Two distinct mechanisms regulate luteovirus transmission efficiency and specificity at the aphid salivary gland

Barley yellow dwarf luteovirus (BYDV) particles are transmitted by aphids in a species-specific manner. Transmission to plants requires that the virus particles be transported across the basal lamina and plasmalemma of the accessory salivary gland (ASG). To characterize the role of the ASG basal lamina in regulating BYDV transmission, five aphid species were microinjected with purified New York isolates BYDV-PAV or -RPV. Both viruses associated specifically only with the ASG basal lamina. The ability of virions to penetrate the basal lamina was separate from the ability to penetrate the plasmalemma. When the salivary glands of vector, Sitobion avenae, or non-vector, Rhopalosiphum maidis, aphids were incubated in vitro with New York isolate BYDV-MAV, virions only attached to the ASG basal lamina of S. avenae. When anionic and cationic ferritin were microinjected into aphids, only cationic ferritin aggregated on the surface of the ASG basal lamina and at openings of plasmalemma invaginations into the cytoplasm, suggesting that these sites had a net negative charge. In vitro studies of anionic and cationic gold penetration of ASG basal laminae indicated a macromolecular size exclusion limit of approximately 20 nm that depended on charge. Anionic gold particles did not accumulate in the basal lamina as densely as the 25 nm BYDV particles, suggesting that the virus particles have a greater affinity for the ASG basal lamina. These results indicate that both the ASG basal lamina and plasmalemma contain specific components independently involved in the recognition and transmission of luteoviruses.