Can non‐Mendelian inheritance of extrachromosomal circular DNA‐mediated EPSPS gene amplification provide an opportunity to reverse resistance to glyphosate?

Amplification of herbicide target genes conferring naturally evolved resistance in weed species is one of the novel and more recently known mechanisms of resistance. Numerous agriculturally important dicot and monocot weeds, including Palmer amaranth ( Amaranthus palmeri ), common waterhemp ( Amaranthus tuberculatus ) and Italian ryegrass ( Lolium multiflorum ), have evolved resistance to glyphosate via this mechanism. Specifically, the extrachromosomal amplification of the 5‐enopyruvlyshikimate‐3‐phosphate synthase ( EPSPS ) gene, the molecular target of glyphosate, was found to be the basis for glyphosate resistance in Amaranthus weeds, for example Palmer amaranth and common waterhemp. Nonetheless, the mechanism of extrachromosomal amplification of the EPSPS gene was different in these weeds. These extrachromosomal elements are newly identified genetic components and represent a paradigm shift in genetics to provide an adaptive advantage to organisms to withstand stress. Also, the extrachromosomal amplified copies are touted to be unstable in many organisms, due to their unpredictable behaviour during mitosis or meiosis, suggesting that they may have not integrated into the host genome. Therefore, it is reasonable to hypothesise that, in the absence of selection, the number of EPSPS copies may dissipate leading to the reversal of glyphosate resistance to susceptibility.