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Olpidium-transmitted viruses

Rochon, D. (2016) Olpidium-transmitted viruses. In: Vector-Mediated Transmission of Plant Pathogens. J.K. Brown, ed. The American Phytopathological Society Press, ISBN 978-0-89054-535-5


Soil transmission of some viruses is facilitated by the zoosporic root-inhabiting fungus Olpidium. This can occur either by binding of the virus to zoospores in the nutrient or soil medium outside of the plant root system or by incorporation of the virus into the sporangium in roots of co-infected plants. The zoospore serves as a vehicle for transfer of the virus from one plant root system to another. Viruses in the families Tombusviridae and Ophioviridae and the unclassified genus Varicosavirus have evolved mechanisms for becoming associated with the zoospore. In the case of tombusviridae members, specific CP sequences and structures serve to facilitate attachment of particles to putative receptors on the zoospore surface. Particles of the tombusvirus, Cucumber necrosis virus (CNV), bind mannose- and fucose-containing glycoproteins present on the coat of the O. bornovanus zoospore. Virions swell when in contact with the zoospore and the ability to swell is essential for subsequent stages of transmission. It is widely believed that spherical viruses swell as part of the disassambly stage during the establishment of infection. Therefore olpidium zoospores not only serve to transmit virus from plant to plant, but also appear to assist virus in the uncoating phase of infection. The primary role of a virus vector is currently believed to be in the dissemination of virus and in breaching of the plant cell wall for virus entry. The possibility that other plant virus vectors play the additional role of assisting in the disassembly stage of infection should be considered.

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