Structure–Function Analysis Reveals the Singularity of Plant Mitochondrial DNA Replication Components: A Mosaic and Redundant System

Abstract

Plants are sessile organisms, and their DNA is particularly exposed to damaging agents. The integrity of plant mitochondrial and plastid genomes is necessary for cell survival. During evolution, plants have evolved mechanisms to replicate their mitochondrial genomes while minimizing the effects of DNA damaging agents. The recombinogenic character of plant mitochondrial DNA, absence of defined origins of replication, and its linear structure suggest that mitochondrial DNA replication is achieved by a recombination-dependent replication mechanism. Here, I review the mitochondrial proteins possibly involved in mitochondrial DNA replication from a structural point of view. A revision of these proteins supports the idea that mitochondrial DNA replication could be replicated by several processes. The analysis indicates that DNA replication in plant mitochondria could be achieved by a recombination-dependent replication mechanism, but also by a replisome in which primers are synthesized by three different enzymes: Mitochondrial RNA polymerase, Primase-Helicase, and Primase-Polymerase. The recombination-dependent replication model and primers synthesized by the Primase-Polymerase may be responsible for the presence of genomic rearrangements in plant mitochondria.

Plant Organelle DNA Maintenance

“…Brieba [2] summarizes the current literature to point out the importance of homologous DNA recombination in maintaining the integrity of plant mitochondrial genomes. Plant mitochondrial DNA (mtDNA) appears to be predominantly linear in nature and lacks any clearly identified replication origins.…”

“…Plant mitochondrial DNA (mtDNA) appears to be predominantly linear in nature and lacks any clearly identified replication origins. DNA replication proteins functional in both mitochondria and chloroplasts have been identified, and surprisingly, there are multiple copies of the genes for most of these proteins [1,2]. Other evidence in the literature suggests the presence of more than one mechanism for the replication of each of the plant organelle genomes [1,2].…”

“…DNA replication proteins functional in both mitochondria and chloroplasts have been identified, and surprisingly, there are multiple copies of the genes for most of these proteins [1,2]. Other evidence in the literature suggests the presence of more than one mechanism for the replication of each of the plant organelle genomes [1,2]. These possibilities include typical primer-driven replication from distinct origins, recombination-dependent replication (RDR) and rolling circle replication.…”

“…The endosymbiotic origin of mitochondria and chloroplasts has long been accepted, suggesting that the DNA replication mechanisms would be similar to their bacterial ancestors. However, none of the DNA replication, DNA recombination or DNA repair proteins required for maintenance of the organelle genomes are encoded in either of these organelle genomes [1,2]. The genes for these proteins are nuclear encoded and the protein products are imported into the proper organelle for function.…”

“…The genes for these proteins are nuclear encoded and the protein products are imported into the proper organelle for function. The analysis of the minimal replisome in plant mitochondria and chloroplasts to date indicates that it is phage-like, most similar to the bacteriophage T7 system [1,2].…”