Daphnia pulex is the first crustacean to have its genome sequenced. Availability of the genome sequence will have implications for research in aquatic ecology and evolution in particular, as addressed by a series of papers published recently in BMC Evolutionary Biology and BMC Genomics.
See research articles http://www.biomedcentral.com/1471-2148/9/78, http://www.biomedcentral.com/1471-2164/10/527, http://www.biomedcentral.com/1471-2148/9/79, http://www.biomedcentral.com/1471-2164/10/175, http://www.biomedcentral.com/1471-2164/10/172, http://www.biomedcentral.com/1471-2164/10/169, http://www.biomedcentral.com/1471-2164/10/170 and http://www.biomedcentral.com/1471-2148/9/243.
Double-stranded (ds) RNA fungal viruses are typically isometric single-shelled particles that are classified into three families, Totiviridae, Partitiviridae and Chrysoviridae, the members of which possess monopartite, bipartite and quadripartite genomes, respectively. Recent findings revealed that mycovirus-related dsRNA viruses are more diverse than previously recognized. Although an increasing number of viral complete genomic sequences have become available, the evolution of these diverse dsRNA viruses remains to be clarified. This is particularly so since there is little evidence for horizontal gene transfer (HGT) among dsRNA viruses.
In this study, we report the molecular properties of two novel dsRNA mycoviruses that were isolated from a field strain of Sclerotinia sclerotiorum, Sunf-M: one is a large monopartite virus representing a distinct evolutionary lineage of dsRNA viruses; the other is a new member of the family Partitiviridae. Comprehensive phylogenetic analysis and genome comparison revealed that there are at least ten monopartite, three bipartite, one tripartite and three quadripartite lineages in the known dsRNA mycoviruses and that the multipartite lineages have possibly evolved from different monopartite dsRNA viruses. Moreover, we found that homologs of the S7 Domain, characteristic of members of the genus phytoreovirus in family Reoviridae are widely distributed in diverse dsRNA viral lineages, including chrysoviruses, endornaviruses and some unclassified dsRNA mycoviruses. We further provided evidence that multiple HGT events may have occurred among these dsRNA viruses from different families.
Our study provides an insight into the phylogeny and evolution of mycovirus-related dsRNA viruses and reveals that the occurrence of HGT between different virus species and the development of multipartite genomes during evolution are important macroevolutionary mechanisms in dsRNA viruses.
Small nucleolar RNAs (snoRNAs) are among the most evolutionarily ancient classes of small RNA. Two experimental screens published in BMC Genomics expand the eukaryotic snoRNA catalog, but many more snoRNAs remain to be found.
See research articles http://www.biomedcentral.com/1471-2164/10/515 and http://www.biomedcentral.com/1471-2164/11/61.
CYCLOIDEA (CYC)-like TCP genes are critical for flower developmental patterning. Exciting recent breakthroughs, including a study by Song et al. published in BMC Evolutionary Biology, demonstrate that CYC-like genes have also had an important role in the evolution of flower form.
See research article http://www.biomedcentral.com/1471-2148/9/244.
Double-stranded RNA (dsRNA) longer than 30 bp is a key activator of the innate immune response against viral infections. It is widely assumed that the generation of dsRNA during genome replication is a trait shared by all viruses. However, to our knowledge, no study exists in which the production of dsRNA by different viruses is systematically investigated. Here, we investigated the presence and localization of dsRNA in cells infected with a range of viruses, employing a dsRNA-specific antibody for immunofluorescence analysis. Our data revealed that, as predicted, significant amounts of dsRNA can be detected for viruses with a genome consisting of positive-strand RNA, dsRNA, or DNA. Surprisingly, however, no dsRNA signals were detected for negative-strand RNA viruses. Thus, dsRNA is indeed a general feature of most virus groups, but negative-strand RNA viruses appear to be an exception to that rule.
