Zaegel Vincent, Guermann Benoît, Le Ret Monique, Andrés Charles, Meyer Denise, Erhardt Mathieu, Canaday Jean, Gualberto José M, Imbault Patrice
Institut de Biologie Moléculaire des Plantes, Centre National de la Recherche Scientifique, Université Louis Pasteur, 67000 Strasbourg, France.
Plant Cell. 2006 Dec;18(12):3548-63. doi: 10.1105/tpc.106.042028. Epub 2006 Dec 22.
Plant mitochondrial genomes exist in a natural state of heteroplasmy, in which substoichiometric levels of alternative mitochondrial DNA (mtDNA) molecules coexist with the main genome. These subgenomes either replicate autonomously or are created by infrequent recombination events. We found that Arabidopsis thaliana OSB1 (for Organellar Single-stranded DNA Binding protein1) is required for correct stoichiometric mtDNA transmission. OSB1 is part of a family of plant-specific DNA binding proteins that are characterized by a novel motif that is required for single-stranded DNA binding. The OSB1 protein is targeted to mitochondria, and promoter-beta-glucuronidase fusion showed that the gene is expressed in budding lateral roots, mature pollen, and the embryo sac of unfertilized ovules. OSB1 T-DNA insertion mutants accumulate mtDNA homologous recombination products and develop phenotypes of leaf variegation and distortion. The mtDNA rearrangements occur in two steps: first, homozygous mutants accumulate subgenomic levels of homologous recombination products; second, in subsequent generations, one of the recombination products becomes predominant. After the second step, the process is no longer reversible by backcrossing. Thus, OSB1 participates in controlling the stoichiometry of alternative mtDNA forms generated by recombination. This regulation could take place in gametophytic tissues to ensure the transmission of a functional mitochondrial genome.
植物线粒体基因组以异质性的自然状态存在，其中亚化学计量水平的替代性线粒体DNA（mtDNA）分子与主要基因组共存。这些亚基因组要么自主复制，要么由罕见的重组事件产生。我们发现拟南芥OSB1（细胞器单链DNA结合蛋白1）对于正确的化学计量mtDNA传递是必需的。OSB1是植物特异性DNA结合蛋白家族的一员，其特征在于具有单链DNA结合所需的新型基序。OSB1蛋白定位于线粒体，启动子-β-葡萄糖醛酸酶融合表明该基因在侧根芽、成熟花粉和未受精胚珠的胚囊中表达。OSB1 T-DNA插入突变体积累mtDNA同源重组产物，并出现叶片斑驳和畸变的表型。mtDNA重排分两步发生：首先，纯合突变体积累亚基因组水平的同源重组产物；其次，在后代中，其中一种重组产物占主导地位。第二步之后，通过回交该过程不再可逆。因此，OSB1参与控制由重组产生的替代性mtDNA形式的化学计量。这种调节可能发生在配子体组织中，以确保功能性线粒体基因组的传递。
