Regulation of transitory starch metabolism by trehalose 6-phosphate and the circadian clock

LUNN JE; MARTINS MCM; HEJAZI M; FETTKE J; STEUP M; FEIL R; FIGUEROA CM; PANDEY PK; STITT M

Manchester

Congreso; SEB Annual Main Meeting; 2014

Society for Experimental Biology

Many plants accumulate transitory starch reserves in their leaves during the day and remobilize them at night to provide carbon and energy for maintenance and growth. Although the pathways of starch synthesis and degradation are well established, their regulation is poorly understood. In Arabidopsis thaliana, transitory starch is degraded in such a way that most, but not quite all, of the starch is remobilised by dawn. If plants are subjected to a premature dusk, they degrade their starch at a lower rate so that their reserves last until the end of the unexpectedly lengthened night and they avoid becoming carbon starved. This adjustment of starch degradation rates is dependent on the circadian clock. The rate of starch degradation is also decreased in plants engineered to have increased levels of trehalose 6-phosphate (Tre6P). High night-time levels of Tre6P appear to inhibit an early step in the pathway of starch degradation in the chloroplasts, probably acting via a cytosolic intermediary. Tre6P is a signal of sucrose availability in plants, suggesting that Tre6P mediates feedback regulation of starch degradation by sucrose, potentially linking starch turnover to demand for sucrose by growing sink organs at night. It is proposed that the rate of starch breakdown is jointly regulated by the circadian clock and Tre6P, with the clock-dependent regulation setting the maximum permissible rate of degradation to prevent premature exhaustion of starch before dawn, while Tre6P links the actual rate of degradation to the demand for sucrose.