Pro-106-Ser mutation and EPSPS overexpression acting together simultaneously in glyphosate-resistant goosegrass (Eleusine indica)

Abstract

Glyphosate has been used for more than 15 years for weed management in citrus groves in the Gulf of Mexico, at up to 3–4 applications per year. Goosegrass (Eleusine indica (L.) Gaertn.) control has sometimes failed. In this research, the mechanisms governing three goosegrass biotypes (Ein-Or from an orange grove, and Ein-Pl1 and Ein-Pl2 from Persian lime groves) with suspected resistance to glyphosate were characterized and compared to a susceptible biotype (Ein-S). Dose-response and shikimate accumulation assays confirmed resistance of the resistant (R) biotypes. There were no differences in glyphosate absorption, but the R biotypes retained up to 62–78% of the herbicide in the treated leaf at 96 h after treatment (HAT), in comparison to the Ein-S biotype (36%). The 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) activity in the Ein-Or and Ein-S biotypes was over 100-fold lower than the Ein-Pl1 and Ein-Pl2 ones. The latter showed a high EPSPS-basal activity, a mutation at Pro-106-Ser position in the EPSPS gene, and EPSPS overexpression. The EPSPS basal and EPSPS overexpression were positively correlated. The R goosegrass biotypes displayed poor glyphosate translocation. Furthermore, this grassweed showed, for the first time, two mechanisms at the target-site level (Pro-106-Ser mutation + EPSPS overexpression) acting together simultaneously against glyphosate.

From tolerance to resistance: mechanisms governing the differential response to glyphosate in Chloris barbata

“…The lower shikimate accumulation in R plants indicates limited interaction of glyphosate with the EPSPS protein, and may be due to either target site or non‐target site resistance mechanisms . However, it is difficult to deduce the mechanism (s) involved in the resistance of each resistant C. barbata population based solely on shikimate accumulation, because this parameter is just a resistance indicator …”

“…Several mutations in the EPSPS gene have been suggested as contributing to glyphosate resistance such as: Val133‐Ile and Pro382‐Leu in E. indica , Asp71‐Met, Ala112‐Ile and Val201‐Met in Ophiopogon japonicus , Liriope platyphylla and L. spicata , and Glu91‐Ala in C. truncata , among others. However, the mutations responsible for conferring resistance to glyphosate must occur in the conserved region of the EPSPS gene, which includes amino acid positions 95 to 107, as demonstrated in E. coli . To date, only two mutations (Thr102 and Pro106) occurring in this region have been found .…”

“…Veracruz (Gulf of Mexico) is the main producer of this citrus fruit, but to cover the large volume of exports, its production has been extended to states with similar environmental characteristics, such as Colima, Guerrero, Michoacán and Oaxaca (Pacific Coast) . Tropical rainfall conditions allow continuous Persian lime production all year round, but also favor the emergence of weeds, such as Bidens pilosa , Eleusine indica and Leptoclhoa virgate , which have been identified as being resistant to glyphosate. They do not have a great impact on yield, but weeds can make cultivation difficult .…”

Mechanisms of glyphosate resistance and response to alternative herbicide‐based management in populations of the three Conyza species introduced in southern Spain

“…NTSR, described as a collection of mechanisms that are by definition not TSR, results from reduced uptake and/or translocation, increased vacuolar sequestration or metabolism to non‐toxic compounds, with consequent decreased levels of glyphosate interacting with EPSPS . TSR mechanisms involve one or more mutations in the DNA encoding the target protein of the herbicide, which leads to changes in amino acids or conformational changes in protein folding . Amplified basal expression of EPSPS for instance, also a TSR mechanism, provides additional active sites for phosphoenolpyruvate and S3P to bind normally and continue to move carbon flux through the shikimate pathway …”

EPSPS duplication and mutation involved in glyphosate resistance in the allotetraploid weed species Poa annua L.

“…The lower glyphosate binding affinity observed with these amino acid substitutions have been attributed to structural changes in the enzyme binding site according to protein crystallography studies . At the whole‐plant level, SNPs at position 106 commonly confer variable levels of resistance in the order of three‐ to nine‐fold compared to susceptible biotypes . Conversely, double amino acid mutations at position 102 and 106 may confer resistance levels up to 180‐fold, commonly accompanied by high fitness costs …”