Introduction. The genus Potyvirus, family Potyviridae, is the largest genus of plant viruses with 180 members or possible members (Brunt, 1992). Potyviruses are flexuous filamentous particles which contain a single-stranded RNA genome of positive polarity possessing a covalently linked 5′-terminal viral protein (VPg) and a 3′-terminal poly(A) tail (reviewed in Riechmann et al., 1992). They are transmitted from plant to plant by aphids in a non-persistent manner, and this process is dependent on the presence of two virus-encoded proteins (reviewed in Pirone, 1991). One of these, the helper component-proteinase (HC-Pro) has attracted renewed attention during the last few years due to its multifunctionality and to it being implicated in different steps of the potyvirus life cycle. The properties, as well as the established and postulated functions of this protein, are reviewed.
AmmarE. D.,
JarlforsU.,
PironeT. P.1994; Association of potyvirus helper component protein with virions and the cuticle lining the maxillary food canal and foregut of an aphid vector. Phytopathology 84:1054–1060
AtreyaC. D.,
PironeT. P.1993; Mutational analysis of the helper component-proteinase gene of a potyvirus: effects of amino acid substitutions, deletions, and gene replacement on virulence and aphid transmissibility. Proceedings of the National Academy of Sciences, USA 90:11919–11923
AtreyaP. L.,
AtreyaC. D.,
PironeT. P.1991; Amino acid substitutions in the coat protein result in loss of insect transmissibility of a plant virus. Proceedings of the National Academy of Sciences, USA 88:7887–7891
AtreyaC. D.,
AtreyaP. L.,
ThomburyD. W.,
PironeT. P.1992; Site-directed mutations in the potyvirus HC-PRO gene affect helper component activity, virus accumulation, and symptom expression in infected tobacco plants. Virology 191:106–111
CantoT.,
Lopez-MoyaJ. J.,
Serra-YoldiM. T.,
Diaz-RuizJ. R.,
Lopez-AbellaD.1995; Different helper component mutations associated with lack of aphid transmissibility in two isolates of potato virus. Phytopathology 85:1519–1524
CarringtonJ. C.,
FreedD. D.,
SandersT. C.1989b; Autocatalytic processing of the potyvirus helper component proteinase in Escherichia coli and in vitro. Journal of Virology 63:4459–4463
CarringtonJ. C.,
FreedD. D.,
OhC.-S.1990; Expression of potyviral polyproteins in transgenic plants reveals three proteolytic activities required for complete processing. EMBO Journal 9:1347–1353
ChoiG. H.,
PawlykD. M.,
NussD. L.1991; The autocatalytic protease p29 encoded by a hypovirulence-associated virus of the chestnut blight fungus resembles the poty virus-encoded protease HC-Pro. Virology 183:747–752
CroninS.,
VerchotJ.,
Haldeman-CahillR.,
SchaadM. C.,
CarringtonJ. C.1995; Long-distance movement factor: a transport function of the potyvirus helper component proteinase. Plant Cell 7:549–559
De MejiaM. V. G.,
HiebertE.,
PurcifullD. E.,
ThomburyD. W.,
PironeT. P.1985; Identification of potyviral amorphous inclusion protein as a nonstructural, virus-specific protein related to helper component. Virology 142:34–43
DoljaV. V.,
HerndonK. L.,
PironeT. P.,
CarringtonJ. C.1993; Spontaneous mutagenesis of a plant potyvirus genome after insertion of a foreign gene. Journal of Virology 67:5968–5975
DoljaV. V.,
HaldemanR.,
RobertsonN. L.,
DoughertyW. G.,
CarringtonJ. C.1994; Distinct functions of capsid protein in assembly and movement of tobacco etch potyvirus in plants. EMBO Journal 13:1482–1491
DoljaV. V.,
Haldeman-CahillR.,
MontgomeryA. E.,
VandenboschK. A.,
