Gene Amplification of EPSPS with a Mutation in Conserved Region: The Evolved Glyphosate Resistance Mechanism in Eleusine indica

Goosegrass (Eleusine indica (L.) Gaertn.) is one of the most vicious weeds worldwide, competing with crops and greatly reducing their yields. Glyphosate, a non-selective, broad spectrum, post-emergence herbicide has inevitably induced severe resistance in many weeds owing to its intensive use. Additionally, control strategies rely on the clarity of resistance mechanisms. In this study, we aimed to investigate the resistance levels and potential resistance mechanisms of two goosegrass populations collected from orchards. Results showed that the resistance indexes of LL and SS populations were 3.8 and 1.9, respectively. A single nucleotide change led to a Pro106Leu (P106L) mutation in the LL population and the SS population had a Pro106Ser (P106S) amino acid substitution. The EPSPS expression in both populations was 2.6 times that of the wild-type population. However, the relative copy number and EPSPS protein content in the LL population were higher than those of the SS population, as indicated by immunoblot analysis and enzyme-linked immunosorbent assays. Overall, we confirmed EPSPS amplification with a P106L mutation, resulting in overproduction of this mutated EPSPS protein, which conferred moderate glyphosate resistance. This study details a case of simultaneous evolution of mutation and amplification in EPSPS of glyphosate resistance weeds.