Loss of potyvirus transmissibility and helper-component activity correlate with non-retention of virions in aphid stylets.
The hypothesis that loss of aphid transmissibility of potyvirus mutants is due to non-retention of virions in the mouthparts was tested by feeding aphids through membranes on purified virions of aphid transmissible (AT or HAT) and non-aphid-transmissible (NAT) tobacco vein mottling virus (TVMV) or tobacco etch virus (TEV), in the presence of functional [potato virus Y (PVY) HC or TVMV HC] or non-functional (PVC HC) helper component (HC). TVMV virions were detected, by electron microscopic examination of immunogold-labelled thin sections, in the food canal or cibarium of 57% of 28 aphids fed on the transmissible combination of TVMV-AT and functional HC, while no virions were found in these structures in 25 aphids fed on the non-transmissible combinations: TVMV-NAT and PVY HC, or TVMV-AT and PVC HC. Autoradiography of intact stylets allowed the examination of much larger numbers of aphids, fed on 125I-labelled TEV; 48% of 523 aphids fed on the TEV-HAT and PVY HC combination retained label in the stylets: this correlated well with the percentage transmission in bioassays. In contrast, in non-transmissible combinations, label was found in the stylets of 0.77% of 389 aphids fed on TEV-NAT and PVY HC, and 1.35% of 223 aphids fed on TEV-HAT and PVC HC. No differences were found in the overall amount of label in the bodies of aphids fed on the transmissible and non-transmissible combinations. There was a strong tendency for virions to be retained in the distal third of the stylets; 56% of aphids positive for TVMV, and 82% of those positive for TEV, had label in this area. These data support the concept that virions retained within the stylets are those that are primarily involved in potyvirus transmission.
Wang
R Y
RY
Department of Plant Pathology, University of Kentucky, Lexington 40546, USA.
Ammuar
E D
ED
Thornbury
D W
DW
Lopez-Moya
J J
JJ
Pirone
T P
TP
D000595:Amino Acid Sequence; D000818:Animals; D001042:Aphids / Q000821:virology*; D007303:Insect Vectors / Q000821:virology*; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D017800:Potyvirus / Q000502:physiology* / Q000648:ultrastructure; D014764:Viral Proteins / Q000502:physiology*; D014771:Virion / Q000502:physiology*
D014764:Viral Proteins