The role of expansin in leaf development: A molecular genetics and AFM approach

Leaf shape formation is a fascinating process involving the coordinated regulation of cell division and cell expansion, which ultimately relies on the control of cell wall expansion. Expansins comprise a large family of cell wall proteins which can non-enzymatically trigger the relaxation of the cell wall for expansion. They have been implicated in organ initiation, cell differentiation and organ growth. However, the exact mechanism of expansin action and functional role of different members of the expansin gene family is unclear. Here, I focus on the largest subgroup of expansins (EXPA) to identify which genes are expressed during different stages of leaf development in Arabidopsis. This information was used to design an inducible artificial microRNA construct to target the knock-down of multiple expansin genes expressed during early leaf development. Through a series of experiments knocking down expansin gene expression at different stages of leaf development, I show that the suppression of expansin gene expression at later stages of leaf development is sufficient to repress leaf growth and alter leaf shape. This molecular genetic approach is combined with an atomic force microscopy (AFM) approach to investigate the role of cell wall mechanics in leaf growth. I describe the use of AFM for probing the leaf primordium mechanics and outline consideration for future work.