From genes to shape: regulatory interactions in leaf development.

In the past two years novel connections were described between auxin function and transcription factor patterning systems involved in both leaf initiation and elaboration of leaf axial patterning. A cascade of small RNA-based regulatory steps was suggested to facilitate delimitation of cell types comprising the upper versus lower parts of the leaf. Developmental regulation of cellular growth emerged as a crucial component in regulation of leaf form with TCP and CUC2 transcription factors playing a key role in this process. Finally, cis-regulatory evolution of developmental genes emerged as a process that likely contributed to diversification of leaf form, while studies in seedless land plants have begun to elucidate the ancestral and derived aspects of leaf development pathways.