Understanding how form emerges in living organisms is a fundamental challenge in biology. Progress, however, has been confounded by the complex chain of interactions linking the organization of mature organ forms to molecular processes. As such, insights into the manner in which individual genes contribute to the development of form have been elusive; even in well-studied model organisms. In this context, leaves are a striking example of the self-organization of form – displaying remarkable diversity within and between species. To study the molecular basis of leaf shape and its diversity the Tsiantis lab has exploited Arabidopsis thaliana and Cardamine hirsuta, two closely related species with distinct leaf shapes. Leaves of A. thaliana have a simple contour (also termed margin) adorned with small protrusions. By contrast, those of C. hirsuta are compound, meaning their leaves are comprised of many leaf-like segments, connected to a common stalk. By comparing the development of these two species the Tsiantis lab has identified many of the key genetic factors underlying their distinct leaf shapes. This opens the door to a detailed understanding of mechanisms shaping leaf form development.
Due to the complexity of leaf development, however, understanding how leaf shape is organized requires computational models, informed by detailed quantitative measurements of growth and gene expression. Such models permit the systematic examination of the interactions linking genetic regulation, cell division and tissue growth to final form. An objective of this project was to develop such a computational modelling framework, as well as the advanced quantification tools required to analyse leaf growth and form. The next objective was to combine these tools with experimental efforts in the Tsiantis lab to obtain fundamental insights into how leaf form is regulated, thus providing essential insights into shape regulation in eukaryotic systems. In this context, a primary aim of this work was achieving a mechanistic explanation of the basis of simple and compound leaf shape development in A. thaliana and C. hirsuta. As leaves are the primary organs for light capture in plants, and their photosynthetic efficiency is influenced by their shape, our work provides an important step towards the engineering of leaf shape for crop improvement.
