Changes in cuticle composition co-regulate drought and herbicide resistance in horseweed (Erigeron canadensis)

Horseweed (Erigeron canadensis) is a widely distributed annual weed that can cause significant yield losses if not properly controlled. Its phenotypic plasticity allows it to rapidly acclimate to new environmental conditions, such as drought and herbicides, such as glyphosate, with the potential for cross stress acclimatization. The objectives of this research were to uncover the physiological and genetic effects at the intersection of drought stress and glyphosate resistance. To this end, we performed greenhouse dose response experiments, RNAseq, 14C glyphosate absorption and translocation, and cuticular lipid profiling via GC/MS. Greenhouse dose-response experiments revealed that, after drought stress, there was a 2.5-3.7 fold reduction in glyphosate sensitivity via a significant reduction in glyphosate absorption, regardless if the starting population was resistant or susceptible to the field use rate already. Cuticular waxes were collected from each population with and without drought stress and were analyzed via GC/MS. When comparing total wax loads of plants grown under WW and DS conditions, we found that drought stress significantly increased total wax loads for all three populations. Additionally drought stress substantial increases the proportion of triterpenoids in the cuticle. By RNAseq, we found serval triterpenoid biosynthesis genes upregulated after drought, which likely drive the changes in cuticle composition and ultimately increased glyphosate resistance following drought. Ultimately, understanding how drought impacts glyphosate resistance is critical for maintaining optimal weed control in the changing climate. HighlightDrought stress induces changes to cuticle composition and gene expression that reduce glyphosate absorption, thereby increasing horseweeds ability to survive glyphosate application.