Regulation of central metabolism by trehalose-6-phosphate

FIGUEROA CM; STITT M; LUNN JE

Waterville Valley

Conferencia; CO2 Assimilation in Plants: From Genome to Biome; 2014

Gordon Research Conferences

Trehalose metabolism is essential for normal growth and metabolism. The intermediate of trehalose biosynthesis, trehalose-6-phosphate (Tre6P), has been identified as an important signal metabolite linking carbon metabolism to growth and development. Arabidopsis thaliana plants over-expressing Tre6P synthase (otsA) and Tre6P phosphatase (otsB) from Escherichia coli show marked changes in leaf size and morphology, flowering time and inflorescence branching. Based on analysis of these plants, we have recently proposed a bi-directional network where Tre6P regulates sucrose levels within an appropriate range and vice versa. To refine our current working model it is necessary to identify the primary targets of Tre6P signalling. To avoid the pleiotropic effects of constitutive over-expression, we established a transgenic line for ethanol-inducible over-expression of otsA. By using this system we determined that Tre6P plays a key role in the control of starch degradation at night. However, the effects of elevated Tre6P during the day are less understood. Plants were grown in a 12 h photoperiod, induced at the beginning of the day and samples were harvested every 2 h. The level of Tre6P increased 4-fold (to 0.79 nmol g-1FW) at 6 h after induction and remained elevated until the end of the day. We found no significant changes in starch accumulation but a transient drop in sucrose levels, which led to a significant increase of the starch/sucrose ratio between 6 and 10 h after induction. The activity of sucrose-phosphate synthase and the levels of the regulatory metabolite fructose-2,6-bisphosphate were not altered in the induced plants. Conversely, we found a significant, transient increase in the levels of malate, fumarate, 2-oxoglutarate, aspartate, and alanine at 6 h after induction. Interestingly, the activity of nitrate reductase peaked at 6 h after induction and remained elevated until the end of the day. Together, these results suggest that high Tre6P stimulates respiratory fluxes into organic acids providing C-skeletons for amino acid synthesis. Nitrate reductase might be activated directly in response to elevated Tre6P or indirectly by increased demand for fixed nitrogen. We will use 13CO2 and 14CO2 labelling to measure photosynthetic carbon fluxes into starch, sucrose, and other metabolites to better understand how Tre6P regulates carbon partitioning.