Low Nucleotide Diversity for the Expanded Organelle and Nuclear Genomes of Volvox carteri Supports the Mutational-Hazard Hypothesis
Low Nucleotide Diversity for the Expanded Organelle and Nuclear Genomes of Volvox carteri Supports the Mutational-Hazard Hypothesis
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DOI：
10.1093/molbev/msq110
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发表时间：
2010-10-01
影响因子：
10.7
通讯作者：
Lee, Robert W.
中科院分区：
文献类型：
--
作者：
Smith, David Roy;Lee, Robert W.
细胞器和核基因组的非编码DNA含量可以有很大的差异。对于这种变异，人们提出了适应性和非适应性两种解释。这项研究提出了一种称为突变危险假说的非适应性解释，并将其应用于多细胞绿藻Volvox carteri的线粒体、叶绿体和核基因组。考虑到卡特氏弧菌细胞器和核基因组的扩展结构(60%-85%非编码DNA)，突变危险假说将预测它们比其他真核生物中更紧凑的对应物种具有更少的沉默位点核苷酸多样性(pi(Silent))-最终反映2N(G)Mu的差异(群体中每个座位有效基因数量的两倍乘以突变率)。这里提供的数据支持这一预测：对7个卡氏弧菌地理分离物的线粒体、叶绿体和核DNA的分析显示，pi值较低(分别为0.00038、0.00065和0.00528)，远低于先前观察到的更紧密的细胞器和核DNA的值(与卡氏弧菌的近亲)。我们的结论是，卡特氏弧菌基因组中大量的非编码DNA含量可以很好地用突变危险假说来解释，并推测导致卡特氏弧菌的祖先从单细胞生命向多细胞生命的转变导致卡特氏弧菌种群规模较小，从而减少了2N(G)Mu。文中还给出了卡特氏弧菌完整的线粒体和叶绿体基因组图谱，并与莱茵弧菌进行了比较。
The noncoding-DNA content of organelle and nuclear genomes can vary immensely. Both adaptive and nonadaptive explanations for this variation have been proposed. This study addresses a nonadaptive explanation called the mutational-hazard hypothesis and applies it to the mitochondrial, plastid, and nuclear genomes of the multicellular green alga Volvox carteri. Given the expanded architecture of the V. carteri organelle and nuclear genomes (60-85% noncoding DNA), the mutational-hazard hypothesis would predict them to have less silent-site nucleotide diversity (pi(silent)) than their more compact counterparts from other eukaryotes-ultimately reflecting differences in 2N(g)mu (twice the effective number of genes per locus in the population times the mutation rate). The data presented here support this prediction: Analyses of mitochondrial, plastid, and nuclear DNAs from seven V. carteri forma nagariensis geographical isolates reveal low values of pi(silent) (0.00038, 0.00065, and 0.00528, respectively), much lower values than those previously observed for the more compact organelle and nuclear DNAs of Chlamydomonas reinhardtii (a close relative of V. carteri). We conclude that the large noncoding-DNA content of the V. carteri genomes is best explained by the mutational-hazard hypothesis and speculate that the shift from unicellular to multicellular life in the ancestor that gave rise to V. carteri contributed to a low V. carteri population size and thus a reduced 2N(g)mu. Complete mitochondrial and plastid genome maps for V. carteri are also presented and compared with those of C. reinhardtii.