ICTV Virus Taxonomy Profile: Potyviridae 2022.

The family Potyviridae includes plant viruses with single-stranded, positive-sense RNA genomes of 8-11 kb and flexuous filamentous particles 650-950 nm long and 11-20 nm wide. Genera in the family are distinguished by the host range, genomic features and phylogeny of the member viruses. Most genomes are monopartite, but those of members of the genus Bymovirus are bipartite. Some members cause serious disease epidemics in cultivated plants. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family Potyviridae, which is available at ictv.global/report/potyviridae.

Comparative study of potyvirid NIa proteases and their cleavage sites.

Nuclear inclusion a protease (NIaPro), a major protease of potyvirids, processes its cognate viral polyprotein at distinct cleavage sites. Although Potyviridae is the largest family of the realm Riboviria, the individual NIaPro enzymes and their cleavage sites are believed to be species-specific. In the present study, the NIaPro amino acid sequences of 165 potyvirids of 10 genera and their 1154 cleavage sites were compared to understand their genus/species-specificity and functional regulation. Of these, the NIaPro of macluraviruses, maintains a constant length of 217 amino acids, while those of other genera allow variation. In particular, poaceviruses exhibited a broad range of NIaPro amino acid sequence lengths. Alignment of 162 NIaPro amino acid sequences showed that the N- and C-terminal regions allow variations, while the central region, with the catalytic triad and S1 subsite, are highly conserved. NIaPro cleavage sites are composed of seven amino acids (heptapeptide) denoted as P6-P5-P4-P3-P2-P1/P1'. A survey of 1154 cleavage sites showed that the P1 position is predominantly occupied by Gln/Glu, as is seen in picornaviruses. The P6 (Glu), P4 (Val/Cys/Gln), P2 (His/Tyr/Leu), and P1' (Ser/Ala/Gly/Met) positions are predominantly occupied by genus-specific residues, while P5 and P3 are not genus-specific. The 6K2-VPg and VPg-NIaPro junctions possess Glu at the P1 position in order to maintain latency.

Complete genome sequence of a German isolate of spartina mottle virus supports its classification as a member of the proposed genus "Sparmovirus" within the family Potyviridae.

Spartina mottle virus (SpMV), an unassigned member of the family Potyviridae, has been known since 1980, when it was first described in England and Wales in symptomatic plants of the genus Spartina. In infected cells, flexuous particles and pinwheel inclusion bodies were found that resemble those of potyvirids. To date, the NCBI database contains only two partial sequences of a German (Nessmersiel) and an Italian (Assisi) isolate, suggesting that SpMV could be the first member of a new genus, called "Sparmovirus", in the family Potyviridae. In this study, the first complete genome sequence of the German SpMV isolate (SpMV Ger) was determined. The genome of SpMV is a single-stranded, monopartite, polyadenylated RNA consisting of 9376 nucleotides. Sequence analysis revealed a genome organization similar to that of classical potyviruses, including many conserved features. In phylogenetic analysis, SpMV could not be assigned to any of the known genera, but it showed the closest relationship to rymoviruses and common reed chlorotic stripe virus (CRCSV, unassigned). Sequence comparisons confirmed that a new genus should be established containing SpMV, CRCSV, and three Bermuda grass mosaic virus isolates, which are considered divergent strains of SpMV.

Arachis virus Y, a new potyvirid from Brazilian forage peanut (Arachis pintoi).

The complete nucleotide sequence of a new member of the family Potyviridae, which we propose to name "Arachis virus Y" (ArVY), is reported from forage peanut plants (Arachis pintoi) exhibiting virus-like symptoms. The ArVY positive-sense RNA genome is 9,213 nucleotides long and encodes a polyprotein with 2,947 amino acids that is predicted to be cleaved into 10 mature proteins. The complete single open reading frame (ORF) of ArVY shares 47% and 34% nucleotide and amino acid sequence identity, respectively, with the closest related virus, soybean yellow shoot virus. Electron microscopic analysis revealed elongated viral particles typical of those found in plant cells infected with potyviruses.

Complete genome sequence of a novel member of the family Potyviridae isolated from Phellodendron amurense Rupr. in Liaoning, China.

