Factors Affecting Organelle Genome Stability in Physcomitrella patens.

Masaki Odahara

doi:10.3390/plants9020145

Abstract

Organelle genomes are essential for plants; however, the mechanisms underlying the maintenance of organelle genomes are incompletely understood. Using the basal land plant Physcomitrella patens as a model, nuclear-encoded homologs of bacterial-type homologous recombination repair (HRR) factors have been shown to play an important role in the maintenance of organelle genome stability by suppressing recombination between short dispersed repeats. In this review, I summarize the factors and pathways involved in the maintenance of genome stability, as well as the repeats that cause genomic instability in organelles in P. patens, and compare them with findings in other plant species. I also discuss the relationship between HRR factors and organelle genome structure from the evolutionary standpoint.

Highlights

Physcomitrella patens is a moss that has been used as a model species for studying cell growth and differentiation [1]
Neither mitochondrial DNA (mtDNA) nor chloroplast DNA (cpDNA) encode proteins that are involved in DNA replication, recombination, and repair; instead, proteins involved in these processes are encoded by nuclear DNA, similar to a large number of proteins that function in chloroplasts and mitochondria
P. patens mitochondrial RECA1 knockout (KO) mutants generated by targeted gene disruption show severe defects in protonema cells, with less-developed gametophores and defective mitochondria characterized by an enlarged shape, disorganized cristae, and lower matrix electron density [7], indicating that RECA1 is essential for normal growth

Summary

Introduction

Physcomitrella patens is a moss (bryophyte) that has been used as a model species for studying cell growth and differentiation [1]. Nuclear DNA of P. patens shows exceptionally high activity of homologous recombination, which enables its use for gene targeting in combination with polyethylene glycol-mediated protoplast transformation [3]. This feature, together with its haploid vegetative growth phase and recent advances in nuclear genome analysis, has accelerated reverse genetic analyses in P. patens [2,4]. Chloroplast and mitochondria in P. patens, as in other plant species and algae, possess their own DNA, which associates with proteins to form nucleoids. P. patens mtDNA forms a single circular structure because of the absence of repeats longer than 80 bp [5,7,8,9]. Neither mtDNA nor cpDNA encode proteins that are involved in DNA replication, recombination, and repair; instead, proteins involved in these processes are encoded by nuclear DNA, similar to a large number of proteins that function in chloroplasts and mitochondria

Plant Homologs of Bacterial Proteins and Their Localization

Maintenance of Mitochondrial Genome Stability by HRR and MSH1

Findings

Maintenance of Chloroplast Genome Stability by HRR Proteins and MSH1