Intensive herbicide use has selected for constitutively elevated levels of stress‐responsive mRNAs and proteins in multiple herbicide‐resistant Avena fatua L

Abstract

Although the individual and collective contributions of these DEGs and proteins to MHR remain to be determined, our results support the idea that intensive herbicide use has selected for MHR populations with altered, constitutively regulated patterns of gene expression that are similar to those in abiotic stress-tolerant plants. © 2017 Society of Chemical Industry.

Stress‐induced evolution of herbicide resistance and related pleiotropic effects

“…As shown in Table , all resistant populations characterized to date exhibit various pleiotropic effects at the whole plant, biochemical, or molecular level. Of these, MHR A. fatua contains more documented molecular changes than other species, as well as several unusual resistance mechanisms, and so it has been used as a model to investigate the primary stress effects associated with the evolution of NTSR . Initial efforts to describe these have focused on constitutive differences between MHR and susceptible populations, because they are most likely to represent changes that would lead to pleiotropic effects.…”

“…Similarly, stress‐induced changes in protein PTMs like phosphorylation and cysteine oxidation modify enzymatic and regulatory activities, allowing plants to rapidly adjust carbon flux . Plant transcriptome, proteome, and PTM changes caused by herbicide stress are quite similar to those resulting from abiotic and biotic stresses, supporting the existence of the SAHR phenotype proposed here. Although not the focus of this review, herbicide safeners also induce similar gene expression changes likely through oxylipin‐mediated signaling, and the unclear relationship between safeners and NTSR evolution is currently under investigation .…”

“…Although all the specific biochemical mechanisms conferring NTSR to this wide array of herbicides are not yet known, resistance to fenoxaprop‐P‐ethyl and imazamethabenz‐methyl may be due to reduced rates of carboxylesterase activity, an enzymatic step necessary for cellular uptake and conversion of these pre‐herbicides into active inhibitors . Enhanced herbicide catabolism does not appear to play a major role in MHR A. fatua , because glutathione S ‐transferase specific activities towards fenoxaprop‐P‐ethyl and imazamethabenz‐methyl were not different between untreated MHR and susceptible plants and only a relatively small number of constitutively elevated xenobiotic catabolism transcripts and proteins were detected in MHR plants . The A. fatua NTSR phenotype is heritable and stable for multiple generations in the absence of herbicide treatment .…”

“…Initial efforts to describe these have focused on constitutive differences between MHR and susceptible populations, because they are most likely to represent changes that would lead to pleiotropic effects. Transcriptome and proteome analyses showed that MHR plants have constitutively higher levels of transcripts and proteins with functions in stress response, disease resistance, redox maintenance, xenobiotic transport and catabolism, transcriptional regulation, and signal transduction . For example, transcripts for three protein kinases including the lectin S‐receptor‐like serine/threonine‐protein kinase LecRK2, a well‐characterized SAR receptor/signal transducer, were constitutively elevated in MHR4 plants.…”

Optimizing RNA‐seq studies to investigate herbicide resistance

“…A general review of the literature (Tables and S1) reveals a wide array of RNA‐seq experimental set‐ups employed by weed researchers over the last few years . These initial set‐up decisions can drastically influence the number of transcripts that appear as significantly differentially expressed by the end of the analysis.…”