Multifaceted interactions between host ESCRT-III and budded virus-related proteins involved in entry and egress of the baculovirus Autographa californica multiple nucleopolyhedrovirus.

The endosomal sorting complex required for transport (ESCRT) is a conserved protein machine mediating membrane remodeling and scission. In the context of viral infection, different components of the ESCRT-III complex, which serve as the core machinery to catalyze membrane fission, are involved in diverse viruses' entry, replication, and/or budding. However, the interplay between ESCRT-III and viral factors in the virus life cycle, especially for that of large enveloped DNA viruses, is largely unknown. Recently, the ESCRT-III components Vps2B, Vps20, Vps24, Snf7, Vps46, and Vps60 were determined for entry and/or egress of the baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV). Here, we identified the final three ESCRT-III components Chm7, Ist1, and Vps2A of Spodoptera frugiperda. Overexpression of the dominant-negative forms of these proteins or RNAi downregulation of their transcripts significantly reduced infectious budded viruses (BVs) production of AcMNPV. Quantitative PCR together with confocal and transmission electron microscopy analysis revealed that these proteins were required for internalization and trafficking of BV during entry and egress of nucleocapsids. In infected Sf9 cells, nine ESCRT-III components were distributed on the nuclear envelope and plasma membrane, and except for Chm7, the other components were also localized to the intranuclear ring zone. Y2H and BiFC analysis revealed that 42 out of 64 BV-related proteins including 35 BV structural proteins and 7 non-BV structural proteins interacted with single or multiple ESCRT-III components. By further mapping the interactome of 64 BV-related proteins, we established the interaction networks of ESCRT-III and the viral protein complexes involved in BV entry and egress.IMPORTANCEFrom archaea to eukaryotes, the endosomal sorting complex required for transport (ESCRT)-III complex is hijacked by many enveloped and nonenveloped DNA or RNA viruses for efficient replication. However, the mechanism of ESCRT-III recruitment, especially for that of large enveloped DNA viruses, remains elusive. Recently, we found the ESCRT-III components Vps2B, Vps20, Vps24, Snf7, Vps46, and Vps60 are necessary for the entry and/or egress of budded viruses (BVs) of Autographa californica multiple nucleopolyhedrovirus. Here, we demonstrated that the other three ESCRT-III components Chm7, Ist1, and Vps2A play similar roles in BV infection. By determining the subcellular localization of ESCRT-III components in infected cells and mapping the interaction of nine ESCRT-III components and 64 BV-related proteins, we built the interaction networks of ESCRT-III and the viral protein complexes involved in BV entry and egress. These studies provide a fundamental basis for understanding the mechanism of the ESCRT-mediated membrane remodeling for replication of baculoviruses.

Aphid Viruses: A Brief View of a Long History.

Aphids are common agricultural pests with a wide range of hosts from agriculture to forestry plants. As known, aphids also serve as the major vectors to transmit plant viruses. Although numerous studies have focused on interactions between aphids and plant viruses, little is known about the aphid viruses, i.e., the insect viruses that are infectious to aphids. In the past four decades, several aphid viruses have been identified in diverse aphid species. In this review, we present a brief view of the aphid pathogenic viruses from several aspects, including classification of aphid viruses and characters of the viral genome, integration of viral sequences in host genomes, infection symptoms and influence on aphids, as well as host range and transmission modes. Taken together, these studies have increased our understanding of the rarely known aphid viruses, and will potentially contribute to the development of new strategies for controlling aphid populations.