Functional Genomics Analysis of Horseweed (Conyza canadensis) with Special Reference to the Evolution of Non–Target-Site Glyphosate Resistance

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 non–target-site resistance candidate genes for follow-on functional genomics analysis.

A Modified phosphate-carrier protein theory is proposed as a non-target site mechanism For glyphosate resistance in weeds

“…The flow of glyphosate into the vacuole is considered to be a new non-target mechanism of glyphosate resistance, but the exact proteins involved in this process remain to be elucidated. Studies that use proteomics have highlighted a tonoplast protein expressed only in the resistant C. canadensis biotype but not in susceptible biotypes (Yuan et al, 2010).…”

Glyphosate‐resistant horseweed made sensitive to glyphosate: low‐temperature suppression of glyphosate vacuolar sequestration revealed by 31P NMR

“…An individual plant easily spreads to adjacent areas, as it is capable of producing more than 200 000 wind‐dispersed seeds 9. However, analysis of horseweed populations using horseweed transcriptome and simple sequence repeats strongly supports the independent selection of GR horseweed 10. The spread of GR weeds, such as horseweed, is a serious challenge to modern agricultural practice 11–13…”

Bacterial glyphosate resistance conferred by overexpression of an E. coli membrane efflux transporter

“…On the other hand, sensitive biotypes succumb to the lethal eVects of glyphosate because there is a greater reservoir of glyphosate in the cytoplasm of source and sink tissues [14]. Characterization of the transcriptome from sensitive and resistant horseweed has identiWed several diVerentially expressed transcripts, with transporter genes among them implicated as candidates for a putative non-target herbicide resistance gene [20,33].…”