Горизонтальный перенос генов и его роль в эволюции

Рефераты статей

Lateral gene transfers and the evolution of eukaryotes: theories and data.

Katz LA.

Int J Syst Evol Microbiol 2002 Sep;52(Pt 5):1893-900

Vertical transmission of heritable material, a cornerstone of the Darwinian theory of evolution, is inadequate to describe the evolution of eukaryotes, particularly microbial eukaryotes. This is because eukaryotic cells and eukaryotic genomes are chimeric, having evolved through a combination of vertical (parent to offspring) and lateral (trans-species) transmission. Observations on widespread chimerism in eukaryotes have led to new and revised hypothesis for the origin and diversification of eukaryotes that provide specific predictions on the tempo (early vs continuous transfers) and mode (nature of donor and recipient lineages) of lateral gene transfers (LGTs). Analyses of available data indicate that LGTs in eukaryotes largely fall into two categories: (1) LGTs from organelles to the nucleus, only a few of which appear to have occurred at the time of the origin of eukaryotes, and (2) anomalous LGTs involving diverse donor and recipient lineages. Further testing of hypotheses on the origin and diversification of eukaryotes will require complete genome sequences from a number of diverse eukaryotes and prokaryotes combined with sequences of targeted genes from a broad phylogenetic sample.

PMID: 12361302

возможно, образование ядра и особой сложной системы регуляции генома было обусловлено становлением симбиоза (анаэробная клетка с аэробными симбионтами). Нужно ведь было теперь регулировать не 1, а 2 разных генома, чтобы они работали слаженно! Кардинально облегчить задачу впоследствии помог переход бол-ства митохондриальных генов в ядро, где они могли более эффективно регулироваться.

Microbial gene transfer: an ecological perspective.

Paul JH.

J Mol Microbiol Biotechnol 1999 Aug;1(1):45-50

Department of Marine Science, University of South Florida, St. Petersburg 33701, USA. jpaul@seas.marine.usf.edu

Microbial gene transfer or microbial sex is a means of exchanging loci amongst prokaryotes and certain eukaryotes. Historically viewed as a laboratory artifact, recent evidence from natural populations as well as genome research has indicated that this process may be a major driving force in microbial evolution. Studies with natural populations have taken two approaches- either adding a defined donor with a traceable gene to an indigenous community, and detecting the target gene in the indigenous bacteria, or by adding a model recipient to capture genes being transferred from the ambient microbial flora. However, both approaches usually require some cultivation of the recipient, which may result in a dramatic underestimation of the ambient transfer frequency. Novel methods are just evolving to study in situ gene transfer processes, including the use of green fluorescent protein (GFP)-marked plasmids, which enable detection of transferrants by epifluorescence microscopy. A transduction-like mechanism of transfer from viral-like particles produced by marine bacteria and thermal spring bacteria to Escherichia coil has been documented recently, indicating that broad host range transduction may be occurring in aquatic environments. The sequencing of complete microbial genomes has shown that they are a mosaic of ancestral chromosomal genes interspersed with recently transferred operons that encode peripheral functions. Archaeal genomes indicate that the genes for replication, transcription, and translation are all eukaryotic in complexity, while the genes for intermediary metabolism are purely bacterial. And in eukaryotes, many ancestral eukaryotic genes have been replaced by bacterial genes believed derived from food sources. Collectively these results indicate that microbial sex can result in the dispersal of loci in contemporary microbial populations as well as having shaped the phylogenies of microbes from multiple, very early gene transfer events.

PMID: 10941783

Evolution of cyanobacteria by exchange of genetic material among phyletically related strains.

Rudi K, Skulberg OM, Jakobsen KS.

J Bacteriol 1998 Jul;180(13):3453-61

Department of Biology, University of Oslo, Norway. knut.rudi@bio.uio.no

The cyanobacterial radiation consists of several lineages of phyletically (morphologically and genetically) related organisms. Several of these organisms show a striking resemblance to fossil counterparts. To investigate the molecular mechanisms responsible for stabilizing or homogenizing cyanobacterial characters, we compared the evolutionary rates and phylogenetic origins of the small-subunit rRNA-encoding DNA (16S rDNA), the conserved gene rbcL (encoding D-ribulose 1,5-bisphosphate carboxylase-oxygenase large subunit), and the less conserved gene rbcX. This survey includes four categories of phyletically related organisms: 16 strains of Microcystis, 6 strains of Tychonema, 10 strains of Planktothrix, and 12 strains of Nostoc. Both rbcL and rbcX can be regarded as neutrally evolving genes, with 95 to 100% and 50 to 80% synonymous nucleotide substitutions, respectively. There is generally low sequence divergence within the Microcystis, Tychonema, and Planktothrix categories both for rbcLX and 16S rDNA. The Nostoc category, on the other hand, consists of three genetically clustered lineages for these loci. The 16S rDNA and rbcLX phylogenies are not congruent for strains within the clustered groups. Furthermore, analysis of the phyletic structure for rbcLX indicates recombinational events between the informative sites within this locus. Thus, our results are best explained by a model involving both intergenic and intragenic recombinations. This evolutionary model explains the DNA sequence clustering for the modern species as a result of sequence homogenization (concerted evolution) caused by exchange of genetic material for neutrally evolving genes. The morphological clustering, on the other hand, is explained by structural and functional stability of these characters. We also suggest that exchange of genetic material for neutrally evolving genes may explain the apparent stability of cyanobacterial morphological characters, perhaps over billions of years.

PMID: 9642201

Важнейшая мысль: описана эволюция прокариот с постоянно идущим горизонтальным переносом генов и из-за этого эволюция идет очень медленно ("стабильность морфологических признаков"). Дискретность морфологического разнообразия объясняется структурной и ФУНКЦИОНАЛЬНОЙ стабильностью признаков. Т.е. дискретностью ниш, а вовсе не эндогамных биосистем – видов или популяций.

* Еще о большой роли горизонтального переноса генов в эволюции эукариот. Особенно – у одноклеточных эукариот много следов такого переноса. Например у анаэробных амитохондриальных эукариот (паразитических) – гены для брожения и т.п. взяты у прокариот. У высших многоклеточных таких фактов меньше. Дополнительные рефераты статей:

1. 12546782

2. 12455953

3. 11693658

4. 9724962