Department of Biological Science, Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan.
PLoS One. 2013 Sep 13;8(9):e74590. doi: 10.1371/journal.pone.0074590. eCollection 2013.
With the rapid accumulation of genomic information from various eukaryotes in the last decade, genes proposed to have been derived from recent horizontal gene transfer (HGT) events have been reported even in non-phagotrophic unicellular and multicellular organisms, but the molecular pathways underlying HGT remain to be explained. The development of in vitro HGT detection systems, which permit the molecular and genetic analyses of donor and recipient organisms and quantify HGT, are helpful in order to gain insight into mechanisms that may contribute to contemporary HGT events or may have contributed to past HGT events. We applied a horizontal DNA transfer system model based on conjugal gene transfer called trans-kingdom conjugation (TKC) from the prokaryote Escherichia coli to the eukaryote Saccharomyces cerevisiae, and assessed whether and to what extent genetic variations in the eukaryotic recipient affect its receptivity to TKC. Strains from a collection of 4,823 knock-out mutants of S. cerevisiae MAT-α haploids were tested for their individual TKC receptivity. Two types of mutants, an ssd1 mutant and respiratory mutants, which are also found in experimental strains and in nature widely, were identified as highly receptive mutants. The TKC efficiency for spontaneously accrued petite (rho (-/0)) mutants of the functional allele (SSD1-V) strain showed increased receptivity. The TKC efficiency of the ssd1Δ mutant was 36% for bacterial conjugation, while that of the petite/ssd1Δ double mutants was even higher (220% in average) compared to bacterial conjugation. This increased TKC receptivity was also observed when other conjugal transfer systems were applied and the donor bacterium was changed to Agrobacterium tumefaciens. These results support the idea that the genomes of certain eukaryotes have been exposed to exogenous DNA more frequently and continuously than previously thought.
在过去十年中，随着各种真核生物的基因组信息的快速积累，即使在非吞噬性单细胞和多细胞生物中，也报告了那些被认为是最近水平基因转移（HGT）事件产生的基因，但 HGT 的分子途径仍有待解释。体外 HGT 检测系统的发展有助于解释 HGT，这些系统允许对供体和受体生物进行分子和遗传分析，并量化 HGT。我们应用了一种基于原核生物大肠杆菌的称为跨王国共轭（TKC）的体外 HGT 检测系统模型，并评估了真核受体中的遗传变异是否以及在何种程度上影响其对 TKC 的接受能力。从酿酒酵母 MAT-α 单倍体的 4823 个敲除突变体中选择了 4823 个菌株，用于测试其个体 TKC 接受能力。两种类型的突变体，即 ssd1 突变体和呼吸突变体，也在实验菌株和自然界中广泛存在，被鉴定为高度接受突变体。功能等位基因（SSD1-V）菌株自发产生的 petite（rho (-/0)）突变体的 TKC 效率显示出更高的接受能力。ssd1Δ 突变体的 TKC 效率为细菌共轭的 36%，而 petite/ssd1Δ 双突变体的 TKC 效率甚至更高（平均为 220%），与细菌共轭相比。当应用其他共轭转移系统并将供体细菌改为根癌农杆菌时，也观察到这种增加的 TKC 接受能力。这些结果支持了这样一种观点，即某些真核生物的基因组比以前认为的更频繁和持续地暴露于外源性 DNA。
