description
- Nitrogen (N) and Phosphorus (P) are major macronutrients impacting plant productivity. They are essential for all aspects of plant growth and are required in large quantities for crop maturation and seed production. However, P and N are poorly available in soils, leading to costly chemical fertiliser applications to sustain crop yields. This extensive, and expensive agrochemical practice comes at a severe cost to our environment and human health via soil, water and air pollution, and contributes substantially to global warming. Lowering chemical fertiliser inputs is essential to protect our health and environment. But how can we reduce the use of chemical fertilizer without decreasing crop yields? Plants have evolved the ability to interact with root-associated endosymbionts to access N from atmospheric N2 and to overcome P limitation of growth. The Arbuscular Mycorrhizal (AM) symbiosis, which delivers phosphate, nitrogen, and other nutrient, is present in 80 % of land plants, including legumes, bread wheat and maize. Legume roots can also associate with nitrogen-fixing bacteria (rhizobia), which reduce N2 to the plant-usable form NH3, within root nodules. Thus, the use of root endosymbionts as a natural source of fertilizer can be part of the solution to reduce fertilizer use without decreasing yield. Although biofertilizer products based on root endosymbionts have been developed, their efficiency remains poor because the capacity of plants to establish endosymbioses is affected by soil quality, prevailing climate and genotype. In recent years it has become clear that new genetic solutions to enhance endosymbioses are essential for endosymbiont based biofertilizers. Notably activation of nuclear calcium signals is essential for the development of endosymbioses. Although the mechanism of activation is unknown, this signalling is impaired by environmental factors (abiotic and biotic stresses). Thus, understanding how nuclear calcium signals are activated can open the way for engineering crops that are more resistant to the environmental stresses that inhibit the activation of root endosymbioses. In this project we aim to identify the mechanism of nuclear calcium signalling activation. Based on extensive preliminary work, we have identified a novel nuclear membrane component which is directly required for the activation of nuclear calcium signalling. This nuclear component has all the characteristics of a nuclear "receptor"; 1) capable of perceiving macromolecular factors induced by endosymbionts, and 2) capable of modulating the activity of ion channels via phosphorylation. We will characterise this nuclear "receptor" further and identify the macromolecular component(s) that activate it, to generate nuclear calcium signals, that initiate endosymbioses. Understanding this new molecular component is essential to understand how environmental factors inhibit endosymbioses. Thus, in the longer term, this project will provide the basis for methods that enhance endosymbioses in crops and reduce the use of chemical fertilizers.