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Abstract

The induction of flowering is a central event in the life cycle of plants. When timed correctly, it helps ensure reproductive success, and therefore has adaptive value. Because of its importance, flowering is under the control of a complex genetic circuitry that integrates environmental and endogenous signals. Trehalose-6-phosphate (T6P) has been shown to act as signaling molecule in coordinating carbohydrate status with diverse developmental processes. Interestingly, Arabidopsis thaliana plants deficient in the key T6P-synthesizing enzyme TREHALOSE-6-PHOSPHATE SYNTHASE 1 (TPS1) are extremely late flowering. We show that T6P regulates expression of several flowering-time related genes throughout the plant. In the leaf vasculature T6P is absolutely required for expression of FLOWERING LOCUS T (FT). In addition, TPS1/T6P regulates the expression of miR156 and some of its target genes of the SQUAMOSA PROMOTER BINDING PROTEIN LIKE (SPL) family of transcription factors at the shoot apex. We hypothesize that the TPS1/T6P pathway provides a way for plants to integrate an environmental signal, the activation of FT in response to increasing day length in spring, with a physiologic signal, the presence of high carbohydrate levels, as indicated by T6P. Together these two inputs ensure that FT is only expressed when the conditions are optimal, that is, day length exceeds a certain minimum and the carbohydrate state of the plant supports the energy-demanding transition to flowering and seed production. In addition, TPS1/T6P modulates flowering through regulation of the miR156/SPL module, which in wild type plants ensures that flowering will eventually occur even in the absence of inductive environmental cues.