Two Novel Hypovirulence-Associated Mycoviruses in the Phytopathogenic Fungus Botrytis cinerea: Molecular Characterization and Suppression of Infection Cushion Formation.

Fangmin Hao,Weidong Chen,Mingde Wu,Jing Zhang,Long Yang,Ting Ding,Guoqing Li

doi:10.3390/v10050254

Fangmin Hao, Weidong Chen + Show 5 more

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https://doi.org/10.3390/v10050254

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Abstract

Botrytis cinerea is a necrotrophic fungus causing disease on many important agricultural crops. Two novel mycoviruses, namely Botrytis cinerea hypovirus 1 (BcHV1) and Botrytis cinerea fusarivirus 1 (BcFV1), were fully sequenced. The genome of BcHV1 is 10,214 nt long excluding a poly-A tail and possesses one large open reading frame (ORF) encoding a polyprotein possessing several conserved domains including RNA-dependent RNA polymerase (RdRp), showing homology to hypovirus-encoded polyproteins. Phylogenetic analysis indicated that BcHV1 may belong to the proposed genus Betahypovirus in the viral family Hypoviridae. The genome of BcFV1 is 8411 nt in length excluding the poly A tail and theoretically processes two major ORFs, namely ORF1 and ORF2. The larger ORF1 encoded polypeptide contains protein domains of an RdRp and a viral helicase, whereas the function of smaller ORF2 remains unknown. The BcFV1 was phylogenetically clustered with other fusariviruses forming an independent branch, indicating BcFV1 was a member in Fusariviridae. Both BcHV1 and BcFV1 were capable of being transmitted horizontally through hyphal anastomosis. Infection by BcHV1 alone caused attenuated virulence without affecting mycelial growth, significantly inhibited infection cushion (IC) formation, and altered expression of several IC-formation-associated genes. However, wound inoculation could fully rescue the virulence phenotype of the BcHV1 infected isolate. These results indicate the BcHV1-associated hypovirulence is caused by the viral influence on IC-formation-associated pathways.

Highlights

Fungi in the genus of Botrytis are able to infect more than 1400 species of cultivated plants, and are responsible for heavy losses of many important agricultural crops [1]
We described the molecular and biological properties of two mycoviruses, Botrytis cinerea hypovirus 1 (BcHV1) and Botrytis cinerea fusarivirus 1 (BcFV1), co-infecting the hypovirulent strain HBtom-372 of B. cinerea with Botrytis cinerea endornavirus 1 (BcEV1)
Notwithstanding numerous mycoviruses have been reported in Botrytis spp., no hypovirus or fusarivirus has been described in species of Botrytis [8]

Summary

Introduction

Fungi in the genus of Botrytis are able to infect more than 1400 species of cultivated plants, and are responsible for heavy losses of many important agricultural crops [1]. Mycoviruses, as a biocontrol agent, have been successfully used for the control of chestnut blight in Europe [3]. This inspired further research of mycoviruses, and many mycoviruses were constantly reported in different groups of plant pathogenic fungi [4], the complex vegetative compatibility groups (VCGs) limits the use of hypovirus for the control of chestnut blight in Northern America [5,6,7]

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