The plant hormone auxin is a jack of all trades: it has a multitude of tasks in the plant. “It influences the development of stem cells into differentiated tissues, but also plays a role in rapid responses to changes in the environment. How can a signal molecule control such very different processes? That is the topic of our research”, explains Scheres. He has been studying plant growth regulation for 20 years, initially at Utrecht University, and now at the Plant Developmental Biology Group of Wageningen University. One of his postdoctoral researchers has continued the published work as group leader in Finland.
Besides auxin, four regulatory proteins (transcription factors) – under the collective name PLETHORA (PLT) – are involved. These proteins turn genes on or off. Auxin itself appears to control the rapid responses of the plant directly. Within only a few minutes, a root changes direction to follow a change in the direction of gravity.
The regulatory proteins in turn affect the location and growth of the zones in which cell division, cell elongation and differentiation take place. These processes are much slower. The location and growth of the zones depends on the gradient of the PLTs. “Previously, we thought that the PLT gradient was linked directly to the auxin gradient. But this does not explain the stable formation of structures under rapidly changing conditions.
Many feedback loops and dependencies appear to be involved in these processes. The growth affects the gradients, and the gradients in turn affect the growth. We already understood many components, but now our understanding of the complete picture is much better”, says Scheres.
The study is a good example of what systems biology can do: an interplay between simulations within mathematical models and focused experiments."