Making a seed pod that can shatter: the role of mechanics in valve margin development in Brassica fruits

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Plants have been bred for centuries as a source of food, medicine, and fuel. Many of the changes introduced by breeding have to do with the optimization of plant development for maximum yield. Recent advances in gene editing have a huge potential to further boost food production but we first need to understand the mechanistic basis of plant development. Our proposal will focus on fruits, which are important in agriculture - directly, as part of human and animal diets, and indirectly through the production and dispersal of seeds. The fruits of many crop plants dry into pods whose seeds are dispersed by a shattering mechanism. Oilseeds in the economically important mustard family (Brassicaceae) fall into this category. Fruit development has been extensively studied in Arabidopsis thaliana. This model species produces an elongated fruit composed of two carpel valves joined at their margins to the replum to which seeds are attached on the interior. However, cellular growth patterns underlying fruit development and shattering remain poorly understood. In this project, we will focus on the quantitative analysis of the development of the valve margins which are critical for pod shatter, a characteristic that influences seed yield. We aim to uncover general principles underlying the development of the valve margin and understand how they are fine-tuned in diverse fruit shapes in Brassicaceae. Our specific objectives will be: (1) Uncover the 3D cellular growth patterns leading to the development of valve margins; (2) Assess the role of mechanical forces in the specification of the valve margins; (3) Generate a mechanical model of the valve margin growth. Confocal microscopy time-lapse imaging combined with 3D image analysis, computer simulations and genetics will be used to trace the origin, growth, and differentiation of the valve margins in various Brassicaceae species. We will measure 3D cellular growth, mechanical properties, and the expression of key patterning genes to understand how physical forces and genetics interact to control the growth and development of the valve margin. Using experimental data, we will create a 3D mechanical model of valve margins to assess how they could be involved in the specification of valve margins. This model will be instrumental in understanding how tissue geometries and pod shatter resistance are controlled by cell mechanics and adjacent tissue arrangements. This research will establish a valuable framework for understanding patterns of growth that determine fruit geometry and pod shattering. The recent development of a pod-shatter-resistant variety of canola is an excellent example of how fundamental knowledge of fruit development has benefitted agriculture. Our research has the potential to identify other factors influencing seed retention in oilseed crops.