Riehle M M, Bennett A F, Long A D
Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697-2525, USA.
Proc Natl Acad Sci U S A. 2001 Jan 16;98(2):525-30. doi: 10.1073/pnas.98.2.525. Epub 2001 Jan 9.
Elucidating the genetic basis of adaptation on a genomewide scale has evaded biologists, but complete genome sequences and DNA high-density array technology make genomewide surveys more tractable. Six lines of Escherichia coli adapted for 2,000 generations to a stressful high temperature of 41.5 degrees C were examined on a genomewide scale for duplication/deletion events by using DNA high-density arrays. A total of five duplication and deletion events were detected. These five events occurred in three of the six lines, whereas the remaining three lines contained no detectable events. Three of the duplications were at 2.85 Mb of the E. coli chromosome, providing evidence for the replicability of the adaptation to high temperature. Four candidate genes previously shown to play roles in stress and starvation survival were identified in the region of common duplication. Expression of the two candidate genes examined is elevated over expression levels in the ancestral lines or the lines without the duplication. In the two cases where the duplication at 2.85 Mb has been further characterized, the timing of the genome reorganization is coincident with significant increases in relative fitness. In both of these cases, the model for the origin of the duplication is a complex recombination event involving insertion sequences and repeat sequences. These results provide additional evidence for the idea that gene duplication plays an integral role in adaptation, specifically as a means for gene amplification.
在全基因组范围内阐明适应的遗传基础一直是生物学家难以解决的问题，但完整的基因组序列和DNA高密度阵列技术使全基因组调查变得更易于处理。利用DNA高密度阵列，在全基因组范围内检测了6株适应41.5℃应激高温2000代的大肠杆菌株系中的重复/缺失事件。共检测到5个重复和缺失事件。这5个事件发生在6个株系中的3个株系中，而其余3个株系未检测到任何事件。其中3个重复发生在大肠杆菌染色体的2.85 Mb处，为适应高温的可重复性提供了证据。在共同重复区域鉴定出4个先前已证明在应激和饥饿存活中起作用的候选基因。所检测的两个候选基因的表达水平高于祖先株系或无重复株系中的表达水平。在对2.85 Mb处的重复进行进一步表征的两个案例中，基因组重组的时间与相对适应性的显著增加相吻合。在这两个案例中，重复起源的模型都是涉及插入序列和重复序列的复杂重组事件。这些结果为基因重复在适应过程中起不可或缺的作用这一观点提供了更多证据，特别是作为基因扩增的一种手段。
