title: Thymidine kinases share a conserved function for nucleotide salvage and play an essential role in Arabidopsis thaliana growth and development.
abstract: Thymidine kinases (TKs) are important components in the nucleotide salvage pathway. However, knowledge about plant TKs is quite limited. In this study, the molecular function of TKs in Arabidopsis thaliana was investigated. Two TKs were identified and named AtTK1 and AtTK2. Expression of both genes was ubiquitous, but AtTK1 was strongly expressed in high-proliferation tissues. AtTK1 was localized to the cytosol, whereas AtTK2 was localized to the mitochondria. Mutant analysis indicated that the two genes function coordinately to sustain normal plant development. Enzymatic assays showed that the two TK proteins shared similar catalytic specificity for pyrimidine nucleosides. They were able to complement an Escherichia coli strain lacking TK activity. 5'-Fluorodeoxyuridine (FdU) resistance and 5-ethynyl 2'-deoxyuridine (EdU) incorporation assays confirmed their activity in vivo. Furthermore, the tk mutant phenotype could be alleviated by nucleotide feeding, establishing that the biosynthesis of pyrimidine nucleotides was disrupted by the TK deficiency. Finally, both human and rice (Oryza sativa) TKs were able to rescue the tk mutants, demonstrating the functional conservation of TKs across organisms. Taken together, our findings clarify the specialized function of two TKs in A. thaliana and establish that the salvage pathway mediated by the kinases is essential for plant growth and development.
authors.affiliation: National Key Laboratory of Plant Molecular Genetics and National Center of Plant Gene Research, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, 200032, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Xu
authors.affiliation: National Key Laboratory of Plant Molecular Genetics and National Center of Plant Gene Research, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, 200032, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Crop Genetics and Germplasm Enhancement, Nanjing Agricultural University, Nanjing, 210095, China.
authors.forename: Dong-Lei
authors.initials: DL
authors.lastname: Yang
authors.affiliation: National Key Laboratory of Plant Molecular Genetics and National Center of Plant Gene Research, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, 200032, China.
authors.forename: Qun
authors.initials: Q
authors.lastname: Li
authors.affiliation: National Key Laboratory of Plant Molecular Genetics and National Center of Plant Gene Research, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, 200032, China.
authors.forename: Zuhua
authors.initials: Z
authors.lastname: He
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004926:Escherichia coli; D017343:Genes, Plant; D006801:Humans; D008928:Mitochondria / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D009711:Nucleotides / Q000378:metabolism*; D012275:Oryza / Q000235:genetics; D010802:Phylogeny; D063245:Plant Development / Q000235:genetics*; D011741:Pyrimidine Nucleosides / Q000378:metabolism; D016415:Sequence Alignment; D013937:Thymidine Kinase / Q000235:genetics* / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D009711:Nucleotides; D011741:Pyrimidine Nucleosides; C000610354:At5g23070 protein, Arabidopsis; D013937:Thymidine Kinase; C000610353:thymidine kinase 1, Arabidopsis
keywords: Arabidopsis thaliana; conservation; pyrimidine; salvage pathway; thymidine kinase