Shoots Nitrogen Uptake and Regulation: the molecular basis of plant Nitrogen foliar nutrition – SNUp-Reg

Foliar fertilization is a widely used tool in agriculture. Despite the recognized benefits of this practice on crops cultures, the molecular mechanisms driving the sensing of mineral and organic nutrients at the leaf level and their absorption are largely unknown. Nitrogen (N) is the most important macronutrient affecting crop growth and yield. Urea and nitrate are the two main organic and inorganic forms of nitrogen used in foliar fertilization. At present, the molecular basis of the roots sensing and transport of different N forms and the response to root supply have been largely studied. At the contrary, there are no evidence for i) the involvement of specific transporters for urea and nitrate leaf uptake, and ii) the involvement of specific genes in the perception and regulation of the foliar uptake. The SNUp-Reg project is an exploratory program, which aim is to discover new molecular elements driving the foliar sensing and acquisition of one main mineral and one main organic form of nitrogen. For that, we will combine molecular physiology, transcriptomic, and genetic approaches in the model species Arabidopsis thaliana. First, we will characterize the kinetic and dynamic of urea and nitrate leaf absorption and translocation in planta. We will made uptake experiments from leaves, treated with isotope-labelled urea and nitrate solutions. Secondly, we will made a genome-wide analysis of the leaf transcriptional response specific to urea or nitrate supply, and resulting from the combination of both. We will generate and analyse the gene regulatory networks driving the responses to leaf nitrogen supply, in order to identify master regulator genes. Thirdly, we will develop a second genome-wide approach, by studying the genetic variation associated to urea and nitrate acquisition from leaves, in 223 Arabidopsis accessions. The aim of this GWAS approach is to find loci linked to the mechanism of acquisition of nitrogen from leaves. We will use an innovative and integrative approach to combine transcriptomic and GWAS data, to prioritize candidate genes for improved foliar nitrogen use efficiency. The function of candidate genes will be validated in the model Arabidopsis, using reverse genetics approaches and shoots live imaging. In the end, we will make a functional transfer trough the cereal crop Durum wheat, with the aim of evaluating the impact on agronomic traits.
At the end of the SNUp-Reg project, we should obtain a list of genes, validated for their role in urea and nitrate absorption in Arabidopsis and Durum wheat leaves, and a model explaining the mechanism of transport and allocation of these molecules from the leaf surface to the rest of the plant. These results on nitrogen-based molecules will have a real potential for the transfer i) to an agronomic context and ii) to other macro or micro-elements important in the foliar feeding.
We think that SNUp-Reg results could have a strong impact on the research community, driving a shift in the plant nutrition domain, from roots to shoots. At long term, the knowledge generated through this research project could be used for the establishment of more sustainable nutrient management systems but also to develop more nutrient-efficient crops.