Arabidopsis thaliana nucleosidase mutants provide new insights into nucleoside degradation

New Phytol. 2011 Jul;191(2):349-59. doi: 10.1111/j.1469-8137.2011.03711.x. Epub 2011 May 20.


A central step in nucleoside and nucleobase salvage pathways is the hydrolysis of nucleosides to their respective nucleobases. In plants this is solely accomplished by nucleosidases (EC 3.2.2.x). To elucidate the importance of nucleosidases for nucleoside degradation, general metabolism, and plant growth, thorough phenotypic and biochemical analyses were performed using Arabidopsis thaliana T-DNA insertion mutants lacking expression of the previously identified genes annotated as uridine ribohydrolases (URH1 and URH2). Comprehensive functional analyses of single and double mutants demonstrated that both isoforms are unimportant for seedling establishment and plant growth, while one participates in uridine degradation. Rather unexpectedly, nucleoside and nucleotide profiling and nucleosidase activity screening of soluble crude extracts revealed a deficiency of xanthosine and inosine hydrolysis in the single mutants, with substantial accumulation of xanthosine in one of them. Mixing of the two mutant extracts, and by in vitro activity reconstitution using a mixture of recombinant URH1 and URH2 proteins, both restored activity, thus providing biochemical evidence that at least these two isoforms are needed for inosine and xanthosine hydrolysis. This mutant study demonstrates the utility of in vivo systems for the examination of metabolic activities, with the discovery of the new substrate xanthosine and elucidation of a mechanism for expanding the nucleosidase substrate spectrum.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / enzymology*
  • Arabidopsis / genetics
  • Arabidopsis / growth & development
  • Arabidopsis / metabolism
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • DNA, Complementary / genetics
  • Gene Knockout Techniques
  • Green Fluorescent Proteins
  • Hydrolysis
  • Inosine / metabolism
  • Mutagenesis, Insertional
  • N-Glycosyl Hydrolases / genetics
  • N-Glycosyl Hydrolases / metabolism*
  • Nucleosides / metabolism*
  • Phenotype
  • Protein Isoforms
  • RNA, Plant / genetics
  • Recombinant Fusion Proteins / isolation & purification
  • Recombinant Fusion Proteins / metabolism
  • Ribonucleosides / metabolism
  • Seedlings / enzymology
  • Seedlings / growth & development
  • Sequence Analysis, DNA


  • Arabidopsis Proteins
  • DNA, Complementary
  • Nucleosides
  • Protein Isoforms
  • RNA, Plant
  • Recombinant Fusion Proteins
  • Ribonucleosides
  • Green Fluorescent Proteins
  • Inosine
  • uridine nucleosidase
  • xanthosine
  • N-Glycosyl Hydrolases
  • URH1 protein, Arabidopsis
  • URH2 protein, Arabidopsis