Functional analysis of plant nucleobase and vitamin C transporters

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Purines and pyrimidines play a key role in nucleic acid and nucleotide metabolism of all cells. In addition, they can be used as nitrogen sources in many microorganisms and plants e.g. for the biosynthesis of secondary compounds such as cytokinins, some alkaloids or of ureides in legumes. On the other hand, ascorbate (vitamin C) represents one of the main antioxidants in plants protecting plant cells against oxidative stress. Synthesized in the cytosol and in mitochondria, it accumulates to millimolar concentrations in different cellular compartments. Interestingly, nucleobases and ascorbate, albeit structurally unrelated, are transported by a family of highly homologous transport proteins, the Nucleobase-Ascorbate Transporters (NATs). The Arabidopsis thaliana genome contains at least 12 genes encoding putative NAT proteins with yet unknown functions. The aim of this project is to elucidate the transport specificities and the physiological roles of the various members of the NAT protein family in organelles and the plasma membrane during development and response to environmental (stress) conditions, e.g. by heterologous expression of the proteins in yeast cells and the ascomycete Aspergillus nidulans, using Nothern blot assays, cDNA microarrays, by (sub)cellular localization studies, and by isolation and characterization of insertion mutants at the molecular, biochemical and physiological levels.