''Donkey orchid symptomless virus'' (DOSV) was first discovered in
Perth, Australia
Perth is the capital and largest city of the Australian state of Western Australia. It is the fourth most populous city in Australia and Oceania, with a population of 2.1 million (80% of the state) living in Greater Perth in 2020. Perth is ...
which is located on the Western side of
Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
biodiverse
Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic ('' genetic variability''), species ('' species diversity''), and ecosystem ('' ecosystem diversity'') ...
and secluded with
desert
A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About on ...
s on the east and northeast side along with the ocean on the south side. It is home to approximately 8,000 indigenous plant species that are accustomed to living in a
Mediterranean climate
A Mediterranean climate (also called a dry summer temperate climate ''Cs'') is a temperate climate sub-type, generally characterized by warm, dry summers and mild, fairly wet winters; these weather conditions are typically experienced in the ...
. This type of climate means that the plants have adapted to living in unfertile soil, dryness, and can withstand frequent
fire
Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products.
At a certain point in the combustion reaction, called the ignition ...
s in the area. Out of 394 terrestrial
orchid
Orchids are plants that belong to the family Orchidaceae (), a diverse and widespread group of flowering plants with blooms that are often colourful and fragrant.
Along with the Asteraceae, they are one of the two largest families of flowering ...
species, 76 of these species are threatened. Reasons contributing to plants being threatened in this area could be due to the rate at which they reproduce fruit, pollinate, or human contact.
Experimental data
Throughout the years 2011-2013, three researchers conducted a study on common donkey orchids. The article that was published in 2013 is titled, ''Donkey Orchid Symptomless Virus: A Viral ‘Platypus’ from Australian Terrestrial Orchids''. Through this experiment the researchers were able to perform an entire genome sequence for ''Donkey orchid symptomless virus''. The unusual thing about this virus is that it does not cause visible symptoms of infection on the orchids, hence the name ''Donkey orchid symptomless virus''.
So far, it has only been looked at in the Australian terrestrial orchid ''
Diuris longifolia
''Diuris longifolia'' is a species of orchid which is endemic to the south-west of Western Australia.
It has a variety of common names including purple pansy orchid, donkey orchid, common donkey orchid and wallflower orchid. It was one of the fi ...
'', commonly named ‘common donkey orchid’ and another terrestrial orchid, ''
Caladenia latifolia
''Caladenia latifolia'', commonly known as pink fairies is a species of orchid endemic to Australia and is common and widespread in the southern half of the continent and in Tasmania. It has a single, hairy leaf and up to four pink (rarely white ...
'' (pink fairy orchid). The plants were growing in a leftover patch of forest in Perth. The virus was identified in 3 plants: 2 common donkey orchids (of which 264 plants were tested) and one plant from the group ''Caladenia latifolia'' (pink fairy orchid) in which 129 were tested. The donkey orchid has ear-like petals which is where its name originated from.
DOSV most likely evolved in
Western Australia
Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...
because it has so far only been found in orchids
endemic
Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...
to the region, but it is possible that it could have been brought overseas from another region, but researchers are not sure where it came from or how it go to Australia. Therefore, no one knows the vector for ''Donkey orchid symptomless virus'' (insect, mammal, etc.).
As of now, DOSV is more uncommon than other plant viruses because it was only found in 2 common donkey orchids out of the 294 that were tested. The uncommonness of this plant virus could be due to the small number of tested plants in this study, the specific area in which the plants were tested from, or that the two orchid species infected by DOSV have not been studied enough. The common donkey orchid is not threatened which could mean a multitude of things, including that the virus itself has a poor method of entry, replication etc. The rarity of the virus could also be due to the inefficient transmission from plant to plant or the unknown
vector
Vector most often refers to:
*Euclidean vector, a quantity with a magnitude and a direction
*Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism
Vector may also refer to:
Mathematic ...
could be uncommon in that region of Australia.
During the experiment that was conducted in 2011, 2012, and 2013, it was proved that
lyophilization
Freeze drying, also known as lyophilization or cryodesiccation, is a low temperature dehydration process that involves freezing the product and lowering pressure, removing the ice by sublimation. This is in contrast to dehydration by most conve ...
(freezing the leaves of the test plants) inactivates the replication of the virus. In the leaves of orchids that were frozen, the virus was not found in the
RNA
Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...
. In the leaves of orchids that were not frozen, DOSV was found in the viral RNA.
In order to assess how DOSV is scattered among wild orchid plants in Western Australia,
RT-PCR
Reverse transcription polymerase chain reaction (RT-PCR) is a laboratory technique combining reverse transcription of RNA into DNA (in this context called complementary DNA or cDNA) and amplification of specific DNA targets using polymerase cha ...
was used to analyze the RNA taken from the leaves of common donkey orchids and the “two primer pairs that were used were DOSV8F5200 and DOSV8R6100; DOSV10F6800 and DOSV10R7700).” Therefore, researchers were able to observe if the virus was in the RNA of the common donkey orchids that were being tested.