Little is known about the genetic mechanisms underlying inducible defenses. Recently, the genome of Daphnia pulex, a model organism for defense studies, has been sequenced. Building on the genome information, recent preliminary studies in BMC Developmental Biology and BMC Molecular Biology have assessed gene response profiles in Daphnia under predation pressure. We review the significance of the findings and highlight future research perspectives.
See research articles http://www.biomedcentral.com/1471-2164/10/527, http://www.biomedcentral.com/1471-2105/6/45, http://www.biomedcentral.com/1471-213X/10/45
Chemosensory receptor genes encode G protein-coupled receptors with which animals sense their chemical environment. The large number of chemosensory receptor genes in the genome and their extreme genetic variability pose unusual challenges for understanding their evolution and function. Two articles in BMC Genomics explore the genetic variation of chemosensory receptor gene repertoires in humans and mice and provide unparalleled insight into the causes and consequences of this variability.
See research articles http://www.biomedcentral.com/1471-2164/13/414 and http://www.biomedcentral.com/1471-2164/13/415
Previously, we reported that three double-stranded RNA (dsRNA) segments, designated L-, M-, and S-dsRNAs, were detected in Sclerotinia sclerotiorum strain Ep-1PN. Of these, the M-dsRNA segment was derived from the genomic RNA of a potexvirus-like positive-strand RNA virus, Sclerotinia sclerotiorum debilitation-associated RNA virus. Here, we present the complete nucleotide sequence of the L-dsRNA, which is 6,043 nucleotides in length, excluding the poly(A) tail. Sequence analysis revealed the presence of a single open reading frame (nucleotide positions 42 to 5936) that encodes a protein with significant similarity to the replicases of the “alphavirus-like” supergroup of positive-strand RNA viruses. A sequence comparison of the L-dsRNA-encoded putative replicase protein containing conserved methyltransferase, helicase, and RNA-dependent RNA polymerase motifs showed that it has significant sequence similarity to the replicase of Hepatitis E virus, a virus infecting humans. Furthermore, we present convincing evidence that the virus-like L-dsRNA could replicate independently with only a slight impact on growth and virulence of its host. Our results suggest that the L-dsRNA from strain Ep-1PN is derived from the genomic RNA of a positive-strand RNA virus, which we named Sclerotinia sclerotiorum RNA virus L (SsRV-L). As far as we know, this is the first report of a positive-strand RNA mycovirus that is related to a human virus. Phylogenetic and sequence analyses of the conserved motifs of the RNA replicase of SsRV-L showed that it clustered with the rubi-like viruses and that it is related to the plant clostero-, beny- and tobamoviruses and to the insect omegatetraviruses. Considering the fact that these related alphavirus-like positive-strand RNA viruses infect a wide variety of organisms, these findings suggest that the ancestral positive-strand RNA viruses might be of ancient origin and/or they might have radiated horizontally among vertebrates, insects, plants, and fungi.
UmV is a double-stranded RNA (dsRNA) virus of the corn fungus Ustilago maydis. There are three viral subtypes, P1, P4 and P6, which differ in the specificity of their secreted killer toxins. Each has three size classes of dsRNAs: H (heavy), M (medium), and L (light). We find that, unique among dsRNA viruses, two segments of different size code for the same product--the toxin resistance factor. The smaller dsRNA (L) is homologous to one end of the larger (M), and may have arisen by replication and packaging of a sub-genomic mRNA. We have also compared all the UmV dsRNAs with each other and with the dsRNAs of the similar yeast virus (ScV) by Northern gel and by 3' sequence analysis. Like those of ScV, many of the UmV dsRNAs have one 3' terminus with the sequence UUUUUCAOH or UUUUUCGOH. The H and L dsRNAs of similar size in different viral subtypes are generally related in sequence. The UmV H dsRNAs of different size are not detectably related in sequence.
Small interfering RNAs can trigger unintended, microRNA-like off-target effects, but the impact of these effects on functional studies has been controversial. A recent study in BMC Genomics shows that microRNA-like effects can predominate among the 'hits' of functional genomics screens.