CarringtonJ. C.1995; Capsid protein determinants involved in cell-to-cell and long distance movement of tobacco etch potyvirus. Virology 206:1007–1016
DornierL. L.,
FranklinK. M.,
ShahaduddinM.,
HellmannG. M.,
OvermeyerJ. H.,
HiremathS. T.,
SiawM. F. E.,
LomonossoffG. P.,
ShawJ. G.,
RhoadsR. E.1986; The nucleotide sequence of tobacco vein mottling virus RNA. Nucleic Acids Research 14:5417–5430
Gal-OnA.,
AntignusY.,
RosnerA.,
RaccahB.1992; A zucchini yellow mosaic virus coat protein gene mutation restores aphid transmissibility but has no effect on multiplication. Journal of General Virology 73:2183–2187
GovierD. A.,
KassanisB.1974a; Evidence that a component other than the virus particle is needed for aphid transmission of potato virus Y. Virology 57:285–286
GovierD. A.,
KassanisB.1974b; A virus-induced component of plant sap needed when aphids acquire potato virus Y from purified preparations. Virology 61:420–426
GranierF.,
Durand-TardifM.,
Casse-DelbartF.,
LecoqH.,
RobagliaC.1993; Mutations in zucchini yellow mosaic virus helper component protein associated with loss of aphid transmissibility. Journal of General Virology 74:2737–2742
GrumetR.,
BadaR.,
HammarS.1992; Analysis of the zucchini yellow mosaic virus (ZYMV) potyviral helper component, possible identification of an aphid-interaction domain. Phytopathology. 82:1176
HarrisonB. D.,
RobinsonD. J.1988; Molecular variation in vector-borne plant viruses: epidemiological significance. Philosophical Transactions of the Royal Society of London Series B 321:447–462
HellmannG. M.,
ThomburyD. W.,
HiebertE.,
ShawJ. G.,
PironeT. P.,
RhoadsR. E.1983; Cell-free translation of tobacco vein mottling virus RNA. II. Immunoprecipitation of products by antisera to cylindrical inclusion, nuclear inclusion, and helper component proteins. Virology 124:434–444
HuetH.,
Gal-OnA.,
MeirE.,
LecoqH.,
RaccahB.1994; Mutations in the helper component protease gene of zucchini yellow mosaic virus affect its ability to mediate aphid transmissibility. Journal of General Virology 75:1407–1414
KassanisB.,
GovierD. A.1971a; New evidence on the mechanism of aphid transmission of potato C and potato aucuba mosaic viruses. Journal of General Virology 10:99–101
KassanisB.,
GovierD. A.1971b; The role of the helper virus in aphid transmission of potato aucuba mosaic virus and potato virus C. Journal of General Virology 13:221–228
LecoqH.,
PitratM.1985; Specificity of the helper-component-mediated aphid transmission of three potyviruses infecting muskmelon. Phytopathology 75:890–893
LegavreT.,
MaiaI. G.,
Casse-DelbartF.,
BernardiF.,
RobagliaC.1996; Switches in the mode of transmission select for or against a poorly aphid-transmissible strain of potato virus Y with reduced helpercomponent and virus accumulation. Journal of General Virology 77:1343–1347
MaiaI. G.,
BernardiF.1996; Nucleic acid-binding properties of a bacterially expressed potato virus Y helper component-proteinase. Journal of General Virology 77:869–877
ThomburyD. W.,
PattersonC. A.,
DessensJ. T.,
PironeT. P.1990; Comparative sequence of the helper component (HC) region of potato virus Y and a HC-defective strain, potato virus C. Virology 178:573–578
ThomburyD. W.,
Van Den Heuvel J. F. J. M.,
LesnawJ. A.,
PironeT. P.1993; Expression of potyvirus proteins in insect cells infected with a recombinant baculovirus. Journal of General Virology 74:2731–2735
WangR. Y.,
AmmarE. D.,
ThomburyD. W.,
Lopez-MoyaJ. J.,
PironeT. P.1996; Loss of potyvirus transmissibility and helpercomponent activity correlates with non-retention of virions in aphid stylets. Journal of General Virology 77:861–867