The ABC of fruit-shape formation in the Brassicaceae

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Despite the great diversity in plant organ shapes, common principles may underlie shape determination. It has been recognised from the early days of genetics that it is possible to differentiate between gene activities that regulate shape and those that only affect size. Recently, key genetic factors involved in determining shape in domesticated fruit crops such as tomato, melon and pepper have been uncovered. Furthermore, tissue-level models of leaf and petal growth have led to the suggestion that shape depends on patterns of anisotropic growth oriented by a polarity field. We have recently extended these studies by demonstrating that such models also can account for the growth patterns and diversity of three-dimensional fruit shapes. Angiosperms (flowering plants) evolved during the Cretaceous Period more than 100 million years ago and quickly colonised terrestrial habitats. A major reason for their success was the formation of fruits that protect and nurture the developing seeds. Moreover, a massive range of diversity in fruit shape arose during a relatively short time, which allowed for the development of ingenious ways of fertilisation as well as strategies for efficient seed dispersal. The Brassicaceae family contains a wealth of diversity in fruit morphologies and includes some of our genetically best characterised model plants and important crop species. Thus, the Brassicaceae family provides an ideal group of plants to study how specific shapes are established. Although many genes controlling fruit patterning in the model plant Arabidopsis thaliana have been identified, processes leading to specific carpel and fruit morphologies are still poorly understood. To unravel these processes, we need to compare the growth and morphological development of differently-shaped fruits. In this project, we will study the molecular and genetic mechanisms that underlie the formation of fruit shape within the Brassicaceae. We will use computational modelling combined with developmental biology and genetics to help understand this diversity. We recently found that simple modulations of a computational model based on experimental data can account for the observed variety of certain fruit shapes among Brassicaceae species. We will expand these studies and include non-model plants with highly diverse fruit shapes. Beyond the fundamental understanding of organ growth, results from this project should help identify strategies for how knowledge of shape and growth can be applied to increase yield of oilseed rape. More generally, understanding the mechanisms underlying organ-shape determination has implications for diverse disciplines ranging from medicine to crop improvement.