The role of the Cucumber mosaic virus 2b protein in viral movement and symptom induction

The Cucumber mosaic virus (CMV) 2b protein is a counter-defense factor and symptom determinant. Conserved domains in the 2b protein sequence were mutated in the 2b gene of strain Fny-CMV. The effects of these mutations were assessed by infection of Nicotiana tabacum, N. benthamiana, and Arabidopsis thaliana (ecotype Col-0) with mutant viruses and by expression of mutant 2b transgenes in A. thaliana. We confirmed that two nuclear localization signals were required for symptom induction and found that the N-terminal domain was essential for symptom induction. The C-terminal domain and two serine residues within a putative phosphorylation domain modulated symptom severity. Further infection studies were conducted using Fny-CMVΔ2b, a mutant that cannot express the 2b protein and that induces no symptoms in N. tabacum, N. benthamiana, or A. thaliana ecotype Col-0. Surprisingly, in plants of A. thaliana ecotype C24, Fny-CMVΔ2b induced severe symptoms similar to those induced by the wild-type virus. However, C24 plants infected with the mutant virus recovered from disease while those infected with the wild-type virus did not. Expression of 2b transgenes from either Fny-CMV or from LS-CMV (a mild strain) in Col-0 plants enhanced systemic movement of Fny-CMVΔ2b and permitted symptom induction by Fny-CMVΔ2b. Taken together, the results indicate that the 2b protein itself is an important symptom determinant in certain hosts. However, they also suggest that the protein may somehow synergize symptom induction by other CMV-encoded factors

Geometagenomics illuminates the impact of agriculture on the distribution and prevalence of plant viruses at the ecosystem scale

Disease emergence events regularly result from human activities such as agriculture, which frequently brings large populations of genetically uniform hosts into contact with potential pathogens. Although viruses cause nearly 50% of emerging plant diseases, there is little systematic information about virus distribution across agro-ecological interfaces and large gaps in understanding of virus diversity in nature. Here we applied a novel landscape-scale geometagenomics approach to examine relationships between agricultural land use and distributions of plantassociated viruses in two Mediterranean-climate biodiversity hotspots (Western Cape region of South Africa and Rhône river delta region of France). In total, we analysed 1725 geo-referenced plant samples collected over two years from 4.5 × 4.5 km2 grids spanning farmlands and adjacent uncultivated vegetation. We found substantial virus prevalence (25.8–35.7%) in all ecosystems, but prevalence and identified family-level virus diversity were greatest in cultivated areas, with some virus families displaying strong agricultural associations. Our survey revealed 94 previously unknown virus species, primarily from uncultivated plants. This is the first effort to systematically evaluate plant-associated viromes across broad agro-ecological interfaces. Our findings indicate that agriculture substantially influences plant virus distributions and highlight the extent of current ignorance about the diversity and roles of viruses in nature

Plant Virus Biodiversity and Ecology

The Plant Virus Biodiversity and Ecology (PVBE) project has been initiated to survey the biodiversity of viruses affecting vascular plants

A novel evolutionary strategy revealed in the Phaeoviruses

Phaeoviruses infect the brown algae, which are major contributors to primary production of coastal waters and estuaries. They exploit a Persistent evolutionary strategy akin to a K- selected life strategy via genome integration and are the only known representatives to do so within the giant algal viruses that are typified by r- selected Acute lytic viruses. In screening the genomes of five species within the filamentous brown algal lineage, here we show an unprecedented diversity of viral gene sequence variants especially amongst the smaller phaeoviral genomes. Moreover, one variant shares features from both the two major sub-groups within the phaeoviruses. These phaeoviruses have exploited the reduction of their giant dsDNA genomes and accompanying loss of DNA proofreading capability, typical of an Acute life strategist, but uniquely retain a Persistent life strategy

Multiple viral infections in Agaricus bisporus - characterisation of 18 unique RNA viruses and 8 ORFans identified by deep sequencing

Thirty unique non-host RNAs were sequenced in the cultivated fungus, Agaricus bisporus, comprising 18 viruses each encoding an RdRp domain with an additional 8 ORFans (non-host RNAs with no similarity to known sequences). Two viruses were multipartite with component RNAs showing correlative abundances and common 3′ motifs. The viruses, all positive sense single-stranded, were classified into diverse orders/families. Multiple infections of Agaricus may represent a diverse, dynamic and interactive viral ecosystem with sequence variability ranging over 2 orders of magnitude and evidence of recombination, horizontal gene transfer and variable fragment numbers. Large numbers of viral RNAs were detected in multiple Agaricus samples; up to 24 in samples symptomatic for disease and 8–17 in asymptomatic samples, suggesting adaptive strategies for co-existence. The viral composition of growing cultures was dynamic, with evidence of gains and losses depending on the environment and included new hypothetical viruses when compared with the current transcriptome and EST databases. As the non-cellular transmission of mycoviruses is rare, the founding infections may be ancient, preserved in wild Agaricus populations, which act as reservoirs for subsequent cell-to-cell infection when host populations are expanded massively through fungiculture

