Flufenacet activity is affected by GST inhibitors in blackgrass (Alopecurus myosuroides) populations with reduced flufenacet sensitivity and higher expression levels of GSTs

Abstract

The WSSA group 15 (HRAC group K3) herbicide flufenacet is a key compound in weed resistance management, primarily used for PRE control of grass-weeds in winter cereal-based crop rotations in Europe. Although resistance to compounds of its mode of action (inhibition of the synthesis of very-long chain fatty acids) generally evolves slowly, reduced flufenacet efficacy due to enhanced glutathione transferase (GST) activity has been described in several blackgrass (Alopecurus myosuroides Huds.) populations. The present study aimed to better understand of the mechanism of flufenacet detoxification in A. myosuroides. Therefore, we characterized four A. myosuroides populations with different levels of flufenacet sensitivity. Flufenacet degradation was significantly slowed down in a sensitive population and a population with reduced flufenacet sensitivity by the use of the GST-inhibitors tridiphane and ethacrynic acid at sublethal rates. Finally, six differentially expressed GSTs and nine transcription factors as well as a keto-acyl-CoA reductase, involved in the biosynthesis of very-long-chain fatty acids were identified as candidate genes among a set of 319 significantly higher expressed gene-associated contigs in an RNA-Seq (RNA sequencing) study with the described A. myosuroides populations. Among a set of 218 contigs with significantly lower expression levels, receptor kinase activity was the most frequent annotation. In summary, the likely GST-mediated reduction in sensitivity evolves in A. myosuroides at a slow rate and can partially be reversed by an interaction between flufenacet and the GST-inhibitors tridiphane and ethacrynic acid. This provides further evidence for enhanced GST activity as a key mechanism in flufenacet resistance in A. myosuroides and supports the hypothesis that the six differentially expressed GSTs detected in the present RNA-Seq study are potentially involved in flufenacet resistance.

Mechanism of Resistance to S-metolachlor in Palmer amaranth

“…These early studies suggested that enhanced metabolism driven by GSTs is the mechanism of tolerance to chloroacetanilide. Recent research on L. Rigidum and A. myosuroides resistance to pyroxasulfone and flufenacet also indicated detoxification by GSTs as the primary mechanism of resistance (Busi et al, 2018;Dücker et al, 2020). The effect of GST inhibitor on the activity of S-metolachlor on A. palmeri in our study and that of Brabham et al (2019) indicate that GSTs endow resistance to S-metolachlor in A. palmeri.…”

“…The tau and phi class GST enzymes were chosen as putative candidate genes conferring resistance to S-metolachlor. To select the GST genes, we first identified the GST genes involved in VLCFA inhibitor tolerance or resistance in other species, such as Z. mays (corn), L. rigidum (rigid ryegrass) and A. myosuroides (blackgrass) from literature (Li et al, 2017a,b;Busi et al, 2018;Dücker et al, 2020). Access to recently sequenced and deposited A. palmeri genome allowed retrieval of putative homologs of such functionally related GST genes.…”

“…Enhanced amount of GSTF1 protein, a biomarker of NTST was found in L. rigidum population that showed reduced sensitivity to VLCFA inhibitors Torra et al (2021). Thus far, resistance to VLCFA inhibitors in weedy species is attributed to NTSR mechanism mediated by enhanced GST activity (Busi et al, 2018;Brabham et al, 2019;Dücker et al, 2020). GSTs from the phi (GSTF) and tau (GSTU) classes are unique to plants and its role has been widely investigated in stress tolerance and secondary metabolism as well as in detoxification of herbicides in crops and weeds (Hatton et al, 1996;Cummins et al, 2011).…”

Editorial: Multiple Herbicide-Resistant Weeds and Non-target Site Resistance Mechanisms: A Global Challenge for Food Production

“…Phase II herbicide metabolism mainly involves conjugation to GSH mediated by GSH S-transferases (GSTs). Metabolic resistance to VLCFA inhibiting herbicides such as flufenacet and pyroxasulfone in Alopecurus myosuroides and L. rigidum populations is possible due to enhanced GST-mediated metabolism via differentially expressed GSTs (Dücker et al, 2019(Dücker et al, , 2020Goggin et al, 2021). In this Research Topic, empirical evidence of herbicide metabolism via CYP-450 is provided in three articles (Yanniccari, Gigón et All types of resistance mechanisms can get stacked in R plants, both TSR and NTSR, but also different genes conferring EHM.…”

Directed Evolution of Phi Class Glutathione Transferases Involved in Multiple-Herbicide Resistance of Grass Weeds and Crops

“…Thereafter, publications on the GST-mediated resistance to multiple herbicides based on an increase in GST activity and/or gene expression were reported [11,[23][24][25][26][27][28]. Notably, detoxifying enzyme levels are greater in domesticated cereal crops than in their competing weeds; thus, these enzymes are largely responsible for differences in herbicide metabolism and selectivity [29][30][31][32][33]. Overexpression of GSTFs has been identified in A. myosuroides and L. rigidum weeds that have demonstrated herbicide tolerance.…”