In September 2017, Phellodendron amurense Rupr. plants showing yellow ringspots on leaves were observed in Liaoning, China. Flexuous filamentous particles (~1000 × 13 nm) were observed in the sap prepared from symptomatic leaves. A virus was detected in the symptomatic leaves by sequencing small RNAs and assembling the genome sequence. The complete genomic RNA was found to be 10,457 nucleotides in length excluding the poly(A) tail and to have the closest phylogenetic relationship to rose yellow mosaic virus (RoYMV), the sole member of newly established genus Roymovirus in the family Potyviridae. The coat protein gene (CP) of this virus shares 49.2% nucleotide and 55.1% amino acid sequence identity with that of RoYMV. These results suggest that this virus, which was named "phellodendron yellow ringspot-associated virus" (PYRaV) is a new member of the genus Roymovirus.

Areca Palm Necrotic Ringspot Virus, Classified Within a Recently Proposed Genus Arepavirus of the Family Potyviridae, Is Associated With Necrotic Ringspot Disease in Areca Palm.

Areca palm (Areca catechu), one of the two most important commercial crops in Hainan, China, has been severely damaged by a variety of pathogens and insects. Here, we report a new disease, tentatively referred to as areca palm necrotic ringspot disease (ANRSD), which is highly epidemic in the main growing regions in Hainan. Transmission electron microscopy observation and small RNA deep sequencing revealed the existence of a viral agent of the family Potyviridae in a diseased areca palm plant (XC1). The virus was tentatively named areca palm necrotic ringspot virus (ANRSV). Subsequently, the positive-sense single-stranded genome of ANRSV isolate XC1 was completely determined. The genome annotation revealed the existence of two cysteine proteinases in tandem (HC-Pro1 and HC-Pro2) in the genomic 5' terminus of ANRSV. Sequence comparison and phylogenetic analysis suggested the taxonomic classification of ANRSV into the recently proposed genus Arepavirus in the family Potyviridae. Given the close relationship of ANRSV with another newly reported arepavirus (areca palm necrotic spindle-spot virus), the exact taxonomic status of ANRSV needs to be further investigated. In this study, a reverse transcription polymerase chain reaction assay for ANRSV-specific detection was developed and a close association between ANRSV and ANRSD was found.

Characterization of Soybean yellow shoot virus, a New Member of the Family Potyviridae Infecting Soybean Plants in Brazil.

A new virus species, belonging to the family Potyviridae and capable of infecting most of the soybean cultivars grown in Brazil, was collected in Lavras, Minas Gerais, Brazil, and named Soybean yellow shoot virus (SoyYSV). In this study, the complete 9,052-nucleotide genome of SoyYSV was determined and the structural, biological, and molecular properties of the virus were investigated. The SoyYSV genome encoded a single polyprotein that could be subsequently cleaved, generating 11 proteins. The SoyYSV genome shared 49% nucleotide and 36% amino acid sequence identity with Blackberry virus Y. However, the P1 protein of SoyYSV was much smaller and lacked the ALK1 domain characteristic of the genus Brambyvirus. Electron microscopy revealed flexuous filamentous virus particles, 760 to 780 nm in length, and cytoplasmic inclusions typical of those found in plant cells infected with Potyviridae species. In addition to soybean, SoyYSV infected species in the Amaranthaceae, Caricaceae, Fabaceae, and Solanaceae families. Among the most common potyviruses present in Brazil, only SoyYSV induced local necrotic lesions in Carica papaya L. SoyYSV was transmissible by Myzus persicae and Aphis gossypii but lacked the HC-Pro domain required for aphid transmission in other potyviruses. No seed transmission in soybean was observed.

Wheat Virus Identification Within Infected Tissue Using Nanopore Sequencing Technology.

Viral diseases are a limiting factor to wheat production. Viruses are difficult to diagnose in the early stages of disease development and are often confused with nutrient deficiencies or other abiotic problems. Immunological methods are useful to identify viruses, but specific antibodies may not be available or require high virus titer for detection. In 2015 and 2017, wheat plants containing Wheat streak mosaic virus (WSMV) resistance gene, Wsm2, were found to have symptoms characteristic of WSMV. Serologically, WSMV was detected in all four samples. Additionally, High Plains wheat mosaic virus (HPWMoV) was also detected in one of the samples. Barley yellow dwarf virus (BYDV) was not detected, and a detection kit was not readily available for Triticum mosaic virus (TriMV). Initially, cDNA cloning and Sanger sequencing were used to determine the presence of WSMV; however, the process was time-consuming and expensive. Subsequently, cDNA from infected wheat tissue was sequenced with single-strand, Oxford Nanopore sequencing technology (ONT). ONT was able to confirm the presence of WSMV. Additionally, TriMV was found in all of the samples and BYDV in three of the samples. Deep coverage sequencing of full-length, single-strand WSMV revealed variation compared with the WSMV Sidney-81 reference strain and may represent new variants which overcome Wsm2. These results demonstrate that ONT can more accurately identify causal virus agents and has sufficient resolution to provide evidence of causal variants.

