Maize Thymidine Kinase Activity Is Present throughout Plant Development and Its Heterologous Expression Confers Tolerance to an Organellar DNA-Damaging Agent.

Manuela Nájera-Martínez,Jorge Vázquez-Ramos,Javier Plasencia,José Antonio Pedroza-García,Luis Jiro Suzuri-Hernández,Cécile Raynaud,Jeannine Drouin-Wahbi,Christelle Mazubert

doi:10.3390/plants9080930

Abstract

Thymidine kinase 1 (TK1) phosphorylates thymidine nucleosides to generate thymidine monophosphate. This reaction belongs to the pyrimidine salvage route that is phylogenetically conserved. In the model plant Arabidopsis thaliana, TK activity contributes to maintain nuclear and organellar genome integrity by providing deoxythymidine-triphosphate (dTTP) for DNA synthesis. Arabidopsis has two TK1 genes (TK1a and TK1b) and double mutants show an albino phenotype and develop poorly. In contrast, maize (Zea mays L.) has a single TK1 (ZmTK1) gene and mutant plants are albino and display reduced genome copy number in chloroplasts. We studied the role of ZmTK1 during development and genotoxic stress response by assessing its activity at different developmental stages and by complementing Arabidopsis tk1 mutants. We found that ZmTK1 transcripts and activity are present during germination and throughout maize development. We show that ZmTK1 translocation to chloroplasts depends on a 72-amino-acid N-signal and its plastid localization is consistent with its ability to complement Arabidopsis tk1b mutants which are hypersensitive to ciprofloxacin (CIP), a genotoxic agent to organellar DNA. Also, ZmTK1 partly complemented the Arabidopsis double mutant plants during development. Our results contribute to the understanding of TK1 function in monocot species as an organellar enzyme for genome replication and repair.

Highlights

Pyrimidine nucleotides are essential components of DNA and RNA
ZmTK1 Transcript and Activity Are Present throughout Maize Development
Since both Thymidine kinase 1 (TK1) Arabidopsis genes have a ubiquitous expression throughout plant development [10], Since both TK1 Arabidopsis genes have a ubiquitous expression throughout plant development we tested whether this was true in maize

Summary

Introduction

Pyrimidine nucleotides are essential components of DNA and RNA. These molecules participate in bioenergetic processes as well as in the synthesis of sucrose, polysaccharides, and phosphoand glycolipids. In plants, they are involved in the biosynthesis of several secondary metabolites [1]. De novo pyrimidine nucleotide biosynthesis starts by the action of the carbamoyl phosphate synthetase. Plants 2020, 9, 930 that uses carbonate, ATP and the amino group from glutamine to generate carbamoyl phosphate. Biosynthesis proceeds in plastids and mitochondria to yield CTP. Ribonucleotide reductase reduces the -OH at the ribose C2’position in UDP to produce dUDP which serves as substrate for a nucleoside diphosphate kinase and is dephosphorylated by a pyrophosphatase to yield dUMP

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