Complete sequence and genome structure of cactus mild mottle virus

Pepper Mild Mottle Virus: An Infectious Pathogen in Pepper Production and a Potential Indicator of Domestic Water Quality

Pepper (Capsicum spp.; Family: Solanaceae; 2n = 24) is an important crop cultivated worldwide for the consumption of its fresh and dried processed fruits. Pepper fruits are used as raw materials in a wide variety of industrial processes. As a multipurpose vegetable crop, there is a need to increase the yield. However, yield productivity of pepper is severely constrained by infectious plant pathogens, including viruses, bacteria, fungi, and oomycetes. The pepper mild mottle virus (PMMoV) is currently one of the most damaging pathogens associated with yield losses in pepper production worldwide. In addition to impacts on pepper productivity, PMMoV has been detected in domestic and aquatic water resources, as well as in the excreta of animals, including humans. Therefore, PMMoV has been suggested as a potential indicator of domestic water quality. These findings present additional concerns and trigger the need to control the infectious pathogen in crop production. This review provides an overview of the distribution, economic impacts, management, and genome sequence variation of some isolates of PMMoV. We also describe genetic resources available for crop breeding against PMMoV.

New World Cactaceae Plants Harbor Diverse Geminiviruses

The family Cactaceae comprises a diverse group of typically succulent plants that are native to the American continent but have been introduced to nearly all other continents, predominantly for ornamental purposes. Despite their economic, cultural, and ecological importance, very little research has been conducted on the viral community that infects them. We previously identified a highly divergent geminivirus that is the first known to infect cacti. Recent research efforts in non-cultivated and asymptomatic plants have shown that the diversity of this viral family has been under-sampled. As a consequence, little is known about the effects and interactions of geminiviruses in many plants, such as cacti. With the objective to expand knowledge on the diversity of geminiviruses infecting cacti, we used previously acquired high-throughput sequencing results to search for viral sequences using BLASTx against a viral RefSeq protein database. We identified two additional sequences with similarity to geminiviruses, for which we designed abutting primers and recovered full-length genomes. From 42 cacti and five scale insects, we derived 42 complete genome sequences of a novel geminivirus species that we have tentatively named Opuntia virus 2 (OpV2) and 32 genomes of an Opuntia-infecting becurtovirus (which is a new strain of the spinach curly top Arizona virus species). Interspecies recombination analysis of the OpV2 group revealed several recombinant regions, in some cases spanning half of the genome. Phylogenetic analysis demonstrated that OpV2 is a novel geminivirus more closely related to viruses of the genus Curtovirus, which was further supported by the detection of three recombination events between curtoviruses and OpV2. Both OpV2 and Opuntia becurtoviruses were identified in mixed infections, which also included the previously characterized Opuntia virus 1. Viral quantification of the co-infected cactus plants compared with single infections did not show any clear trend in viral dynamics that might be associated with the mixed infections. Using experimental Rhizobium-mediated inoculations, we found that the initial accumulation of OpV2 is facilitated by co-infection with OpV1. This study shows that the diversity of geminiviruses that infect cacti is under-sampled and that cacti harbor diverse geminiviruses. The detection of the Opuntia becurtoviruses suggests spill-over events between viruses of cultivated species and native vegetation. The threat this poses to cacti needs to be further investigated.

A Novel Divergent Geminivirus Identified in Asymptomatic New World Cactaceae Plants

Cactaceae comprise a diverse and iconic group of flowering plants which are almost exclusively indigenous to the New World. The wide variety of growth forms found amongst the cacti have led to the trafficking of many species throughout the world as ornamentals. Despite the evolution and physiological properties of these plants having been extensively studied, little research has focused on cactus-associated viral communities. While only single-stranded RNA viruses had ever been reported in cacti, here we report the discovery of cactus-infecting single-stranded DNA viruses. These viruses all apparently belong to a single divergent species of the family Geminiviridae and have been tentatively named Opuntia virus 1 (OpV1). A total of 79 apparently complete OpV1 genomes were recovered from 31 different cactus plants (belonging to 20 different cactus species from both the Cactoideae and Opuntioideae clades) and from nine cactus-feeding cochineal insects (Dactylopius sp.) sampled in the USA and Mexico. These 79 OpV1 genomes all share > 78.4% nucleotide identity with one another and < 64.9% identity with previously characterized geminiviruses. Collectively, the OpV1 genomes display evidence of frequent recombination, with some genomes displaying up to five recombinant regions. In one case, recombinant regions span ~40% of the genome. We demonstrate that an infectious clone of an OpV1 genome can replicate in Nicotiana benthamiana and Opuntia microdasys. In addition to expanding the inventory of viruses that are known to infect cacti, the OpV1 group is so distantly related to other known geminiviruses that it likely represents a new geminivirus genus. It remains to be determined whether, like its cactus hosts, its geographical distribution spans the globe.

