Population genomics of picophytoplankton unveils novel chromosome hypervariability.
Population genomics of picophytoplankton unveils novel chromosome hypervariability.
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DOI：
10.1126/sciadv.1700239
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发表时间：
2017-07
期刊：
影响因子：
13.6
通讯作者：
Piganeau G
中科院分区：
文献类型：
--
作者：
Blanc-Mathieu R;Krasovec M;Hebrard M;Yau S;Desgranges E;Martin J;Schackwitz W;Kuo A;Salin G;Donnadieu C;Desdevises Y;Sanchez-Ferandin S;Moreau H;Rivals E;Grigoriev IV;Grimsley N;Eyre-Walker A;Piganeau G
浮游真核植物形成了庞大的泛型种群，并进化出了原始的高变异性机制来抵抗病毒的攻击。形成微浮游生物（直径在0.3到3 μm之间）的微小光合微生物是许多海洋生态系统食物网的基础，它们对环境变化的适应性取决于持续的遗传变异。尽管对海洋细菌组成部分的基因组和表型多样性进行了深入研究，但对存在的每种真核生物物种的基因组和表型多样性知之甚少。我们报告了最小的光合真核生物——牛油Ostreococcus tauri（绿藻门，Mamiellophyceae）天然种群的基因组多样性水平。与克隆进化或隐种的预期相反，观察到的基因组多态性谱表明一个大的泛型种群（有效种群大小为1.2 × 107），普遍存在有性繁殖的证据。低覆盖率染色体的从头组装揭示了两个大的候选交配型位点，它们的重组受到抑制，其起源可能早于Mamiellophyceae类的物种形成事件。这种高遗传多样性与菌株之间的巨大表型差异有关。引人注目的是，分离物对自然环境中大量存在的大型双链DNA病毒的抗性与单个高变染色体的大小呈正相关，该染色体包含44至156 kb的菌株特异性序列。我们的发现强调了病毒在塑造海洋微真核生物基因组多样性中的作用。
Phytoplanktonic eukaryotes form huge panmictic populations and have evolved original hypervariability mechanisms to resist viral attack. Tiny photosynthetic microorganisms that form the picoplankton (between 0.3 and 3 μm in diameter) are at the base of the food web in many marine ecosystems, and their adaptability to environmental change hinges on standing genetic variation. Although the genomic and phenotypic diversity of the bacterial component of the oceans has been intensively studied, little is known about the genomic and phenotypic diversity within each of the diverse eukaryotic species present. We report the level of genomic diversity in a natural population of Ostreococcus tauri (Chlorophyta, Mamiellophyceae), the smallest photosynthetic eukaryote. Contrary to the expectations of clonal evolution or cryptic species, the spectrum of genomic polymorphism observed suggests a large panmictic population (an effective population size of 1.2 × 107) with pervasive evidence of sexual reproduction. De novo assemblies of low-coverage chromosomes reveal two large candidate mating-type loci with suppressed recombination, whose origin may pre-date the speciation events in the class Mamiellophyceae. This high genetic diversity is associated with large phenotypic differences between strains. Strikingly, resistance of isolates to large double-stranded DNA viruses, which abound in their natural environment, is positively correlated with the size of a single hypervariable chromosome, which contains 44 to 156 kb of strain-specific sequences. Our findings highlight the role of viruses in shaping genome diversity in marine picoeukaryotes.