EPSPS target site mechanisms confer glyphosate resistance in Arctotheca calendula

BACKGROUND: The first case of glyphosate resistance was reported in a capeweed population from Western Australia in our previous study. This current study investigates the resistance mechanisms in the population. RESULTS: Target-site EPSPS gene sequencing revealed two partial sequences of the EPSPS transcripts (1001 bp and 998 bp), and the full-length sequence (1551 bp) containing the 1001-bp transcript was cloned as it was found in the resistant plants. A known resistance-endowing target-site mutation in the 1551-bp transcript was identified in the resistant plants, resulting in the Pro-106-Ser substitution. The subpopulation derived from these mutant plants exhibited >10-fold resistance to glyphosate compared to the susceptible population. Additionally, the EPSPS gene (1551 bp) was constitutively expressed at a higher level (4.3-fold) in the resistant than in the susceptible populations. However, 14C-glyphosate foliar uptake was similar with no visual difference in 14C-glyphosate translocation from leaves to other parts of a plant, between the resistant and susceptible population. CONCLUSION: Glyphosate resistance in the studied population is associated with both a target-site mutation (Pro-106-Ser) and increased EPSPS gene expression.