See research article http://www.biomedcentral.com/1471-2164/11/175
Simply hearing the song produced by another bird of the same species triggers the regulation of microRNAs (miRNAs) in high-order auditory parts of the zebra finch brain. Some of the identified miRNAs appear to be unique to birds, possibly to songbirds. These findings, reported in BMC Genomics, highlight the complexities of gene regulation associated with vocal communication and point to possible key regulators of song-triggered gene networks.
See research article:http://www.biomedcentral.com/1471-2164/12/277
Selection and constraints put limits on morphological evolution. Mammalian teeth are no exception, and the need for them to meet precisely exerts exacting constraints on a staggering array of developmental and functional factors that must be integrated to maintain their performance as they evolve. A study in BMC Evolutionary Biology demonstrates that mandibular movement is an important component of this integration, and one that should not be neglected in the quantitiative study of the evolution of tooth morphology.
See research article http://www.biomedcentral.com/1471-2148/12/146/
dental occlusion; evolutionary constraints; morphological integration; complexity; orientation patch counts
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.
See research article: http://www.biomedcentral.com/1471-2148/11/13
Expressed sequence tag analyses of the annelid Pomatoceros lamarckii, recently published in BMC Evolutionary Biology, are consistent with less extensive gene loss in the Lophotrochozoa than in the Ecdysozoa, but it would be premature to generalize about patterns of gene loss on the basis of the limited data available.
See research article http://www.biomedcentral.com/1471-2148/9/240.
Within their territories, damselfish cultivate particular algae for consumption. A recent study in BMC Evolutionary Biology shows extensive variation among and within fish species in the composition of these algal 'gardens', varying from monocultures to cultures of mixed species, and in the mode of cultivation. This fish-algal agriculture may provide insight into the early stages of domestication.
See research article http://www.biomedcentral.com/1471-2148/10/185
A novel, sequence-independent strategy has been developed for the amplification of full-length cDNA copies of the genes of double-stranded RNA (dsRNA) viruses. Using human (Bristol) group C rotavirus as an example, a single amino-linked modified oligonucleotide (primer 1) was ligated to either end of each dsRNA genome segment by using T4 RNA ligase. Following reverse transcription, annealing, and repair of cDNA strands, amplification of the viral dsRNA genome was accomplished by polymerase chain reaction using a single complementary oligonucleotide (primer 2). Northern (RNA) hybridization of cDNA to virus dsRNA indicated that it was possible to generate cDNA representing the complete genome from very small clinical samples. This technique was used to determine the complete nucleotide sequence (728 bp) and coding assignment of gene 10, which revealed an open reading frame of 212 amino acids with limited homology to NS26 from human group A rotavirus. In contrast to previous tailing methods, the addition of one defined primer allowed unequivocal identification of terminal nucleotides and should be generally applicable to viruses with segmented dsRNA genomes and especially for analysis of clinical samples, for which very limited quantities of biological material are available.
A re-examination of the mitochondrial genomes of unisexual salamander lineages, published in BMC Evolutionary Biology, shows them to be the oldest unisexual vertebrates known, having been around for 5 million years. This presents a challenge to the prediction that lack of genetic recombination is a fast track to extinction.
See research article http://www.biomedcentral.com/1471-2148/10/238
A recent study in BMC Evolutionary Biology has reconstructed the molecular phylogeny of a large Mediterranean cave-dwelling beetle clade, revealing an ancient origin and strong geographic structuring. It seems likely that diversification of this clade in the Oligocene was seeded by an ancestor already adapted to subterranean life.
