Regulation of Flowering Time by Trehalose-6-Phoshate Signaling

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The induction of flowering is a central event in the life cycle of plants. Because of its importance, flowering is under the control of a complex genetic circuitry that integrates endogenous (hormones, carbohydrates, age) and environmental signals (temperature, photoperiod). Under inductive photoperiod, FLOWERING LOCUS T (FT), a key regulator of flowering time in Arabidopsis thaliana, is induced in the leaf vasculature and acts as a long distance signal to initiate flowering at the shoot meristem. The disaccharide trehalose-6-phosphate (T6P) has been shown to act as signalling molecule in coordinating carbohydrate status with developmental processes. Arabidopsis thaliana plants deficient in the T6P-synthesizing enzyme TREHALOSE-6-PHOSPHATE SYSNTHASE 1 (TPS1) flower extremely late. We recently showed that TPS1/T6P signalling regulates the expression of several flowering-time genes throughout the plant. In the leaf vasculature T6P/TPS1 is absolutely required for the induction of FT, whereas at the shoot apical meristem (SAM) MIR156 and its targets, the SQUAMOSA PROMOTER BINDING PROTEIN LIKE (SPL) genes are targeted by T6P/TPS signalling. Together the environmental (photoperiod) and physiologic (T6P/TPS1) signals ensure that flowering commences only when the conditions are optimal, that is, day length exceeds a certain minimum and the carbohydrate status supports the energy-demanding transition to flowering and seed production. However, many questions regarding the function of T6P/TPS1 remain open.Here we propose a series of experiments with the aim to better integrate T6P/TPS1 signalling into the canonical flowering time pathways. Our preliminary results suggest that T6P/TPS1 regulates flowering in part through the modulation of cell-cycle-dependent SAM maintenance, a previously unexplored aspect that we wish to investigate further. In addition, we have preliminary evidence that T6P/TPS1 affects the ability of plants to respond to changes in ambient temperature as well as chilling (vernalization) treatments. The connection between the T6P/TPS1 pathway and the temperature-dependent regulation of flowering will be analysed. Apart from the above-mentioned analyses that focus on known genes and pathways we will also identify novel components of the T6P/TPS1 signalling pathway. To this end we have already carried out a large-scale mutagenesis screen to identify suppressors of late flowering of the tps1 mutant. As part of the priority program we will identify and characterize in detail the causal genes and place them into the T6P/TPS1 signalling pathway. In summary, the proposed experiments will provide valuable insight into the integration of carbohydrate signalling and flowering time pathways.