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1.
Among different species of eukaryotes, the extent and evolutionary significance of horizontal gene transfer remains poorly understood. A newly published study by Friesen and colleagues indicates that a recent gene transfer between two species of fungi has enabled the recipient to rapidly acquire high virulence on wheat. The study highlights a mechanism by which diseases can suddenly emerge, but also brings up the controversial issues of how horizontal gene transfer occurs and whether fungal incompatibility barriers to gene flow are more 'leaky' than was previously thought.  相似文献   

2.
The advantages and disadvantages of being polyploid   总被引:7,自引:0,他引:7  
Polyploids - organisms that have multiple sets of chromosomes - are common in certain plant and animal taxa, and can be surprisingly stable. The evidence that has emerged from genome analyses also indicates that many other eukaryotic genomes have a polyploid ancestry, suggesting that both humans and most other eukaryotes have either benefited from or endured polyploidy. Studies of polyploids soon after their formation have revealed genetic and epigenetic interactions between redundant genes. These interactions can be related to the phenotypes and evolutionary fates of polyploids. Here, I consider the advantages and challenges of polyploidy, and its evolutionary potential.  相似文献   

3.
4.
Introduced species, those dispersed outside their natural ranges by humans, now cause almost all biological invasions, i.e., entry of organisms into habitats with negative effects on organisms already there. Knowing whether introduction tends to give organisms specific ecological advantages or disadvantages in their new habitats could help understand and control invasions. Even if no specific species traits are associated with introduction, introduced species might out-compete native ones just because the pool of introduced species is very large (“global competition hypothesis”). Especially in the case of intentional introduction, high initial propagule pressure might further increase the chance of establishment, and repeated introductions from different source populations might increase the fitness of introduced species through hybridization. Intentional introduction screens species for usefulness to humans and so might select for rapid growth and reproduction or carry species to suitable habitats, all which could promote invasiveness. However, trade offs between growth and tolerance might make introduced species vulnerable to extreme climatic events and cause some invasions to be transient (“reckless invader hypothesis”). Unintentional introduction may screen for species associated with human-disturbed habitats, and human disturbance of their new habitats may make these species more invasive. Introduction and natural long-distance dispersal both imply that species have neither undergone adaptation in their new habitats nor been adapted to by other species there. These two characteristics are the basis for many well-known hypotheses about invasion, including the “biotic resistance”, “enemy release”, “evolution of increased competitive ability” and “novel weapon” hypotheses, each of which has been shown to help explain some invasions. To the extent that biotic resistance depends upon local adaption by native species, altering selection pressures could reduce resistance and promote invasion (“local adaptation hypothesis”), and restoring natural regimes could reverse this effect.  相似文献   

5.

Background  

We report on the probable horizontal transfer of a mitochondrial gene, cytb, between species of Neotropical bruchid beetles, in a zone where these species are sympatric.  相似文献   

6.
Davison J 《Nature biotechnology》2004,22(11):1349; author reply 1349-1349; author reply 1350
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7.
Monitoring and modeling horizontal gene transfer   总被引:1,自引:0,他引:1  
Monitoring efforts have failed to identify horizontal gene transfer (HGT) events occurring from transgenic plants into bacterial communities in soil or intestinal environments. The lack of such observations is frequently cited in biosafety literature and by regulatory risk assessment. Our analysis of the sensitivity of current monitoring efforts shows that studies to date have examined potential HGT events occurring in less than 2 g of sample material, when combined. Moreover, a population genetic model predicts that rare bacterial transformants acquiring transgenes require years of growth to out-compete wild-type bacteria. Time of sampling is there-fore crucial to the useful implementation of monitoring. A population genetic approach is advocated for elucidating the necessary sample sizes and times of sampling for monitoring HGT into large bacterial populations. Major changes in current monitoring approaches are needed, including explicit consideration of the population size of exposed bacteria, the bacterial generation time, the strength of selection acting on the transgene-carrying bacteria, and the sample size necessary to verify or falsify the HGT hypotheses tested.  相似文献   

8.
The interconnection between biofilm formation and horizontal gene transfer   总被引:1,自引:0,他引:1  
Recent research has revealed that horizontal gene transfer and biofilm formation are connected processes. Although published research investigating this interconnectedness is still limited, we will review this subject in order to highlight the potential of these observations because of their believed importance in the understanding of the adaptation and subsequent evolution of social traits in bacteria. Here, we discuss current evidence for such interconnectedness centred on plasmids. Horizontal transfer rates are typically higher in biofilm communities compared with those in planktonic states. Biofilms, furthermore, promote plasmid stability and may enhance the host range of mobile genetic elements that are transferred horizontally. Plasmids, on the other hand, are very well suited to promote the evolution of social traits such as biofilm formation. This, essentially, transpires because plasmids are independent replicons that enhance their own success by promoting inter-bacterial interactions. They typically also carry genes that heighten their hosts' direct fitness. Furthermore, current research shows that the so-called mafia traits encoded on mobile genetic elements can enforce bacteria to maintain stable social interactions. It also indicates that horizontal gene transfer ultimately enhances the relatedness of bacteria carrying the mobile genetic elements of the same origin. The perspective of this review extends to an overall interconnectedness between horizontal gene transfer, mobile genetic elements and social evolution of bacteria.  相似文献   

