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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.

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Cell growth and morphology of RECG KO plants.A. Colonies of wild type (WT), RECG KO (recG-2) or RECA1 KO plants cultivated on agar medium for four weeks. B. Protonemal cells. Bars = 5 mm in (A) and 50 μm in (B). Atrophic protonemal cells (S3 Fig.) are shown as RECG KO cells.
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pgen.1005080.g003: Cell growth and morphology of RECG KO plants.A. Colonies of wild type (WT), RECG KO (recG-2) or RECA1 KO plants cultivated on agar medium for four weeks. B. Protonemal cells. Bars = 5 mm in (A) and 50 μm in (B). Atrophic protonemal cells (S3 Fig.) are shown as RECG KO cells.

Mentions: Efficient targeting of nuclear genes [28] and a sequenced nuclear genome [24] enable easy knock-out of nuclear genes in P. patens. Thus, we knocked out the RECG gene to analyze the in vivo role of RECG (S2 Fig.). To investigate the effect of RECG KO on the growth and development of P. patens, we compared the RECG KO lines (named recG-1 and recG-2) with wild type (WT). After inoculation on agar medium, we observed that P. patens initially formed colonies composed of filamentous protonemal cells, and gametophores subsequently developed in the colonies. The RECG KO colonies appeared small and had less developed gametophores, which indicates defects in growth and development, although the extent of the defects were milder than those of the RECA1 KO strain (Fig. 3A). The RECG KO colonies consisted of protonemal cells with heterogeneity in growth; relatively normal (recG-N) and atrophic (recG-A) protonemal cells. The recG-A protonemal cells were shorter and darker than the recG-N protonemal cells, while the recG-A cells are still shorter and darker than the WT (S3A Fig.). The atrophic protonemal cells of the RECG KO colonies were shorter than those of WT and were dense with plastids, likely due to a reduction in cell volume. Notably, the morphological abnormalities of the RECG KO and RECA1 KO colonies were similar (Fig. 3B). These morphological effects imply that RECG plays an important role in the growth and development of P. patens, and suggest that RECG and RECA1 share similar roles.


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)

Cell growth and morphology of RECG KO plants.A. Colonies of wild type (WT), RECG KO (recG-2) or RECA1 KO plants cultivated on agar medium for four weeks. B. Protonemal cells. Bars = 5 mm in (A) and 50 μm in (B). Atrophic protonemal cells (S3 Fig.) are shown as RECG KO cells.
© Copyright Policy
Related In: Results  -  Collection

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

pgen.1005080.g003: Cell growth and morphology of RECG KO plants.A. Colonies of wild type (WT), RECG KO (recG-2) or RECA1 KO plants cultivated on agar medium for four weeks. B. Protonemal cells. Bars = 5 mm in (A) and 50 μm in (B). Atrophic protonemal cells (S3 Fig.) are shown as RECG KO cells.
Mentions: Efficient targeting of nuclear genes [28] and a sequenced nuclear genome [24] enable easy knock-out of nuclear genes in P. patens. Thus, we knocked out the RECG gene to analyze the in vivo role of RECG (S2 Fig.). To investigate the effect of RECG KO on the growth and development of P. patens, we compared the RECG KO lines (named recG-1 and recG-2) with wild type (WT). After inoculation on agar medium, we observed that P. patens initially formed colonies composed of filamentous protonemal cells, and gametophores subsequently developed in the colonies. The RECG KO colonies appeared small and had less developed gametophores, which indicates defects in growth and development, although the extent of the defects were milder than those of the RECA1 KO strain (Fig. 3A). The RECG KO colonies consisted of protonemal cells with heterogeneity in growth; relatively normal (recG-N) and atrophic (recG-A) protonemal cells. The recG-A protonemal cells were shorter and darker than the recG-N protonemal cells, while the recG-A cells are still shorter and darker than the WT (S3A Fig.). The atrophic protonemal cells of the RECG KO colonies were shorter than those of WT and were dense with plastids, likely due to a reduction in cell volume. Notably, the morphological abnormalities of the RECG KO and RECA1 KO colonies were similar (Fig. 3B). These morphological effects imply that RECG plays an important role in the growth and development of P. patens, and suggest that RECG and RECA1 share similar roles.

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