Functions of Cytidine Triphosphate Synthase and Inosine Monophosphate Dehydrogenase in Balancing of Nucleotide Pools and Genome integrity

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Nucleotide biosynthesis is a dynamic process and markedly upregulated during periods of growth and acclimation to abiotic stimuli, such as cold, to meet the demand of nucleic acid synthesis. Provision of (deoxy-)CTP and (deoxy-)GTP are key in this process as these molecules are typically lowest among nucleotides and need to be increased to avoid nucleotide limitation and imbalance. The protein families of Cytidintriphosphate Synthases (CTPS) and Inosinmonophosphate Dehydrogenases (IMPDH) are mainly responsible to provide CTP and GTP. Among the five CTPS isoforms in Arabidopsis, CTPS2 was identified as main player for the provision of CTP for chloroplast RNA and DNA synthesis. The reason for the pivotal function of CTPS2 and no other isoform is not fully clear and we propose to do a deeper characterization of the biochemical properties of CTPS2 and test different complementation-lines to unravel whether distinct expression patterns or isoform specific biochemical features are required. This analysis will be done in parallel to the analysis of the two IMPDH isoforms, recently preliminary characterized by us. Interestingly, IMPDH2 T-DNA insertion lines phenocopied amiRNA mutants of CTPS2, indicating that those two isoforms are of central importance for nucleotide balancing. In this project we will cooperate with the groups of Claus-Peter Witte (University of Hannover) to investigate the effect of mutants on (deoxy-)nucleotide levels and Julia Bornhorst (University of Wuppertal) to analyzed DNA damage in mutants (triggert by abiotic stimuli such as UV-light. In addition, we will test for a physical interaction of CTPS and IMPDH isoforms that might exist to allow for perfect coregulation of corresponding enzyme activities, as already observed in mammalians.