Limits...
RECG maintains plastid and mitochondrial genome stability by suppressing extensive recombination between short dispersed repeats.

Odahara M, Masuda Y, Sato M, Wakazaki M, Harada C, Toyooka K, Sekine Y - PLoS Genet. (2015)

Bottom Line: This result suggests that mitochondrial genomic instability is responsible for the defective phenotypes of RECG KO plants.Such loci were sometimes associated with a decrease in the levels of normal mtDNA and significant decrease in the number of transcripts derived from the loci.These results suggest that RECG plays a role in the maintenance of both plastid and mitochondrial genome stability by suppressing aberrant recombination between dispersed short repeats; this role is crucial for plastid and mitochondrial functions.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Science, College of Science, Rikkyo (St. Paul's) University, Toshima-ku, Tokyo, Japan.

ABSTRACT
Maintenance of plastid and mitochondrial genome stability is crucial for photosynthesis and respiration, respectively. Recently, we have reported that RECA1 maintains mitochondrial genome stability by suppressing gross rearrangements induced by aberrant recombination between short dispersed repeats in the moss Physcomitrella patens. In this study, we studied a newly identified P. patens homolog of bacterial RecG helicase, RECG, some of which is localized in both plastid and mitochondrial nucleoids. RECG partially complements recG deficiency in Escherichia coli cells. A knockout (KO) mutation of RECG caused characteristic phenotypes including growth delay and developmental and mitochondrial defects, which are similar to those of the RECA1 KO mutant. The RECG KO cells showed heterogeneity in these phenotypes. Analyses of RECG KO plants showed that mitochondrial genome was destabilized due to a recombination between 8-79 bp repeats and the pattern of the recombination partly differed from that observed in the RECA1 KO mutants. The mitochondrial DNA (mtDNA) instability was greater in severe phenotypic RECG KO cells than that in mild phenotypic ones. This result suggests that mitochondrial genomic instability is responsible for the defective phenotypes of RECG KO plants. Some of the induced recombination caused efficient genomic rearrangements in RECG KO mitochondria. Such loci were sometimes associated with a decrease in the levels of normal mtDNA and significant decrease in the number of transcripts derived from the loci. In addition, the RECG KO mutation caused remarkable plastid abnormalities and induced recombination between short repeats (12-63 bp) in the plastid DNA. These results suggest that RECG plays a role in the maintenance of both plastid and mitochondrial genome stability by suppressing aberrant recombination between dispersed short repeats; this role is crucial for plastid and mitochondrial functions.

Show MeSH

Related in: MedlinePlus

Ultrastructure of RECG KO protonemal cells.Protonemal cells of WT, RECG KO normal (recG-N), and RECG KO atrophic (recG-A) were analyzed by TEM. A to C. Images of transversion sections of WT (A), recG-6N (B), and recG-6A (C) cells. Filled and blank arrowheads denote examples of mitochondrion and plastid, respectively. D to G. Mitochondria of WT (D), recG-3N (E), recG-3A (F), and recG-6N (G) cells. Cristae were appeared as small regions with low electron density. Asterisks denote examples of enlarged cristae. H to J. Plastids of WT (H), recG-3N (I), and recG-3A (J) cells. Examples of starch grains are indicated by S. Bars = 5 μm in (A) to (C), 500 nm in (D) to (G), and 1 μm in (H) to (J).
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4358946&req=5

pgen.1005080.g004: Ultrastructure of RECG KO protonemal cells.Protonemal cells of WT, RECG KO normal (recG-N), and RECG KO atrophic (recG-A) were analyzed by TEM. A to C. Images of transversion sections of WT (A), recG-6N (B), and recG-6A (C) cells. Filled and blank arrowheads denote examples of mitochondrion and plastid, respectively. D to G. Mitochondria of WT (D), recG-3N (E), recG-3A (F), and recG-6N (G) cells. Cristae were appeared as small regions with low electron density. Asterisks denote examples of enlarged cristae. H to J. Plastids of WT (H), recG-3N (I), and recG-3A (J) cells. Examples of starch grains are indicated by S. Bars = 5 μm in (A) to (C), 500 nm in (D) to (G), and 1 μm in (H) to (J).

Mentions: To analyze the effect of the RECG KO on the ultrastructure of subcellular components, especially on those of mitochondria and plastids, we observed RECG KO cells by transmission electron microscopy (TEM). Since the RECG KO plant appeared to be composed of recG-N and recG-A protonemal cells, these two cell types were analyzed separately. TEM analyses revealed that the RECG KO had various effects on the ultrastructure of mitochondria, plastids, and other cell components. Both recG-N and recG-A mitochondria had a lower number of cristae and cristae enlargement (Fig. 4D-F), and recG-A cell mitochondria showed weaker matrix staining, indicating a lower electron density of the mitochondrial matrix (Fig. 4F). Some RECG KO mitochondria were abnormally extended (Fig. 4B, C and G), and their sizes were sometimes comparable to those of plastids (S3B Fig.). The extended mitochondria were more frequently observed in recG-N cells than in recG-A cells. It is notable that these mitochondrial abnormalities, including a lower number of cristae, cristae disorganization, weaker matrix staining, and stretching, are also observed in RECA1 KO mitochondria [6]. We further analyzed the stretching by performing TEM on serial thin sections to elucidate the three-dimensional structure of the extended mitochondria, and found that one of these mitochondria penetrated 16 serial thin sections (S3C Fig.) and that the edge of each mitochondrion was swollen (S3D Fig.). This result suggested that the extended mitochondria were actually disc-shaped with thick edges.


