An organellar thymidine kinase is required for the efficient replication of the maize plastidial genome.
Fiche publication
Date publication
octobre 2018
Journal
Plant physiology
Auteurs
Membres identifiés du Cancéropôle Est :
Mme KOECHLER Sandrine, Dr ERHARDT Mathieu
Tous les auteurs :
Le Ret M, Belcher S, Graindorge S, Wallet C, Koechler S, Erhardt M, Williams-Carrier R, Barkan A, Gualberto JM
Lien Pubmed
Résumé
Thymidine kinase (TK) is a key enzyme of the salvage pathway that recycles thymidine nucleosides to produce dTTP. We identified the single TK of maize, denoted CPTK1, as an essential factor in the replication of the plastidial genome (cpDNA), demonstrating the essential function of the salvage pathway during chloroplast biogenesis. CPTK1 localizes to both plastids and mitochondria. Its absence results in an albino phenotype, reduced cpDNA copy number, and a severe deficiency for plastidial ribosomes. No significant effect was found on mitochondria, indicating that they are less reliant on the salvage pathway. Arabidopsis has two thymidine kinases, TK1A and TK1B, that apparently resulted from a gene duplication after the divergence of monocots and dicots. Similar but less severe effects were observed for Arabidopsis tk1a tk1b double mutants in comparison to those in maize cptk1. We found that TK1B is important not only for cpDNA replication, but also for its repair in conditions of replicative stress, and that it has little impact on the mitochondrial phenotype. In the maize cptk1 mutant, the DNA from the small single copy region of the plastidial genome was reduced to a greater extent than other regions, suggesting preferential abortion of replication in this region. This is accompanied by the accumulation of truncated genomes that result, at least in part, from unfaithful microhomology-mediated repair. These and other results suggest that the loss of normal cpDNA replication elicits the mobilization of new replication origins around the rpoB transcription unit, and imply that increased transcription at rpoB is associated with the initiation of cpDNA replication.
Référence
Plant Physiol.. 2018 Oct 10;: