A novel genome-wide approach to understand the genetic basis for morphological diversification of leaves

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A key problem in biology is to understand how different organisms come to have different forms. In plants, this variation in form is obvious in the many different leaf shapes one sees during a walk in the park. Leaves are also interesting to study because they play a key role in the food chain being the main photosynthetic organs of land plants and thus responsible for CO2 fixation in terrestrial ecosystems. For these reasons, understanding how diversity in leaf form is generated is of considerable interest to scientists. To study this problem we work with hairy bittercress (Cardamine hirsuta), which is a plant that has leaves fully subdivided into smaller leaflets. The presence of leaflets makes this plant very different to its close relative thale cress (Arabidopsis thaliana), which has entire, undivided leaves. We already know a lot about how an entire leaf shape is produced in thale cress because it is easy to grow and do experiments with. Hairy bittercress is also very easy to work with in the lab, so we use it to understand how leaflets are produced. We now want to understand how the genetic make up of the hairy bittercress differs to that of the thale cress resulting in leaflets being produced in only the former species . Specifically we will test whether hairy bittercress leaves produce leaflets because certain genes in this plant carry different information to thale cress genes. To achieve this we will divide the hairy bittercress genome into many small pieces and introduce each piece of this genome into the thale cress. The few thale cress plants that receive a 'leaflet producing' part of the hairy bittercress genome should now produce leaves that resemble the divided leaves of hairy bittercress. This approach will allow us to isolate 'leaflet producing' genes and find out whether the 'leaflet producing information' resides in the regulatory sequences that control when, where and how much a gene is expressed, or in the protein-coding sequences that determine the biochemical activity of a gene product. Isolation of such 'leaflet producing genes' will form the basis for future research where we will reduce or increase their activity within bitter cress to test to what degree leaflet production is sensitive to alterations of their activity.