Involvement of Epigenetic Mechanisms in Herbicide Resistance: The Case of Conyza canadensis

Abstract

Glyphosate is the most important herbicide globally, and horseweed (Conyza canadensis) has been one of the most commonly encountered weed species that has developed resistance to it in various parts of the world, including Greece. After glyphosate application, horseweed populations show a wide range of phenotypic plasticity in response to selection pressure. In previous work, we have proposed a herbicide resistance mechanism that is not due to a point mutation at the codon 106 of EPSP synthase but most likely due to a synchronized overexpression of EPSPS and the ABC transporter genes. In the current study, it is hypothesized that the observed phenotypic alterations and differential expression of the EPSPS gene could be attributed to epigenetic changes. DNA methylation plays a pivotal role in many biological procedures such as gene expression, differentiation, and cellular proliferation. Sodium bisulfite sequencing was used to detect epigenetic changes that occur at the C5 position of cytosine residues within CpGdi nucleotides in two horseweed populations (resistant vs. susceptible). Results show differential methylation pattern between the two populations. This work will elucidate the naturally increased resistance of C. Canadensis to glyphosate and set the bases for future development of techniques that restrict weed resistance to herbicides.

Re-registration Challenges of Glyphosate in the European Union

“…The evolution of resistance was shown to occur due to gene amplification (Chen et al, 2017;Dolatabadian et al, 2017;Fernandez-Escalada et al, 2017;Han et al, 2017;Jugulam and Gill, 2018). Epigenetic alterations through increased levels of DNA and histone methylation were identified in response to exposure to glyphosate (Nardemir et al, 2015;Kim et al, 2017;Margaritopoulou et al, 2018;Markus et al, 2018). The results suggest that epigenetic pathways may influence the regulation of genes important for herbicide detoxification (Markus et al, 2018).…”

Target site as the main mechanism of resistance to imazamox in a Euphorbia heterophylla biotype

“…Differential herbicide transport between R and S plants can be attributed to ATP-dependent [ATP-binding cassette (ABC)] transporters 53 , which move the molecule into the vacuole or extracellular space 30,54–56 . Changes in the expression of NTSR genes, related to herbicide-metabolizing enzyme(s) or transporter proteins, can lead to an increase in herbicide degradation or translocation, respectively 57,58 .…”

Mechanisms of evolved herbicide resistance

“…For example, changes in the methylation status of a gene could affect its expression. Epigenetic involvement in evolved herbicide resistance is an understudied topic, although differential methylation of EPSPS recently was reported between glyphosateresistant and sensitive biotypes of C. canadensis (180). It is not yet clear, however, if this differential methylation contributes to resistance.…”