Metagenomic analysis of viruses associated with maize lethal necrosis in Kenya.

BACKGROUND: Maize lethal necrosis is caused by a synergistic co-infection of Maize chlorotic mottle virus (MCMV) and a specific member of the Potyviridae, such as Sugarcane mosaic virus (SCMV), Wheat streak mosaic virus (WSMV) or Johnson grass mosaic virus (JGMV). Typical maize lethal necrosis symptoms include severe yellowing and leaf drying from the edges. In Kenya, we detected plants showing typical and atypical symptoms. Both groups of plants often tested negative for SCMV by ELISA. METHODS: We used next-generation sequencing to identify viruses associated to maize lethal necrosis in Kenya through a metagenomics analysis. Symptomatic and asymptomatic leaf samples were collected from maize and sorghum representing sixteen counties. RESULTS: Complete and partial genomes were assembled for MCMV, SCMV, Maize streak virus (MSV) and Maize yellow dwarf virus-RMV (MYDV-RMV). These four viruses (MCMV, SCMV, MSV and MYDV-RMV) were found together in 30 of 68 samples. A geographic analysis showed that these viruses are widely distributed in Kenya. Phylogenetic analyses of nucleotide sequences showed that MCMV, MYDV-RMV and MSV are similar to isolates from East Africa and other parts of the world. Single nucleotide polymorphism, nucleotide and polyprotein sequence alignments identified three genetically distinct groups of SCMV in Kenya. Variation mapped to sequences at the border of NIb and the coat protein. Partial genome sequences were obtained for other four potyviruses and one polerovirus. CONCLUSION: Our results uncover the complexity of the maize lethal necrosis epidemic in Kenya. MCMV, SCMV, MSV and MYDV-RMV are widely distributed and infect both maize and sorghum. SCMV population in Kenya is diverse and consists of numerous strains that are genetically different to isolates from other parts of the world. Several potyviruses, and possibly poleroviruses, are also involved.

Wuhan poty-like virus 1 is a possible member of the genus Macluravirus.

We have analysed the genome sequence of Wuhan poty-like virus 1 (WuPLV1), reported as an unclassified RNA virus in GenBank (Accession no: KX884573.1). Based on the polyprotein sequence identity (ranging from 55.2 to 71.1%), with classifiable members of the Macluravirus genus of the plant virus family Potyviridae, we suggest that WuPLV1 represents a possible new species of Macluravirus, although the virus was isolated from the Chinese land snail Mastigeulota kiangsinensis, which is not known to be a host or vector of macluraviruses.

Complete genomic sequence of a novel macluravirus, alpinia oxyphylla mosaic virus (AloMV), identified in Alpinia oxyphylla.

A macluravirus, tentatively named alpinia oxyphylla mosaic virus (AloMV), was identified in Alpinia oxyphylla, and its complete genomic sequence determined. The positively single-stranded RNA genome is comprised of 8213 nucleotides excluding the poly (A) tail, and contains one large open reading frame encoding a polyprotein of 2,626 amino acids. Blastp search showed that the polyprotein of AloMV shared 48%~68% aa sequence identities with other reported macluraviruses. Phylogenetic analysis based on the nucleotide sequence of the polyprotein showed that AloMV, together with all other macluraviruses, clustered into the same group most closely related to cardamom mosaic virus, sharing 66.3% nt and 68% aa sequence identities, respectively. These data above suggest that AloMV represents an isolate of a putative new member within the genus Macluravirus.

Complete genome sequence of a novel virus, classifiable within the Potyviridae family, which infects passion fruit (Passiflora edulis).