9.
中国米草生态工程的功与过   总被引:5,自引:0,他引:5  
米草生态工程在我国已经走过40年的发展历程,成为中国海岸线一道绿色长城.米草生态工程曾经发挥了显著的生态效益和经济效益,如保滩护堤、促淤造陆、改良盐土、净化水质等,同时也出现了一些负面作用,如绞杀土著物种、侵占航道、危害贝类养殖等.米草的种群爆发可能是因为富营养化、温室效应以及一些可能的人为因素.对待米草,应该科学分析与对待,在种群爆发地区进行科学防治的同时,还应充分发挥其生态与经济效益.  相似文献   

10.
In a horizontal gene transfer (HGT) event, a gene is transferred between two species that do not have an ancestor-descendant relationship. Typically, no more than a few genes are horizontally transferred between any two species. However, several studies identified pairs of species between which many different genes were horizontally transferred. Such a pair is said to be linked by a highway of gene sharing. We present a method for inferring such highways. Our method is based on the fact that the evolutionary histories of horizontally transferred genes disagree with the corresponding species phylogeny. Specifically, given a set of gene trees and a trusted rooted species tree, each gene tree is first decomposed into its constituent quartet trees and the quartets that are inconsistent with the species tree are identified. Our method finds a pair of species such that a highway between them explains the largest (normalized) fraction of inconsistent quartets. For a problem on n species and m input quartet trees, we give an efficient O(m + n(2))-time algorithm for detecting highways, which is optimal with respect to the quartets input size. An application of our method to a dataset of 1128 genes from 11 cyanobacterial species, as well as to simulated datasets, illustrates the efficacy of our method.  相似文献   

11.
Using a new template based on an alignment of 145 nonvertebrate globins we examined several recently determined sequences of putative globins and globin-like hemeproteins. We propose that all globins have evolved from a family of ancestral, approx. 17-kDa hemeproteins, which displayed the globin fold and functioned as redox proteins. Once atmospheric O2 became available the acquisition of oxygen-binding properties was initiated, culminating in the various highly specialized functions known as present. During this evolutionary process, we suggest that (1) high oxygen affinity may have been acquired repeatedly and (2) the formation of chimeric proteins containing both a globin and a flavin binding domain was an additional and distinct evolutionary trend. Furthermore, globin-like hemeproteins encompass hemeproteins produced through convergent evolution from nonglobin ancestral proteins to carry out O2-binding functions as well as hemeproteins whose sequences exhibit the loss of some or all of the structural determinants of the globin fold. We also propose that there occurred two cases of horizontal globin gene transfer, one from an ancestor common to the ciliates Paramecium and Tetrahymena and the green alga Chlamydomonas to a cyanobacterium ancestor and the other, from a eukaryote ancestor of the yeasts Saccharomyces and Candida to a bacterial ancestor of the proteobacterial genera Escherichia, Alcaligenes, and Vitreoscilla.   相似文献   

12.
A phylogenetic study of the isopenicillin-N-synthetase (IPNS) gene sequence from prokaryotic and lower eukaryotic producers of β-lactam antibiotics by means of a maximum-likelihood approach has been carried out. After performing an extensive search, rather than invoking a global molecular clock, the results obtained are best explained by a model with three rates of evolution. Grouped in decreasing order, these correspond toA. nidulans and then to the rest of the eukaryotes and prokaryotes, respectively. The estimated branching date between prokaryotic and fungal IPNS sequences (852 ±106 MY) strongly supports the hypothesis that the IPNS gene was horizontally transferred from bacterial β-lactam producers to filamentous fungi. Correspondence to: A. Moya  相似文献   

13.
The phylogenetic relationships of a collection of streptomycete soil isolates and type strains were resolved by sequence analysis of trpB,a housekeeping gene involved in tryptophan biosynthesis. The analysis confirmed that two isolates were recipients in a gene transfer event, demonstrated by phylogenetic incongruency between trpB and strB1 trees. One strain had acquired the entire streptomycin biosynthetic cluster, whilst the other contained only strRAB1, the resistance gene and two flanking genes from the cluster. Sequence analysis of trpB, as part of a polyphasic approach, was a useful tool in determining intra-generic relationships within the genus Streptomyces.  相似文献   

