Enzymes involved in organellar DNA replication in photosynthetic eukaryotes

Abstract

Plastids and mitochondria possess their own genomes. Although the replication mechanisms of these organellar genomes remain unclear in photosynthetic eukaryotes, several organelle-localized enzymes related to genome replication, including DNA polymerase, DNA primase, DNA helicase, DNA topoisomerase, single-stranded DNA maintenance protein, DNA ligase, primer removal enzyme, and several DNA recombination-related enzymes, have been identified. In the reference Eudicot plant Arabidopsis thaliana, the replication-related enzymes of plastids and mitochondria are similar because many of them are dual targeted to both organelles, whereas in the red alga Cyanidioschyzon merolae, plastids and mitochondria contain different replication machinery components. The enzymes involved in organellar genome replication in green plants and red algae were derived from different origins, including proteobacterial, cyanobacterial, and eukaryotic lineages. In the present review, we summarize the available data for enzymes related to organellar genome replication in green plants and red algae. In addition, based on the type and distribution of replication enzymes in photosynthetic eukaryotes, we discuss the transitional history of replication enzymes in the organelles of plants.

Keywords: mitochondria; organellar genome; plastids; replication.

FIGURE 1

Phylogenetic tree of Family A DNA polymerases. Reproduced from Moriyama et al. (2014) with permission.

FIGURE 2

Processivity of CmPOP and CmPolI. Reactions were performed in reaction buffer (50 mM Tris-HCl [pH 8.0], 5 mM MgCl₂, 1 mM DTT, 0.01% BSA, 50 μM dATP, 50 μM dTTP, 50 μM dGTP, 50 μM dCTP, and 10 nM ³²P–labeled M13mp18-M1) at 37°C for 5 min. The reaction products were analyzed in 5% polyacrylamide gels containing 7 M urea. Reproduced from Moriyama et al. (2008) with permission.

FIGURE 3

Phylogenetic trees of enzymes related to organellar genome replication. Simplified phylogenetic trees (A–D). A detailed phylogenetic tree based on plant 5′–3′ exonuclease and the 5′–3′ exonuclease domains of bacterial PolI (E). Schematic comparison of the structure of PolI and plant 5′–3′ exonuclease (F). Modified from Moriyama et al. (2014) with permission.

FIGURE 4

Proposed model for the exchange of organellar replication enzymes during the evolution of photosynthetic eukaryotes.