13 ERA-CAPS: Plant root diffusional barriers: Genesis and implications for nutrient efficiency and stress tolerance

Plant roots perform the critical function of controlling the uptake of water and essential mineral nutrients from the soil. This function is required by all land plants for their normal growth and development. Specialized cells in the root called the endodermis play a key role in controlling the transport of water and mineral nutrients from the roots to the leaves. These specialized cells have important cell wall modifications that acts as barriers to block the uncontrolled entry of water and mineral nutrients into the plant. Despite the importance of these barriers the molecular processes that control their development remain relatively unknown. By closely inspecting plants that contain mutations in genes thought to be involved in the development of these barriers the project team hopes to build a model that explains the mechanisms involved in the development of these barriers along with their function in water and nutrient uptake by the root as well as their role in preventing infection of roots by pathogens. Global food security is an issue of major international significance. The human population is predicted to reach 9 billion by 2050, increasing world demand for cereal by at least 1,000 million tons, a 50% increase on current levels. This increase needs to be achieved against a predicted decline in global crop production due to climate change causing reduced precipitation in many parts of the world where crops are currently grown. The root is the central plant organ required for water and mineral nutrient uptake from the soil by plants. More efficient water and mineral nutrient uptake by plants is needed to drive the increasing food production required to meet the challenge of increasing global crop production by 50% over the next 40 years. A better understanding of the mechanisms underlying root function will be central to the development of crops with the improved root systems needed to achieve such increased productivity to ensure global food security.

We have designed an ambitious interdisciplinary research programme integrating molecular plant science with analytical chemistry, whole plant physiology and modelling. This programme aims to deliver a complete understanding of the biology of Casparian strips and suberin, across scales, from molecules to the whole plant. Such information will enable a molecularly directed manipulation of Casparian strips and suberin, providing new pathways for the development of crop varieties with improved nutrient and water use efficiencies, and enhanced resistance to root pathogens, salinity and water stress. Such traits are essential if we are to develop crops that are more resilient to the predicted impacts of climate change on soil fertility, and to improve yields in a more sustainable manner to deliver the yield gains required to meet future population growth. By employing genomic, molecular genetic, chemical, biochemical and cell biological approaches we will discover and characterize the genes and molecular mechanisms involved in the biosynthesis of Casparian strips and suberin. Genetic resources characterized and developed through this mechanistic investigation will be leveraged to understand, at the root and whole plant level, the role of these physical and chemical barriers in mineral nutrient and water uptake, and root parasitic nematode infection. The ecological and adaptive function of these barriers to agriculturally relevant abiotic stresses such as water, mineral nutrient (deficiency and excess) and salinity will also be established. Building on this new understanding, mathematical models integrating molecular mechanistic knowledge with physiological processes at the tissue and whole plant level will also be built, providing predicative capacity to connect barrier properties with whole plant function.

The beneficiaries of this research span the full spectrum of stack holders in the global agricultural enterprise, including private sector seed companies and public sector plant breeders, commercial and subsistence farmers, agricultural commodity traders, consumers and the wider general public.

Results from the research will have a significant positive impact on agricultural and horticultural crop yields through improved mineral nutrient and water use efficiencies and enhanced stress tolerance (e.g. salinity, flooding, drought, nutrient deficiencies, trace element toxicities and root pathogens). Such improvements will provide direct commercial benefits to seed companies by allowing the development and sale of cultivars better adapted to current and future changing environmental conditions. Commercial farmers will benefit economically through improved and sustainable yields with less inputs (fertilizers, water and pesticides) and through the ability to utilize new cultivars to adapt their agricultural practices to changing climatic conditions. Further, such improvements in agricultural and horticultural crops will also benefit subsistence farmers with limited access to inorganic fertilizers (primarily nitrogen, phosphate and potassium, secondarily sulphur and magnesium) and pesticides, helping to reduce the cost burden such inputs impose by improving their value/cost ratio. Improved water use efficiency and stress tolerance will also improve yields for subsistence farmers cultivating marginal lands. In addition, reduced utilization of fertilizers, achieved through improved mineral nutrient use efficiencies, will limit the environmental and ecological damage their production and excess use causes, benefiting the general public through enhanced quality of life.

Results from the research will also impact food quality by helping to increase the content of essential mineral nutrients and reduce toxic trace elements in food crops. For most of the world's population plants are the major source of essential minerals such as calcium, potassium, manganese, iron and zinc, and therefore efforts to improve the mineral nutrient content of staple foods such as rice, maize and cassava will have a positive impact on public health both in the UK and internationally. Plants are also the primary entry point for a variety of toxic minerals into the food chain such as arsenic and cadmium, and being able to limit there accumulation in food would also have a positive impact on public health both in the UK and internationally.

The ability to generate improved plant-based feedstocks for lignocellulosic biofuels through improvements in both the agronomic properties of the crop (improved mineral nutrient, water use efficiency and abiotic stress tolerance) and its chemical composition (lignin) will economically benefit seed companies and farmers in the UK through the creation of opportunities to generate, sell and cultivate new crops. Such improved biofuels feedstock would also be cultivated on more marginal agricultural lands competing less with food crops, helping to minimize the impact on overall food production.

By providing improved agricultural and horticultural crops for food production the proposed research will help move the UK and international agricultural systems towards more sustainable food production, providing improved food security against the backdrop of a changing earth's climate and surface chemistry. Further, the improved plant-based feedstocks for the production of lignocellulosic biofuels that will be enabled by this research will help transition the UK and global fossil fuel-based economies to more sustainable energy practices.