Scientists at the University of Georgia and the University of Colorado recently discovered that gene amplification in resistant Palmer has led to this unexpected resistance to glyphosate. Most plants have one gene that produces an enzyme that binds with glyphosate. But this single gene cannot produce enough enzyme, known as EPSPS, so glyphosate normally overwhelms and kills the plant.

Glyphosate kills by blocking the production of specific amino acids that are made in plants, but not animals, making it a relatively safe herbicide. Plants try to fight back by producing EPSPS, but non-resistant plants don’t produce enough enzyme to protect themselves.

Resistant Palmer amaranth has a new defense: Amplifying the gene for EPSPS to create multiple copies on different strands of the plant’s DNA. These plants with multiple EPSPS genes can produce enough of the enzyme to bind with and overcome glyphosate, making it ineffective in killing the weed.

“This is something brand new that’s never shown up before in plants,” Burton said. “This plant has so many of these enzymes that they swamp Roundup.”

Burton and his research colleagues are looking at the transcriptome, or RNA, of both resistant and non-resistant Palmer, in hopes of understanding how the plant developed this gene amplification. Jenn Schaff at the North Carolina State Genomic Sciences Laboratory performed the transcriptome sequencing, and Elizabeth Scholl in Plant Pathology performed the initial bioinformatic analysis.