Protective Microbiota: From Localized to Long-Reaching Co-Immunity

Resident microbiota do not just shape host immunity, they can also contribute to host protection against pathogens and infectious diseases. Previous reviews of the protective roles of the microbiota have focused exclusively on colonization resistance localized within a microenvironment. This review shows that the protection against pathogens also involves the mitigation of pathogenic impact without eliminating the pathogens (i.e., “disease tolerance”) and the containment of microorganisms to prevent pathogenic spread. Protective microorganisms can have an impact beyond their niche, interfering with the entry, establishment, growth, and spread of pathogenic microorganisms. More fundamentally, we propose a series of conceptual clarifications in support of the idea of a “co-immunity,” where an organism is protected by both its own immune system and components of its microbiota

Ribozyme-based insulator parts buffer synthetic circuits from genetic context

Synthetic genetic programs are built from circuits that integrate sensors and implement temporal control of gene expression. Transcriptional circuits are layered by using promoters to carry the signal between circuits. In other words, the output promoter of one circuit serves as the input promoter to the next. Thus, connecting circuits requires physically connecting a promoter to the next circuit. We show that the sequence at the junction between the input promoter and circuit can affect the input-output response (transfer function) of the circuit. A library of putative sequences that might reduce (or buffer) such context effects, which we refer to as 'insulator parts', is screened in Escherichia coli. We find that ribozymes that cleave the 5′ untranslated region (5′-UTR) of the mRNA are effective insulators. They generate quantitatively identical transfer functions, irrespective of the identity of the input promoter. When these insulators are used to join synthetic gene circuits, the behavior of layered circuits can be predicted using a mathematical model. The inclusion of insulators will be critical in reliably permuting circuits to build different programs.Life Technologies, Inc.United States. Defense Advanced Research Projects Agency (DARPA CLIO N66001-12-C-4018)United States. Office of Naval Research (N00014-10-1-0245)National Science Foundation (U.S.) (CCF-0943385)National Institutes of Health (U.S.) (AI067699)National Science Foundation (U.S.). Synthetic Biology Engineering Research Center (SynBERC, SA5284-11210

Natural occurrence of Cucumber mosaic virus infecting water mint (Mentha aquatica) in Antalya and Konya, Turkey

A virus causing a disease in mint (the aromatic and culinary plant) has recently become a problem in the Taurus Mountains, a mountain range in the Mediterranean region of Turkey. To detect the virus and investigate its distribution in the region, mint leaf samples were collected from the vicinity of spring areas in the plateaus of Antalya and Konya in 2009. It was found that Cucumber mosaic virus (CMV) was detected in 27.08% of symptomatic samples tested by DAS-ELISA. To the best of our knowledge, this is the first report of CMV on mint plants in this region of Turkey

The remarkable evolutionary history of endornaviruses

The family Endornaviridae contains several members from diverse hosts, including plants, fungi and oomycetes. They are found as large dsRNA elements with a nick in the coding strand. All members encode a conserved RNA-dependent RNA polymerase, but no other domain that is conserved among all members. Based on the conserved domain database comparison the various domains have different origins, indicating a highly modular evolutionary history. In some cases, domains with similar putative functions are found that are derived from different protein families, indicating convergent evolution for a required function. © 2011 SGM

The role of porcine reproductive and respiratory syndrome (PRRS) virus structural and non-structural proteins in virus pathogenesis

Porcine reproductive and respiratory syndrome (PRRS) is an economically devastating viral disease affecting the swine industry worldwide. The etiological agent, PRRS virus (PRRSV), possesses a RNA viral genome with nine open reading frames (ORFs). The ORF1a and ORF1b replicase-associated genes encode the polyproteins pp1a and pp1ab, respectively. The pp1a is processed in nine non-structural proteins (nsps): nsp1a, nsp1b, and nsp2 to nsp8. Proteolytic cleavage of pp1ab generates products nsp9 to nsp12. The proteolytic pp1a cleavage products process and cleave pp1a and pp1ab into nsp products. The nsp9 to nsp12 are involved in virus genome transcription and replication. The 30 end of the viral genome encodes four minor and three major structural proteins. The GP2a, GP3 and GP4 (encoded by ORF2a, 3 and 4), are glycosylated membrane associated minor structural proteins. The fourth minor structural protein, the E protein (encoded by ORF2b), is an unglycosylated membrane associated protein. The viral envelope contains two major structural proteins: a glycosylated major envelope protein GP5 (encoded by ORF5) and an unglycosylated membrane M protein (encoded by ORF6). The third major structural protein is the nucleocapsid N protein (encoded by ORF7). All PRRSV non-structural and structural proteins are essential for virus replication, and PRRSV infectivity is relatively intolerant to subtle changes within the structural proteins. PRRSV virulence is multigenic and resides in both the non-structural and structural viral proteins. This review discusses the molecular characteristics, biological and immunological functions of the PRRSV structural and nsps and their involvement in the virus pathogenesis