Pleiotropic costs of niche expansion in the RNA bacteriophage Φ6
Pleiotropic costs of niche expansion in the RNA bacteriophage Φ6
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DOI：
10.1534/genetics.105.051136
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发表时间：
2006-02-01
期刊：
影响因子：
3.3
通讯作者：
Burch, CL
中科院分区：
文献类型：
--
作者：
Duffy, S;Turner, PE;Burch, CL
自然系统和实验系统都未能普遍证明通用性和专门性之间的权衡。当权衡确实发生时，如果不剖析适应的遗传基础，很难将其归因于拮抗多效性，而且以前很少有实验提供这些遗传数据。在这里，我们研究了RNA病毒Phi 6中扩展宿主范围（通用性）的进化，这是一个实验模型系统，可以很容易地识别适应性突变。我们从三种新型假单胞菌宿主中分离出10个自发宿主范围突变体，并确定这些突变是否会对标准实验室宿主施加适应性成本。测序显示，每个突变体在Phi 6基因P3上有9个非同义起始点之一，这在宿主附着中很重要。这9个模仿中有7个在原始宿主上是昂贵的，证实了拮抗多效性的存在。除了这种遗传上强加的成本外，我们还发现了噬菌体在宿主类型之间转换时发生的通用性的表观遗传成本。我们的研究结果证实了Phi 6中存在两种通用性成本，遗传成本和环境成本，但它们也表明成本并不总是很大。无成本的生态位扩展的可能性意味着不同的生态条件可能有利于RNA病毒的宿主转移。
Natural and experimental systems have failed to universally demonstrate a trade-off between generalism and specialism. When a trade-off does occur it is difficult to attribute its cause to antagonistic pleiotropy without dissecting the genetic basis of adaptation, and few previous experiments provide these genetic data. Here we investigate the evolution of expanded host range (generalism) in the RNA virus Phi 6, an experimental model system allowing adaptive mutations to be readily identified. We isolated 10 spontaneous host range mutants on each of three novel Pseudomonas hosts and determined whether these mutations imposed fitness costs on the standard laboratory host. Sequencing revealed that each mutant had one of nine nonsynonymous initiations in the Phi 6 gene P3, important in host attachment. Seven of these nine imitations were costly on the original host, confirming the existence of antagonistic pleiotropy. In addition to this genetically imposed cost, we identified an epigenetic cost of generalism that occurs when phage transition between host types. Our results confirm the existence in Phi 6 of two costs of generalism, genetic and environmental, but they also indicate that the cost is not always large. The possibility for cost-free niche expansion implies that varied ecological conditions may favor host shifts in RNA viruses.