Abstract

Flowering is a key adaptive trait in plants and involves a major reprogramming of development, during which groups of undifferentiated cells on the flanks of the shoot apex (primordia) are specified to form flowers instead of leaves. Typically for higher plants, Arabidopsis thaliana integrates environmental and endogenous signals to precisely regulate flowering time. Once initiated, the floral transition is rapid and irreversible on the flanks of the shoot, while nearby cells in the centre of the apex are maintained in an undifferentiated state, supporting future meristematic growth. As well as requiring precise temporal control, flowering is tightly spatially regulated in the plant. Axillary meristems, which are located at the base of each leaf, are maintained in a poised vegetative state despite the activation of flowering in the shoot apical meristem (SAM). To understand the underlying regulatory logic of the floral transition, we have used a combination of modelling and experiments to define a network of regulatory hubs. Our network predicts flowering behaviour for different genotypes and displays key properties of the floral transition such as signal integration and irreversibility. The model suggests that a proportional control mechanism may be active to flexibly counterbalance an otherwise runaway feedback circuit, allowing a pool of undifferentiated cells to be maintained despite strong differentiation signals in nearby cells. This simple yet robust control strategy may help to understand how flowering plants have been able to evolve such a diversity of life histories.