The root system anchors the plant and its cells absorb water and nutrients. Since plants are sessile organisms, controlling external compound entry is essential for plant survival. In vascular plants, the endodermis is the innermost root ground tissue cell layer that controls entry to the plant vasculature by formation of a barrier for free diffusion of solutes from the soil. Moreover, many plant species also contain an exodermis layer which also acts as a barrier. The exodermis is located internal to the epidermis layer. In a differentiated state, cells of both layers contain a Casparian strip. In Arabidopsis the Casparian strip is a lignin-like structure that is deposited as a ring in the transverse section of cells and around the secondary cell wall. Recently, the developmental framework of endodermis differentiation has been described in Arabidopsis and some important molecular players identified. Here, we explore whether endodermis and exodermis differentiation are regulated similarly. Since Arabidopsis does not contain an exodermis layer, the proposed project will use the tomato root as a model system to address endodermis and exodermis differentiation at the phenotypic and molecular level. Moreover, we will address whether there are differences among species that grow in different environments similar to the environment in which their growth has been adapted. In order to address this problem, newly developed tools and technology will be used to obtain a tomato root cell-type specific transcriptome as well as data analyses required for system biology and genomic approaches. The proposed project will shed new light on endodermis and exodermis development in tomato at the phenotypic and molecular level and will lay the foundation for study in other plant species.

Crop domestication revolutionised human life. This process induced changes in plant traits that produced plants that grew faster and generated higher yields. However, remarkably little is known about how plant roots have changed throughout the domestication process. Climate change is causing increasing droughts in many parts of the world. Given that roots are the way that water enters the plant, they are key for understanding drought tolerance. Root traits from crop ancestors could offer a route to increasing drought tolerance of modern crops. To do this, we need to focus our efforts on the impact of domestication on roots and the rhizosphere (the zone around the root including microbes), rather than only aboveground traits as traditionally done. WILD-ROOTS will therefore test the overall hypothesis that crop domestication led to changes in root and rhizosphere traits which decreased the drought tolerance of crops compared to their wild relatives. WILD-ROOTS will make a holistic study of the roots and rhizospheres of a wide range of crops from diverse origins. There will be a focus on root exudation and volatile organic compound (VOC) emission, which are vital root processes that are crucial for many types of interactions with plants, animals, microbes and the soil itself. Changes in root exudates and VOCs have been observed during drought conditions, but their roles in the drought tolerance of plants remains unclear. WILD-ROOTS will (1) evaluate domestication effects on the roots and rhizosphere, then (2) elucidate the mechanisms relating belowground traits to drought tolerance, and finally (3) use this knowledge to modernise crop models and identify belowground traits to be exploited for drought-proofing current crops. The results will reshape our fundamental knowledge of both the crop domestication process and how root exudation influences drought tolerance, as well as offering new approaches to boost the food security of current and future agricultural systems.