See research article http://www.biomedcentral.com/1471-2148/10/29
Viruses have been discovered in numerous fungal species, but unlike most known animal or plant viruses, they are rarely associated with deleterious effects on their hosts. The knowledge about viruses among entomopathogenic fungi is very limited, although their existence is suspected because of the presence of virus-like double-stranded RNA (dsRNA) in isolates of several species. Beauveria bassiana is one of the most-studied species of entomopathogenic fungi; it has a cosmopolitan distribution and is used as a biological control agent against invertebrates in agriculture. We analyzed a collection of 73 isolates obtained at different locations and from different habitats in Spain and Portugal, searching for dsRNA elements indicative of viral infections. The results revealed that the prevalence of viral infections is high; 54.8% of the isolates contained dsRNA elements with viral characteristics. The dsRNA electropherotypes of infected isolates indicated that virus diversity was high in the collection analyzed and that mixed virus infections occurred in fungal isolates. However, a hybridization experiment indicated that dsRNA bands that are similar in size do not always have similar sequences. Particular virus species or dsRNA profiles were not associated with locations or types of habitats, probably because of the ubiquity and efficient dispersion of this fungus as an airborne species. The sequence of one of the most common dsRNA elements corresponded to the 5.2-kbp genome of a previously undescribed member of the Totiviridae family, termed B. bassiana RNA virus 1 (BbRV1).
Transposable elements are best interpreted as genomic parasites, proliferating in genomes through their over-replication relative to the rest of the genome. A new study examining correlations across Drosophila species between transposable element numbers and rates of host evolution has brought into focus one of the most complex questions in transposable element biology-what it is that determines the proportion of the genome that is transposable elements.
See research article: http://www.biomedcentral.com/1471-2148/11/258/
The relatedness of several double-stranded RNAs (dsRNA's) present in the virus-like particles of yeast was examined by T1 fingerprint analysis. The dsRNA's examined were L, the dsRNA encoding the capsid polypeptide of yeast virus-like particles; M, which appears to code for a toxic polypeptide and for resistance to the effects of the toxin; and two S dsRNA's present in particles analogous to the defective interfering particles of animal viruses. S3, a dsRNA of 0.46 X 10(6) daltons, was derived entirely from M, a dsRNA of 1.2 X 10(6) daltons. S1, a dsRNA of 0.92 X 10(6) daltons, was a duplication of S3. This conclusion has also been reached independently by heteroduplex mapping techniques (H. M. Fried and G. R. Fink, personal communication). S1 and S3, at least in one yeast strain, were unstable in sequence, apparently due to the accumulation of sequence variants of the same molecular weight. L was a species of 3 X 10(6) daltons, unrelated in sequence to M, S1, or S3. S1, S3, and M had a 3' T1 dodecanucleotide in common.
p53 has been well characterized as a tumor suppressor gene, but its role in antiviral defense remains unclear. A recent report has demonstrated that p53 can be induced by interferons and is activated after vesicular stomatitis virus (VSV) infection. We observed that different nononcogenic viruses, including encephalomyocarditis virus (EMCV) and human parainfluenza virus type 3 (HPIV3), induced down-regulation of p53 in infected cells. Double-stranded RNA (dsRNA) and a mutant vaccinia virus lacking the dsRNA binding protein E3L can also induce this effect, indicating that dsRNA formed during viral infection is likely the trigger for down-regulation of p53. The mechanism of down-regulation of p53 by dsRNA relies on translation inhibition mediated by the PKR and RNase L pathways. In the absence of p53, the replication of both EMCV and HPIV3 was retarded, whereas, conversely, VSV replication was enhanced. Cell cycle analysis indicated that wild-type (WT) but not p53 knockout (KO) fibroblasts undergo an early-G1 arrest following dsRNA treatment. Moreover, in WT cells the onset of dsRNA-induced apoptosis begins after p53 levels are down-regulated, whereas p53 KO cells, which lack the early-G1 arrest, rapidly undergo apoptosis. Hence, our data suggest that the down-regulation of p53 facilitates apoptosis, thereby limiting viral replication.
