RESUMO
Alfalfa (Medicago sativa L.), also known as lucerne, is a major forage crop worldwide. In the United States, it has recently become the third most valuable field crop, with an estimated value of over $9.3 billion. Alfalfa is naturally infected by many different pathogens, including viruses, obligate parasites that reproduce only inside living host cells. Traditionally, viral infections of alfalfa have been considered by breeders, growers, producers and researchers to be diseases of limited importance, although they are widespread in all major cultivation areas. However, over the past few years, due to the rapid development of high-throughput sequencing (HTS), viral metagenomics, bioinformatics tools for interpreting massive amounts of HTS data and the increasing accessibility of public data repositories for transcriptomic discoveries, several emerging viruses of alfalfa with the potential to cause serious yield losses have been described. They include alfalfa leaf curl virus (family Geminiviridae), alfalfa dwarf virus (family Rhabdoviridae), alfalfa enamovirus 1 (family Luteoviridae), alfalfa virus S (family Alphaflexiviridae) and others. These discoveries have called into question the assumed low economic impact of viral diseases in alfalfa and further suggested their possible contribution to the severity of complex infections involving multiple pathogens. In this review, we will focus on viruses of alfalfa recently described in different laboratories on the basis of the above research methodologies.
RESUMO
Genomoviruses (family Genomoviridae) are circular single-stranded DNA viruses that have been mainly identified through metagenomics studies in a wide variety of samples from various environments. Here, we describe 98 genomes of genomoviruses found associated with members of 19 plant families from Australia, Brazil, France, South Africa and the USA. These 98 genomoviruses represent 29 species, 26 of which are new, in the genera Gemykolovirus (n = 37), Gemyduguivirus (n = 9), Gemygorvirus (n = 8), Gemykroznavirus (n = 6), Gemycircularvirus (n = 21) and Gemykibivirus (n = 17).
Assuntos
Infecções por Vírus de DNA/virologia , Vírus de DNA/isolamento & purificação , Genoma Viral , Plantas/virologia , Austrália , Brasil , Vírus de DNA/classificação , França , Metagenômica , Filogenia , África do Sul , Estados UnidosRESUMO
A novel virus infecting yams (Dioscorea spp.), tentatively named "yam asymptomatic virus 1" (YaV1), was characterized and sequenced from an asymptomatic D. alata plant from Vanuatu. Sequence comparisons and phylogenetic analysis showed that YaV1 is a novel ampelovirus and has the smallest genome among "subgroup 1" members. RT-PCR-based screening of a yam germplasm collection conserved in Guadeloupe showed that YaV1 is prevalent in D. alata, D. bulbifera, D. cayennensis subsp. rotundata, D. esculenta and D. trifida accessions but causes no apparent symptoms. Additional phylogenetic analysis revealed a low variability of YaV1 in Guadeloupe in a limited part of the genome, and suggested the occurrence of plant-to-plant transmission.
Assuntos
Closteroviridae/classificação , Dioscorea/virologia , Filogenia , Doenças das Plantas/virologia , Closteroviridae/isolamento & purificação , Closteroviridae/patogenicidade , Variação Genética , Genoma Viral , Guadalupe , Prevalência , Reação em Cadeia da Polimerase em Tempo RealRESUMO
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.
Assuntos
Cactaceae/virologia , Geminiviridae/genética , Genoma Viral , Filogenia , Doenças das Plantas/virologia , Animais , Geminiviridae/classificação , Geminiviridae/isolamento & purificação , Hemípteros/virologia , México , Recombinação Genética , Nicotiana/virologia , Estados UnidosRESUMO
BACKGROUND: In Africa and Asia, sugarcane is the host of at least seven different virus species in the genus Mastrevirus of the family Geminiviridae. However, with the exception of Sugarcane white streak virus in Barbados, no other sugarcane-infecting mastrevirus has been reported in the New World. Conservation and exchange of sugarcane germplasm using stalk cuttings facilitates the spread of sugarcane-infecting viruses. METHODS: A virion-associated nucleic acids (VANA)-based metagenomics approach was used to detect mastrevirus sequences in 717 sugarcane samples from Florida (USA), Guadeloupe (French West Indies), and Réunion (Mascarene Islands). Contig assembly was performed using CAP3 and sequence searches using BLASTn and BLASTx. Mastrevirus full genomes were enriched from total DNA by rolling circle amplification, cloned and sequenced. Nucleotide and amino acid sequence identities were determined using SDT v1.2. Phylogenetic analyses were conducted using MEGA6 and PHYML3. RESULTS: We identified a new sugarcane-infecting mastrevirus in six plants sampled from germplasm collections in Florida and Guadeloupe. Full genome sequences were determined and analyzed for three virus isolates from Florida, and three from Guadeloupe. These six genomes share >88% genome-wide pairwise identity with one another and between 89 and 97% identity with a recently identified mastrevirus (KR150789) from a sugarcane plant sampled in China. Sequences similar to these were also identified in sugarcane plants in Réunion. CONCLUSIONS: As these virus isolates share <64% genome-wide identity with all other known mastreviruses, we propose classifying them within a new mastrevirus species named Sugarcane striate virus. This is the first report of sugarcane striate virus (SCStV) in the Western Hemisphere, a virus that most likely originated in Asia. The distribution, vector, and impact of SCStV on sugarcane production remains to be determined.
Assuntos
Geminiviridae/classificação , Geminiviridae/isolamento & purificação , Saccharum/virologia , Clonagem Molecular , Análise por Conglomerados , DNA Viral/química , DNA Viral/genética , DNA Viral/isolamento & purificação , Florida , Guadalupe , Filogenia , Reunião , Análise de Sequência de DNA , Homologia de Sequência , Sequenciamento Completo do GenomaRESUMO
The geminiviruses are a family of small, non-enveloped viruses with single-stranded, circular DNA genomes of 2500-5200 bases. Geminiviruses are transmitted by various types of insect (whiteflies, leafhoppers, treehoppers and aphids). Members of the genus Begomovirus are transmitted by whiteflies, those in the genera Becurtovirus, Curtovirus, Grablovirus, Mastrevirus and Turncurtovirus are transmitted by specific leafhoppers, the single member of the genus Topocuvirus is transmitted by a treehopper and one member of the genus Capulavirus is transmitted by an aphid. Geminiviruses are plant pathogens causing economically important diseases in most tropical and subtropical regions of the world. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the taxonomy of the Geminiviridae which is available at www.ictv.global/report/geminiviridae.