An Integrative Analysis of Fruit Shape in Capsella rubella and Arabidopsis thaliana

Plant organs develop from a small number of cells into a wide variety of shapes. This development is coordinated by underlying genetic factors that control the organisation and patterning of growth. The Arabidopsis fruit has been studied in detail and genes involved in fruit shape development and organisation have been uncovered. Related species that have divergent fruit forms have not been studied in the same detail and it remains unclear if the mechanisms and genes controlling growth organisation and patterning in fruit are common. Here, I give a general description of fruit shape changes within a time framework for Capsella rubella, which has an elaborate heart-shaped fruit. I used clonal analysis to generate a description of regional growth dynamics within the tissue. Using this data, I generated computational models to explore the coordination of growth and polarity in the Capsella fruit. Based on observations of morphology, growth dynamics and model outputs, Capsella fruit development can be divided into three phases. It is likely that there is a proximodistal polarity field that deforms locally as the fruit grows. Changes in growth rates and orientations parallel and perpendicular to this polarity field during the different phases can account for the morphology and clonal patterns of the Capsella fruit. In addition, I investigated factors important for the development of the heart-shaped fruit of Capsella through forward and reverse genetic approaches. I found FRUITFULL is an important factor for the development of the heart-shape fruit of Capsella but may not be important for the evolutionary differences in fruit shape within the family Simplified versions of the Capsella fruit model accounted for fruit shapes of related species including Arabidopsis. This indicates that the Capsella fruit is a more elaborate form of the evolutionary conserved mechanisms that underlie fruit development in the Brassicaceae