Acetyl-CoA carboxylase overexpression in herbicide-resistant large crabgrass (Digitaria sanguinalis)
Laforest, M., Soufiane, B., Simard, M.J., Obeid, K., Page, E., Nurse, R.E. (2017). Acetyl-CoA carboxylase overexpression in herbicide-resistant large crabgrass (Digitaria sanguinalis). Pest Management Science, [online] 73(11), 2227-2235. http://dx.doi.org/10.1002/ps.4675
Plain language summary
Herbicides are used to control weeds in crops. The purpose of the active ingredient in a herbicide is to block one of the vital functions of the target plant in order to control the plant’s growth. Because of the functions that they target, some herbicides are specific to grasses and are called graminicides. Producers in Ontario observed in 2015 that graminicides were failing to control large crab grass. Graminicides are grouped into several subclasses, and large crab grass is resistant to the two subclasses that were tested. Genetic studies showed that the gene responsible for the function targeted by the herbicide is expressed 3.4 to 9.3 times more in herbicide-resistant plants than in susceptible plants. These studies also showed that the gene was amplified (5 to 7 times more copies) in resistant plants. This the first case, after glyphosate resistance in certain weeds, in which the amplification of a gene explains the phenomenon of resistance. Because we know what the mechanism is, we can create a genetic test for rapidly diagnosing similar cases of resistance in large crab grass. The test provides early confirmation of resistance and informs producers so that they can make the best decisions in terms of their cropping practices.
BACKGROUND: The occurrence of herbicide-resistant weed biotypes is increasing and this report of an acetyl-CoA carboxylase (ACCase) inhibitor-resistant Digitaria sanguinalis L. Scop. from southwestern Ontario is another example. The identified weed escaped control in an onion and carrot rotation in which graminicides were used for several consecutive years. Our goal was to characterize the level and mechanism of resistance of the biotype. RESULTS: The biotype was resistant to all five ACCase inhibitor herbicides tested. Gene-expression profiling was performed because none of the mutations known to confer resistance in the ACCase gene were detected. RNASeq and quantitative reverse-transcriptase PCR (qRT-PCR) results indicated that transcription of ACCase was 3.4–9.3 times higher in the resistant biotype than the susceptible biotype. ACCase gene copy number was determined by qPCR to be five to seven times higher in the resistant compared with the susceptible biotype. ACCase gene overexpression was directly related to the increase of the ACCase gene copy number. CONCLUSION: Our results are consistent with the hypothesis that overexpression of the herbicide target gene ACCase confers resistance to the herbicide. This is the first reported case of target gene duplication conferring resistance to a herbicide other than glyphosate. © 2017 Society of Chemical Industry. See related Article.