The Leyser Group's research is aimed at understanding the role of plant hormones in plant developmental plasticity, using the regulation of shoot branching as a model. Axillary meristems, which are established in each leaf axil formed from the primary shoot apical meristem, can remain dormant or activate to produce a branch. The decision to activate or not involves integration of diverse environmental, physiological and developmental inputs, and is mediated by a network of interacting hormonal signals that generate a rich source of systemically transmitted information, which is locally interpreted to regulate branching. At its hub is the polar auxin transport system, which extends throughout the plant, transporting auxin basipetally from shoot apices to the roots. The system is dynamically modeled and remodeled by auxin itself. Our current data suggest that shoot apical meristems compete for common auxin transport paths to the root. High auxin in the main stem, exported from already active meristems, prevents the activation of further meristems by reducing the sink strength of the mains stem for auxin. Other hormonal signals can influence branching by modulating the auxin transport network and/or the ability of buds to compete for access to it. For example, strigolactones can reduce the accumulation of auxin transporters at the plasma membrane making it more difficult for buds to activate.
We are working to understand the dynamic properties of this hormonal network and their implications for adaptive developmental plasticity.