Elucidation of pyrimidine salvage and integration into nucleotide metabolism
Final Report Abstract
The synthesis of pyrimidine nucleotides, an essential process in every organism, is accomplished by de novo synthesis or by salvaging pyrimdines from e.g. nucleic acid turnover. Here, we identify two Arabidopsis thaliana uridine/cytidine kinases, UCK1 and UCK2, which are located in the cytosol and are responsible for the majority of pyrimidine salvage activity in vivo. In addition, the chloroplast has an active uracil salvage pathway. Uracil phosphoribosyltransferase (UPP) catalyzes the initial step in this pathway and is required for the establishment of photosynthesis, as revealed by analysis of upp mutants. The upp knockout mutants are unable to grow photoautotrophically and knockdown mutants exhibit a variegated phenotype, with leaves that have chlorotic pale areas. Moreover, the upp mutants did not show altered expression of chloroplast-encoded genes, but reduced transcript accumulation of the Light Harvesting Complex B nuclear genes LHCB1.2 and LHCB2.3. An active UPP homolog from Escherichia coli failed to complement the upp mutant phenotype when targeted to the chloroplast, suggesting that the catalytic function of UPP is not the important factor for the chloroplast phenotype. Indeed, the expression of catalytically inactive Arabidopsis UPP, generated by introduction of point mutations, did complement the upp chloroplast phenotype. These results suggest that UPP has a vital function in chloroplast biogenesis unrelated to its catalytic activity and driven by a moonlighting function.
Publications
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(2019) Pyrimidine Salvage: Physiological Functions and Interaction with Chloroplast Biogenesis. Plant physiology 180 (4) 1816–1828
Ohler, Lisa; Niopek-Witz, Sandra; Mainguet, Samuel E.; Möhlmann, Torsten
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(2019) PUMPKIN, the sole plastid UMP kinase, associates with group II introns and alters their metabolism. Plant Physiol. 179: 248-264
Schmid L-M, Ohler L, Möhlmann T, Brachmann A, Muino JM, Leister D, Meurer J, Manavski N
