Release of Rice dwarf virus from insect vector cells involves secretory exosomes derived from multivesicular bodies

Plant reoviruses in insect vector cells are sequestered in spherical multivesicular compartments. We demonstrated previously that the plant-infecting reovirus Rice dwarf virus (RDV) exploits multivesicular compartments for the transport and release of viral particles from infected insect vector cells. These multivesicular compartments contain small vesicles and, morphologically, they resemble previously reported endosomal multivesicular bodies (MVBs) exploited by enveloped RNA viruses during budding from the plasma membrane of infected cells. Electron microscopy revealed that, at a late stage of infection, RDV virions are released, together with small vesicles similar to secreted vesicles (exosomes), from infected cells. The incorporation of lysosomes into the multivesicular compartments raised the possibility that functions of host MVBs are required for the efficient release of RDV virions from infected insect vector cells. An actin-myosin transport system has been shown to mediate the transport of these multivesicular compartments. In this addendum, we provide evidence for the proposed model of release of RDV virions from infected insect vector cells that exploits secretory exosomes derived from MVBs.