Fitness costs associated with acetyl‐coenzyme A carboxylase mutations endowing herbicide resistance in American sloughgrass (Beckmannia syzigachne Steud.)

Abstract

Weed resistance to herbicide can be conferred by gene mutations, and some mutations can cause pleiotropic effects in some cases. We investigated the pleiotropic effects associated with five specific ACCase mutations (Ile1781Leu, Trp2027Cys, Ile2041Asn, Asp2078Gly, and Gly2096Ala) on the plant growth, seed production, and resource competitiveness in American sloughgrass. Resistant plants (M/M) homozygous for specific ACCase mutation and susceptible wild‐type plants (W/W) were derived from single heterozygous mother plant (M/W) by genotyping. Plant growth assay and neighborhood experiments were performed to quantify variation between M/M plants and W/W plants. The Ile1781Leu mutation resulted in slight increases in plant growth in pure stands and improved resource competitiveness under low‐competition conditions in pot experiments, but no clear variation was observed under high competitive pressure or field conditions. During competition with wheat plants under field conditions, American sloughgrass plants containing Ile2041Asn ACCase exhibited a significantly lower (12.5%) aboveground biomass but no distinct differences in seed production or resource competitiveness. No significant detrimental pleiotropic effects associated with Gly2096Ala were detected in American sloughgrass. The Trp2027Cys mutation distinctly reduced seed production, especially under high competitive pressure, but did not significantly alter plant growth. The Asp2078Gly mutation consistently reduced not only plant growth and seed production but also resource competitiveness. Synthesis . The Trp2027Cys and Asp2078Gly mutations led to significant fitness costs, which may reduce the frequency of resistance alleles and reduce the propagation speed of resistant weeds in the absence of ACCase inhibitor herbicides. The Ile1781Leu, Ile2041Asn, and Gly2096Ala mutations displayed no obvious fitness costs or displayed very small fitness penalties, which would likely have no effect on the establishment of resistant weeds in the field.

Standing genetic variation fuels rapid evolution of herbicide resistance in blackgrass

“…Some TSR mutations were less common than others. For example, Trp2027Cys and Asp2078Gly were underrepresented, consistent with these mutations reducing fitness in the absence of herbicide selection in other species 41,42,43,44 . The most common mutation was Ile1781Leu, consistent with pleiotropic effects of this substitution that increase fitness also in the absence of selection 41,42 (Figure 3a-c, Supplementary extended data Figure 1).…”

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

“…Notably, all the populations used in the current study simultaneously possessed a homozygous ACCase gene mutation producing 2078-Gly. Fitness costs associated with this amino acid substitution have been reported in different grass species such as L. rigidum , Beckmannia syzigachne , and Alopecurus myosuroides ( Vila-Aiub et al , 2015 b ; Menchari et al , 2008 ; Du et al , 2019 ). This suggests that the ACCase gene mutation causing 2078-Gly should have deleterious effects in A. aequalis , making the prediction of evolutionary dynamics more complex for the resistant populations used in this study.…”

“…After seed germination, 2 cm-tall seedlings of both wheat and A. aequalis were simultaneously transplanted into 20.5×40 cm (diameter×height) plastic pots containing 50% sandy loam and 50% nursing medium. Four A. aequalis plants per pot were subjected to competition from neighboring wheat at densities of 0, 30, 60, 120, and 240 plants per m 2 ( Vila-Aiub et al , 2009 a ; Du et al , 2019 ). Pots were placed outdoors during the normal A. aequalis growing season and were regularly rearranged to randomize any environmental differences.…”

No fitness cost associated with Asn-2041-Ile mutation in winter wild oat (Avena ludoviciana) seed germination under various environmental conditions

“…According to the results, Ile-2041-Asn mutation was responsible for the resistance to the ACCase inhibitor in winter wild oat from Iran. Various researchers have reported Ile-2041-Asn mutation in the ACCase encoding gene as a mechanism of resistance to ACCase inhibiting herbicides, including Papapanagiotou et al 30 , Du et al 19 , 32 , Shergill et al 33 , Anthimidou et al 34 , etc.…”