Many plants accumulate substantial starch reserves in their leaves during the day, and remobilise them at night to provide carbon and energy for maintenance and growth. In this paper we explore the role of a sugar signalling metabolite, trehalose-6-phosphate (Tre6P), in regulating the accumulation and turnover of transitory starch in Arabidopsis leaves. Ethanol-induced overexpression of trehalose-phosphate synthase (TPS) during the day increased Tre6P levels up to 11-fold. There was a transient increase in the rate of starch accumulation in the middle of the day, but this was not linked to reductive activation of ADP-glucose pyrophosphorylase. A 2 to 3-fold increase in Tre6P during the night led to significant inhibition of starch degradation. Maltose and maltotriose did not accumulate, suggesting that Tre6P affects an early step in the pathway of starch degradation in the chloroplasts. Starch granules isolated from induced plants had a higher Pi content than granules from non-induced control plants, consistent with either disruption of the phosphorylation-dephosphorylation cycle that is essential for efficient starch breakdown, or with inhibition of starch hydrolysis by β-amylase. Non-aqueous fractionation of leaves showed that Tre6P is predominantly located in the cytosol, with estimated in vivo Tre6P concentrations of 4-7 µM in the cytosol, 0.2-0.5 µM in the chloroplasts and 0.05 µM in the vacuole. It is proposed that Tre6P is a component in a signalling pathway that mediates feedback regulation of starch breakdown by sucrose, potentially linking starch turnover to demand for sucrose by growing sink organs at night.
Martins MC, Hejazi M, Fettke J, Steup M, Feil R, Krause U, Arrivault S, Vosloh D, Figueroa CM, Ivakov A, Yadav UP, Piques M, Metzner D, Stitt M, Lunn JE.
Plant Physiology. 2013 Sep 16 http://dx.doi.org/10.1104/pp.113.226787