We report the complete nucleotide sequence of a new member of the Potyviridae family isolated from passion fruit plants grown in Israel, called Passiflora edulis symptomless virus (PeSV). The PeSV genome is 9,928 nucleotides long and encodes a 3,173 amino acids polyprotein that is predicted to be proteolytically cleaved into 10 mature peptides. Our phylogenetic analysis shows that PeSV represents a new species, and is most closely related to rose yellow mosaic virus (RoYMV). According to currently accepted criteria for genus demarcation, both viruses should be assigned as representative isolates of new species in the recently approved genus, Roymovirus, in the Potyviridae family.

Analysis of the complete genomic sequence of a novel virus, areca palm necrotic spindle-spot virus, reveals the existence of a new genus in the family Potyviridae.

A novel virus, tentatively named "areca palm necrotic spindle-spot virus" (ANSSV), was identified in Areca catechu L. in Hainan, China, and its complete genomic sequence was determined. Its positive-sense single-stranded RNA genome is comprised of 9,437 nucleotides (nt), excluding the poly (A) tail, and contains one large open reading frame encoding a polyprotein of 3,019 amino acids (aa). A Blastp search showed that the polyprotein of ANSSV shared a maximum of 31%-32% aa sequence identity (with 86%-95% coverage) with all seven known macluraviruses. Nucleotide sequence comparison of the ORF of ANSSV to those of macluraviruses revealed identities ranging from 41.0% to 44.6%, which is less than the inter-genus identity values for the family Potyviridae. Phylogenetic analysis based on either the aa or nt sequence of the polyprotein did not cluster ANSSV into any established or unassigned genus of the family Potyviridae. Therefore, we suggest that ANSSV is the first member of a previously unrecognized genus of the family Potyviridae.

Rymovirus: a cautionary tale.

A recent proposal that the genus Rymovirus be assimilated into the genus Potyvirus is examined, discussed, and rejected. It illustrates the danger of using 'sequence identity' as a proxy for phylogenetic relatedness to distinguish closely related but distinct groups of viruses.

Analysis of the complete genome sequence of a potyvirus from passion fruit suggests its taxonomic classification as a member of a new species.

The complete genomic sequence of a telosma mosaic virus (TeMV) isolate (named PasFru), identified in passion fruit in China, was determined. The entire RNA genome of PasFru comprises 10,049 nucleotides (nt) excluding the poly(A) tail and encodes a polyprotein of 3,173 amino acids (aa), flanked by 5' and 3' untranslated regions (UTR) of 276 and 251 nt, respectively. Compared with the previous TeMV isolate Hanoi from Telosma cordata, the only documented isolate with the entire genome sequence annotated, PasFru had an extra 87 nt and 89 aa residues at the 3'-end of 5'UTR and the N-terminus of the P1 protein, respectively, which contributed to the genome size difference between PasFru and Hanoi (10,049 nt versus 9,689 nt). Pairwise sequence comparisons showed that PasFru shares 73.6% nt and 80.9% aa sequence identity with the Hanoi isolate at the whole-genome and polyprotein level, respectively, and these values are below the corresponding threshold values for species demarcation in the family Potyviridae. These data suggest that TeMV-PasFru should be classified as a new member of the genus Potyvirus.

Complete genome sequence of yam chlorotic necrosis virus, a novel macluravirus infecting yam.

The complete genome sequence of a novel member of the genus Macluravirus was determined from yam plants with chlorotic and necrotic symptoms in China. The genomic RNA consists of 8,261 nucleotides (nt) excluding the 3'-terminal poly(A) tail, containing one long open reading frame (ORF) encoding a large putative polyprotein of 2,627 amino acids. Its genomic structure is typical of macluraviruses, which lack the P1 protein, N-terminal HC-Pro, and D-A-G motif for aphid transmission that are found in potyviruses. The virus shares 56.3-63.8% sequence identity at the genome sequence level and 49.7-63.9% at the polyprotein sequence level with other members of the genus Macluravirus. Phylogenetic analysis based on the complete polyprotein sequence of representative members of the family Potyviridae clearly places the virus within the genus Macluravirus. These results suggest that the virus, tentatively named "yam chlorotic necrosis virus" (YCNV), should be considered a member of a novel species in the genus Macluravirus.

ICTV Virus Taxonomy Profile: Potyviridae.

