Abstract
Emergence of glyphosate-resistant horseweed (Conyza canadensis) biotypes is an example of how unrelenting use of a single mode of action herbicide in agricultural weed control drives genetic adaptation in targeted species. While in other weeds glyphosate resistance arose from target site mutation or target gene amplification, the resistance mechanism in horseweed uses neither of these, being instead linked to reduced herbicide uptake and/or translocation. The molecular components underpinning horseweed glyphosate-resistance remain unknown. Here, we used an in vitro leaf disc system for comparative analysis of proteins extracted from control and glyphosate-treated tissues of glyphosate-resistant and glyphosate-susceptible biotypes. Analysis of shikimic acid accumulation, ABC-transporter gene expression, and cell death were used to select a suitable glyphosate concentration and sampling time for enriching proteins pivotal to glyphosate resistance. Protein gel analysis and mass spectrometry identified mainly chloroplast proteins differentially expressed between the biotypes before and after glyphosate treatment. Chloroplasts are the organelles in which the shikimate pathway, which is targeted by glyphosate, is located. Calvin cycle enzymes and proteins of unknown function were among the proteins identified. Our study provides candidate proteins that could be pivotal in engendering resistance and implicates chloroplasts as the primary sites driving glyphosate-resistance in horseweed.
Highlights
Emergence of glyphosate-resistant horseweed (Conyza canadensis) biotypes is an example of how unrelenting use of a single mode of action herbicide in agricultural weed control drives genetic adaptation in targeted species
Through active transport of glyphosate by ABC transporters[21,22], has been described as the main resistance mechanism in several glyphosate-resistant weeds, including Conyza spp.[23]. This is supported by glyphosate-induced up-regulation of ABC transporters mainly M10 and M11 genes observed in glyphosate-resistant C. canadensis[24]
Herbicide metabolism has been implicated in a Spanish C. canadensis biotype, where glyoxylate sarcosine and AMPA were detected in the resistant biotype[17]
Summary
Emergence of glyphosate-resistant horseweed (Conyza canadensis) biotypes is an example of how unrelenting use of a single mode of action herbicide in agricultural weed control drives genetic adaptation in targeted species. (Asteraceae family) are highly invasive problematic annual weed species reported in more than 40 different crops in 70 countries[1,2] These plants are very prolific, with estimations of a single horseweed plant producing up to 200,000 seeds, which are dispersed by wind to infest new territory[1,3]. Through active transport of glyphosate by ABC transporters[21,22], has been described as the main resistance mechanism in several glyphosate-resistant weeds, including Conyza spp.[23] This is supported by glyphosate-induced up-regulation of ABC transporters mainly M10 and M11 genes observed in glyphosate-resistant C. canadensis[24]. Other researchers have reported increased EPSPS mRNA expression levels in glyphosate-resistant populations of Conyza spp.[25]
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