<i>Cryphonectria nitschkei</i>
            Virus 1 Structure Shows that the Capsid Protein of Chrysoviruses Is a Duplicated Helix-Rich Fold Conserved in Fungal Double-Stranded RNA Viruses

Jiang

et al. 2014

J Virol

103

Botryosphaeria dothidea is an important pathogenic fungus causing fruit rot, leaf and stem ring spots and dieback, stem canker, stem death or stool mortality, and decline of pear trees. Seven double-stranded RNAs (dsRNAs; dsRNAs 1 to 7 with sizes of 3,654, 2,773, 2,597, 2,574, 1,823, 1,623, and 511 bp, respectively) were identified in an isolate of B. dothidea exhibiting attenuated growth and virulence and a sectoring phenotype. Characterization of the dsRNAs revealed that they belong to two dsRNA mycoviruses. The four largest dsRNAs (dsRNAs 1 to 4) are the genomic components of a novel member of the family Chrysoviridae (tentatively designated Botryosphaeria dothidea chrysovirus 1 [BdCV1]), a view supported by the morphology of the virions and phylogenetic analysis of the putative RNA-dependent RNA polymerases (RdRps). Two other dsRNAs (dsRNAs 5 and 6) are the genomic components of a novel member of the family Partitiviridae (tentatively designated Botryosphaeria dothidea partitivirus 1 [BdPV1]), which is placed in a clade distinct from other established partitivirus genera on the basis of the phylogenetic analysis of its RdRp. The smallest dsRNA, dsRNA7, seems to be a noncoding satellite RNA of BdPV1 on the basis of the conservation of its terminal sequences in BdPV1 genomic segments and its cosegregation with BdPV1 after horizontal transmission. This is the first report of a chrysovirus and a partitivirus infecting B. dothidea and of a chrysovirus associated with the hypovirulence of a phytopathogenic fungus. IMPORTANCEOur studies identified and characterized two novel mycoviruses, Botryosphaeria dothidea chrysovirus 1 (BdCV1) and Botryosphaeria dothidea partitivirus 1 (BdPV1), associated with the hypovirulence of an important fungus pathogenic to fruit trees. This is the first report of a chrysovirus and a partitivirus infecting B. dothidea and of a chrysovirus associated with the hypovirulence of a phytopathogenic fungus. BdCV1 appears to be a good candidate for the biological control of the serious disease induced by B. dothidea. Additionally, BdPV1 is placed in a clade distinct from the established genera. The BdCV1 capsid has two major structural proteins, and the capsid is distinct from that made up by a single polypeptide of the typical chrysoviruses. BdPV1 is the second partitivirus in which the putative capsid protein shares no significant identity with any mycovirus protein.A small accompanying dsRNA that is presumed to be a noncoding satellite RNA of BdPV1 is the first of its kind reported for a partitivirus.

Section: Discussionmentioning

confidence: 59%

Hypovirulence of the Phytopathogenic Fungus Botryosphaeria dothidea: Association with a Coinfecting Chrysovirus and a Partitivirus

Jiang

et al. 2014

J Virol

103

Journal of General Virology

“…These viruses are currently classified into 10 families (Totiviridae, Birnaviridae, Megabirnaviridae, Partitiviridae, Picobirnaviridae, Cystoviridae, Chrysoviridae, Quadriviridae, Reoviridae and the proposed family Botybirnaviridae; Table 1). Except for birnaviruses and chrysoviruses (Coulibaly et al, 2005;Luque et al, 2010Luque et al, , 2014Gó mez-Blanco et al, 2012), all of these viruses have single conserved capsid layers that enclose their dsRNA genomes. The conserved capsid layer is a mostly central and contiguous icosahedral shell containing 120 chemically identical copies of a coat protein (CP) that has an a-helix-rich a+b hold, which has T51 icosahedral symmetry.…”

mentioning

confidence: 99%

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

Miyazaki

Salaipeth

Kanematsu

et al. 2015

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 T51 (so-called T52) 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.

“…Birnaviruses have a single Tϭ13 shell that encapsidates a polyploid dsRNA genome organized as ribonucleoprotein complexes (21,22). Chrysoviruses, a group of dsRNA mycoviruses with a multipartite genome, have a Tϭ1 capsid with 60 subunits of a single 982-amino-acid capsid protein (CP) (23)(24)(25). The CP is formed by a repeated ␣-helical core, indicative of gene duplication, and the capsid architecture is similar to that of the 120-subunit Tϭ1 layer of reoviruses, cystoviruses, megabirnaviruses, and totiviruses (26).…”

mentioning

confidence: 99%

Heterodimers as the Structural Unit of the T=1 Capsid of the Fungal Double-Stranded RNA Rosellinia necatrix Quadrivirus 1

Luque

Mata

González-Camacho

et al. 2016

J Virol

Self Cite

Most double-stranded RNA (dsRNA) viruses are transcribed and replicated in a specialized icosahedral capsid with a T‫1؍‬ lattice consisting of 60 asymmetric capsid protein (CP) dimers. These capsids help to organize the viral genome and replicative complex(es). They also act as molecular sieves that isolate the virus genome from host defense mechanisms and allow the passage of nucleotides and viral transcripts. Rosellinia necatrix quadrivirus 1 (RnQV1), the type species of the family Quadriviridae, is a dsRNA fungal virus with a multipartite genome consisting of four monocistronic segments (segments 1 to 4). dsRNA-2 and dsRNA-4 encode two CPs (P2 and P4, respectively), which coassemble into ϳ450-Å-diameter capsids. We used three-dimensional cryo-electron microscopy combined with complementary biophysical techniques to determine the structures of RnQV1 virion strains W1075 and W1118. RnQV1 has a quadripartite genome, and the capsid is based on a single-shelled T‫1؍‬ lattice built of P2-P4 dimers. Whereas the RnQV1-W1118 capsid is built of full-length CP, P2 and P4 of RnQV1-W1075 are cleaved into several polypeptides, maintaining the capsid structural organization. RnQV1 heterodimers have a quaternary organization similar to that of homodimers of reoviruses and other dsRNA mycoviruses. The RnQV1 capsid is the first T‫1؍‬ capsid with a heterodimer as an asymmetric unit reported to date and follows the architectural principle for dsRNA viruses that a 120-subunit capsid is a conserved assembly that supports dsRNA replication and organization. IMPORTANCEGiven their importance to health, members of the family Reoviridae are the basis of most structural and functional studies and provide much of our knowledge of dsRNA viruses. Analysis of bacterial, protozoal, and fungal dsRNA viruses has improved our understanding of their structure, function, and evolution, as well. Here, we studied a dsRNA virus that infects the fungus Rosellinia necatrix, an ascomycete that is pathogenic to a wide range of plants. Using three-dimensional cryo-electron microscopy and analytical ultracentrifugation analysis, we determined the structure and stoichiometry of Rosellinia necatrix quadrivirus 1 (RnQV1). The RnQV1 capsid is a T‫1؍‬ capsid with 60 heterodimers as the asymmetric units. The large amount of genetic information used by RnQV1 to construct a simple T‫1؍‬ capsid is probably related to the numerous virus-host and virus-virus interactions that it must face in its life cycle, which lacks an extracellular phase.