14.
The give-and-take of DNA: horizontal gene transfer in plants   总被引:1,自引:0,他引:1  
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15.
16.
Aeromonas species are common inhabitants of aquatic environments and relevant as human pathogens. Their potential as pathogens may be related in part to lateral transfer of genes associated with toxin production, biofilm formation, antibiotic resistance, and other virulence determinants. Natural transformation has not been characterized in aeromonads. DNA from wild-type, prototrophic strains that had been isolated from environmental sources was used as donor DNA in transformation assays with auxotrophs as the recipients. Competence was induced in 20% nutrient broth during the stationary phase of growth. Optimal transformation assay conditions for one chosen isolate were in Tris buffer with magnesium or calcium, pH 5–8, and a saturating concentration of 0.5 μg of DNA per assay (3.3 ng of DNA μl−1) at 30 °C. Sodium was also required and could not be replaced with ammonium, potassium, or lithium. The maximal transformation frequency observed was 1.95 × 10−3 transformants (recipient cell)−1. A survey of environmental Aeromonas auxotrophic recipients (n = 37), assayed with donor DNA from other wild-type environmental aeromonads under optimal assay conditions, demonstrated that 73% were able to act as recipients, and 100% were able to act as donors to at least some other aeromonads. Three different transformation groups were identified based on each isolates’ ability to transform other strains with its DNA. The transformation groups roughly corresponded to phylogenetic groups. These results demonstrate that natural transformation is a general property of Aeromonas environmental isolates with implications for the genetic structures of coincident Aeromonas populations.  相似文献   

17.
Sequencing of expressed genes has shown that nematodes, particularly the plant-parasitic nematodes, have genes purportedly acquired from other kingdoms by horizontal gene transfer. The prevailing orthodoxy is that such transfer has been a driving force in the evolution of niche specificity, and a recent paper in BMC Evolutionary Biology that presents a detailed phylogenetic analysis of cellulase genes in the free-living nematode Pristionchus pacificus at the species, genus and family levels substantiates this hypothesis.  相似文献   

18.
Determining the influence of horizontal gene transfer (HGT) on phylogenomic analyses and the retrieval of a tree of life is relevant for our understanding of microbial genome evolution. It is particularly difficult to differentiate between phylogenetic incongruence due to noise and that resulting from HGT. We have performed a large-scale, detailed evolutionary analysis of the different phylogenetic signals present in the genomes of Xanthomonadales, a group of Proteobacteria. We show that the presence of phylogenetic noise is not an obstacle to infer past and present HGTs during their evolution. The scenario derived from this analysis and other recently published reports reflect the confounding effects on bacterial phylogenomics of past and present HGT. Although transfers between closely related species are difficult to detect in genome-scale phylogenetic analyses, past transfers to the ancestor of extant groups appear as conflicting signals that occasionally might make impossible to determine the evolutionary origin of the whole genome.  相似文献   

19.
How much horizontal gene transfer (HGT) between species influences bacterial phylogenomics is a controversial issue. This debate, however, lacks any quantitative assessment of the impact of HGT on phylogenies and of the ability of tree-building methods to cope with such events. I introduce a Markov model of genome evolution with HGT, accounting for the constraints on time -- an HGT event can only occur between concomitantly living species. This model is used to simulate multigene sequence data sets with or without HGT. The consequences of HGT on phylogenomic inference are analyzed and compared to other well-known phylogenetic artefacts. It is found that supertree methods are quite robust to HGT, keeping high levels of performance even when gene trees are largely incongruent with each other. Gene tree incongruence per se is not indicative of HGT. HGT, however, removes the (otherwise observed) positive relationship between sequence length and gene tree congruence to the estimated species tree. Surprisingly, when applied to a bacterial and a eukaryotic multigene data set, this criterion rejects the HGT hypothesis for the former, but not the latter data set.  相似文献   

20.
We discuss the impact of horizontal gene transfer (HGT) on phylogenetic reconstruction and taxonomy. We review the power of HGT as a creative force in assembling new metabolic pathways, and we discuss the impact that HGT has on phylogenetic reconstruction. On one hand, shared derived characters are created through transferred genes that persist in the recipient lineage, either because they were adaptive in the recipient lineage or because they resulted in a functional replacement. On the other hand, taxonomic patterns in microbial phylogenies might also be created through biased gene transfer. The agreement between different molecular phylogenies has encouraged interpretation of the consensus signal as reflecting organismal history or as the tree of cell divisions; however, to date the extent to which the consensus reflects shared organismal ancestry and to which it reflects highways of gene sharing and biased gene transfer remains an open question. Preferential patterns of gene exchange act as a homogenizing force in creating and maintaining microbial groups, generating taxonomic patterns that are indistinguishable to those created by shared ancestry. To understand the evolution of higher bacterial taxonomic units, concepts usually applied in population genetics need to be applied.  相似文献   

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