Novel and divergent viruses associated with Australian orchid-fungus symbioses

Abstract

Terrestrial orchids represent a symbiotic union between plants and mycorrhizal fungi. This study describes the occurrence and nature of viruses associated with one population of wild Pterostylis sanguinea orchids, including their fungal symbionts, over two consecutive years. A generic sequencing approach, which combined dsRNA-enrichment from plant and mycelial tissues, random amplification and high throughput shotgun sequencing was used to identify novel viruses. The majority of the virus-like sequences represent partial genomes, and their identification is based solely on de novo assembly of sequencing data. In orchid leaf tissues we found three isolates of a novel totivirus and an unclassified virus; both resemble fungus-infecting viruses. Two isolates of Ceratobasidium sp that were isolated from orchid underground stems contained at least 20 viruses, 16 of which were previously described as alphapartitiviruses and betapartitiviruses. A novel hypovirus and a mitovirus were genetically distant from existing members of the genera and did not readily fit into recognised subgroups.

The virome from a collection of endomycorrhizal fungi reveals new viral taxa with unprecedented genome organization

“…Our work reports, for the first time, mycoviruses associated with ERM fungi and increases the diversity of mycoviruses characterized in ORM fungi ( Ong et al. 2016 , 2017 , 2018 ). In addition to new viruses related to established taxa, we present three virus types with unprecedented genome organizations, one of which represents a completely new virus group that was not possible to reliably include in the monophyletic phylogenetic tree comprising the vast majority of RNA viruses ( Wolf et al.…”

“…In particular, no mycoviruses have been reported from ERM fungi so far, and a few mycoviruses have been characterized in ORM fungi from Australia, including a newly described hypovirus and a mitovirus that could not be ascribed to known taxa of the same genera ( Ong et al. 2016 , 2017 , 2018 ).…”

A Comprehensive Study of Orchid Seed Production Relative to Pollination Traits, Plant Density and Climate in an Urban Reserve in Western Australia

“…However, suspected symptoms of virus infection were sometimes observed before plants disappeared. Viruses are common in WA orchids, but usually do not cause visual symptoms [58]. There was some predation of seedpods by insects, but these impacts were relatively minor compared to other studies (e.g., Light and MacConaill [47]).…”

Viruses of endophytic and pathogenic forest fungi

“…For example, a mycovirus was detected in Colletotrichum gloeosporioides, an endophyte which harms cashew trees (Anacardium occidentale L.) by causing anthracnose [35]. Furthermore, viruses from the Endornaviridae family, which can infect plants, fungi and oomycetes, were found in root mycorrhizal Ceratobasidium fungi [36,37]. Ong et al studied the fungal symbionts of Pterostylis sanguinea, a wild orchid from western Australia, and found 22 novel mycoviruses from the investigated fungi [37].…”

“…Furthermore, viruses from the Endornaviridae family, which can infect plants, fungi and oomycetes, were found in root mycorrhizal Ceratobasidium fungi [36,37]. Ong et al studied the fungal symbionts of Pterostylis sanguinea, a wild orchid from western Australia, and found 22 novel mycoviruses from the investigated fungi [37]. Moreover, mycoviruses not only infect filamentous, phytopathogenic fungi, but have also been reported in edible mushrooms, which demonstrates their commercial significance [38,39].…”