The replication and transcription of double-stranded RNA (dsRNA) viruses occur within a polymerase complex particle in which the viral genome is enclosed throughout the entire life cycle of the virus. A single protein subunit in the polymerase complex is responsible for the template-dependent RNA polymerization activity. The isolated polymerase subunit of the dsRNA bacteriophage φ6 was previously shown to replicate and transcribe given RNA molecules. In this study, we show that this enzyme also catalyzes nontemplated nucleotide additions to single-stranded and double-stranded nucleic acid molecules. This terminal nucleotidyltransferase activity not only is a property of the isolated enzyme but also is detected to take place within the viral nucleocapsid. This is the first time terminal nucleotidyltransferase activity has been reported for a dsRNA virus as well as for a viral particle. The results obtained together with previous high-resolution structural data on the φ6 RNA-dependent RNA polymerase suggest a mechanism for terminal nucleotidyl addition. We propose that the activity is involved in the termination of the template-dependent RNA polymerization reaction on the linear φ6 genome.
Occurrence of extrachromosomal dsRNA elements has been described in the red-yeast Xanthophyllomyces dendrorhous, with numbers and sizes that are highly variable among strains with different geographical origin. The studies concerning to the encapsidation in viral-like particles and dsRNA-curing have suggested that some dsRNAs are helper viruses, while others are satellite viruses. However, the nucleotide sequences and functions of these dsRNAs are still unknown. In this work, the nucleotide sequences of four dsRNAs of the strain UCD 67–385 of X. dendrorhous were determined, and their identities and genome structures are proposed. Based on this molecular data, the dsRNAs of different strains of X. dendrorhous were analyzed.
The complete sequences of L1, L2, S1 and S2 dsRNAs of X. dendrorhous UCD 67–385 were determined, finding two sequences for L1 dsRNA (L1A and L1B). Several ORFs were uncovered in both S1 and S2 dsRNAs, but no homologies were found for any of them when compared to the database. Instead, two ORFs were identified in each L1A, L1B and L2 dsRNAs, whose deduced amino acid sequences were homologous with a major capsid protein (5’-ORF) and a RNA-dependent RNA polymerase (3’-ORF) belonging to the Totiviridae family. The genome structures of these dsRNAs are characteristic of Totiviruses, with two overlapped ORFs (the 3’-ORF in the −1 frame with respect to the 5’-ORF), with a slippery site and a pseudoknot in the overlapped regions. These structures are essential for the synthesis of the viral polymerase as a fusion protein with the viral capsid protein through −1 ribosomal frameshifting. In the RNase protection analysis, all the dsRNAs in the four analyzed X. dendrorhous strains were protected from enzymatic digestion. The RT-PCR analysis revealed that, similar to strain UCD 67–385, the L1A and L1B dsRNAs coexist in the strains VKM Y-2059, UCD 67–202 and VKM Y-2786. Furthermore, determinations of the relative amounts of L1 dsRNAs using two-step RT-qPCR revealed a 40-fold increment of the ratio L1A/L1B in the S2 dsRNA-cured strain compared to its parental strain.
Three totiviruses, named as XdV-L1A, XdV-L1B and XdV-L2, were identified in the strain UCD 67–385 of X. dendrorhous. The viruses XdV-L1A and XdV-L1B were also found in other three X. dendrorhous strains. Our results suggest that the smaller dsRNAs (named XdRm-S1 and XdRm-S2) of strain UCD 67–385 are satellite viruses, and particularly that XdRm-S2 is a satellite of XdV-L1A.
X. dendrorhous; dsRNA; Totivirus; Mycovirus
A new study of divergence in freshwater fish provides strong evidence of rapid, temperature-mediated adaptation. This study is particularly important in the ongoing debate over the extent and significance of evolutionary response to climate change because divergence has occurred in relatively few generations in spite of ongoing gene flow and in the aftermath of a significant genetic bottleneck, factors that have previously been considered obstacles to evolution. Climate change may thus be more likely to foster contemporary evolutionary responses than has been anticipated, and I argue here for the importance of investigating their possible occurrence.
See Research article: http://www.biomedcentral.com/1471-2148/10/350/abstract