Analyzing Arabidopsis thaliana root proteome provides insights into the molecular bases of enantioselective imazethapyr toxicity

Abstract

Imazethapyr (IM) is a widely used chiral herbicide that inhibits the synthesis of branched-chain amino acids (BCAAs). IM is thought to exert its toxic effects on amino acid synthesis mainly through inhibition of acetolactate synthase activity, but little is known about the potential effects of IM on other key biochemical pathways. Here, we exposed the model plant Arabidospsis thaliana to trace S- and R-IM enantiomer concentrations and examined IM toxicity effects on the root proteome using iTRAQ. Conventional analyses of root carbohydrates, organic acids, and enzyme activities were also performed. We discovered several previously unknown key biochemical pathways targeted by IM in Arabidospsis. 1,322 and 987 proteins were differentially expressed in response to R- and S-IM treatments, respectively. Bioinformatics and physiological analyses suggested that IM reduced the BCAA tissue content not only by strongly suppressing BCAA synthesis but also by increasing BCAA catabolism. IM also affected sugar and starch metabolism, changed the composition of root cell walls, increased citrate production and exudation, and affected the microbial community structure of the rhizosphere. The present study shed new light on the multiple toxicity mechanisms of a selective herbicide on a model plant.

Enantioselectivity in degradation and ecological risk of the chiral pesticide ethiprole

“…Hence, the chiral conversion of ( S )‐ethiprole to its antipode influenced these bacterial OTUs. A soil microcosm study found that soil samples treated with ( R )‐imazethapyr had the lowest diversity compared whereas ( S )‐imazethapyr‐treated samples appeared to be more diverse based on Shannon's and Simpson's diversity indices (Qian et al, ). However, the presence of rac ‐ethiprole caused massive reductions of indicator species, with only OTU113 ( Oryzihumus ) and 464 (candidate division WPS‐1 ) observed in paddy rice soil following ethiprole addition.…”

Herbicide-related signaling in plants reveals novel insights for herbicide use strategies, environmental risk assessment and global change assessment challenges

“…The importance of these interferences with herbicide effects strongly indicates that major questions concerning the precise mechanisms through which herbicides affect and kill plants remain to be addressed (Qian et al, 2015b;Vivancos et al, 2011). Recent developments using mutation approaches have revealed unexpected links between herbicide tolerance and plant regulatory genes that are unrelated to herbicide targets or herbicide metabolisms (Faus et al, 2015;Fukudome et al, 2014;Kurepa et al, 1998;Ramel et al, 2012;Sanchez-Villarreal et al, 2013;Sharkhuu et al, 2014;Smeets et al, 2013).…”

“…Mechanisms of primary sensing of xenobiotic structures, which have been characterized in animal cells, have however remained elusive in the case of plant cells (Ramel et al, 2012), even if various situations of plant-xenobiotic interactions suggest that such primary sensing may also exist in plant cells (Ramel et al, 2012). Qian et al (2015aQian et al ( , 2015b have shown that low levels of imazethapyr induced major metabolic and molecular changes in flowers or in roots. However, these imazethapyr treatments were carried out at IC50 concentrations yielding some level of toxicity.…”

“…Increase of asparagine levels (up to 6-fold) as occurs under conditions of subtoxic herbicide contamination (Serra et al, 2015a) could also contribute to enhanced susceptibility to plant viruses in relation with infection-related ammonium toxicity (Fernández-Calvino et al, 2016). Finally, herbicide-induced changes in phagostimulating metabolites (sucrose, serine, alanine) and in essential branched-chain amino acids (Qian et al, 2015b;Serra et al, 2013Serra et al, , 2015aSerra et al, , 2015b could affect feeding stimulation of insects (Hervé et al, 2014) or nitrogen quality of forage for livestock and wild animals (Savary-Auzeloux et al, 2003).…”

Effects of herbicide mixtures on freshwater microalgae with the potential effect of a safener

“…IODO inhibits the acetolactate synthase (ALS), an enzyme involved in the synthesis of the three proteinogenic branched-chain amino acids, and thus impairs protein synthesis. In this line, imazethapyr, which also inhibits ALS, targets several hundred proteins that are differentially expressed by Arabidopsis thaliana under treatment with this herbicide (Qian et al, 2015). The mechanism(s) involved in the differential toxicity of MixDs and MixDsw/oIODO remain(s) to be determined.…”