ARS | Publication request: Functional genomics analysis of horseweed (Conyza canadensis) with special reference to the evolution of non-target-site glyphosate resistance

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 22, 2009
Publication Date: April 6, 2010
Citation: Yuan, J.S., Abercrombie, L., Cao, Y., Halfhill, M.D., Zhou, X., Peng, Y., Hu, J., Rao, M.R., Heck, G.R., Larosa, T.J., Sammons, R.D., Wang, X., Ranjan, P., Johnson, D.H., Wadl, P.A., Scheffler, B.E., Rinehart, T.A., Trigiano, R.N., Stewart, Jr, C.N. 2010. Functional genomics analysis of horseweed (Conyza canadensis) with special reference to the evolution of non-target-site glyphosate resistance. Weed Science. 58:109-117.

Interpretive Summary: Glyphosate is an important herbicide for modern agriculture practices. Many modern cultivars of soybean, cotton and corn have resistance to this broad spectrum herbicide thus allowing its use on a large number of acres across the United States. However such wide usage means the probability of weeds developing resistance increases. Horseweed is once such type of weed that has documented resistance that has occurred in separate locations in the U.S.A. The form of resistance in horseweed does not directly involve the target site of the herbicide which would be similar to changing a lock so the key (herbicide) no longer functions. Instead a different mechanism of resistance appears to have happened in independent events. In this work gene expression of resistant horseweed plants were examined. The results indicate that horseweed might be sequestering the herbicide away for important parts of the plant cell and thus providing protection through separation.

Technical Abstract: The evolution of glyphosate resistance in weedy species places an environmentally benign herbicide in peril. The first report of a dicot plant with evolved glyphosate resistance was horseweed, which occurred in 2001. Since then, several species have evolved glyphosate resistance and genomic information about nontarget resistance mechanisms in any of them ranges from none to little. Here, we report a study combining iGentifier transcriptome analysis, cDNA sequencing, and a heterologous microarray analysis to explore potential molecular and transcriptomic mechanisms of nontarget glyphosate resistance of horseweed. The results indicate that similar molecular mechanisms might exist for nontarget herbicide resistance across multiple resistant plants from different locations, even though resistance among these resistant plants likely evolved independently and available evidence suggests resistance has evolved at least four separate times. In addition, both the microarray and sequence analyses identified nontarget-site resistance candidate genes for follow-on functional genomics analysis.