The P2 capsid protein of the nonenveloped rice dwarf phytoreovirus induces membrane fusion in insect host cells

Abstract

Insect transmission is an essential process of infection for numerous plant and animal viruses. How an insect-transmissible plant virus enters an insect cell to initiate the infection cycle is poorly understood, especially for nonenveloped plant and animal viruses. The capsid protein P2 of rice dwarf virus (RDV), which is nonenveloped, is necessary for insect transmission. Here, we present evidence that P2 shares structural features with membrane-fusogenic proteins encoded by enveloped animal viruses. When RDV P2 was ectopically expressed and displayed on the surface of insect Spodoptera frugiperda cells, it induced membrane fusion characterized by syncytium formation at low pH. Mutational analyses identified the N-terminal and a heptad repeat as being critical for the membrane fusion-inducing activity. These results are corroborated with results from RDV-infected cells of the insect vector leafhopper. We propose that the RDV P2-induced membrane fusion plays a critical role in viral entry into insect cells. Our report that a plant viral protein can induce membrane fusion has broad significance in studying the mechanisms of virus entry into insect cells and insect transmission of nonenveloped plant and animal viruses.

Rice Dwarf Viruses with Dysfunctional Genomes Generated in Plants Are Filtered Out in Vector Insects: Implications for the Origin of the Virus

“…Moreover, all 12 proteins were detected in RDV-infected VCM that had been maintained for 6 years with weekly transfer (Table 1, VCM6), with slightly reduced accumulation of P2, P9, and Pns11 compared to levels in VCM newly inoculated with strain O (Table 1, VCM0). The P2 outer capsid protein functions in virus adsorption to and penetration into vector insect cells (16,17,19,27). Pns10 forms tubules approximately 85 nm in diameter that mediate transportation of viral particles to neighboring healthy vector insect cells (6,20).…”

“…Similar to another phytoreovirus, Wound tumor virus (15), RDV gradually lost its transmissibility by insect vectors, becoming a TD strain, when RDV-infected plants were propagated vegetatively for more than 4 years in a greenhouse (7). Possibly relevant mutations have been mapped to a nonsense substitu-tion in S2, which encodes an outer capsid protein required for insect transmission (17,19,25,27).…”

Electron microscopic imaging revealed the flexible filamentous structure of the cell attachment protein P2 ofRice dwarf viruslocated around the icosahedral 5-fold axes

“…Therefore, P2 is a putative cell attachment protein to interact with undefined receptors on insect vector cells, and this interaction is required for the host recognition of RDV (12). Moreover, the entry of RDV involves clathrinmediated endocytosis (13), and P2 induces membrane fusion in insect vector cells (14). Atomic structures of the major capsid components P3 and P8 have been determined by X-ray crystallography (15), and a hierarchical capsid assembly mechanism has been…”

Multiple Functions of Rice Dwarf Phytoreovirus Pns10 in Suppressing Systemic RNA Silencing

“…It is transmitted by insect vectors (Nephotettix cincticeps or Resilia dorsalis) in a circulative manner and causes severe dwarf diseases of rice (31). The RDV genome comprises 12 segmented dsRNAs, which encode seven structural proteins and at least six nonstructural proteins (48). The seven structural proteins are products of segments S1, S2, S3, S5, S7, S8, and S9 (48,50).…”

“…The RDV genome comprises 12 segmented dsRNAs, which encode seven structural proteins and at least six nonstructural proteins (48). The seven structural proteins are products of segments S1, S2, S3, S5, S7, S8, and S9 (48,50). The six nonstructural proteins are products of S4, S6, S10, S11, and S12, respectively (3,21).…”