Sugar-induced increases in trehalose 6-phosphate are correlated with redox activation of ADPglucose pyrophosphorylase and higher rates of starch synthesis in Arabidopsis thaliana

Abstract

Tre6P (trehalose 6-phosphate) is implicated in sugar-signalling pathways in plants, but its exact functions in vivo are uncertain. One of the main obstacles to discovering these functions is the difficulty of measuring the amount of Tre6P in plant tissues. We have developed a highly specific assay, using liquid chromatography coupled to MS-Q3 (triple quadrupole MS), to measure Tre6P in the femto-picomole range. The Tre6P content of sucrose-starved Arabidopsis thaliana seedlings in axenic culture increased from 18 to 482 pmol x g(-1) FW (fresh weight) after adding sucrose. Leaves from soil-grown plants contained 67 pmol x g(-1) FW at the end of the night, which rose to 108 pmol x g(-1)FW after 4 h of illumination. Even greater changes in Tre6P content were seen after a 6 h extension of the dark period, and in the starchless mutant, pgm. The intracellular concentration of Tre6P in wild-type leaves was estimated to range from 1 to 15 microM. It has recently been reported that the addition of Tre6P to isolated chloroplasts leads to redox activation of AGPase (ADPglucose pyrophosphorylase) [Kolbe, Tiessen, Schluepmann, Paul, Ulrich and Geigenberger (2005) Proc. Natl. Acad. Sci. U.S.A. 102, 11118-11123]. Using the new assay for Tre6P, we found that rising sugar levels in plants are accompanied by increases in the level of Tre6P, redox activation of AGPase and the stimulation of starch synthesis in vivo. These results indicate that Tre6P acts as a signalling metabolite of sugar status in plants, and support the proposal that Tre6P mediates sucrose-induced changes in the rate of starch synthesis.

Acclimation of metabolism to light in Arabidopsis thaliana: the glucose 6‐phosphate/phosphate translocator GPT2 directs metabolic acclimation

“…Seven metabolites directly involved in starch and/or sucrose metabolism were identified [glucose 1‐phosphate (G1P), glucose 6‐phosphate (G6P), fructose 1, 6‐bisphosphate (F16BP), fructose 6‐phosphate (F6P), sucrose 6′‐phosphate (S6P), ADP‐glucose and UDP glucose], in addition to T6P, which is an important sugar signalling metabolite (Lunn et al . 2006). In general, concentrations of these significantly and substantially increased in both Ws‐4 wild‐type and gpt2.2 plants by the end of the first day of HL treatment; only levels of glucose 1‐phosphate (G1P) and UDP‐glucose in wild type did not change significantly.…”

“…T6P is increased by high sucrose levels (Lunn et al . 2006) and has been shown to inhibit SnRK1 in vitro (Zhang et al . 2009; Delatte et al .…”

“…Frozen tissue powder was extracted using chloroform–methanol as described in Lunn et al . (2006). Phosphorylated intermediates and organic acids were quantified by high‐performance anion‐exchange chromatography coupled to tandem mass spectrometry, operating in negative ion mode, as described in Lunn et al .…”

“…Phosphorylated intermediates and organic acids were quantified by high‐performance anion‐exchange chromatography coupled to tandem mass spectrometry, operating in negative ion mode, as described in Lunn et al . (2006). Metabolites were quantified by comparison against authentic standards.…”

Light-dependent activation of phosphoenolpyruvate carboxylase by reversible phosphorylation in cluster roots of white lupin plants: diurnal control in response to photosynthate supply

“…Tre6P is an essential signal metabolite linking plant growth and development to carbon and nitrogen metabolism, and the sucrose-Tre6P nexus model postulates that Tre6P functions as both a signal and regulator of intracellular sucrose levels (Lunn et al, 2006;Yadav et al, 2014;Figueroa et al, 2016). Our results demonstrate that Pi limitation alone cannot completely account for the phosphorylation status of CR PEPC, and to the best of our knowledge provide the first evidence for the diurnal post-translational control of any CR protein by reversible phosphorylation.…”