Evolution of EPSPS double mutation imparting glyphosate resistance in wild poinsettia (Euphorbia heterophylla L.)

Abstract

The evolution of glyphosate resistance (GR) in weeds is an increasing problem. Glyphosate has been used intensively on wild poinsettia (Euphorbia heterophylla L.) populations for at least 20 years in GR crops within South America. We investigated the GR mechanisms in a wild poinsettia population from a soybean field in southern Brazil. The GR population required higher glyphosate doses to achieve 50% control (LD 50) and 50% dry mass reduction (MR 50) compared to a glyphosate susceptible (GS) population. The ratio between the LD 50 and MR 50 of GR and GS resulted in resistance factors (RF) of 6.9-fold and 6.1-fold, respectively. Shikimate accumulated 6.7 times more in GS than in GR when leaf-discs were incubated with increasing glyphosate concentrations. No differences were found between GR and GS regarding non-target-site mechanisms. Neither population metabolized glyphosate to significant levels following treatment with 850 g ha-1 glyphosate. Similar levels of 14 C-glyphosate uptake and translocation were observed between the two populations. No differences in EPSPS expression were found between GS and GR. Two target site mutations were found in all EPSPS alleles of homozygous resistant plants: Thr102Ile + Pro106Thr (TIPT-mutation). Heterozygous individuals harbored both alleles, wild-type and TIPT. Half of GR individuals were heterozygous, suggesting that resistance is still evolving in the population. A genotyping assay was developed based on the Pro106Thr mutation, demonstrating high efficiency to identify homozygous, heterozygous or wild-type EPSPS sequences across different plants. This is the first report of glyphosate-resistant wild-poinsettia harboring an EPSPS double mutation (TIPT) in the same plant.

A Target-Site Mutation Confers Cross-Resistance to ALS-Inhibiting Herbicides in Erigeron sumatrensis from Brazil

“…However, it is not possible to clarify in this work what is the frequency of the Pro197Ser among all ALS alleles. Heterozygosis in mutations that provide resistance to herbicides in polyploid species are frequently reported, for example in GR Bidens subalternans, Euphorbia heterophylla [26,27], and Lolium multiflorum resistant to inhibitors of ALS [28].…”

Glyphosate resistance evolution to lethal and sublethal doses in chemostat populations of model organismChlamydomonas reinhardtii

“…While mutations may have accumulated subsequently to improve resistance, the short time frame of the experiment limits the likelihood of polygenic resistance mechanisms. Furthermore, sequential point mutation genotypes changing the structure of EPSPS tend to render it highly insensitive to glyphosate and confer very high resistance [52,53,54,55], meaning we would then have expected to see a reduction in death rate, if not evidence of growth, at the very high doses of glyphosate tested in the death assays. A single substitution causing a structural change to EPSPS may instead cause a moderate resistance increase at variable cost depending on species [56,57,58,59,60].…”

Multiple Resistance Mechanisms Involved in Glyphosate Resistance in Eleusine indica

“…Since then, the different mutation types (Pro106His, Pro106Ala, and Pro106Thr) were found in some GR weeds [ 13 , 14 , 15 , 16 ]. Subsequently, the Thr102 mutation, the double mutation (Thr102 + Pro106) and even the triple mutation had been reported in GR weeds [ 17 , 18 , 19 , 20 ]. In addition, EPSPS gene amplification was also a common TSR mechanism, and had been observed in at least eight GR weed species [ 11 ].…”