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Plant organellar DNA polymerases paralogs exhibit dissimilar nucleotide incorporation fidelity

The coding sequences of plant mitochondrial and chloroplast genomes present a lower mutation rate than the coding sequences of animal mitochondria. However, plant mitochondrial genomes frequently rearrange and present high mutation rates in their noncoding sequences. DNA replication in plant organel...

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Published in:The FEBS journal 2018-11, Vol.285 (21), p.4005-4018
Main Authors: Ayala‐García, Víctor M., Baruch‐Torres, Noe, García‐Medel, Paola L., Brieba, Luis G.
Format: Article
Language:English
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Summary:The coding sequences of plant mitochondrial and chloroplast genomes present a lower mutation rate than the coding sequences of animal mitochondria. However, plant mitochondrial genomes frequently rearrange and present high mutation rates in their noncoding sequences. DNA replication in plant organelles is carried out by two DNA polymerases (DNAP) paralogs. In Arabidopsis thaliana at least one DNAP paralog (AtPolIA or AtPolIB) is necessary for plant viability, suggesting that both genes are partially redundant. To understand how AtPolIs replicate genomes that present low and high mutation rates, we measured their nucleotide incorporation for all 16‐base pair combinations in vitro. AtPolIA presents an error rate of 7.26 × 10−5, whereas AtPolIB has an error rate of 5.45 × 10−4. Thus, AtPolIA and AtPolIB are 3.5 and 26‐times less accurate than human mitochondrial DNAP γ. The 8‐fold difference in fidelity between both AtPolIs results from a higher catalytic efficiency in AtPolIA. Both AtPolIs extend from mismatches and the fidelity of AtPolIs ranks between high fidelity and lesion bypass DNAPs. The different nucleotide incorporation fidelity between AtPolIs predicts a prevalent role of AtPolIA in DNA replication and AtPolIB in DNA repair. We hypothesize that in plant organelles, DNA mismatches generated during DNA replication are repaired via recombination‐mediated or DNA mismatch repair mechanisms that selectively target the coding region and that the mismatches generated by AtPolIs may result in the frequent expansion and rearrangements present in plant mitochondrial genomes. In flowering plants, organellar DNA polymerases are a duplicated gene product with high sequence identity. In the plant model Arabidopsis thaliana these gene products present an 8‐fold difference in nucleotide incorporation fidelity. We hypothesize that the faithful polymerase is involved in organellar DNA replication.
ISSN:1742-464X
1742-4658
DOI:10.1111/febs.14645