Discovery and Characterization of a Novel Bipartite Botrexvirus From the Phytopathogenic Fungus Botryosphaeria dothidea.

Mengmeng Yang,Wenxing Xu,Guoping Wang,Feng Xiao,Xiaoqi Zhou,Yashuang Guo,Ni Hong,Yanxiang Wang,Zuokun Yang

doi:10.3389/fmicb.2021.696125

Abstract

In this study, we describe a novel positive, single-stranded (+ss) RNA mycovirus, named Botryosphaeria dothidea botrexvirus 1 (BdBV1), from a phytopathogenic fungus Botryosphaeria dothidea showing abnormal morphology and attenuated virulence. BdBV1 is phylogenetically related to Botrytis virus X (BotVX) and is the second potential member of the proposed genus Botrexvirus in the family Alphaflexiviridae. However, it differs from the monopartite BotVX in that BdBV1 possesses a bipartite genome comprised of two ssRNA segments (RNA1 and RNA2 with lengths of 5,035 and 1,063 nt, respectively). BdBV1 RNA1 and RNA2 encode putative RNA-dependent RNA polymerase (RdRp) and coat protein (CP) genes, which share significant identity with corresponding genes in both fungal and plant viruses. Moreover, open reading frames (ORFs) 2–4 of BdBV1 RNA1 shared no detectable identity with any known viral proteins. Immunosorbent electron microscopy (ISEM) analysis using an antibody against the virus CP generated in vitro revealed that BdBV1 is encapsidated in filamentous particles. A comparison of the biological effects of BdBV1 infection on symptoms and growth in isogenic lines of virus-free and virus-infected B. dothidea revealed that BdBV1 is probably involved in reduced growth and virulence of the host fungus. This study describes and characterizes a novel bipartite botrexvirus, which is closely related to uni- and multi-partite fungal and plant viruses and contributes useful information to a better understanding of virus evolution.

Highlights

Mycoviruses are widely distributed in all major groups of fungi (Ghabrial et al, 2015)
Mycoviruses Identified in Botryosphaeria dothidea Strain L153
BdPV1 RNA-dependent RNA polymerase (RdRp) shares the highest identity of 99.5% (E-value = 0) with that of the isolate LW-1 from B. dothidea, whose double-stranded RNA (dsRNA) were confirmed by agarose gel analysis of the dsRNA extraction as expected sizes (Supplementary Figure 1A)

Summary

Introduction

Mycoviruses (fungal viruses) are widely distributed in all major groups of fungi (Ghabrial et al, 2015). The vast majority of reported mycoviruses have double-stranded RNA (dsRNA) or linear positive single-stranded RNA (+ssRNA) genomes, and a few ssDNA or negative (−) ssRNA mycoviruses have been described The discovery of more novel mycoviruses has expanded our understanding of the origin, ecology, and evolutionary pathways of viruses (Ghabrial and Suzuki, 2009; Jia et al, 2017; Li et al, 2020; Sato et al, 2020). Most dsRNA viruses are comprised of segmented genomes (Supplementary Table 1; Ghabrial et al, 2015), including the families Partitiviridae (two or three genomic segments, 1.4– 2.3 kbp), Chrysoviridae (three to seven genomic segments, 2.4– 3.6 kbp), and Polymycoviridae (four to eight genomic segments, 7.5–12.5 kbp) (Kanhayuwa et al, 2015; Jia et al, 2017; Sato et al, 2018). Some + ssRNA viruses express their proteins through the 3 -co-terminal subgenomic RNAs (sgRNAs) such as the allexiviruses in the family Alphaflexiviridae and okaviruses in the family Roniviridae, while there are no reports concerning + ssRNA viruses displaying 3 -co-terminal genomic RNAs

Methods

Results

Conclusion