Aldo-keto reductase may contribute to glyphosate resistance in Lolium rigidum

We have previously demonstrated that an aldo-keto reductase (AKR) from Echinochloa colona (EcAKR4-1) can metabolize glyphosate and confers glyphosate resistance. This study aims to investigate if the EcAKR4-1 orthologs from Lolium rigidum also play a role in glyphosate resistance in non-target-site based, glyphosate-resistant (R) L. rigidum populations from Western Australia.

The full-length L. rigidum AKR gene (LrAKR4C10) orthologous to EcAKR4-1, together with a distinct LrAKR1, were cloned from plants of a glyphosate-susceptible (S) (VLR1) and three glyphosate R L. rigidum populations (WALR50, WALR60 and WALR70). Reverse transcription quantitative polymerase chain reaction (RT-qPCR) results showed that basal expression levels of the two LrAKR genes did not differ between the R and S populations, but their expression was significantly induced by glyphosate (up to 4.3-fold) or 2,4-D treatment (up to 3.4-fold) in R populations. Escherichia coli cells transformed respectively with LrAKR4C10 and LrAKR1 were more tolerant to glyphosate. Rice (Oryza sativa) seedlings overexpressing each of the two LrAKR gene survived glyphosate rates that were lethal to the green fluorescence protein (GFP) control plants. Structural modeling predicts a similar way of glyphosate binding and detoxification by LrAKR4C10 and EcAKR4-1, but an alternative way of glyphosate binding by LrAKR1. Relatively lower capacity of the two LrAKRs in conferring glyphosate resistance than the known EcAKR4-1 was discussed in relation to structural interaction.

Glyphosate-induced higher expression of the two LrAKR genes in L. rigidum populations contributes to a moderate level of glyphosate resistance likely through enhanced glyphosate metabolism. The herbicide 2,4-D can also induce the LrAKR expression, indicating the potential antagonistic effect of 2,4-D to glyphosate. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.