivity of ALS to ALS-inhibiting herbicides without significant changes in extractable ALS activity. The 197-Tyr mutation slightly decreased the substrate affinity (corresponding to an increased Km for pyruvate) and maximum reaction velocity (Vmax) of ALS, whereas the 574-Leu mutation significantly increased these kinetics. Significant decrease or increase in plant growth associated, respectively, with the 197-Tyr and 574-Leu resistance mutations was highly correlated with their impact on ALS kinetics, suggesting more likely persistence of the 574-Leu mutation than the 197-Tyr mutation if herbicide application is discontinued.

Design of Acetohydroxyacid Synthase Herbicide-Resistant Germplasm through MB-QSAR and CRISPR/Cas9-Mediated Base-Editing Approaches

“…Our prediction results showed that different AHAS mutations had different levels of herbicide resistance, and in most cases, the herbicide resistance level of multi-point mutations was higher than that of single-point mutations (Table ). These results were consistent with the previously published literature. ,,,, Target-site resistance, caused by the mutation of the key amino acid of a target enzyme, is the most common mechanism leading to resistance to an AHAS inhibitor . Currently, at least 28 resistance-endowing amino acid substitutions at eight conserved positions in the AHAS enzyme have been identified in weed biotypes with field-evolved resistance .…”

“…These results were consistent with the previously published literature. 9,14,34,35,45 Target-site resistance, caused by the mutation of the key amino acid of a target enzyme, is the most common mechanism leading to resistance to an AHAS inhibitor. 9 Currently, at least 28 resistance-endowing amino acid substitutions at eight conserved positions in the AHAS enzyme have been identified in weed biotypes with field-evolved resistance.…”

“…9 Currently, at least 28 resistance-endowing amino acid substitutions at eight conserved positions in the AHAS enzyme have been identified in weed biotypes with field-evolved resistance. 45 Among them, the P197 codon of AHAS is the most common mutation site. 14 In rice, the four different mutations in the P197 codon, P197S, P197F, P197Y, and P197A, exhibited different resistance patterns toward five representative AHAS inhibitors.…”

Cyhalofop‐butyl resistance conferred by a novel Trp‐2027‐Leu mutation of acetyl‐CoA carboxylase and enhanced metabolism in Leptochloa chinensis

“…To our best knowledge, this study reports for the first time the Trp‐2027‐Leu substitution of ACCase conferring cyhalofop‐butyl resistance in weed species. The rarity of Trp‐2027‐Leu of ACCase may be partially due to its possible adverse pleiotropic effects on plant growth by changing enzyme functionality 42,43 . A dCAPS marker was then successfully developed to specifically detect the Trp‐2027‐Leu mutation in Leptochloa chinensis without performing gene sequencing.…”

Trp-574-Leu mutation in wild mustard (Sinapis arvensis L.) as a result of als inhibiting herbicide applications

“…Mutations in codons 197 and 574 are considered to be important points for ALS inhibitors ( Powles & Yu, 2010 ; Tranel et al, 2019 ; Zhao et al, 2020 ). Trp-574-Leu has the ability to develop resistance to all groups of ALS inhibitor herbicides ( Pandolfo et al, 2016 ).…”