Polycistronic Genome Segment Evolution and Gain and Loss of FAST Protein Function during Fusogenic Orthoreovirus Speciation

Abstract

<jats:p>The Reoviridae family is the only non-enveloped virus family with members that use syncytium formation to promote cell–cell virus transmission. Syncytiogenesis is mediated by a fusion-associated small transmembrane (FAST) protein, a novel family of viral membrane fusion proteins. Previous evidence suggested the fusogenic reoviruses arose from an ancestral non-fusogenic virus, with the preponderance of fusogenic species suggesting positive evolutionary pressure to acquire and maintain the fusion phenotype. New phylogenetic analyses that included the atypical waterfowl subgroup of avian reoviruses and recently identified new orthoreovirus species indicate a more complex relationship between reovirus speciation and fusogenic capacity, with numerous predicted internal indels and 5’-terminal extensions driving the evolution of the orthoreovirus’ polycistronic genome segments and their encoded FAST and fiber proteins. These inferred recombination events generated bi- and tricistronic genome segments with diverse gene constellations, they occurred pre- and post-orthoreovirus speciation, and they directly contributed to the evolution of the four extant orthoreovirus FAST proteins by driving both the gain and loss of fusion capability. We further show that two distinct post-speciation genetic events led to the loss of fusion in the waterfowl isolates of avian reovirus, a recombination event that replaced the p10 FAST protein with a heterologous, non-fusogenic protein and point substitutions in a conserved motif that destroyed the p10 assembly into multimeric fusion platforms.</jats:p>

ICTV Virus Taxonomy Profile: Spinareoviridae 2022

“…The positive-sense strands of each duplex are modified with a 5′-terminal type 1 cap structure but no 3′-poly(A) tail. The viral RNAs are mostly monocistronic with relatively short 5′-and 3′-non-coding regions, although some segments have a second or third functional ORF [2,3].…”

Fungal Viruses Unveiled: A Comprehensive Review of Mycoviruses

“…The genome characteristics of mycoviruses, including size and segmentation, exhibit variation across families and genera. Specifically, the genomes of dsRNA mycoviruses can range from non-segmented, as observed in Amalgaviridae and Totiviridae , to bisegmented in Megabirnaviridae , Partitiviridae , and Botybirnavirus , quadripartite in Quadriviridae , or multisegmented in Chrysoviridae , Polymycoviridae , and Spinareoviridae [ 5 , 337 , 338 , 339 , 340 , 341 , 342 , 343 ]. Furthermore, genome size among dsRNA mycoviruses is highly diverse, with some families containing mycoviruses with genomes as small as 3.0 kb and others having members with genomes as large as 29 kb [ 338 , 339 ].…”

Dynamics of Germinosome Formation and FRET-Based Analysis of Interactions between GerD and Germinant Receptor Subunits in Bacillus cereus Spores

“…A Nikon Eclipse Ti-E microscope (Nikon Instruments, Tokyo, Japan) equipped with a sCmos camera (Hamamatsu Flash 4.0 V2, Hamamatsu City, Japan), phase-contrast, and wide-field fluorescence components was used to detect the sensitized emission FRET, using fluorescent reporter proteins SGFP2 and mScarlet-I in dormant spores of B. cereus , as previously described [ 15 , 42 , 49 , 50 ]. Briefly, the spectral bleed-through (BT) and cross-excitation (CE) factors of donor or acceptor were determined with spores expressing only SGFP2 or mScarlet-I.…”