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A red and far-red light receptor mutation confers resistance to the herbicide glyphosate.

Sharkhuu A, Narasimhan ML, Merzaban JS, Bressan RA, Weller S, Gehring C - Plant J. (2014)

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.Furthermore, transcript analysis suggested that this diurnal oscillation was not only dependent on phyB but was also due to circadian regulatory mechanisms.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.

View Article: PubMed Central - PubMed

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.

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A model proposing controls of the shikimate pathway.PhyB exerts control over the pathway by changing its active and non-active, Pfr and Pr, conformations according to the light quality (R:FR). The R:FR increases gradually from the onset of light till midday and decreases towards evening. Expression of DAHPS1 and SK1 is repressed by the circadian component CCA1 during the day, while phyB (Pfr) promotes the accumulation of DHQS and EPSPS1 in response to high R:FR through the interaction with PIF4 and PIF5. During the evening, EC elements have a role in stabilizing PIF4 and PIF5. Arrows and blunt end lines indicate stimulatory and inhibitory effects respectively, and dashed arrows indicate transcriptional activation. The proposed feed-back regulation of the circadian clock and EC-dependent regulation are shown as embossed arrows.
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fig06: A model proposing controls of the shikimate pathway.PhyB exerts control over the pathway by changing its active and non-active, Pfr and Pr, conformations according to the light quality (R:FR). The R:FR increases gradually from the onset of light till midday and decreases towards evening. Expression of DAHPS1 and SK1 is repressed by the circadian component CCA1 during the day, while phyB (Pfr) promotes the accumulation of DHQS and EPSPS1 in response to high R:FR through the interaction with PIF4 and PIF5. During the evening, EC elements have a role in stabilizing PIF4 and PIF5. Arrows and blunt end lines indicate stimulatory and inhibitory effects respectively, and dashed arrows indicate transcriptional activation. The proposed feed-back regulation of the circadian clock and EC-dependent regulation are shown as embossed arrows.

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).


A red and far-red light receptor mutation confers resistance to the herbicide glyphosate.

Sharkhuu A, Narasimhan ML, Merzaban JS, Bressan RA, Weller S, Gehring C - Plant J. (2014)

A model proposing controls of the shikimate pathway.PhyB exerts control over the pathway by changing its active and non-active, Pfr and Pr, conformations according to the light quality (R:FR). The R:FR increases gradually from the onset of light till midday and decreases towards evening. Expression of DAHPS1 and SK1 is repressed by the circadian component CCA1 during the day, while phyB (Pfr) promotes the accumulation of DHQS and EPSPS1 in response to high R:FR through the interaction with PIF4 and PIF5. During the evening, EC elements have a role in stabilizing PIF4 and PIF5. Arrows and blunt end lines indicate stimulatory and inhibitory effects respectively, and dashed arrows indicate transcriptional activation. The proposed feed-back regulation of the circadian clock and EC-dependent regulation are shown as embossed arrows.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4260087&req=5

fig06: A model proposing controls of the shikimate pathway.PhyB exerts control over the pathway by changing its active and non-active, Pfr and Pr, conformations according to the light quality (R:FR). The R:FR increases gradually from the onset of light till midday and decreases towards evening. Expression of DAHPS1 and SK1 is repressed by the circadian component CCA1 during the day, while phyB (Pfr) promotes the accumulation of DHQS and EPSPS1 in response to high R:FR through the interaction with PIF4 and PIF5. During the evening, EC elements have a role in stabilizing PIF4 and PIF5. Arrows and blunt end lines indicate stimulatory and inhibitory effects respectively, and dashed arrows indicate transcriptional activation. The proposed feed-back regulation of the circadian clock and EC-dependent regulation are shown as embossed arrows.
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).

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.Furthermore, transcript analysis suggested that this diurnal oscillation was not only dependent on phyB but was also due to circadian regulatory mechanisms.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.

View Article: PubMed Central - PubMed

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
Related in: MedlinePlus