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. 2023 Feb:325:199037.
doi: 10.1016/j.virusres.2022.199037. Epub 2022 Dec 31.

Molecular and biological characteristics of a novel chrysovirus infecting the fungus phytopathogenic Setosphaeria turcica f.sp. sorghi

Yun Zheng  1 , Shuangshuang Yin  1 , Yinxiao Zhao  1 , Siyu Li  1 , Zhou Lu  1 , Zikuo Li  1 , Qingchao Deng  1 , Zhanbiao Li  2 , Songbai Zhang  3 , Shouguo Fang  4
Affiliations

Molecular and biological characteristics of a novel chrysovirus infecting the fungus phytopathogenic Setosphaeria turcica f.sp. sorghi

Yun Zheng et al. Virus Res. 2023 Feb.

Abstract

A new double-stranded RNA (dsRNA) virus has been identified in the filamentous fungus Setosphaeria turcica f.sp. sorghi, whose genome consists of four segments (dsRNA1-4). Each dsRNA carries single open reading frame (ORF) flanked by 5' and 3' untranslated regions (UTRs) containing strictly conserved termini. The putative protein encoded by dsRNA1 showed 80.50% identity to the RNA-dependent RNA polymerase (RdRp) of the most closely related virus, Alternaria alternata chrysovirus 1 (AaCV1), belonging to the Chrysoviridae. dsRNA2 encodes the putative coat protein, while dsRNA3 and dsRNA4 respectively encode the hypothetical proteins of unknown functions. Phylogenetic analysis based on the RdRp protein indicated the virus clustered with members of the genus Betachrysovirus in the family Chrysoviridae. Based on the dsRNA profile, amino acid sequence comparisons, and phylogenetic analyses, the mycovirus is thought to be a new member of the family Chrysoviridae and designated as Setosphaeria turcica chrysovirus 1 (StCV1). Moreover, obvious differences were observed in the colony, mycelial and spore morphology between StCV1-infected and virus-cured strains of S. turcica f.sp. sorghi. StCV1 infection strongly reduced colony growth rate, spore production ability and virulence on host fungus. To our knowledge, this is the first report about mycovirus infecting S. turcica f.sp. sorghi and also the first chrysovirus infecting S. turcica.

Keywords: Chrysovirus; Genetic diversity; Setosphaeria turcica chrysovirus 1; Setosphaeria turcica f.sp. sorghi.

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Conflict of interest statement

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Fig 1
Fig. 1
Identification and molecular characteristics of Setosphaeria turcica chrysovirus1 (StCV1). (A)Agarose gel electrophoresis of the dsRNAs from S. turcica f.sp. Sorghi strain SNJ38. Lane M, DNA marker. (B) Diagrammatic representation of the genomic organization of StCV1. The open reading frames (ORFs) and the untranslated regions (UTRs) are shown by a rectangle box and a single line, respectively.
Fig 2
Fig. 2
Multiple sequence alignments of the 5′- and 3′-terminal regions of the coding strands for the four dsRNA segments of StCV1. The colors of yellow represent 100% nucleotide identity in the shade.
Fig 3
Fig. 3
Phylogenetic analysis of the RdRp regions of StCV1 and selected dsRNA viruses of the family Chrysoviridae. The phylogenetic tree was constructed using the NJ method with 1000 replicates in MEGA 7.0. Bootstrap values larger than 50% are shown, the position of StCV1 is indicated by a black dot.
Fig 4
Fig. 4
Biological properties of the infected and isogenic virus-cured S. turcica f.sp. sorghi strains. The strain SNJ38 is infected with StCV1; the strain SNJ38–1 has completely eliminated virus and is virus-free. (A) Colony morphology of SNJ38 and SNJ38 −1 (PDA, 7 days, 28 °C). (B) Mycelial morphology of strains (PDA, 3days, 28 °C) at high magnification (1000 ×). (C) Spore morphology of strains (PDA, 10days, 28 °C) at high magnification (1000 ×). (D) Histogram of mycelial growth rate of strains (PDA, 7days, 28 °C). (E) Histogram of spore concentration of strains (PDA, 10days, 28 °C). Statistical analyses were performed by the t-test at the P<0.05 level, and different letters indicate a significant difference (n = 6 in each group).
Fig 5
Fig. 5
Disease spot representative images (A) and histogram of the frequency of flecks formation(B) on sorghum leaf (number/10cm2) inoculated with water and strains (1 × 104conidia·mL−1 spore suspension) at 7days. Statistical analyses were performed by the one-way ANOVA at the P<0.05 level, and different letters indicate a significant difference (n = 6 in each group).
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