Abstract
Glyphosate is a non-selective herbicide that inhibits the shikimate pathway’s enzyme EPSPS (5-enolpyruvylshikimate-3-phosphate synthase) preventing the production of aromatic amino acids. This herbicide is largely used and appreciated because it controls a wide range of annual and perennial weeds but it has a minimal environmental impact when compared with other herbicides. Initially it was thought that resistance to glyphosate was not easy to evolve but the continuous applications, as it happened for other herbicides, have induced the development of several glyphosate-resistant weeds. Glyphosate resistance can be developed as target-site and non-target-site mechanisms. In the target-site mechanism of resistance, either a mutation on the EPSPS enzyme (enzyme modification) or the overexpression of the EPSPS enzyme have been found to confer resistance. In the non-target-site mechanism of glyphosate resistance, the herbicide translocation and neutralization is observed. Pumping glyphosate into vacuoles via membrane transporters has been suggested as a possible process involved in the restricted glyphosate translocation. As a consequence, a different vacuolar organization or plasticity could be an interesting character or marker to correlate to glyphosate resistance. Vacuolar markers AleuGFP (Sar1 dependent sorting) or GFPChi (Sar1 independent sorting) respectively can be used to monitor independent vacuolar sorting mechanisms during glyphosate induced stress. We observed that the adaptive reaction of tobacco protoplasts vacuolar system to the treatment with glyphosate, can be mimicked by the overexpression of a Triticum durum TdGST gene. Previous analysis evidenced that the herbicide glyphosate increased TdGST expression, confirming the role of GST in the protection against xenobiotics. Non-target-site glyphosate resistance mechanisms may correlate with an independent regulation of cell compartmentalization and herbicide induced genes may have a direct effect on it.
Highlights
Glutathione S-transferases (GSTs) are soluble proteins that catalyze the chemical modification of xenobiotic by covalent linkage to endogenous glutathione and transfer of the resulting conjugates from the cytosol to the vacuole
GFPChi and AleuGFP Fluorescence Is Altered by Glyphosate and GST Overexpression
The reporters were transiently expressed in tobacco protoplasts and their fluorescence pattern was identical to the pattern previously described
Summary
Glutathione S-transferases (GSTs) are soluble proteins that catalyze the chemical modification of xenobiotic by covalent linkage to endogenous glutathione and transfer of the resulting conjugates from the cytosol to the vacuole We investigated the alteration induced by GST overexpression and/or glyphosate treatment on the vacuolar sorting pathway using two known vacuolar markers: AleuGFP (Sar dependent sorting) and GFPChi (Sar independent sorting) [4]. These reporter proteins follow two different and independent routes to the vacuole [4,5,6] and can be used to monitor independent mechanisms during glyphosate induced stress. The correlation of non-target-site glyphosate resistance mechanisms [8] with an independent regulation of cell compartmentalization will be discussed
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