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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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Status of organelle DNA in recG-N and recG-A cells.Relative copy number of DNA resulting from recombination between mitochondrial short repeats (ccmF-atp9, nad7-nad9, mtR5, mtR12, mtR13, and mtIR; A) per mitochondrial rpl2 and plastidic short repeats (ptIR-1 and ptDR-1; B) per plastid ndhH in cells mainly comoposed of recG-N or recG-A cells were measured by qPCR using three independent RECG KO lines. WT was given a value of 1. The data represent mean of three replicates ± SD. *p<0.05, **p<0.01.
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pgen.1005080.g009: Status of organelle DNA in recG-N and recG-A cells.Relative copy number of DNA resulting from recombination between mitochondrial short repeats (ccmF-atp9, nad7-nad9, mtR5, mtR12, mtR13, and mtIR; A) per mitochondrial rpl2 and plastidic short repeats (ptIR-1 and ptDR-1; B) per plastid ndhH in cells mainly comoposed of recG-N or recG-A cells were measured by qPCR using three independent RECG KO lines. WT was given a value of 1. The data represent mean of three replicates ± SD. *p<0.05, **p<0.01.

Mentions: To investigate the relationship between the heterogeneity of atrophic phenotype of RECG KO plants appearing as recG-A and recG-N cells (S3A Fig.) and the stability of plastid and mitochondrial genomes, we compared the status of organelle DNA in recG-A and recG-N cells. We separately extracted total genomic DNA from protonemal cells mainly composed of recG-A cells or recG-N cells and measured the amount of mtDNA and ptDNA resulting from recombination between short repeats, using qPCR as described above (Fig. 6C and 8C). qPCR analyses of mtDNA showed that the number of the DNA molecules resulting from recombination between most of the tested repeats was higher in recG-A cells than that in recG-N cells. The levels of these recombination products in recG-N cells were still higher than those in WT cells (Fig. 9A). The levels of recombination product from ccmF-atp9 repeats (originally identified as repeats involved in the mtDNA instability, Fig. 5A) and R12 significantly increased in recG-A cells (Fig. 9A). However, the qPCR analysis of ptDNA showed no significant difference between the amounts of ptIR-1 or ptDR-1 recombination products in recG-A and recG-N cells (Fig. 9B).


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)

Status of organelle DNA in recG-N and recG-A cells.Relative copy number of DNA resulting from recombination between mitochondrial short repeats (ccmF-atp9, nad7-nad9, mtR5, mtR12, mtR13, and mtIR; A) per mitochondrial rpl2 and plastidic short repeats (ptIR-1 and ptDR-1; B) per plastid ndhH in cells mainly comoposed of recG-N or recG-A cells were measured by qPCR using three independent RECG KO lines. WT was given a value of 1. The data represent mean of three replicates ± SD. *p<0.05, **p<0.01.
© Copyright Policy
Related In: Results  -  Collection

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

pgen.1005080.g009: Status of organelle DNA in recG-N and recG-A cells.Relative copy number of DNA resulting from recombination between mitochondrial short repeats (ccmF-atp9, nad7-nad9, mtR5, mtR12, mtR13, and mtIR; A) per mitochondrial rpl2 and plastidic short repeats (ptIR-1 and ptDR-1; B) per plastid ndhH in cells mainly comoposed of recG-N or recG-A cells were measured by qPCR using three independent RECG KO lines. WT was given a value of 1. The data represent mean of three replicates ± SD. *p<0.05, **p<0.01.
Mentions: To investigate the relationship between the heterogeneity of atrophic phenotype of RECG KO plants appearing as recG-A and recG-N cells (S3A Fig.) and the stability of plastid and mitochondrial genomes, we compared the status of organelle DNA in recG-A and recG-N cells. We separately extracted total genomic DNA from protonemal cells mainly composed of recG-A cells or recG-N cells and measured the amount of mtDNA and ptDNA resulting from recombination between short repeats, using qPCR as described above (Fig. 6C and 8C). qPCR analyses of mtDNA showed that the number of the DNA molecules resulting from recombination between most of the tested repeats was higher in recG-A cells than that in recG-N cells. The levels of these recombination products in recG-N cells were still higher than those in WT cells (Fig. 9A). The levels of recombination product from ccmF-atp9 repeats (originally identified as repeats involved in the mtDNA instability, Fig. 5A) and R12 significantly increased in recG-A cells (Fig. 9A). However, the qPCR analysis of ptDNA showed no significant difference between the amounts of ptIR-1 or ptDR-1 recombination products in recG-A and recG-N cells (Fig. 9B).

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