Heisler Group

Previous and current research

In addition to providing us with the air we breathe, the food we eat and much of the energy we use, plants exhibit a unique beauty associated with their strikingly symmetrical patterns of development. Multicellularity also evolved independently in plants giving us an opportunity to compare and contrast the developmental strategies used in different kingdoms. We investigate plant development by focusing on the process of lateral organ formation (leaves or flowers) in the model species Arabidopsis thaliana.We are taking a broad approach that includes trying to understand organ positioning, differentiation and growth and how these different processes are coordinated. Experimentally, we have developed confocal-based methods to image growing plant tissues, enabling us to obtain dynamic high-resolution data (making full use of the different GFP spectral variants), which we can also incorporate directly into mathematical developmental models.

Recent work has revealed that primordial positions in plants are specified by local, high concentrations of an intercellular signalling molecule, auxin (indole-3-acetic acid). In turn, the formation of these auxin concentration maxima depends on a polar auxin transport system that directs auxin flux towards sites of primordial emergence. Polar auxin transport at the plant shoot apex plant is mediated by the auxin efflux carrier PIN1-FORMED1 (PIN1). This is member of a small family of membrane-bound auxin efflux proteins that are localised in a polar fashion to different sides of cells so that auxin efflux occurs in a directional manner. When primordia are specified, PIN1 localisation in meristem epidermal cells is on the sides of the cells facing towards the initiation site. Amajor goal of our research in the near and long-termfuture is to understand the mechanisms and signals responsible for coordinating and directing this polar localisation pattern underlying primordium positioning. Auxin not only induces primordium growth but also helps to regulate genes that help specify different organ cell types. Understanding how auxin induces different sets of genes in different domains of growing primordia is another focus for our lab. In particular we are interested in how the ‘top’ and ‘bottom’ or adaxial and abaxial cell types of primordia are specified and the downstream role of these cell types in controlling organ shape. Lastly, we are also working towards understanding the mechanical basis of morphogenesis by developing methods to mechanically perturb and track cells, quantify growth patterns and correlate these data with gene activities and the plant cytoskeleton to better understand how genes and mechanics relate to one another.

Future projects and goals

There are many interesting questions we are pursuing, using any technique that seems appropriate, including:

• Understanding the patterning processes that specify adaxial and abaxial cell types;
• Understanding the mechanism by which adaxial and abaxial cell types regulate organ morphogenesis;
• Understanding the basis of supra-cellular patterning of the plant cytoskeleton and how it is coordinated with auxin transport;
• Understanding how polar auxin transport is patterned and its role in development.