The role of extrachromosomal DNA in rapid adaption in pigweed

Authors: SASKI, CHRISTOPHER - Clemson University; Molin, William

Submitted to: Research Outreach
Publication Type: Popular Publication
Publication Acceptance Date: 10/29/2020
Publication Date: 3/2/2021
Citation: Saski, C., Molin, W.T. 2021. The role of extrachromosomal DNA in rapid adaption in pigweed. Research Outreach. 120:30-33. https://doi.org/10.32907/RO-120-3033.
DOI: https://doi.org/10.32907/RO-120-3033

Interpretive Summary: Dr Christopher Saski from Clemson University and Dr William Molin from the U.S. Department of Agriculture are conducting research to determine how are weeds becoming resistant to the herbicides used to control them. Plants, like other living organisms, have genetic stress-avoidance mechanisms that allow them to become resistant to specific chemicals when continuously exposed to them. In Pigweed an extrachromosomal circular DNA (eccDNA) structure known as the replicon of pigweed, which contains the EPSPS gene, the gene product of which is the target of the herbicide glyphosate was found to confer resistance to glyphosate. The replicon is a feature of the glyphosate-resistant pigweed genome that gives the pigweed selective advantage to survive glyphosate treatments and proliferate – and has characteristics similar to some human cancers.

Technical Abstract: Gene amplification has been observed in many bacteria and eukaryotes as response to various selective pressures such as antibiotics, cytotoxic drugs, pesticides, herbicides and other stressful environmental conditions. An increase in gene copy number is often found as extra-chromosomal elements that usually contain autonomously replicating circular DNA molecules (eccDNAs). Amaranthus palmeri, a crop weed, can develop herbicide resistance to glyphosate [N-(phosphonomethyl) glycine] by amplification of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene, the molecular target of glyphosate. However, biological questions regarding the source of the amplified EPSPS, the nature of the amplified DNA structures, and mechanisms responsible for maintaining this gene amplification in cells and their inheritance, remain unknown. Here we report that amplified EPSPS copies in glyphosate-resistant (GR) A. palmeri are present in the form of eccDNAs with various conformations. The eccDNAs are transmitted during cell division in mitosis and meiosis to the soma and germ cells and the progeny by as yet unknown mechanism of tethering to mitotic and meiotic chromosomes.