Potyvirus is the largest genus of plant viruses causing significant losses in a
wide range of crops. Potyviruses are aphid transmitted in a nonpersistent
manner and some of them are also seed transmitted. As important
pathogens, potyviruses are much more studied than other plant viruses
belonging to other genera and their study covers many aspects of
plant virology, such as functional characterization of viral proteins, molecular
interaction with hosts and vectors, structure,taxonomy,
evolution, epidemiology, and diagnosis. Biotechnological applications of
potyviruses are also being explored. During this last decade, substantial
advances have been made in the understanding of the molecular biology of
these viruses and the functions of their various proteins
Potyvirus is a genus of positive-strand RNA viruses in the family
Potyviridae. Plants serve as natural hosts. The genus is named after
member virus potato virus Y. Potyviruses account for about thirty
percent of the currently known plant viruses.
The first potyvirus probably originated 15,000–30,000 years
ago, in a Eurasian grass host, by acquiring crucial changes to
its coat protein and HC-Pro protein, which enabled it to be
transmitted by migrating host-seeking aphids.
Potyvirus is a genus of positive-strand RNA viruses in the family Potyviridae.
Plants serve as natural hosts. The genus is named after member virus potato
virus Y. Potyviruses account for about thirty percent of the currently
known plant viruses. Like begomoviruses, members of this genus may cause
significant losses in agricultural, pastoral, horticultural, and ornamental crops.
More than 200 species of aphids spread potyviruses, and most are from the
subfamily Aphidinae (genera Macrosiphum and Myzus). The genus contains
The virion is non-enveloped with a flexuous and filamentous nucleocapsid, 680 to 900 nanometers
(nm) long and is 11–20 nm in diameter. The nucleocapsid contains around 2000 copies of the
capsid protein. The symmetry of the nucleocapsid is helical with a pitch of 3.4 nm.
• The genome is a linear, positive-sense, single-stranded RNA ranging in size from 9,000–
12,000 nucleotide bases. Most potyviruses have non-segmented genomes, though a number
of species are bipartite. The base composition is: 21–23.51–26% G; 23–30.15–44% A; 14.9–
22.41–28% C; 15.6–24.41–30.9% U.
• In the species with a single genome, at the 5' end a protein is covalently linked (the VPg protein).
It encodes a single open reading frame (ORF) expressed as a 350 kDa polyprotein precursor. This
is processed into ten smaller proteins: protein 1 protease (P1-Pro), helper component
protease (HC-Pro), protein 3 (P3), cylindrical inclusion (CI), viral protein genome-linked (Vpg),
nuclear inclusion A (NIa), nuclear inclusion B (NIb), capsid protein (CP) and two small putative
proteins known as 6K1 and 6K2. The P3 cistron also encodes a second protein—P3N-PIPO—
which is generated by a +2 frameshift.
10. PROPERTIES OF THE VIRAL PROTEIN
• P1-Pro (~33 kiloDaltons (kDa) in molecular weight) is a serine protease.
• HC-Pro (~52 KDa) is a proteasethat is also involved in aphid transmission. As a proteaseit cleaves a glycine-glycinedipeptide at its own C-
terminus. Italso interacts with eukaryotic initiation factor 4 (eIF4). Itacts as a viral RNA silencing suppressor.
• P3 (~41 kDa) the function is not known. Itinteracts with large subunitof the ribulose-1,5-bisphosphatecarboxylase/oxygenase.
• CI (~71 kDa) is an RNA helicase with ATPaseactivity. It is also involved in membrane attachment.
• NIa (~50 kDa) is cleaved into NIa-Pro a protease(~27 kDa) and the VPg (~22 kDa) protein.
• NIb (~59 kDa) is an RNA-dependent RNA polymerase.
• 6K1 (~6 kDa) the function is not known. 6K2 (~6 kDa) protein, having a single trans membranedomain, is accumulating in the host cellular
membranes and is thought to play a role in forming the replication vesicles of the virus.
• P3N-PIPO(~25 kDa) the function is not known but it appears to be essential. Itinteracts with both the large and small subunits of the
• CP the capsid protein ranges between 30 and 35 kDa in weight.
• VPg protein interacts with eukaryotic initiation factor 4E (eIF4E).
This interaction appears to be essential to viral infectivity. Two proteases,
P1 and the helper component protease(HC) catalyseonly autoproteolytic reactions at their respective C termini. The remaining cleavage
reactions are catalysed by either trans-proteolytic or autoproteolytic mechanisms by the small nuclear inclusion protein (NIa-Pro).This latter
protein is an evolutionary homology of the picornavirus 3Cproteinase.
11. LIFE CYCLE
• Replication may occur in the cytoplasm, nuclei, chloroplasts, Golgi apparatus, cell
vacuoles or more rarely in unusual sites.
• Potyviruses make proteinaceous inclusions in infected plant cells. These may be
crystals in either the cytoplasm or in the nucleus, as amorphous X-bodies,
membranous bodies, viroplasms or pinwheels. The inclusions may or may not
(depending on the species) contain virions. These inclusions can be seen in the light
microscope in leaf strips of infected plant tissue stained with Orange-Green (protein
stain) but not Azure A (nucleic acid stain). There are four different kinds of
• Replication follows the positive-stranded RNA virus replication model. Positive-
stranded RNA virus transcription is the method of transcription. Translation takes
place by -1 ribosomal frameshifting. The virus exits the host cell by tubule-guided
viral movement. Plants serve as the natural host. The virus is transmitted via a
vector (insects). Transmission routes are vector and mechanical.
Potyviruses evolved between 6,600 and 7,250 years ago. They appear to
have evolved in southwestEurasia or north Africa. The estimated mutation rate is
about 1.15×10−4 nucleotide substitutions/site/year.
Agriculture was introduced into Australia in the 18th century. This introduction
also included plant pathogens. Thirty eight potyvirus species have been isolated
in Australia. Eighteen potyviruses have been found only in Australia and are
presumed to be endemic there. The remaining twenty appear to have been
introduced with agriculture
• Unique discoloration pattern of cucurbit leaves with yellowish
sections in between green regions. Initial serrated appearance of leaf
margins can also be noticed. Stunted inward curling leaves with a
“wired” or strapped appearance.
• Léonard, S; Plante, D; Wittmann, S; Daigneault, N; Fortin, MG; Laliberté, JF
(2000). "Complex formation between potyvirus VPg and translation eukaryotic initiation
factor 4E correlates with virus infectivity". J Virol. 74 (17): 7730–
7737. doi:10.1128/jvi.74.17.7730-7737.2000. PMC 112301.PMID 10933678.
• ^ "Materials and Methods for the Detection of Viral Inclusions". Universityof Florida -
Institute of Food and Agricultural Sciences. Archived from the original on 19 February 2012.
• ^ Christie, R.G. and Edwardson, J.R. (1977). Fla Agric. Exp. Stn Monog. No. 9, 150 pp.
• ^ How do you diagnose a virus infection in a plant? Archived 4 August2012 at archive.today
• ^ Florida Department of Agriculture and Consumer Services: Florida plant viruses and t