North, East, South, West: mapping vascular tissues onto the Arabidopsis root

- Cell division and cell fate specification determine vascular pattern.
- A group of transcription factors specify the size of the vascular cylinder.
- Auxin, cytokinin and class III HD-ZIP protein levels determine cell fate.
- Recent research is uncovering how these processes interact to control patterning.

The Arabidopsis root has provided an excellent model for understanding patterning processes and cell fate specification. Vascular patterning represents an especially interesting process, as new positional information must be generated to transform an approximately radially symmetric root pole into a bisymmetric structure with a single xylem axis. This process requires both growth of the embryonic tissue alongside the subsequent patterning. Recently researchers have identified a series of transcription factors that modulate cell divisions to control vascular tissues growth. Spatial regulation in the signalling of two hormones, auxin and cytokinin, combine with other transcription factors to pattern the xylem axis. We are now witnessing the discovery of increasingly complex interactions between these hormones that can be interpreted through the use of mathematical models.