Role of pyrimidine salvage pathway in the maintenance of organellar and nuclear genome integrity

• Published in: The Plant journal : for cell and molecular biology 2019-02, Vol.97 (3), p.430-446
• Main Authors: Pedroza‐García, José‐Antonio, Nájera‐Martínez, Manuela, Mazubert, Christelle, Aguilera‐Alvarado, Paulina, Drouin‐Wahbi, Jeannine, Sánchez‐Nieto, Sobeida, Gualberto, José M., Raynaud, Cécile, Plasencia, Javier
• Format: Article
• Language: English
• Subjects: Arabidopsis; Arabidopsis - genetics; Arabidopsis - growth & development; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Autotrophy; Biochemistry, Molecular Biology; Biosynthesis; Carbon sources; Cell Nucleus - metabolism; Chloroplasts; Chloroplasts - metabolism; Deoxyribonucleic acid; DNA; DNA Damage; Gene expression; Genes; Genome, Plant - genetics; Genomes; Genotoxic chemicals; Genotoxicity; Germination; Heterotrophy; Integrity; Kinases; Life Sciences; Molecular biology; Nucleosides; nucleotide metabolism; Nucleotides; Nucleotides - metabolism; Nutrient availability; Pyrimidines - metabolism; Salvage; Sugar; Thymidine; Thymidine - metabolism; Thymidine kinase; Thymidine Kinase - genetics; Thymidine Kinase - metabolism
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/tpj.14128

Summary Nucleotide biosynthesis proceeds through a de novo pathway and a salvage route. In the salvage route, free bases and/or nucleosides are recycled to generate the corresponding nucleotides. Thymidine kinase (TK) is the first enzyme in the salvage pathway to recycle thymidine nucleosides as it phosphorylates thymidine to yield thymidine monophosphate. The Arabidopsis genome contains two TK genes −TK1a and TK1b− that show similar expression patterns during development. In this work, we studied the respective roles of the two genes during early development and in response to genotoxic agents targeting the organellar or the nuclear genome. We found that the pyrimidine salvage pathway is crucial for chloroplast development and genome replication, as well as for the maintenance of its integrity, and is thus likely to play a crucial role during the transition from heterotrophy to autotrophy after germination. Interestingly, defects in TK activity could be partially compensated by supplementation of the medium with sugar, and this effect resulted from both the availability of a carbon source and the activation of the nucleotide de novo synthesis pathway, providing evidence for a compensation mechanism between two routes of nucleotide biosynthesis that depend on nutrient availability. Finally, we found differential roles of the TK1a and TK1b genes during the plant response to genotoxic stress, suggesting that different pools of nucleotides exist within the cells and are required to respond to different types of DNA damage. Altogether, our results highlight the importance of the pyrimidine salvage pathway, both during plant development and in response to genotoxic stress. Significance Statement The Arabidopsis genome contains two genes coding for thymidine kinase (TK1a and TK1b) that share 58% amino acid identity. This study presents evidence on the distinct roles of TK1a and TK1b genes during the DNA damage response to genotoxic stress, and finds that the thymidine salvage pathway is critical for chloroplast development, genome replication and integrity. Sugars compensate for the lack of TK activity by inducing the nucleotide de novo synthesis pathway.