RECG maintains plastid and mitochondrial genome stability by suppressing extensive recombination between short dispersed repeats.

Odahara M, Masuda Y, Sato M, Wakazaki M, Harada C, Toyooka K, Sekine Y - PLoS Genet. (2015)

Ultrastructure of RECG KO protonemal cells.Protonemal cells of WT, RECG KO normal (recG-N), and RECG KO atrophic (recG-A) were analyzed by TEM. A to C. Images of transversion sections of WT (A), recG-6N (B), and recG-6A (C) cells. Filled and blank arrowheads denote examples of mitochondrion and plastid, respectively. D to G. Mitochondria of WT (D), recG-3N (E), recG-3A (F), and recG-6N (G) cells. Cristae were appeared as small regions with low electron density. Asterisks denote examples of enlarged cristae. H to J. Plastids of WT (H), recG-3N (I), and recG-3A (J) cells. Examples of starch grains are indicated by S. Bars = 5 μm in (A) to (C), 500 nm in (D) to (G), and 1 μm in (H) to (J).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4358946&req=5

pgen.1005080.g004: Ultrastructure of RECG KO protonemal cells.Protonemal cells of WT, RECG KO normal (recG-N), and RECG KO atrophic (recG-A) were analyzed by TEM. A to C. Images of transversion sections of WT (A), recG-6N (B), and recG-6A (C) cells. Filled and blank arrowheads denote examples of mitochondrion and plastid, respectively. D to G. Mitochondria of WT (D), recG-3N (E), recG-3A (F), and recG-6N (G) cells. Cristae were appeared as small regions with low electron density. Asterisks denote examples of enlarged cristae. H to J. Plastids of WT (H), recG-3N (I), and recG-3A (J) cells. Examples of starch grains are indicated by S. Bars = 5 μm in (A) to (C), 500 nm in (D) to (G), and 1 μm in (H) to (J).
Mentions: To analyze the effect of the RECG KO on the ultrastructure of subcellular components, especially on those of mitochondria and plastids, we observed RECG KO cells by transmission electron microscopy (TEM). Since the RECG KO plant appeared to be composed of recG-N and recG-A protonemal cells, these two cell types were analyzed separately. TEM analyses revealed that the RECG KO had various effects on the ultrastructure of mitochondria, plastids, and other cell components. Both recG-N and recG-A mitochondria had a lower number of cristae and cristae enlargement (Fig. 4D-F), and recG-A cell mitochondria showed weaker matrix staining, indicating a lower electron density of the mitochondrial matrix (Fig. 4F). Some RECG KO mitochondria were abnormally extended (Fig. 4B, C and G), and their sizes were sometimes comparable to those of plastids (S3B Fig.). The extended mitochondria were more frequently observed in recG-N cells than in recG-A cells. It is notable that these mitochondrial abnormalities, including a lower number of cristae, cristae disorganization, weaker matrix staining, and stretching, are also observed in RECA1 KO mitochondria [6]. We further analyzed the stretching by performing TEM on serial thin sections to elucidate the three-dimensional structure of the extended mitochondria, and found that one of these mitochondria penetrated 16 serial thin sections (S3C Fig.) and that the edge of each mitochondrion was swollen (S3D Fig.). This result suggested that the extended mitochondria were actually disc-shaped with thick edges.

Bottom Line: This result suggests that mitochondrial genomic instability is responsible for the defective phenotypes of RECG KO plants.Such loci were sometimes associated with a decrease in the levels of normal mtDNA and significant decrease in the number of transcripts derived from the loci.These results suggest that RECG plays a role in the maintenance of both plastid and mitochondrial genome stability by suppressing aberrant recombination between dispersed short repeats; this role is crucial for plastid and mitochondrial functions.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Science, College of Science, Rikkyo (St. Paul's) University, Toshima-ku, Tokyo, Japan.

ABSTRACT
Maintenance of plastid and mitochondrial genome stability is crucial for photosynthesis and respiration, respectively. Recently, we have reported that RECA1 maintains mitochondrial genome stability by suppressing gross rearrangements induced by aberrant recombination between short dispersed repeats in the moss Physcomitrella patens. In this study, we studied a newly identified P. patens homolog of bacterial RecG helicase, RECG, some of which is localized in both plastid and mitochondrial nucleoids. RECG partially complements recG deficiency in Escherichia coli cells. A knockout (KO) mutation of RECG caused characteristic phenotypes including growth delay and developmental and mitochondrial defects, which are similar to those of the RECA1 KO mutant. The RECG KO cells showed heterogeneity in these phenotypes. Analyses of RECG KO plants showed that mitochondrial genome was destabilized due to a recombination between 8-79 bp repeats and the pattern of the recombination partly differed from that observed in the RECA1 KO mutants. The mitochondrial DNA (mtDNA) instability was greater in severe phenotypic RECG KO cells than that in mild phenotypic ones. This result suggests that mitochondrial genomic instability is responsible for the defective phenotypes of RECG KO plants. Some of the induced recombination caused efficient genomic rearrangements in RECG KO mitochondria. Such loci were sometimes associated with a decrease in the levels of normal mtDNA and significant decrease in the number of transcripts derived from the loci. In addition, the RECG KO mutation caused remarkable plastid abnormalities and induced recombination between short repeats (12-63 bp) in the plastid DNA. These results suggest that RECG plays a role in the maintenance of both plastid and mitochondrial genome stability by suppressing aberrant recombination between dispersed short repeats; this role is crucial for plastid and mitochondrial functions.

Show MeSH
Related in: MedlinePlus