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Abstract:
Plants integrate diverse environmental and endogenous signals to ensure the timely transitions between
developmental stages. Trehalose 6-phosphate (T6P) has been implicated as a signal of sucrose status (1),
thereby serving as a link between developmental processes and the metabolic and energy status of the plant.
However, the molecular mechanisms by which this signal is integrated into the complex developmental networks
are not well understood. T6P is synthesized from G6P and UDPG by TREHALOSE 6-PHOSPHATE SYNTHASE
1 (TPS1). A homozygous T-DNA insertion line is embryo lethal, with arrested embryos at the early torpedo stage,
which is exactly when sucrose levels rise (2). TPS1 is expressed in vascular tissue throughout a plant's life, but it
also shows a distinct expression domain in the peripheral zone of the shoot apical meristem (SAM) from the heart
stage of embryogenesis until right before the transition to flowering (3), where it obviously plays a role in cell cycle
regulation and meristem maintenance. We found that T6P levels rise in the SAM over time, increasing more than
two-fold during the floral transition in long day conditions as well as in short days. Interestingly, increasing TPS1
expression in the stem cells alone is sufficient to induce precocious flowering, while reducing T6P content by
TREHALOSE 6-PHOSPHATE PHOSPHATASE (TPP) over-expression in the stem cells delays flowering (3). We
have recently shown that T6P plays a central role in the induction of flowering acting, in the leaves via the
FLOWERING LOCUS T node of the photoperiod pathway and at the SAM via the age pathway (3).
Recently it was shown that sugars, in particular glucose and sucrose, control the timing of the vegetative phase
change by regulating the expression of MIR156A and MIR156C (4, 5). 35S:amiR-TPS1 plants with reduced levels
of TPS1 and T6P are late flowering but are still able to set viable seeds. These plants have significantly more
juvenile leaves, arguing for a delay in the vegetative phase change. The idea of T6P acting downstream of
sucrose to regulate the vegetative phase transition is further supported by our transcript and genetic analyses.
In summary, previous observations and our own data suggest that T6P is crucial for the correct timing of
developmental transitions in general.
