Constitutive redox and phosphoproteome changes in multiple herbicide resistant Avena fatua L. are similar to those of systemic acquired resistance and systemic acquired acclimation

Abstract

Plants are routinely confronted with numerous biotic and abiotic stressors, and in response have evolved highly effective strategies of systemic acquired resistance (SAR) and systemic acquired acclimation (SAA), respectively. A much more evolutionarily recent abiotic stress is the application of herbicides to control weedy plants, and their intensive use has selected for resistant weed populations that cause substantial crop yield losses and increase production costs. Non-target site resistance (NTSR) to herbicides is rapidly increasing worldwide and is associated with alterations in generalized stress defense networks. This work investigated protein post-translational modifications associated with NTSR in multiple herbicide resistant (MHR) Avena fatua, and their commonalities with those of SAR and SAA. We used proteomic, biochemical, and immunological approaches to compare constitutive protein profiles in MHR and herbicide susceptible (HS) A. fatua populations. Phosphoproteome and redox proteome surveys showed that post-translational modifications of proteins with functions in core cellular processes were reduced in MHR plants, while those involved in xenobiotic and stress response, reactive oxygen species detoxification and redox maintenance, heat shock response, and intracellular signaling were elevated in MHR as compared to HS plants. More specifically, MHR plants contained constitutively elevated levels of three protein kinases including the lectin S-receptor-like serine/threonine-protein kinase LecRK2, a well-characterized component of SAR. Analyses of superoxide dismutase enzyme activity and protein levels did not reveal constitutive differences between MHR and HS plants. The overall results support the idea that herbicide stress is perceived similarly to other abiotic stresses, and that A. fatua NTSR shares analogous features with SAR and SAA. We speculate that MHR A. fatua's previous exposure to sublethal herbicide doses, as well as earlier evolution under a diversity of abiotic and biotic stressors, has led to a heightened state of stress preparedness that includes NTSR to a number of unrelated herbicides.

Stress‐induced evolution of herbicide resistance and related pleiotropic effects

“…28 In the first phosphoproteome and redox proteome comparisons between resistant and susceptible plants of any species, PTMs of proteins with functions in core cellular processes were shown to be constitutively reduced in MHR A. fatua plants, perhaps in association with certain fitness costs. 79 PTMs of proteins involved in xenobiotic and stress response, ROS detoxification/redox maintenance, heat shock response, and intracellular signaling were more abundant in MHR than susceptible plants. Overall, this suite of constitutive changes in MHR A. fatua populations could represent pleiotropic effects of NTSR, or it is more likely that they are an evolutionary signature of ongoing stress responses like systemic acquired acclimation or SAR, of which NTSR is only one aspect.…”

“…Resistance to flucarbazone, imazamethabenz‐methyl, and pinoxaden is controlled by three separate but linked nuclear genes . 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 .…”

“…By contrast, levels of heat shock protein (HSP) transcripts and proteins were constitutively lower than in susceptible plants . In the first phosphoproteome and redox proteome comparisons between resistant and susceptible plants of any species, PTMs of proteins with functions in core cellular processes were shown to be constitutively reduced in MHR A. fatua plants, perhaps in association with certain fitness costs . PTMs of proteins involved in xenobiotic and stress response, ROS detoxification/redox maintenance, heat shock response, and intracellular signaling were more abundant in MHR than susceptible plants.…”

“…Of all the changes associated with MHR A. fatua discussed above, perhaps the most intriguing is the constitutive reduction of HSP transcripts and proteins and altered HSP PTM patterns . In all eukaryotes, HSPs are typically induced and subjected to PTMs in response to heat shock as well as a wide variety of biotic and abiotic stresses, and they are implicated in hormetically induced epigenetic effects on phenotype .…”

The phosphorylated redox proteome of Chlamydomonas reinhardtii: Revealing novel means for regulation of protein structure and function

“…Recent advances in proteome-wide studies of methionine oxidation in Arabidopsis thaliana have shown that it may serve as a rheostat to control the phosphorylation of proximal residues, further revealing the widespread consequences of redox signaling [11] , [12] . Similarly, proteins with both reversible cysteine oxidation and phosphorylation sites are largely recognized [13] , [14] , yet studies identifying proteoforms simultaneously affected by these modifications are sparse [15] , [16] . Discovery and targeted validation of these PTMs and the effect on protein structure and function are particularly lacking for photosynthetic organisms and must be advanced to begin meaningful definition of signaling pathways [17] .…”