Abstract

A unique feature of plant development is the ability to alter body plan in response to environmental conditions. The primary body axis of plants is laid down during embryogenesis with the establishment of the shoot apical meristem at one end and a root apical meristem at the other. Post-embryonically, the meristems elaborate this basic axis, but in addition secondary meristems arise in both the root and shoot, which give rise to new axes of growth- lateral branches. It is this ability to produce lateral branches that gives plants their spectacular plasticity of form. As a model for understanding the role of plant hormones in plant developmental plasticity, we are investigating the hormonal control of shoot branching. We are focusing on two hormones that inhibit branching-auxin, which has been known to regulate branching for 80 years; and a novel hormone, which has not yet been chemically defined. In Arabidopsis, the novel hormone came to light through the analysis of mutants at 4 loci, called MAX1 -MAX4, with increased shoot branching. These genes define an additional pathway that interacts with auxin to mediate branch inhibition. Grafting studies have demonstrated that three of these loci are involved in the production of a long-range graft transmissible signal that inhibits bud growth, and this is consistent with the molecular identities of these genes. Interestingly, both auxin and the novel hormone signal through pathways involving targeted protein degradation. Progress in understanding the modes of action and interaction of these hormones in the control of shoot branching will be presented.

http://www.york.ac.uk/depts/biol/staff/hmol.htm