Global phylogenetic analysis of soybean dwarf virus isolates and their associations with aphid vectors and severe disease in soybeans.

Soybean dwarf virus (SbDV) was first described in Japan as an agent of severe soybean disease transmitted by the foxglove aphid, Aulacorthum solani, with separable yellowing (Y) and dwarfing (D) strains. SbDV of both Y and D genotypes were later documented in other countries. For three decades, SbDV isolates were assessed to evaluate risk to U.

Soybean Aphid (Hemiptera: Aphididae) Feeding Behavior is Largely Unchanged by Soybean Mosaic Virus but Significantly Altered by the Beetle-Transmitted Bean Pod Mottle Virus.

The soybean aphid (Aphis glycines Matsumura) is an economically important invasive pest of soybean. In addition to damage caused by soybean aphid feeding on the phloem sap, this insect also transmits many plant viruses, including soybean mosaic virus (SMV). Previous work has shown that plant viruses can change plant host phenotypes to alter the behavior of their insect vectors to promote virus spread, known as the vector manipulation hypothesis.

Coat protein expression strategy of maize rayado fino virus and evidence for requirement of CP1 for leafhopper transmission.

Marafiviruses, including maize rayado fino virus (MRFV) and oat blue dwarf virus (OBDV), encode two carboxy co-terminal coat proteins, CP1 and CP2, which encapsidate the genome to form icosahedral virions. While CP2 expression is expected to be solely driven from a second start codon of a subgenomic RNA under a marafibox promoter sequence, the larger CP1 with an in-frame N-terminal extension relative to CP2 could potentially be expressed either by proteolytic release from the MRFV polyprotein or from subgenomic RNA translation. We examined MRFV CP expression strategy with a series of mutations in the CP coding region and identified mutants viable and nonviable for systemic plant infection.

Critical residues for proteolysis activity of maize chlorotic dwarf virus (MCDV) 3C-like protease and comparison of activity of orthologous waikavirus proteases.

Maize chlorotic dwarf virus (MCDV) encodes a 3C-like protease that cleaves the N-terminal polyprotein (R78) as previously demonstrated. Here, we examined amino acid residues required for catalytic activity of the protease, including those in the predicted catalytic triad, amino acid residues H2667, D2704, and C2798, as well as H2817 hypothesized to be important in substrate binding. These and other residues were targeted for mutagenesis and tested for proteolytic cleavage activity on the N-terminal 78 kDa MCDV-S polyprotein substrate to identify mutants that abolished catalytic activity.

Transcriptome of the Maize Leafhopper () and Its Transcriptional Response to Maize Rayado Fino Virus (MRFV), Which It Transmits in a Persistent, Propagative Manner.

The corn leafhopper (Dalbulus maidis) is an important vector of maize rayado fino virus (MRFV), a positive-strand RNA (+ssRNA) marafivirus which it transmits in a persistent propagative manner. The interaction of D. maidis with MRFV, including infection of the insect and subsequent transmission to new plants, is not well understood at the molecular level.

Simultaneous gene expression and multi-gene silencing in Zea mays using maize dwarf mosaic virus.

Background: Maize dwarf mosaic virus (MDMV), a member of the genus Potyvirus, infects maize and is non-persistently transmitted by aphids. Several plant viruses have been developed as tools for gene expression and gene silencing in plants. The capacity of MDMV for both gene expression and gene silencing were examined.

Maize Yellow Mosaic Virus Interacts with Maize Chlorotic Mottle Virus and Sugarcane Mosaic Virus in Mixed Infections, But Does Not Cause Maize Lethal Necrosis.

A maize-infecting polerovirus, variously named maize yellow dwarf virus RMV2 (MYDV RMV2), MYDV-like, and maize yellow mosaic virus (MaYMV), is frequently found in mixed infections in plants also infected with maize chlorotic mottle virus (MCMV) and sugarcane mosaic virus (SCMV), known to synergistically cause maize lethal necrosis (MLN). MaYMV was discovered in deep sequencing studies precipitated by recent MLN emergence and is prevalent at global locations with MLN, but its role in or contribution to disease was not known. We examined how MaYMV impacted disease development in mixed infections with MCMV, SCMV, and both MCMV and SCMV compared with mock-inoculated plants.

First report of cDNA clone-launched infection of maize plants with the polerovirus maize yellow mosaic virus (MaYMV).

