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A Soluble Form of the Tomato spotted wilt virus (TSWV) Glycoprotein G_N (G_N-S) Inhibits Transmission of TSWV by Frankliniella occidentalis

First, third, fifth, and eighth authors: Department of Entomology, University of Wisconsin, Madison 53706; second, fourth, and sixth authors: Department of Entomology, University of California, Davis 95616; seventh author: Department of Plant Pathology, University of Wisconsin and U.S. Department of Agriculture, Vegetable Crops Research Unit, Madison, WI 53706.

Tomato spotted wilt virus (TSWV) is an economically important virus that is transmitted in a persistent propagative manner by its thrips vector, Frankliniella occidentalis. Previously, we found that a soluble form of the envelope glycoprotein G_N (G_N-S) specifically bound thrips midguts and reduced the amount of detectable virus inside midgut tissues. The aim of this research was to (i) determine if G_N-S alters TSWV transmission by thrips and, if so, (ii) determine the duration of this effect. In one study, insects were given an acquisition access period (AAP) with G_N-S mixed with purified virus and individual insects were assayed for transmission. We found that G_N-S reduced the percent of transmitting adults by eightfold. In a second study, thrips were given an AAP on G_N-S protein and then placed on TSWV-infected plant material. Individual insects were assayed for transmission over three time intervals of 2 to 3, 4 to 5, and 6 to 7 days post-adult eclosion. We observed a significant reduction in virus transmission that persisted to the same degree throughout the time course. Real-time reverse transcription polymerase chain reaction analysis of virus titer in individual insects revealed that the proportion of thrips infected with virus was reduced threefold when insects were preexposed to the G_N-S protein as compared to no exposure to protein, and nontransmitters were not infected with virus. These results demonstrate that thrips transmission of a tospovirus can be reduced by exogenous viral glycoprotein.

Additional keywords:Bunyaviridae, plant virology, Thysanoptera, virus entry, virus--vector interactions, western flower thrips.