A key question in biology is how a given phenotype is generated from a genotype. We now have a good understanding of the role of transcriptional control in generating a phenotype. However, there is a major observation that is still not understood: multiple phenotypes can derive from one genome in one environment. This variability between genetically identical individuals in the same environment has been overlooked for a long time. Transcriptional variability has been observed between cells but also between individuals in multicellular organisms. While this variability might be partly caused by the micro-environment, there is evidence that it is at least partly genetically controlled and is biologically relevant. One of the factors that has been shown to regulate gene expression variability between cells, is chromatin. However we still don’t have a proof of the role of chromatin in cell-to-cell variability in plants and its possible role in inter-individual gene expression variability has not been studied yet. I will use a combination of transcriptomic, imaging and targeted functional studies to define the role of chromatin in inter-individual and cell-to-cell transcriptional variability, and its phenotypic consequences using genes involved in nitrate nutrition in Arabidopsis. The response to nitrate is a good model for such study, as not only have I observed that some of the main factors of the response to nitrate show high variability, but nitrate availability in the soil is also spatially and temporally heterogeneous in the wild. The project will highlight the control of transcriptional variability and its role in the genotype to phenotype link.