An East African isolate of the maize-associated polerovirus, maize yellow mosaic virus (MaYMV) was previously shown to cause leaf reddening on singly infected maize plants (Zea mays). Here we describe the construction of a full-length infectious clone of an East African isolate and, for the first time, show infectivity of clone-derived transcripts in the primary host, maize, through vascular puncture inoculation (VPI), as well as in the dicotyledonous research model plant species, Nicotiana benthamiana, through agrobacterium inoculation. Characteristic leaf reddening symptoms were observed in a subset of maize plants inoculated with clone-derived transcripts, and infection was confirmed by RT-PCR and Northern blot analyses.

Engineering for virus-induced gene silencing.

(MRFV) is the type species of the genus in the family . It infects maize (), its natural host, to which it is transmitted by leafhoppers including and in a persistent-propagative manner. The MRFV monopartite RNA genome encodes a precursor polyprotein that is processed into replication-associated proteins.

A Recently Discovered Maize Polerovirus Causes Leaf Reddening Symptoms in Several Maize Genotypes and is Transmitted by Both the Corn Leaf Aphid () and the Bird Cherry-Oat Aphid ().

A maize-infecting polerovirus variously named maize yellow dwarf virus RMV2 (MYDV-RMV2) and maize yellow mosaic virus (MaYMV) has been discovered and previously described in East Africa, Asia, and South America. It was identified in virus surveys in these locations instigated by outbreaks of maize lethal necrosis (MLN), known to be caused by coinfections of unrelated maize chlorotic mottle virus (MCMV) and any of several maize-infecting potyviruses, and was often found in coinfections with MLN viruses. Although sequenced in many locations globally and named for symptoms of related or coinfecting viruses, and with an infectious clone reported that experimentally infects , rudimentary biological characterization of MaYMV in maize, including insect vector(s) and symptoms in single infections, has not been reported until now.

Maize lethal necrosis viruses and other maize viruses in Rwanda.

Maize lethal necrosis (MLN) is emergent in East Africa, first reported in 2011 in Kenya, and is devastating to maize production in the region. MLN is caused by coinfection of maize with the emergent maize chlorotic mottle virus (MCMV) and any of several maize-infecting potyviruses endemic in East Africa and worldwide. Here, we examined the distribution of MCMV and sugarcane mosaic virus (SCMV), the major viruses contributing to MLN in Rwanda.

Fundamental Aspects of Plant Viruses-An Overview on Focus Issue Articles.

Given the importance of and rapid research progress in plant virology in recent years, this Focus Issue broadly emphasizes advances in fundamental aspects of virus infection cycles and epidemiology. This Focus Issue comprises three review articles and 18 research articles. The research articles cover broad research areas on the identification of novel viruses, the development of detection methods, reverse genetics systems and functional genomics for plant viruses, vector and seed transmission studies, viral population studies, virus-virus interactions and their effect on vector transmission, and management strategies of viral diseases.

Maize Lethal Necrosis: An Emerging, Synergistic Viral Disease.

Maize lethal necrosis (MLN) is a disease of maize caused by coinfection of maize with maize chlorotic mottle virus (MCMV) and one of several viruses from the Potyviridae, such as sugarcane mosaic virus, maize dwarf mosaic virus, Johnsongrass mosaic virus or wheat streak mosaic virus. The coinfecting viruses act synergistically to result in frequent plant death or severely reduce or negligible yield. Over the past eight years, MLN has emerged in sub-Saharan East Africa, Southeast Asia, and South America, with large impacts on smallholder farmers.

The Role of Viruses in the Phytobiome.

Viruses are an important but sequence-diverse and often understudied component of the phytobiome. We succinctly review current information on how plant viruses directly affect plant health and physiology and consequently have the capacity to modulate plant interactions with their biotic and abiotic environments. Virus interactions with other biota in the phytobiome, including arthropods, fungi, and nematodes, may also impact plant health.

Barley stripe mosaic virus (BSMV) as a virus-induced gene silencing vector in maize seedlings.

Barley stripe mosaic virus (BSMV) was the first reported and still widely used virus-induced gene silencing (VIGS) vector for monocotyledons including wheat and barley. Despite BSMV's reported infectivity on maize (Zea mays), the use of the virus as a vector in maize has not been optimized. Here, we assayed infectivity of BSMV in different maize cultivars by vascular puncture inoculation.

Complete sequence and diversity of a maize-associated Polerovirus in East Africa.

