title: A conserved, Mg²+-dependent exonuclease degrades organelle DNA during Arabidopsis pollen development.
abstract: In plant cells, mitochondria and plastids contain their own genomes derived from the ancestral bacteria endosymbiont. Despite their limited genetic capacity, these multicopy organelle genomes account for a substantial fraction of total cellular DNA, raising the question of whether organelle DNA quantity is controlled spatially or temporally. In this study, we genetically dissected the organelle DNA decrease in pollen, a phenomenon that appears to be common in most angiosperm species. By staining mature pollen grains with fluorescent DNA dye, we screened Arabidopsis thaliana for mutants in which extrachromosomal DNAs had accumulated. Such a recessive mutant, termed defective in pollen organelle DNA degradation1 (dpd1), showing elevated levels of DNAs in both plastids and mitochondria, was isolated and characterized. DPD1 encodes a protein belonging to the exonuclease family, whose homologs appear to be found in angiosperms. Indeed, DPD1 has Mg²⁺-dependent exonuclease activity when expressed as a fusion protein and when assayed in vitro and is highly active in developing pollen. Consistent with the dpd phenotype, DPD1 is dual-targeted to plastids and mitochondria. Therefore, we provide evidence of active organelle DNA degradation in the angiosperm male gametophyte, primarily independent of maternal inheritance; the biological function of organellar DNA degradation in pollen is currently unclear.
authors.affiliation: Institute of Plant Science and Resources, Okayama University, Kurashiki, Okayama 710-0046, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Matsushima
authors.forename: Lay Yin
authors.initials: LY
authors.lastname: Tang
authors.forename: Lingang
authors.initials: L
authors.lastname: Zhang
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamada
authors.forename: David
authors.initials: D
authors.lastname: Twell
authors.forename: Wataru
authors.initials: W
authors.lastname: Sakamoto
mesh_terms: D017360:Arabidopsis / Q000166:cytology / Q000201:enzymology* / Q000254:growth & development / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D017124:Conserved Sequence / Q000235:genetics; D018742:DNA, Chloroplast / Q000378:metabolism; D004272:DNA, Mitochondrial / Q000378:metabolism; D018744:DNA, Plant / Q000378:metabolism*; D005092:Exonucleases / Q000378:metabolism*; D005095:Exoribonucleases / Q000235:genetics / Q000378:metabolism*; D017343:Genes, Plant / Q000235:genetics; D005816:Genetic Complementation Test; D018525:Germination; D040582:Inheritance Patterns / Q000235:genetics; D008274:Magnesium / Q000378:metabolism*; D058503:Mesophyll Cells / Q000166:cytology / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D050505:Mutant Proteins / Q000302:isolation & purification; D009154:Mutation / Q000235:genetics; D009928:Organ Specificity; D015388:Organelles / Q000235:genetics*; D010641:Phenotype; D018087:Plastids / Q000378:metabolism; D011058:Pollen / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism / Q000648:ultrastructure; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012098:Reproduction
chemical_list: D029681:Arabidopsis Proteins; D018742:DNA, Chloroplast; D004272:DNA, Mitochondrial; D018744:DNA, Plant; D050505:Mutant Proteins; D011993:Recombinant Fusion Proteins; C561083:DPD1 protein, Arabidopsis; D005092:Exonucleases; D005095:Exoribonucleases; D008274:Magnesium