Presence of Grapevine leafroll-associated virus 3 in primary salivary glands of the mealybug vector Planococcus citri suggests a circulative transmission mechanism |
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Authors: | Miguel Cid Sonia Pereira Cristina Cabaleiro Franco Faoro Antonio Segura |
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Institution: | (1) Dpto. de Fisioloxía Vexetal. Facultade de Bioloxía, Universidade de Santiago de Compostela, Santiago de Compostela, 15782, Spain;(2) Dpto. de Producción Vexetal. Escola Politécnica Superior, Universidade de Santiago de Compostela, Lugo, 27002, Spain;(3) Istituto di Virologia Vegetale, Sezione di Milano, Consiglio Nazionale delle Ricerche, Via Celoria 2, Milano, 20133, Italy |
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Abstract: | Grapevine leafroll-associated virus 3 (GLRaV-3) is a mealybug-transmissible ampelovirus. Though the transmission mechanism has been described as semipersistent
on the basis of temporal parameters, definitive proof of this mechanism has never been provided. In the present study, we
carried out preliminary assays to establish the location of the virus in its vector, Planococcus citri. After dissecting the insects, GLRaV-3 was detected by means of IC-RT-PCR in the salivary glands, intestine and Malpighian
tubes, but not in the sucking apparatus. Immunogold labelling of the capsid protein revealed the presence of the virus in
some cells of the primary salivary glands, but not in the alimentary channel of the stylet, or in the accessory salivary glands.
The strong labelling of the electron-dense secretion vesicles in some cells of the primary salivary glands, together with
the non-detection of the virus in the sucking apparatus suggests that the transmission mechanism may be different from that
previously described. We propose a circulative transmission mechanism based on a specific transportation route for the viral
particles from the midgut or hindgut to the salivary glands. As the transmission mechanism is generally a common feature of
a viral genus, the existence of a circulative transmission mechanism for other mealybug-transmitted ampeloviruses is expected.
Organ by organ analysis of GLRaV-1, another ampelovirus not transmissible by P. citri, showed the absence of the virus in the salivary glands, thus providing further, though indirect, evidence in favour of circulative
transmission for this virus genus. |
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Keywords: | Ampelovirus Citrus mealybug GLRaV-3 Grapevine leafroll Semipersistent transmission |
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