Gene amplification confers glyphosate resistance in Amaranthus palmeri

Abstract

The herbicide glyphosate became widely used in the United States and other parts of the world after the commercialization of glyphosate-resistant crops. These crops have constitutive overexpression of a glyphosate-insensitive form of the herbicide target site gene, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). Increased use of glyphosate over multiple years imposes selective genetic pressure on weed populations. We investigated recently discovered glyphosate-resistant Amaranthus palmeri populations from Georgia, in comparison with normally sensitive populations. EPSPS enzyme activity from resistant and susceptible plants was equally inhibited by glyphosate, which led us to use quantitative PCR to measure relative copy numbers of the EPSPS gene. Genomes of resistant plants contained from 5-fold to more than 160-fold more copies of the EPSPS gene than did genomes of susceptible plants. Quantitative RT-PCR on cDNA revealed that EPSPS expression was positively correlated with genomic EPSPS relative copy number. Immunoblot analyses showed that increased EPSPS protein level also correlated with EPSPS genomic copy number. EPSPS gene amplification was heritable, correlated with resistance in pseudo-F 2 populations, and is proposed to be the molecular basis of glyphosate resistance. FISH revealed that EPSPS genes were present on every chromosome and, therefore, gene amplification was likely not caused by unequal chromosome crossing over. This occurrence of gene amplification as an herbicide resistance mechanism in a naturally occurring weed population is particularly significant because it could threaten the sustainable use of glyphosate-resistant crop technology.5-enolpyruvylshikimate-3-phosphate synthase | herbicide resistance | mobile genetic element | evolution | Palmer amaranth

DETECTION OF GLYPHOSATE-RESISTANT PALMER AMARANTH (Amaranthus palmeri) IN AGRICULTURAL AREAS OF MATO GROSSO, BRAZIL

“…From another standpoint, Gaines et al (2010) Collectively, the data presented herein leads to the conclusion that the Brazilian Detection of glyphosate-resistant palmer amaranth ...…”

A Modified phosphate-carrier protein theory is proposed as a non-target site mechanism For glyphosate resistance in weeds

“…Analysis of fluorescence in situ hybridization has shown that EPSPs gene copies were present on almost all chromosomes of the genome of A. palmeri and appeared to be distributed randomly (Gaines et al, 2010). The high number of copies and their location on the genome suggests the action of transposon-like proteins or RNAmediated mechanisms.…”

“…Another mechanism for glyphosate resistance was identified recently in biotypes of Amaranthus palmeri from Georgia, USA (Gaines et al, 2010). The number of EPSPs gene copies in susceptible population ranged Table 2 -Glyphosate resistance mechanisms identified in 11 weed species from 1 to 1.3, whereas in resistant biotype this number ranged from 5 to more than 160 copies of the gene.…”

“…This enzyme in the resistant biotype expressed 35-fold more compared to the susceptible biotype. Also, the higher number of EPSPs gene copies resulted in an increased level of expressed mRNA, which consequently, leads to higher levels of glyphosate resistance (Gaines et al, 2010).…”

Glyphosate-Resistant Palmer Amaranth (Amaranthus palmeri) in Nebraska: Confirmation, EPSPS Gene Amplification, and Response to POST Corn and Soybean Herbicides

“…Glyphosate resistance has been conferred by a) target site mutation in the EPSPS gene, making it insensitive to the target protein (Kaundun et al 2011;Perez-Jones et al 2007;Yu et al 2007), b) reduced absorption and translocation of glyphosate (Dinelli et al 2008;Yu et al 2007;Wakelin et al 2004), c) increased glyphosate sequestration (Ge et al 2010), and d) EPSPS gene amplification (Chandi et al 2012;Gaines et al 2010;Jugulam et al 2014;Whitaker et al 2013). The presence of EPSPS gene copies (>100 copies) distributed throughout the genome has been confirmed in a GR Palmer amaranth biotype from Georgia (Gaines et al 2010). Additionally, EPSPS gene amplification has been reported in Palmer amaranth populations from North Carolina (Chandi et al 2012;Whitaker et al 2013), Mississippi (Ribeiro et al 2014), and New Mexico (Mohseni-Moghadam et al 2013a).…”