Novel and divergent viruses associated with Australian orchid-fungus symbioses.

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 challenges of using high-throughput sequencing to track multiple bipartite mycoviruses of wild orchid-fungus partnerships over consecutive years.

The bipartite alpha- and betapartitiviruses are recorded from a wide range of fungi and plants. Using a combination of dsRNA-enrichment, high-throughput shotgun sequencing and informatics, we report the occurrence of multiple new partitiviruses associated with mycorrhizal Ceratobasidium fungi, themselves symbiotically associated with a small wild population of Pterostylis sanguinea orchids in Australia, over two consecutive years. Twenty-one partial or near-complete sequences representing 16 definitive alpha- and betapartitivirus species, and further possible species, were detected from two fungal isolates.

Novel Endorna-like viruses, including three with two open reading frames, challenge the membership criteria and taxonomy of the Endornaviridae.

Viruses associated with wild orchids and their mycorrhizal fungi are poorly studied. Using a shotgun sequencing approach, we identified eight novel endornavirus-like genome sequences from isolates of Ceratobasidium fungi isolated from pelotons within root cortical cells of wild indigenous orchid species Microtis media, Pterostylis sanguinea and an undetermined species of Pterostylis in Western Australia. They represent the first endornaviruses to be described from orchid mycorrhizal fungi and from the Australian continent.

A novel member of the Tombusviridae from a wild legume, Gompholobium preissii.

As part of an investigation into viruses of wild plants in Australia, a contiguous sequence of 3935 nucleotides was obtained after shotgun sequencing of RNA isolated from an asymptomatic wild legume, Gompholobium preissii. Phylogenetic analysis of the sequence revealed that it most closely resembled that of Trailing lespedeza virus 1 (TLV1), a virus isolated from a wild legume in America. The proposed virus, named Gompholobium virus A, and TLV1 are genetically closest to viruses in the genera Alphacarmovirus and Pelarspovirus, family Tombusviridae, but they share features distinguishing them from both groups.