進(jìn)化生物學(xué)研究面臨的一個最大挑戰(zhàn)就是破譯復(fù)雜結(jié)構(gòu)的起源,。如今,，科學(xué)家終于揭開了細(xì)菌鞭毛——一種像尾巴一樣的微小結(jié)構(gòu)，用于游水以及侵入宿主——進(jìn)化的步驟,。一項(xiàng)新的研究表明,，鞭毛是細(xì)菌祖先的一個特定基因連續(xù)復(fù)制的結(jié)果。這一發(fā)現(xiàn)不但回答了關(guān)于復(fù)雜結(jié)構(gòu)進(jìn)化的一個重要問題,，同時為對付進(jìn)化論反對者的對立觀點(diǎn)提供了新的“彈藥”,。
大約有50多個基因與鞭毛的構(gòu)造及功能有關(guān)。對于鞭毛起源,，科學(xué)家曾提出多種假設(shè),，但是沒有一種理論能夠在遺傳水平上對這種細(xì)胞器官如何出現(xiàn)給出充分的說明。為了搞清這一問題,，美國圖森市亞利桑那大學(xué)的進(jìn)化生物學(xué)家Howard Ochman與博士后Renyi Liu在獲取了41種生有鞭毛的細(xì)菌的全部基因組后,，對所有微生物中與鞭毛相關(guān)的24種基因進(jìn)行了研究。
在每一種細(xì)菌中,，這24種基因彼此都非常類似,，但是它們與基因組中的其他基因卻沒有相同之處?？紤]到這些基因均存在于所有長鞭毛的細(xì)菌中,，Ochman認(rèn)為，該發(fā)現(xiàn)意味著這一系列基因源于這些細(xì)菌共有祖先的一個特定基因的復(fù)制,?；虻募?xì)微變化會產(chǎn)生新的功能。每個基因都與一個不同的形態(tài)特征有關(guān),，例如產(chǎn)生蛋白質(zhì)從而形成鞭毛的運(yùn)動神經(jīng),、絲狀體和其他結(jié)構(gòu)成分。此外,，研究人員創(chuàng)建的一棵進(jìn)化樹表明,，這些基因出現(xiàn)的位置與鞭毛演化步驟的順序相互一致。Ochman和Liu最近在美國《國家科學(xué)院院刊》網(wǎng)絡(luò)版上報告了這一研究成果,。
布盧明頓市印第安納大學(xué)的進(jìn)化生物學(xué)家Michael Lynch表示,，這一發(fā)現(xiàn)突出了生物進(jìn)化的幾個重要原則。他說：“復(fù)雜結(jié)構(gòu)是建立在簡單結(jié)構(gòu)基礎(chǔ)之上的,，而這項(xiàng)研究成果正是上述理論的最好證明,。”布朗大學(xué)的細(xì)胞生物學(xué)家Ken Miller同時指出，對于那些“智能設(shè)計”的支持者而言,，這項(xiàng)研究提供了一個有力的反例,，表明鞭毛能夠從一個簡單基因進(jìn)化而來,。Miller說：“通過在許多生有鞭毛細(xì)菌的共同祖先中驗(yàn)證這一假設(shè)，研究人員清楚地證明了這些基因源自另一個基因的復(fù)制過程,。”
原始出處:
Published online before print April 16, 2007, 10.1073/pnas.0700266104
PNAS | April 24, 2007 | vol. 104 | no. 17 | 7116-7121
OPEN ACCESS ARTICLE
Stepwise formation of the bacterial flagellar system
Renyi Liu*, and Howard Ochman*,,
Departments of *Biochemistry and Molecular Biophysics and Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721
Edited by Francisco J. Ayala, University of California, Irvine, CA, and approved March 8, 2007 (received for review January 11, 2007)
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.
bacterial evolution | biological complexity | gene duplication