The Potyviridae is the largest family of RNA plant viruses, members of which have single-stranded, positive-sense RNA genomes and flexuous filamentous particles 680-900 nm long and 11-20 nm wide. There are eight genera, distinguished by the host range, genomic features and phylogeny of the member viruses. Genomes range from 8.2 to 11.3 kb, with an average size of 9.7 kb. Most genomes are monopartite but those of members of the genus Bymovirus are bipartite. Some members cause serious disease epidemics in cultivated plants. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the taxonomy of the Potyviridae, which is available at www.ictv.global/report/potyviridae.

Variability in P1 gene redefines phylogenetic relationships among cassava brown streak viruses.

BACKGROUND: Cassava brown streak disease is emerging as the most important viral disease of cassava in Africa, and is consequently a threat to food security. Two distinct species of the genus Ipomovirus (family Potyviridae) cause the disease: Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV). To understand the evolutionary relationships among the viruses, 64 nucleotide sequences from the variable P1 gene from major cassava producing areas of east and central-southern Africa were determined. METHODS: We sequenced an amplicon of the P1 region of 31 isolates from Malawi and Tanzania. In addition to these, 33 previously reported sequences of virus isolates from Uganda, Kenya, Tanzania, Malawi and Mozambique were added to the analysis. RESULTS: Phylogenetic analyses revealed three major P1 clades of Cassava brown streak viruses (CBSVs): in addition to a clade of most CBSV and a clade containing all UCBSV, a novel, intermediate clade of CBSV isolates which has been tentatively called CBSV-Tanzania (CBSV-TZ). Virus isolates of the distinctive CBSV-TZ had nucleotide identities as low as 63.2 and 63.7% with other members of CBSV and UCBSV respectively. CONCLUSIONS: Grouping of P1 gene sequences indicated for distinct sub-populations of CBSV, but not UCBSV. Representatives of all three clades were found in both Tanzania and Malawi.

Is it time to retire the genus Rymovirus from the family Potyviridae?

In the most recent Report of the International Committee on Taxonomy of Viruses (9th Report, 2011) (King et al., Virus Taxonomy, Elsevier, New York, 2011) the family Potyviridae is described as comprising seven genera - Potyvirus, Ipomovirus, Macluravirus, Rymovirus, Tritimovirus, Brambyvirus and Bymovirus - despite previous suggestions questioning the validity of the taxonomic status of the genus Rymovirus. Since then the ICTV website records that an eighth genus Poacevirus has been approved for the Potyviridae family. The creation of the genus Rymovirus at the 1990 Potyvirus Taxonomy Workshop in Braunschweig, Germany was based on two things: (i) the incorrect assumption that the genomes of all mite-transmitted members of the Potyviridae would have strong sequence similarity to that of wheat streak mosaic virus, the only mite-transmitted member of this genus for which sequence data were available at that time, and (ii) that the genus should be named Rymovirus (based on a virus for which there was no sequence information) rather than a name based on wheat streak mosaic virus (e.g., "Whestremovirus") because ryegrass mosaic virus (RGMV) was the first mite-transmitted virus to be described and thus should take precedence. When sequence data for RGMV became available in 1995, these data showed that RGMV was very different from wheat streak mosaic virus (WSMV) and should not be assigned to the same genus. WSMV was subsequently re-assigned to a new genus, Tritimovirus, while the genus Rymovirus was retained. In this author's opinion, this retention is not justified, and the removal of Rymovirus as a distinct genus in the family Potyviridae is recommended. There may be merit when assigning it to the genus Potyvirus in sequestering these viruses in a rymovirus subgroup, as is done with other potyviruses, to reflect their different mode of transmission.

The complete genome sequence of a novel virus, bellflower veinal mottle virus, suggests the existence of a new genus within the family Potyviridae.

A new virus was isolated from a bellflower (Campanula takesimana) plant showing veinal mottle symptoms, and its complete genome sequence was determined. The viral genome consists of a positive-sense single-stranded RNA of 8,259 ribonucleotides. Electron microscopic observation revealed that the viral genome is packaged as a filamentous particle with an average length of approximately 760 nm. BLAST searches of protein databases showed that the encoded polyprotein has a maximum amino acid sequence identity of 34.1% (with 95% coverage) to that of the isolate AD of Chinese yam necrotic mosaic virus (CYNMV; genus Macluravirus). Phylogenetic analysis and comparison of the encoded amino acid sequences with those of other viruses demonstrated that the identified virus shows minimal sequence similarity to known viruses and should therefore be considered a member of a new genus in the family Potyviridae. The name bellflower veinal mottle virus (BVMoV) is proposed for this new virus.