Glyphosate-Resistant Goosegrass. Identification of a Mutation in the Target Enzyme 5-Enolpyruvylshikimate-3-Phosphate Synthase

Abstract

The spontaneous occurrence of resistance to the herbicide glyphosate in weed species has been an extremely infrequent event, despite over 20 years of extensive use. Recently, a glyphosate-resistant biotype of goosegrass (Eleusine indica) was identified in Malaysia exhibiting an LD 50 value approximately 2-to 4-fold greater than the sensitive biotype collected from the same region. A comparison of the inhibition of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) activity by glyphosate in extracts prepared from the resistant (R) and sensitive (S) biotypes revealed an approximately 5-fold higher IC 50 (glyphosate) for the (R) biotype. Sequence comparisons of the predicted EPSPS mature protein coding regions from both biotypes revealed four single-nucleotide differences, two of which result in amino acid changes. One of these changes, a proline to serine substitution at position 106 in the (R) biotype, corresponds to a substitution previously identified in a glyphosate-insensitive EPSPS enzyme from Salmonella typhimurium. Kinetic data generated for the recombinant enzymes suggests that the second substitution identified in the (R) EPSPS does not contribute significantly to its reduced glyphosate sensitivity. Escherichia coli aroA (EPSPS deficient) strains expressing the mature EPSPS enzyme from the (R) biotype exhibited an approximately 3-fold increase in glyphosate tolerance relative to strains expressing the mature EPSPS from the (S) biotype. These results provide the first evidence for an altered EPSPS enzyme as an underlying component of evolved glyphosate resistance in any plant species.

First case of glyphosate resistance in France

“…Amino acid substitutions of proline to serine, proline to threonine, proline to alanine, and proline to leucine at position 106 of the EPSPS protein were found to confer glyphosate resistance in grass weeds (Perez-Jones et al 2007;Wakelin and Preston 2006;Baerson et al 2002). Hence, in the EPSPS protein reported here, the same proline to serine amino acid substitution as described by Perez-Jones et al 2007 is likely to take a part in glyphosate resistance in the resistant L. rigidum population.…”

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

“…Malaysia, in which mutations in EPSPs gene caused the substitution of amino acid proline to serine at position 106 (P 106 S) (Baerson et al, 2002). The resistance factor in these population was found to be five, in other words, the resistant biotypes were five-fold less sensitive than the susceptible biotypes.…”

Resistance to ACCase inhibitors in Eleusine indica from Brazil involves a target site mutation

“…Herbicides from alternative modes of action other than ACCase inhibitors would be recommended strategy to deal with the E. indica resistance. However, caution should be taken to avoid selection pressure from only one herbicide option, because worldwide there have been reported evolved resistant E. indica populations to glyphosate (Ng et al, 2003;Baerson et al, 2002;Kaundun et al, 2011), to metribuzin (Brosnan et al, 2008), and to glufosinate and paraquat (Seng et al, 2010 …”