Detection of Co-Infection of Notocactus leninghausii f. cristatus with Six Virus Species in South Korea

Co-infection with two virus species was previously reported in some cactus plants. Here, we showed that Notocactus leninghausii f. cristatus can be co-infected with six different viruses: cactus mild mottle virus (CMMoV)-Nl, cactus virus X (CVX)-Nl, pitaya virus X (PiVX)-Nl, rattail cactus necrosis-associated virus (RCNaV)-Nl, schlumbergera virus X (SchVX)-Nl, and zygocactus virus X (ZyVX)-Nl. The coat protein sequences of these viruses were compared with those of previously reported viruses. CMMoV-Nl, CVX-Nl, PiVX-Nl, RCNaV-Nl, SchVX-Nl, and ZyVX-Nl showed the greatest nucleotide sequence homology to CMMoV-Kr (99.8% identity, GenBank accession NC_011803), CVX-Jeju (77.5% identity, GenBank accession LC12841), PiVX-P37 (98.4% identity, GenBank accession NC_024458), RCNaV (99.4% identity, GenBank accession NC_016442), SchVX-K11 (95.7% identity, GenBank accession NC_011659), and ZyVX-B1 (97.9% identity, GenBank accession NC_006059), respectively. This study is the first report of co-infection with six virus species in N. leninghausii f. cristatus in South Korea.

Molecular characterisation of a novel recombinant Ribgrass mosaic virus strain FSHS

Background

The genus Tobamovirus (Virgaviridae) comprises 33 accepted species with the recent addition of eight new viruses and is divided in to three subgroups based on the origin of assembly of the virion and host range. Within the subgroup 1 tobamoviruses the orchid-associated tobamovirus was hypothesized to be a chimeric derivative of recombinations between genome fragments from subgroup 3 and 1. Recombination events involving RdRp, movement and coat protein genes are recorded within subgroup 1 and 2. However natural recombinations have not previously been reported between subgroup 3 tobamoviruses.

Findings

The organization and phylogenetic analyses of the complete genome and the different ORFs placed the new isolate within the Ribgrass mosaic virus clade of subgroup 3 tobamoviruses. Recombination detection analyses indicated that the isolate was a chimeric genome with fragments of high similarity to Ribgrass mosaic virus (RMV) strains NZ-439 (HQ667978) and Actinidia-AC (GQ401365.1) infecting herbaceous Plantago sp. and woody Actinidia spp., respectively. The recombinant differed across the whole genome by 3-8 % from other published RMV genomes.

Conclusion

In this investigation we report an intra-specific recombination between RMV strains NZ-439 (HQ667978) and Actinidia-AC (GQ401365.1), in the replicase component between viral-methyltransferase and viral-helicase regions, resulting in a novel RMV strain FSHS (JQ319720.1) that represents the first described natural recombinant within the RMV cluster of subgroup 3 tobamoviruses.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-016-0487-5) contains supplementary material, which is available to authorized users.

Natural recombination between tobacco and tomato mosaic viruses

Tobacco mosaic virus (TMV) is a positive-sense plant RNA virus which has a wide host range and a worldwide distribution. Other than a troublesome pathogen, TMV is regarded as a model system pioneering biologic research for a century. The tomato strain of TMV has been recognized to be a distinct tobamovirus as the tomato mosaic virus (ToMV). Recombination has been increasingly recognized as an important factor generating genetic diversity in many RNA viruses. However, it is still unclear whether recombination can function in driving the evolution of tobamoviruses. Herein, based on sequence comparison, we found three recombinants involving each viral gene, all of which might be derived from homologous or aberrant homologous recombination between TMV and ToMV. The study provided evidence that recombination did contribute to the genetic diversity of tobamoviruses.

Co-divergence and host-switching in the evolution of tobamoviruses

The proposed phylogenetic structure of the genus Tobamovirus supports the idea that these viruses have codiverged with their hosts since radiation of the hosts from a common ancestor. The determinations of genome sequence for two strains of Passion fruit mosaic virus (PafMV), a tobamovirus from plants of the family Passifloraceae (order Malpighiales) from which only one other tobamovirus (Maracuja mosaic virus; MarMV) has been characterized, combined with the development of Bayesian analysis methods for phylogenetic inference, provided an opportunity to reassess the co-divergence hypothesis. The sequence of one PafMV strain, PfaMV-TGP, was discovered during a survey of plants of the Tallgrass Prairie Preserve for their virus content. Its nucleotides are only 73 % identical to those of MarMV. A conserved ORF not found in other tobamovirus genomes, and encoding a cysteine-rich protein, was found in MarMV and both PafMV strains. Phylogenetic tree construction, using an alignment of the nucleotide sequences of PafMV-TGP and other tobamoviruses resulted in a major clade containing isolates exclusively from rosid plants. Asterid-derived viruses were exclusively found in a second major clade that also contained an orchid-derived tobamovirus and tobamoviruses infecting plants of the order Brassicales. With a few exceptions, calibrating the virus tree with dates of host divergence at two points resulted in predictions of divergence times of family specific tobamovirus clades that were consistent with the times of divergence of the host plant orders.

The complete genome sequence of a member of a new species of tobamovirus (rattail cactus necrosis-associated virus) isolated from Aporcactus flagelliformis

In this study, we identified a new tobamovirus from diseased Aporcactus flagelliformis cactus plants, named it rattail cactus necrosis-associated virus (RCNaV), and determined its complete genome sequence. The full RCNaV genome consisted of 6,506 nucleotides and contained four open reading frames coding for proteins of M(r) 128 kDa (3,441 nt), 185 kDa (4,929 nt), 55 kDa (1452 nt), 36 kDa (1,005 nt) and 19 kDa (513 nt) from the 5' to 3' end, respectively. The overall similarities for the four ORFs of RCNaV were from 32.5% to 64.1% and from 17.0% to 67.3% to those of the other tobamoviruses, at the nucleotide and amino acid level, respectively. Comparison of the coding and non-coding regions of the virus with those of other tobamoviruses showed that RCNaV is the most closely related to cactus mild mottle virus.