Institut für Biologie, Humboldt-Universität, Chausseestraße 117, D-10115 Berlin, Germany.
Plant J. 2010 Dec;64(6):948-59. doi: 10.1111/j.1365-313X.2010.04389.x. Epub 2010 Nov 4.
Plant mitochondrial genomes are split into sub-genomes, i.e. genes are distributed across various sub-genomic molecules. To investigate whether copy numbers vary between individual mitochondrial genes, we used quantitative real-time PCR in combination with flow cytometric determination of nuclear DNA quantities to determine absolute per-cell-copy numbers of four mitochondrial genes in various Arabidopsis organs and the leaves of tobacco (Nicotiana tabacum) and barley (Hordeum vulgare). The copy numbers of the investigated mitochondrial genes (atp1, rps4, nad6 and cox1) not only differed from each other, but also varied between organs and changed during the development of cotyledons and leaves in Arabidopsis. We found no correlation between altered gene copy numbers, transcript levels and O(2) consumption. However, per cell, both the number of mitochondria and the number of gene copies increased with growing cell size. Gene copy numbers varied from approximately 40 (cox1 in young leaves) to approximately 280 (atp1 in mature leaves), and the mean number of mitochondria was approximately 300 in young leaves and 450 in mature leaves. Thus, cells are polyploid with respect to their mitochondrial genomes, but individual mitochondria may contain only part of the genome or even no DNA at all. Our data supports structural models of the mitochondrial genome in non-dividing cells of angiosperms that predict localization of the genes on sub-genomic molecules rather than master chromosomes. The data indicate control of the number of individual genes according to the genotype and developmental program(s) via amplification and/or degradation of sub-genomic molecules.
植物线粒体基因组分为亚基因组，即基因分布在各种亚基因组分子上。为了研究个体线粒体基因的拷贝数是否存在差异，我们使用实时定量 PCR 结合核 DNA 数量的流式细胞术测定，来确定拟南芥不同器官以及烟草（Nicotiana tabacum）和大麦（Hordeum vulgare）叶片中四个线粒体基因的每个细胞的绝对拷贝数。所研究的线粒体基因（atp1、rps4、nad6 和 cox1）的拷贝数不仅彼此不同，而且在器官之间也存在差异，并在拟南芥子叶和叶片的发育过程中发生变化。我们没有发现基因拷贝数变化、转录水平和 O(2)消耗之间存在相关性。然而，每个细胞中，线粒体的数量和基因拷贝数都随着细胞大小的增加而增加。基因拷贝数从大约 40（幼叶中的 cox1）到大约 280（成熟叶中的 atp1）不等，幼叶中平均有大约 300 个线粒体，而成熟叶中有大约 450 个线粒体。因此，细胞的线粒体基因组是多倍体的，但单个线粒体可能只包含基因组的一部分，甚至没有 DNA。我们的数据支持了被子植物非分裂细胞中线粒体基因组的结构模型，该模型预测基因位于亚基因组分子上，而不是主染色体上。这些数据表明，通过亚基因组分子的扩增和/或降解，根据基因型和发育程序控制个体基因的数量。
