A red and far-red light receptor mutation confers resistance to the herbicide glyphosate.
Bottom Line: Glyphosate is a widely applied broad-spectrum systemic herbicide that inhibits competitively the penultimate enzyme 5-enolpyruvylshikimate 3-phosphate synthase (EPSPS) from the shikimate pathway, thereby causing deleterious effects.A glyphosate-resistant Arabidopsis mutant (gre1) was isolated and genetic analyses indicated that a dysfunctional red (R) and far-red (FR) light receptor, phytochrome B (phyB), caused this phenotype.Our data offer an explanation of the well documented observation that glyphosate treatment at various times throughout the day, with their specific composition of light quality and intensity, results in different efficiencies of the herbicide.
Affiliation: Department of Biological and Environmental Science and Engineering, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Jeddah, Saudi Arabia; Department of Horticulture and Landscape Architecture, Purdue University, 47907, West Lafayette, Indiana, USA.Show MeSH
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Mentions: The shikimate pathway is considered to be a key link between carbohydrate metabolism and the biosynthesis of aromatic amino acids and many secondary metabolites (Singh et al., 1991; Herrmann, 1995a) and consists of a sequence of six metabolic steps that lead to the synthesis of chorismate (Figure S1). The fact that gre1 is a light receptor mutant that affects chorismate biosynthesis makes it a potentially highly useful tool for the study of light effects on the pathway. Our results suggested that the glyphosate resistance of gre1 is not related to any modification of the target enzyme but is the consequence of increased activity of the entire shikimate pathway due to altered regulation of the pathway caused by dysfunctional phyB (Figures4 and S6). It is noteworthy that the gre1 mutant shows less shikimate accumulation in response to glyphosate under low R:FR light condition and this result is indicative of an active shikimate pathway (Figure3b). Accumulation of shikimate, an intermediate product of the shikimate pathway, is considered one of the immediate physiological responses to glyphosate inhibition (Amrhein et al., 1980; Smart et al., 1985). These findings, together with our studies on circadian regulatory mechanisms, give rise to a more detailed proposed model of the regulation of the pathway that can, at least in part, explain the link between glyphosate resistance and light quality (Figure6).
Affiliation: Department of Biological and Environmental Science and Engineering, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Jeddah, Saudi Arabia; Department of Horticulture and Landscape Architecture, Purdue University, 47907, West Lafayette, Indiana, USA.