Echinochloa is an extremely damaging and widespread warm-season global weed species. This particular glyphosate-resistant population studied, evolved within the Ord River irrigation region in tropical northern Western Australia.
Former AHRI postdoc Todd Gaines, Ord agronomist Andrew Cripps and Stephen Powles documented glyphosate resistance in this Echinochloa population (Gaines, Cripps & Powles, 2012). Subsequently, AHRI PhD student Goh Sou Sheng did good work on this population and found that resistance was non-target-site based. Thus, we knew that glyphosate resistance in this Echinochloa population was non-target-site based but we did not know the mechanism(s).
Now, following a good collaborative effort, in this Plant Physiology paper, it is clearly established that glyphosate resistance in this Echinochloa population is due to an enhanced capacity to metabolise glyphosate, catalysed by an Aldo-keto reductase gene. The first author on the paper is Dr Pan Lang, now at the Hunan Agricultural University, Changsha, China. Pan Lang spent one year in our AHRI laboratory on a China Scholarship Council award and he continued this research upon his return to China.
RNA-seq work identified that an Aldo-keto reductase gene is up-regulated in glyphosate-resistant plants. Glyphosate metabolism in the glyphosate-resistant Echinochloa was established by LC-MS. For definitive proof, the full-length Ec AKR4-1 gene was expressed in transgenic rice and E Coli, where it conferred glyphosate resistance due to enhanced rates of glyphosate metabolism via the AMPA pathway. Structural interaction of the EcAKR4-1 and glyphosate was also explored through collaboration with molecular modeller Alex Nyporko. Therefore, the study provides direct evidence of the evolution of a plant AKR that metabolizes glyphosate and thereby confers glyphosate resistance. It is expected that this work will result in many other studies which will show glyphosate resistance due to glyphosate metabolism (which surprisingly thus far has not been well documented) and stimulate a search for other glyphosate metabolism genes.
Authors: Pan, L., Yu, Q., Han, H., Mao. L., Nyporko, A., Fan, L., Bai, L., Powles, S.B