Final Report Summary - THE PLANT ENDODERMIS (The plant endodermis - unraveling functions of a crucial barrier) In agriculture-based food production, we stand face to face with an increasing demand for food combined with decreasing resources available for fertilization. Thus, a prerequisite for sustaining efficient food production is to increase the ability of our currently employed crop species to grow efficiently with lower amounts of nutrients available. Plants take up essential nutrients and block out unwanted compounds from the soil by means of employing filtering systems that are deposited within the inner cell layers in the roots. One of these filter systems consist of a lignin-based deposition between cells in the endodermal layer. This is known as the Casparian strip, which functions as an apoplastic filter blocking diffusion between cells, much like tight junctions in mammals. However, a second more dynamic, filter is made through deposition of the wax-containing polymer suberin across the entire surface of old endodermal cells. In contrast to the Casperian strip, this filter can function as a blockage of transport across the plasma membrane. Deposition of suberin is highly dynamic and gives rise to individual unsuberized cells that have intuitively been termed “passage cells” as these are believed to retain the ability to facilitate transport of nutrients in an otherwise sealed of part of the root. In this context, the aim of this project has been to, on one hand, characterize factors that determine the establishment of passage cells, as well as identify markers that define these unknown cells. The results obtained in this project have given us a better understanding of these filters that control nutrient uptake in roots. With this knowledge, we are one step closer to develop novel agricultural tools aimed at improving the plants’ ability to utilize the scarce nutrients, and hence allow for a better exploitation of our limited natural resources. Work performed since the beginning of this project:• Novel markers of passage cells have been identified and characterized in the model plant Arabidopsis thaliana• Genetic factors involved in the development of passage cells have been identified• Lines for transcriptional analysis of specific cells in the endodermis has been generated• Arabidopsis lines with knockout of passage cell-specific genes with changes in passage cell abundance established.• Physiological analyses of established tools initiatedMain results achieved:• Novel candidates for passage cell markers found via coexpression analyses and confirmed in homozygous lines carrying fluorescence reporters.• These reporters have show a previously unknown connectivity between passage cells and individual cortex cells putatively underlining transcellular-coupled transport in plants and expanding currently employed root developmental models to include ground cell tissues.• Factors known to be involved in the establishment of xylem has been identified as playing an independent role in passage cell specification• The role of connection between vascular cylinder development (protoxylem) and passage cells has been found to be dependent on hormonal equilibrium (auxin/cytokinin) through analysis of suberization of the endodermis.• Ribosomal pull-down for transcriptional characterization of endodermal cells initiatedBased on the obtained in this project, we have gained a deeper understanding of the mechanisms that underlie nutritional transport and uptake into roots. In combination, the obtained data allow us to implement novel developmental aspects into physiological models of root interaction with the surroundings. As nutrient uptake and distribution are important factors in optimization of crop growth and food production, the long term socioeconomic impact consists of improved crops that are more efficient in utilizing artificial fertilization, and thus an improved agricultural production machinery.
