Molecular Characterization of a Debilitation-Associated Partitivirus Infecting the Pathogenic Fungus Aspergillus flavus.

Yinhui Jiang,Wenfeng Yu,Qinrong Wang,Jingxian Wang,Bi Yang,Jianjiang Zhou

doi:10.3389/fmicb.2019.00626

Abstract

The opportunistic human pathogenic fungus Aspergillus flavus is known to be infected with mycoviruses. In this study, we report a novel mycovirus A. flavus partitivirus 1 (AfPV1) that was originally isolated from the abnormal colonial morphology isolate LD-3-8 of A. flavus. AfPV1 has spherical virus-like particles about 40 nm in diameter, and three double-stranded RNA (dsRNA) segments (dsRNA1, 2, and 3 with lengths of 1.7, 1.4, and 1.1 kbp, respectively) were packaged in the virions. dsRNA1, dsRNA2, and dsRNA3 each contained a single open reading frame and potentially encoded 62, 42, and 32 kDa proteins, respectively. The dsRNA1 encoded protein shows similarity to the RNA-dependent RNA polymerase (RdRp) of partitiviruses, and the dsRNA2 product has no significant similarity to any other capsid protein (CP) in the GenBank databases, beside some homology with the hypothetical “capsid” protein of a few partitiviruses. The dsRNA3 encodes a protein with no similarity to any protein in the GenBank database. SDS-PAGE and polypeptide mass fingerprint-mass spectrum (PMF-MS) analyses indicated that the CP of the AfPV1 was encoded by dsRNA2. Phylogenetic analysis showed that the AfPV1 and relative viruses were found in an unclassified group inside the Partitiviridae family. AfPV1 seems to result in debilitation symptoms, but had no significant effects to murine pathogenicity. These findings provide new insights into the partitiviruses taxonomy and the interactions between viruses and A. flavus.

Highlights

Mycoviruses are widespread in almost all major groups of fungi (Ghabrial and Suzuki, 2009; Pearson et al, 2009), and most cause no obvious effects in their hosts, but some do cause obvious symptoms resulting in debilitated virulence, slow growth rate, and poor sporulation (Ghabrial and Suzuki, 2009; Yu et al, 2010; Liu et al, 2014; Xie and Jiang, 2014)
No other significant similarity can be found between the putative protein encoded by dsRNA2 and any other capsid protein (CP) sequences, except identities of 76 and 59% with the hypothetical proteins encoded by Botryosphaeria dothidea virus 1 and C. acutatum RNA virus 1 (Table 1)
The results unequivocally indicated that the CP of the A. flavus partitivirus 1 (AfPV1) was encoded by dsRNA2, which is similar to the finding for C. acutatum RNA virus 1 (Zhong et al, 2014a)

Summary

Introduction

Mycoviruses are widespread in almost all major groups of fungi (Ghabrial and Suzuki, 2009; Pearson et al, 2009), and most cause no obvious effects in their hosts, but some do cause obvious symptoms resulting in debilitated virulence, slow growth rate, and poor sporulation (Ghabrial and Suzuki, 2009; Yu et al, 2010; Liu et al, 2014; Xie and Jiang, 2014). Partitiviruses generally possess two essential dsRNA genome segments (1.3–2.5 kbp in length) containing an open reading frame (ORF), respectively (Nibert et al, 2014). Most partitiviruses are typically associated with no obvious effects on their fugal hosts (Nibert et al, 2014). Some interesting reports have clarified about the role of partitivirus in resistance to salinity, regulation of mycotoxin production, and for affecting biocontrol potential in their hosts (Nerva et al, 2017, 2018; Chun et al, 2018)

Methods

Results

Conclusion