What are the limits of the packaging capacity for genomic RNA in the cores of rotaviruses and of other members of the Reoviridae?

Species A rotaviruses (RVAs) can package additional homologous genomic sequences which have emerged by partial duplication events (genome rearrangements). Due to the availability of a plasmid only-based reverse genetics system for RVs, various heterologous sequences have been rescued as fusion genes into viable RVAs. Using cryo-electron microscopy, the native structures of the dsRNA genome of Cytoplasmic Polyhedrosis Virus, a member of the Cypovirus genus of the Reoviridae, and partially of Rotavirus and Orbivirus, have been determined. These structural and some functional data were used to calculate the volume occupied by the viral genome in relation to the volume available in viral cores. The native dsRNA genomes were estimated to occupy only one to two thirds of the space available in core particles of the genera Cypovirus, Rotavirus, Orbivirus, Orthoreovirus, and Coltivirus in the Reoviridae family. The findings raise the captivating question of the upper limit of the recombinant RNA packaging capacity of reovirus particles.