Viral classification structure
''Donkey orchid symptomless virus'' is a
positive-sense single-stranded RNA virus
Positive-strand RNA viruses (+ssRNA viruses) are a group of related viruses that have positive-sense, single-stranded genomes made of ribonucleic acid. The positive-sense genome can act as messenger RNA (mRNA) and can be directly translated into ...
. The virus is in the order ''
Tymovirales
''Tymovirales'' is an order of viruses with five families. The group consists of viruses which have positive-sense, single-stranded RNA genomes. Their genetic material is protected by a special coat protein.
Description
Tymoviruses are mainly ...
'' and the
replicase
RNA-dependent RNA polymerase (RdRp) or RNA replicase is an enzyme that catalyzes the replication of RNA from an RNA template. Specifically, it catalyzes synthesis of the RNA strand complementary to a given RNA template. This is in contrast to ...
lineage is ''
Potexvirus
''Potexvirus'' is a genus of pathogenic viruses in the order ''Tymovirales'', in the family ''Alphaflexiviridae''. Plants serve as natural hosts. There are 48 species in this genus, three of which are assigned to a subgenus. Diseases associated ...
''-like. It is believed that the virion of DOSV is more like a ‘
flexuous
{{Short pages monitor
The RNA from the plants was previously extracted in order to see if the RNA contains the virus. From here, researchers were able to sequence the
genome
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...
of the virus. The results from the sequencing concluded that the genome contains “7
open reading frame
In molecular biology, open reading frames (ORFs) are defined as spans of DNA sequence between the start and stop codons. Usually, this is considered within a studied region of a prokaryotic DNA sequence, where only one of the six possible readin ...
s along with a 5’ untranslated region and a 3’ UTR” (untranslated region). The 5’UTR and the 3’UTR (146-147 nt in length) do not share any identity with any other known virus, so these regions of the genome are specific to DOSV.
''Donkey orchid symptomless virus'' also has a putative coat protein and a movement protein. The movement protein in DOSV helps the virus move from an infected cell to a completely healthy cell. This then allows the virus to infect the healthy cell by entering and taking over the cell’s machinery to perform translation of the viral
mRNA
In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of Protein biosynthesis, synthesizing a protein.
mRNA is ...
along with replication of the viral genome. Once the virus replicates itself in the cell, it can take over the cell and cause cell death.
Entry into cell
There has not been any research conducted on the virus’s entry into plant cells, but since it is closely related to ''Furovirus'', the virus could possibly have a similar way of entry. ''Furovirus'' enters its way into a plant cell by penetrating the
plasma membrane
The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...
and then the viral RNA is released into the
cytoplasm
In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. The ...
of the cell. From here on out, the virus uses the cell’s own machinery to carry out
transcription
Transcription refers to the process of converting sounds (voice, music etc.) into letters or musical notes, or producing a copy of something in another medium, including:
Genetics
* Transcription (biology), the copying of DNA into RNA, the fir ...
There is not much information on the replication and transcription of ''Donkey orchid symptomless virus'' because there has not been much research conducted. However, as mentioned before, DOSV is closely related to ''Furovirus'' which carries out transcription and replication by using the plant cell’s own machinery.
The replicase in DOSV shares similar identity with plant viruses of the family, ''
Alphaflexiviridae
''Alphaflexiviridae'' is a family of viruses in the order ''Tymovirales''. Plants and fungi serve as natural hosts. There are 65 species in this family, assigned to six genera. Diseases associated with this family include: mosaic and ringspot sy ...
'', which are also (+)ssRNA viruses that use plants as their host. Viruses in the ''Alphaflexiviridae'' family enter the plant cells and replicate in the same fashion as the ''Furovirus''.
Another virus that is in ''Alphaflexiviridae'' and is very similar to DOSV is the '' Platypuvirus''. This virus replicates similarly to the other mentioned virus (''Furovirus'') in that it enters the cell by penetrating and the replication occurs by using “viral factories” in the cell.
Modulation of host processes/interaction with host
There has not been much research conducted on the exact interaction with the host or how the host processes are affected. This could be due to the fact that
plant virus
Plant viruses are viruses that affect plants. Like all other viruses, plant viruses are obligate intracellular parasites that do not have the molecular machinery to replicate without a host. Plant viruses can be pathogenic to higher plants.
M ...
es are not as heavily studied as
animal virus
Animal viruses are viruses that infect animals. Viruses infect all cellular life and although viruses infect every animal, plant, fungus and protist species, each has its own specific range of viruses that often infect only that species.
Vertebra ...
es. However, researchers have found that the virus causes the leaves to become
necrotic
Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...
. The plant itself does not necessarily exhibit visible symptoms on the outside, but it does on the inside.
Associated disease(s)
When the virus replicates in the plant it can cause infection which has led to the following visible symptoms: leaf distortion, mosaic patterns on the leaves, and stunting.
Tropism
Though research has not been conducted on the reaction of the common donkey orchid to DOSV, researchers ''have'' noticed that most of the orchids in the Western Australian region seem to be healthy. This could be due to the vector of the virus (which is not known) to be unsuccessful when infecting the orchids, the type of environment the orchids are located in or it could be due to survival of the fittest among the orchid population.