Liu Renyi, Ochman Howard
Department of Biochemistry and Molecular Biophysics, University of Arizona, Tucson, AZ 85721, USA.
Proc Natl Acad Sci U S A. 2007 Apr 24;104(17):7116-21. doi: 10.1073/pnas.0700266104. Epub 2007 Apr 16.
Elucidating the origins of complex biological structures has been one of the major challenges of evolutionary studies. The bacterial flagellum is a primary example of a complex apparatus whose origins and evolutionary history have proven difficult to reconstruct. The gene clusters encoding the components of the flagellum can include >50 genes, but these clusters vary greatly in their numbers and contents among bacterial phyla. To investigate how this diversity arose, we identified all homologs of all flagellar proteins encoded in the complete genome sequences of 41 flagellated species from 11 bacterial phyla. Based on the phylogenetic occurrence and histories of each of these proteins, we could distinguish an ancient core set of 24 structural genes that were present in the common ancestor to all Bacteria. Within a genome, many of these core genes show sequence similarity only to other flagellar core genes, indicating that they were derived from one another, and the relationships among these genes suggest the probable order in which the structural components of the bacterial flagellum arose. These results show that core components of the bacterial flagellum originated through the successive duplication and modification of a few, or perhaps even a single, precursor gene.
阐明复杂生物结构的起源一直是进化研究的主要挑战之一。细菌鞭毛是一种复杂结构的主要例子，其起源和进化历史已被证明难以重建。编码鞭毛组件的基因簇可以包含超过50个基因，但这些基因簇在细菌门类中的数量和内容差异很大。为了研究这种多样性是如何产生的，我们在来自11个细菌门类的41种有鞭毛物种的完整基因组序列中鉴定了所有鞭毛蛋白的同源物。基于这些蛋白质中每一种的系统发生出现情况和历史，我们能够区分出24个结构基因的古老核心集，这些基因存在于所有细菌的共同祖先中。在一个基因组内，许多这些核心基因仅与其他鞭毛核心基因显示序列相似性，这表明它们是彼此衍生而来的，并且这些基因之间的关系表明了细菌鞭毛结构组件出现的可能顺序。这些结果表明，细菌鞭毛的核心组件起源于少数几个甚至可能是单个前体基因的连续复制和修饰。
