Connections among Genotype, Phenotype and Fitness in Escherichia coli High Temperature Lines

提高对进化遗传适应过程的理解必须部分地依赖于更好地理解遗传变化如何与生物体结构和功能特征（表型）的变化联系在一起，从而提高生殖成功率（即适应性）。然而，基因型和表型之间的关系尚不清楚，限制了对进化过程的理解。这项由该奖项资助的工作将以前所未有的规模研究大肠杆菌基因型和表型之间的关系。通过人工选择实验，该细菌在100多个重复种群中适应了一年的热应激（42.2℃）。通过基因组测序，每个种群的一个克隆都被完全分型。这笔拨款将表征这些复制群体的表型，然后将这些表型明确地与已知的基因型联系起来。将被测量的表型包括基因表达模式和细胞代谢特征。特别令人感兴趣的将是通过转录终止基因rho或RNA聚合酶亚基基因rpoB突变适应的克隆之间的对比。这项工作将确定这些不同的遗传解决方案是否会导致表型上类似的功能变化，以及这两种适应途径是否互斥。为了解决后一个问题，将rho和rpoB突变引入到单一遗传背景中，并在高温下确定双突变体的进化适合度。通过描述与适应相关的表型变化和遗传相互作用，这项工作将影响进化理论的核心，包括关于适应过程的经典观点。此外，该项目还将继续开展一项成功的推广项目，向K-12教师介绍实验室模块，以大肠杆菌模型为基础，促进课堂上进化论的“动手”教学。

An improved understanding of the process of evolutionary genetic adaptation must rely in part on a better understanding of how genetic changes are linked to changes in structural and functional characteristics of organisms (phenotypes) that result in improved reproductive success (i.e., fitness). However, the relationship between genotype and phenotype is not well understood, limiting an understanding of the evolutionary process. The work funded by this award will investigate the relationship between genotype and phenotype on an unprecedented scale in the bacterium Escherichia coli. The bacterium has been adapted through artificial selection experiments to thermal stress (42.2 C) for one year in over 100 replicate populations. A clone from each population has been genotyped completely by genomic sequencing. This grant will characterize the phenotypes of these replicate populations and then relate these phenotypes explicitly to the known genotypes. The phenotypes that will be measured include patterns of gene expression and features of cell metabolism. Of particular interest will be a contrast between clones that adapted by mutations in either the transcriptional termination gene rho or the RNA polymerase subunit gene rpoB. The work will determine whether these different genetic solutions lead to similar functional changes in phenotypes and whether the two adaptive pathways are mutually exclusive. To address the latter issue, mutations of both rho and rpoB will be introduced into a single genetic background, and the evolutionary fitness of double mutants will be determined at high temperature. By characterizing both phenotypic changes and genetic interactions associated with adaptation, this work will impact the heart of evolutionary theory, including classical views on the adaptive process. In addition, this project will continue a successful outreach project that introduced K-12 teachers to lab modules that facilitate "hands on" teaching of evolution in the classroom, based on the E. coli model.