Since 2011-2012, Maize lethal necrosis (MLN) has emerged in East Africa, causing massive yield loss and propelling research to identify viruses and virus populations present in maize. As expected, next generation sequencing (NGS) has revealed diverse and abundant viruses from the family Potyviridae, primarily sugarcane mosaic virus (SCMV), and maize chlorotic mottle virus (MCMV) (Tombusviridae), which are known to cause MLN by synergistic co-infection. In addition to these expected viruses, we identified a virus in the genus Polerovirus (family Luteoviridae) in 104/172 samples selected for MLN or other potential virus symptoms from Kenya, Uganda, Rwanda, and Tanzania.

Complete Genome Sequence of a New Maize-Associated Cytorhabdovirus.

A new 11,877-nucleotide cytorhabdovirus sequence with 6 open reading frames has been identified in a maize sample. It shares 50 and 51% genome-wide nucleotide sequence identity with northern cereal mosaic cytorhabdovirus and barley yellow striate mosaic cytorhabdovirus, respectively.

Johnsongrass mosaic virus Contributes to Maize Lethal Necrosis in East Africa.

Maize lethal necrosis (MLN), a severe virus disease of maize, has emerged in East Africa in recent years with devastating effects on production and food security where maize is a staple subsistence crop. In extensive surveys of MLN-symptomatic plants in East Africa, sequences of Johnsongrass mosaic virus (JGMV) were identified in Uganda, Kenya, Rwanda, and Tanzania. The East African JGMV is distinct from previously reported isolates and infects maize, sorghum, and Johnsongrass but not wheat or oat.

Identification of a maize chlorotic dwarf virus silencing suppressor protein.

Maize chlorotic dwarf virus (MCDV), a member of the genus Waikavirus, family Secoviridae, has a 11784 nt (+)ssRNA genome that encodes a 389kDa proteolytically processed polyprotein. We show that the N-terminal 78kDa polyprotein (R78) of MCDV acts as a suppressor of RNA silencing in a well-established assay system. We further demonstrate that R78 is cleaved by the viral 3C-like protease into 51 and 27kDa proteins (p51 and p27), and that p51 is responsible for silencing suppressor activity.

Soil-borne wheat mosaic virus infectious clone and manipulation for gene-carrying capacity.

A full-length infectious cDNA clone of soil-borne wheat mosaic virus (SBWMV; genus Furovirus; family Virgaviridae) was developed for agrobacterium delivery. The cloned virus can be agroinfiltrated to Nicotiana benthamiana for subsequent infection of wheat (Triticum aestivum, L.).

ORF43 of maize rayado fino virus is dispensable for systemic infection of maize and transmission by leafhoppers.

Maize rayado fino virus (MRFV) possesses an open reading frame (ORF43) predicted to encode a 43 kDa protein (p43) that has been postulated to be a viral movement protein. Using a clone of MRFV (pMRFV-US) from which infectious RNA can be produced, point mutations were introduced to either prevent initiation from three potential AUG initiation codons near the 5'-end of ORF43 or prematurely terminate translation of ORF43. Inoculation of maize seed via vascular puncture inoculation (VPI) resulted in plants exhibiting symptoms typical of MRFV infection for all mutants tested.

Sequence diversity of wheat mosaic virus isolates.

Wheat mosaic virus (WMoV), transmitted by eriophyid wheat curl mites (Aceria tosichella) is the causal agent of High Plains disease in wheat and maize. WMoV and other members of the genus Emaravirus evaded thorough molecular characterization for many years due to the experimental challenges of mite transmission and manipulating multisegmented negative sense RNA genomes. Recently, the complete genome sequence of a Nebraska isolate of WMoV revealed eight segments, plus a variant sequence of the nucleocapsid protein-encoding segment.

Maize Lethal Necrosis (MLN), an Emerging Threat to Maize-Based Food Security in Sub-Saharan Africa.

In sub-Saharan Africa, maize is a staple food and key determinant of food security for smallholder farming communities. Pest and disease outbreaks are key constraints to maize productivity. In September 2011, a serious disease outbreak, later diagnosed as maize lethal necrosis (MLN), was reported on maize in Kenya.

Infectious Maize rayado fino virus from Cloned cDNA.

A full-length cDNA clone was produced from a U.S. isolate of Maize rayado fino virus (MRFV), the type member of the genus Marafivirus within the family Tymoviridae.

Co-infection and Disease Severity of Ohio Maize dwarf mosaic virus and Maize chlorotic dwarf virus Strains.

Two major maize viruses have been reported in the United States: Maize dwarf mosaic virus (MDMV) and Maize chlorotic dwarf virus (MCDV). These viruses co-occur in regions where maize is grown, such that co-infections are likely. Co-infection of different strains of MCDV is also observed, and a synergistic enhancement of symptoms in co-infected plants was previously reported.