Molecular characterization of two new alternaviruses identified in members of the fungal family Nectriaceae

Abstract

Since the first report in 2009, at least ten additional viruses have been identified and assigned to the proposed virus family Alternaviridae. Here we report two new mycoviruses tentatively assigned to this family, both identified as members of the fungal family Nectriaceae, which were isolated from surface-disinfected apple roots (Malus x domestica, Borkh.) affected by apple replant disease (ARD). ARD is a highly complex, worldwide-occurring disease resulting from plant reactions to a disturbed (micro)-biome and leads to high economic losses every year. The first alternavirus characterized in this study was identified in a Dactylonectria torresensis isolate. The virus was tentatively named dactylonectria torresensis alternavirus 1 (DtAV1) as the first member of the proposed new species Alternavirus dactylonectriae. The second virus was identified in an isolate of Ilyonectria robusta and was tentatively named ilyonectria robusta alternavirus 1 (IrAV1) as the first member of the proposed new species Alternavirus ilyonectriae. Full genomic sequences of the viruses were determined and are presented. Further, we found hints for putative components of a methyl transferase machinery using in silico approaches. This putative protein domain is encoded by segment 2. However, this result only establishes the basis for subsequent studies in which the function must be confirmed experimentally in vitro. Thus, this is the first study where a function is predicted to all three genomic segments within the group of the alternaviruses. These findings provide further insights into the virome of ARD-associated fungi and are therefore another brick in the wall of understanding the complexity of the disease.

A Novel Strain of Fusarium oxysporum Alternavirus 1 Isolated from Fusarium oxysporum f. sp. melonis Strain T-BJ17 Confers Hypovirulence and Increases the Sensitivity of Its Host Fungus to Difenoconazole and Pydiflumetofen

“…It was stated that the criteria for demarcating species should consider the number of dsRNA segments and the presence and homology of dsRNA 4 (https://ictv.global/files/ proposals/approved?fid=11959#block-teamplus-page-title, accessed on 5 March 2024). Thus far, eighteen mycoviruses have been assigned as members of the family Alternaviridae [11,[13][14][15][16][17][18][19][47][48][49][50][51][52][53][54][55]. Except for FaAV1, which is composed of two dsRNA segments [13], the remaining seventeen alternaviruses contain three or four dsRNA segments [11,[14][15][16][17][18][19][47][48][49][50][51][52][53][54][55].…”

“…It was stated that the criteria for demarcating species should consider the number of dsRNA segments and the presence and homology of dsRNA 4 ( , accessed on 5 March 2024). Thus far, eighteen mycoviruses have been assigned as members of the family Alternaviridae [ 11 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ]. Except for FaAV1, which is composed of two dsRNA segments [ 13 ], the remaining seventeen alternaviruses contain three or four dsRNA segments [ 11 , 14 , 15 , 16 , 17 , 18 , 19 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ].…”

“…Thus far, eighteen mycoviruses have been assigned as members of the family Alternaviridae [ 11 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ]. Except for FaAV1, which is composed of two dsRNA segments [ 13 ], the remaining seventeen alternaviruses contain three or four dsRNA segments [ 11 , 14 , 15 , 16 , 17 , 18 , 19 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ]. Among them, eleven alternaviruses, namely Aspergillus heteromorphus alternavirus 1 (AheAV1) [ 49 ], Cordyceps chanhua alternavirus 1 (CcAV1) [ 52 ], Dactylonectria torresensis alternavirus 1 (DtAV1) [ 53 ], FgAV1 [ 14 ], FiAV1 [ 15 ], FnAV1 [ 16 ], FpgAV1 [ 18 ], FpAV1 [ 17 ], Ilyonectria crassa alternavirus 1 (IcAV1) [ 51 ], Ilyonectria robusta alternavirus 1 (IrAV1) [ 53 ], and Suillus luteus alternavirus 1 (SluAV1) [ 55 ], contain three dsRNA segments, while six alternaviruses, including AaV1 [ 47 ], Aspergillus foetidus virus (AfV) [ 54 ], Aspergillus virus 341 (AsV341) [ …”

Complete genome sequence of a novel alternavirus isolated from the phytopathogenic fungus Colletotrichum fioriniae

“…The family Alternaviridae was not proposed in 2013 until the discovery of the Aspergillus foetidus virus (AfV) [7], and attributed to the previously discovered Aspergillus virus 341 (AsV341) [8], Alternaria alternata virus 1 (AaV1) [9] and AfV. To date, fourteen mycoviruses belong to the family Alternaviridae [7][8][9][10][11][12][13][14][15][16][17][18][19].…”

“…Members of the family Alternaviridae have two genome types, one containing four dsRNA segments and one containing three dsRNA segments. The viral genome ranges from 3.6kb (dsRNA1) to 1.4kb (dsRNA4) [7][8][9][10][11][12][13][14][15][16][17][18][19], and the 3'-UTRs of each monocistronic dsRNA segment is polyadenylated [13,16,20].…”