Megabirnavirus structure reveals a putative 120-subunit capsid formed by asymmetrical dimers with distinctive large protrusions

Rosellinia necatrix megabirnavirus 1 (RnMBV1) W779 is a bi-segmented dsRNA virus and a strain of the type species Rosellinia necatrix megabirnavirus 1 of the family Megabirnaviridae. RnMBV1 causes severe reduction of both mycelial growth of Rosellinia necatrix in synthetic medium and fungal virulence to plant hosts, and thus has strong potential for virocontrol (biological control using viruses) of white rot. The structure of RnMBV1 was examined by cryo-electron microscopy and three-dimensional reconstruction at 15.7 Å resolution. The diameter of the RnMBV1 capsid was 520 Å, and the capsid was composed of 60 asymmetrical dimers in the T=1 (so-called T=2) lattice that is well conserved among dsRNA viruses. However, RnMBV1 has putatively 120 large protrusions with a width of ∼45 Å and a height of ∼50 Å on the virus surface, making it distinguishable from the other dsRNA viruses.