The genetic basis for leaf shape diversity: exploiting the Arabidopsis relative Cardamine hirsuta

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A key challenge in biology is to understand how organismal forms are generated and the basis for their diversity. Genetic analyses in model systems have identified key regulators sculpting the body plans of metazoa and seed plants. However, less is known about how the balance of conservation versus divergence in such regulatory pathways generated the tremendous morphological diversity of multicellular eukaryotes. One impediment to answering these questions is the paucity of suitable experimental platforms where genetic tools can be utilized to unambiguously study the evolution of gene function in a genome-wide, unbiased fashion. We have made an important step in overcoming this problem by developing the Arabidopsis thaliana relative Cardamine hirsuta into a powerful system for studying morphological evolution. We are working to understand the molecular mechanisms through which leaf morphology evolved in these species to produce simple, undivided leaves in A. thaliana and dissected leaves with distinct leaflets in C. hirsuta. Our recent identification of a novel leaf complexity gene that is absent from the A. thaliana genome is a key finding. Here, we propose to exploit this system further, first by elucidating the genetic networks underlying the basis for diversity in leaf geometry and second, to understand whether such diversity arose in response to natural selection.