Arabidopsis nucleoside hydrolases involved in intracellular and extracellular degradation of purines

• Published in: The Plant journal : for cell and molecular biology Vol. 65; no. 5; pp. 703 - 711
• Main Authors: Jung, Benjamin, Hoffmann, Christiane, Möhlmann, Torsten
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.03.2011; Blackwell
• Subjects: adenosine; apoplast; Arabidopsis; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis Proteins; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Biochemistry; Biological and medical sciences; Cellular biology; Enzymes; enzymology; Flowers & plants; Fundamental and applied biological sciences. Psychology; Gene Knockout Techniques; genetics; hydrolases; Hydrolysis; inosine; metabolism; Mutagenesis, Insertional; mutants; Mutation; N-Glycosyl Hydrolases; N-Glycosyl Hydrolases - genetics; N-Glycosyl Hydrolases - metabolism; nucleoside hydrolase; pathogens; Plant biology; Plant physiology and development; Plants, Genetically Modified; Plants, Genetically Modified - enzymology; Plants, Genetically Modified - genetics; purine; purines; Purines - metabolism; Ribonucleosides; Ribonucleosides - metabolism; RNA, Plant; RNA, Plant - genetics; uridine; xanthosine; Adenosine; Enzyme; Apoplast; Extracellular; Arabidopsis thaliana; Degradation; nucleoside hydrolase; Cruciferae; Dicotyledones; Angiospermae; Hydrolases; Inosine; Nucleoside; Spermatophyta; Purine; xanthosine; Intracellular
• ISSN: 0960-7412; 1365-313X; 1365-313X
• DOI: 10.1111/j.1365-313X.2010.04455.x

Recently, the first plant nucleoside hydrolase, NSH1 (former designation URH1), was identified at the molecular level. This enzyme's highest hydrolysis capacity is for uridine, thereby balancing pyrimidine salvage and catabolism. NSH1 was found to be less efficient in the hydrolysis of further nucleosides. However, it remained unclear whether purine nucleosides are processed by NSH1. Moreover, the biochemical and physiological functions of further NSH isoforms in Arabidopsis has not been analyzed. Here we show that NSH1 is also able to hydrolyze xanthosine with high efficiency, and thus represents the leading activity in purine and pyrimidine breakdown in a cell. A knockout mutant for NSH1 showed symptoms of accelerated senescence, accompanied by marked accumulation of uridine and xanthosine under conditions of prolonged darkness. The closest, so far uncharacterized, homolog of NSH1, NSH2, was found to act during the late phase of senescence and may support inosine breakdown. NSH3, another NSH isoform, surprisingly functions as an extracellular, purine-specific hydrolase that is involved in degradation of extracellular nucleosides and may participate in wound and pathogen responses.