Researchers make breakthrough in glyphosate resistance in pigweeds

Kansas State University researchers have discovered how weeds develop resistance to the popular herbicide glyphosate, a finding that could have broad future implications in agriculture and many other industries. 

"Herbicide resistance in weeds has been a huge problem, not only in Kansas and the U.S. but many parts of the world," said Mithila Jugulam, a K-State weed scientist and co-author of the PNAS article. "What we found that was new was how these weeds have evolved resistance to glyphosate in such a short time. If you look at the evolution of glyphosate resistance in Palmer amaranth, based on our research, it appears to have occurred very rapidly."

"We found that glyphosate-resistant Palmer amaranth plants carry the glyphosate target gene in hundreds of copies," Jugulam said. "Therefore, even if you applied an amount much higher than the recommended dose of glyphosate, the plants would not be killed."

When chromosome experts in the team looked at these glyphosate-resistant weeds, the glyphosate target gene, along with other genes actually escaped from the chromosomes and formed a separate, self-replicating circular DNA structure.

Scientists refer to this structure as extra-chromosomal circular DNA (eccDNA). Each eccDNA has one copy of the gene that produces an enzyme that is the target for glyphosate. „Because of the presence of hundreds of eccDNAs in each cell, the amount of the enzyme is also abundant," Bikram Gill said. "Therefore, the plant is not affected by glyphosate application and thus the weed is resistant to the herbicide."