Leaf development: what it needs to be complex.

Formation of dissected compound leaves involves the transient maintenance of an indeterminate environment and the generation of new growth axes that will generate leaflets. Recent work has revealed additional multi-layered mechanisms controlling the activities of the KNOXI homeodomains factors that play a prominent role in the control of indeterminacy associated with compound leaf development. Patterning and individualisation of the leaflets has been shown to involve gradients of the phytohormone auxin and the contribution of the NAM/CUC3 boundary genes. Identification of these novel actors governing compound leaf development opens the opportunity for further comparative studies aimed at understanding the molecular basis of leaf shape evolution.