The role of guanosine deaminase in ureide production in soybean nodules and in purine nucleotide catabolism of Arabidopsis

• Applicant: Professor Dr. Claus-Peter Witte
• Subject Area: Plant Biochemistry and Biophysics
• Term: from 2014 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 255997898

Purine nucleotides can be fully catabolized in plants to recycle nutrients. We recently described an enzyme from Arabidopsis, guanosine deaminase (GSDA), involved in this process. GSDA catalyzes the deamination of guanosine to xanthosine which in Arabidopsis is exclusively synthesized by GSDA. Other sources for xanthosine, like the dephosphorylation of XMP, seem not to be relevant. In soybean however, it is generally assumed that the generation of the ureides (purine base breakdown products that serve as primary nitrogen transport compounds from the nodules to the shoot) runs via XMP dephosphorylation. If true, GSDA of soybean would not be required for ureide production in nodules. (1) We propose to experimentally evaluate the route of ureide generation in soybean nodules and assess the role of GSDA in this process. In Arabidopsis, our preliminary experiments indicated that GSDA may be of central importance for all or at least the bulk of purine nucleotide catabolism (of GMP and also AMP). (2) By performing metabolite analyses of a range of single and double mutants, a map of of the purine nucleotide catabolic pathway will be drawn and the overall importance of GSDA investigated. This will potentially result in a completely new view on purine nucleotide catabolism in vivo.Arabidopsis mutants of GSDA show distinct phenotypes like low germination and susceptibility to prolonged darkness. (3) A detailed phenotypic analysis of GSDA mutants in the context of other mutants of purine nucleotide catabolism will be performed to evaluate and quantify the observed defects. We speculate that defective sugar remobilization may be in part responsible for the phenotypic alterations.GSDA is a novel enzyme only found in plants. Microbes have structurally similar enzymes with specificity for guanine. (4) By generating a crystal structure of GSDA from Arabidopsis we would like to understand the molecular basis for the guanosine specificity of this enzyme.

• DFG Programme: Research Grants