Gene expression in response to glyphosate treatment in fleabane (Conyza bonariensis) – glyphosate death response and candidate resistance genes

BACKGROUND This study takes a whole‐transcriptome approach to assess gene expression changes in response to glyphosate treatment in glyphosate‐resistant fleabane. We assessed gene expression changes in both susceptible and resistant lines so that the glyphosate death response could be quantified, and constitutively expressed candidate resistance genes identified. There are three copies of the glyphosate target site (5‐enolpyruvylshikimate‐3‐phosphate; EPSPS) gene in Conyza and because Conyza bonariensis is allohexaploid, there is a baseline nine copies of the gene in any individual. RESULTS Many genes were differentially expressed in response to glyphosate treatment. Known resistance mutations are present in EPSPS2 but they are present in a glyphosate‐susceptible line as well as resistant lines and therefore not sufficient to confer resistance. EPSPS1 is expressed four times more than EPSPS2, further reducing the overall contribution of these mutations. CONCLUSION We demonstrate that glyphosate resistance in C. bonariensis is not the result of EPSPS mutations or overexpression, but due to a non‐target‐site mechanism. A large number of genes are affected by glyphosate treatment. We present a list of candidate non‐target‐site‐resistance (NTSR) genes in fleabane for future studies into these mechanisms. © 2017 Society of Chemical Industry EPSPS mutations in the polyploid Conyza bonariensis are not responsible for glyphosate resistance. This study characterises the glyphosate gene expression response, and identifies new candidate genes for non‐target‐site resistance.