Genome Organization and Functional Analysis of a Novel Mycovirus in Ustilaginoidea virens Strain Uv263

doi:10.7668/hbnxb.20195221

Abstract

Abstract:

In order to deeply explore the diversity of mycoviruses in Ustilaginoidea virens,this study used an abnormal strain Uv263 of U.virens isolated from diseased rice samples collected from Hainan Province as experimental material to identify potential mycoviruses in this strain,and analyze the relationship between the genome organization and function of mycoviruses.The results showed that strain Uv263 was infected by a novel mycovirus named Ustilaginoidea virens RNA virus 7 (UvRV7).UvRV7 was a double stranded RNA virus with 5 082 bp in total length and 60.29% GC content.UvRV7 encoded two large open reading frames (ORF1 and ORF2),which encoded the coat protein (CP) and RNA-dependent RNA polymerase (RdRP),respectively.The BlastP comparison showed that the RdRP amino acid sequence of UvRV7 shared the highest similarity with that of Thelebolus microsporus totivirus 1,at 48.49%.The results of multiple alignment based on the amino acid sequence of UvRV7 RdRP showed that the RdRP sequence contained a total of eight conserved motifs,among which the most typical GDD motif in the RdRP conserved domain was identified in the Ⅵ motif.The phylogenetic analysis showed that UvRV7 was the most closely related to Thelebolus microsporus totivirus 1 and clustered with representative viruses of the genus Victorivirus in the family Totiviridae.The results of genome organization and evolutionary analyses both indicated that UvRV7 was a novel mycovirus in the genus Victorivirus.Transmission electron microscopy observations showed that UvRV7 formed a spherical viral particle of about 45 nm.Horizontal and vertical transmission experiments showed that UvRV7 could be efficiently transmitted vertically by conidia and efficiently transmitted horizontally between vegetatively compatible strains.Taken together,this study elucidated the genome organization and evolutionary relationships of the novel mycovirus UvRV7 in U.virens,and provided a potential biocontrol agent and theoretical basis for the biological control of rice false smut.

Key words: Rice false smut, Mycovirus, Biocontrol, Totiviridae, Victorivirus

CLC Number:

S435.111.46

HE Zhenrui, ZHAO Wenhua, YANG Yingqing, YANG Mei, ZHOU Erxun. Genome Organization and Functional Analysis of a Novel Mycovirus in Ustilaginoidea virens Strain Uv263[J]. Acta Agriculturae Boreali-Sinica, 2025, 40(3): 141-148. doi: 10.7668/hbnxb.20195221.

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Figures/Tables 6

Fig.1 Characterization of the mycovirus in Ustilaginoidea virens strain Uv263 A.RT-PCR verification of mycovirus in strain Uv263:M.2 000 bp Marker,1.Before digestion,2.After digestion;B.RT-PCR of dsRNA with mycovirus-specific primers before and after deoxyribonuclease Ⅰ(DNase Ⅰ) (digestion of ssDNA and dsDNA) and S1 nuclease (digestion of ssDNA or ssRNA) treatments.

Fig.2 Cloning of the terminal sequences of UvRV7 in Ustilaginoidea virens strain Uv263 by RACE

Fig.3 Schematic representation of the genomic organization of mycovirus UvRV7 in Ustilaginoidea virens strain Uv263

Fig.4 Multiple alignment and phylogenetic analysis of mycovirus UvRV7 in Ustilaginoidea virens strain Uv263 A.Multiple alignment of the conserved RdRP amino acid motifs of UvRV7 and the representative viruses from the family Totiviridae:Black.The overlapped conserved sequences of selected viruses,Gray.The partially overlapped conserved sequences among viruses;B.Phylogenetic analysis of mycovirus UvRV7:Red stars.The mycovirus UvRV7.

Fig.5 Validation and observation of mycovirus UvRV7 viral particles in Ustilaginoidea virens strain Uv263 A.UvRV7 PCR validation in a mixture of different sucrose concentrations:Sucrose concentrations of 1—6 are 10%,20%,30%,40%,50%, and 60%,respectively;B.Electron micrograph of UvRV7 virus particles,red arrows indicate viral particles with icosahedral symmetry.

Fig.6 Validation of horizontal and vertical transmission efficiencies of mycovirus UvRV7 in Ustilaginoidea virens strain Uv263 A.Validation of UvRV7 horizontal transmission efficiency;B.Validation of UvRV7 vertical transmission efficiency.

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