See text
43-518: Orthotospovirus is a genus of negative-strand RNA viruses , in the family Tospoviridae of the order Bunyavirales , which infects plants. Tospoviruses take their name from the species Tomato spotted wilt orthotospovirus (TSWV) which was discovered in Australia in 1919. TSWV remained the only known member of the family until the early 1990s when genetic characterisation of plant viruses became more common. There are now at least twenty species in
86-466: A cap on viral mRNA or snatches a cap from host mRNA and attaches that cap to viral mRNA. Within the phylum, −ssRNA viruses that infect arthropods appear to be basal and the ancestors of all other −ssRNA viruses. Arthropods frequently live together in large groups, which allows for viruses to be transmitted easily. Over time, this has led to arthropod −ssRNA viruses gaining a high level of diversity. While arthropods host large quantities of viruses, there
129-571: A combined six classes, five of which are monotypic down to lower taxa: Negative-strand RNA viruses are classified as Group V in the Baltimore classification system, which groups viruses together based on their manner of mRNA production and which is often used alongside standard virus taxonomy, which is based on evolutionary history. Therefore, Group V and Negarnaviricota are synonymous. Negative-strand RNA viruses caused many widely known diseases. Many of these are transmitted by arthropods, including
172-531: A high population of thrips. For instance TSWV is an agricultural pest in Asia, America, Europe and Africa. Over the past 15 years outbreaks of Tomato spotted wilt disease have become more prevalent in these regions. Therefore, TSWV is described as an emerging viral disease of plants. The increased prevalence is largely because of the successful survival of the thrips vector Frankliniella occidentalis . Another thrips, Scirtothrips dorsalis , has also been implicated in
215-409: A second common tospovirus found in ornamentals, Impatiens necrotic spot virus (INSV). Cytological studies of TSWV and INSV have shown that these viruses produce granular inclusions in the cytoplasm of infected plants. These inclusions can be seen in the light microscope with proper staining techniques. These inclusions can be diagnostic. Tospoviruses are prevalent in warm climates in regions with
258-885: A serious plant disease. It has been shown that acquiring TSWV (which only occurs during the larval stages) causes more feeding in the thrips which results in a longer life span eventually. Western flower thrips are a year-round pest, but are less destructive during wet weather. WFTs especially like the color blue , being attracted to blue card material and even more so to blue lights. They are somewhat interested in yellow and barely interested in white . Traps can still function even if surrounded with mesh to exclude beneficials such as hoverflies and bees. Commercial semiochemical pheromone lures are also available which can be used in conjunction with blue sticky traps to maximise sticky trap catches of western flower thrips. Damage can be reduced by growing barriers of nonhost plants around crops and by eliminating reservoir plants, plants to which
301-466: Is a prominent trait among many −ssRNA viruses, and −ssRNA viruses range from having genomes with one segment, typical for members of the order Mononegavirales , to genomes with ten segments, as is the case for Tilapia tilapinevirus . There is no clear trend over time that determines the number of segments, and genome segmentation among −ssRNA viruses appears to be a flexible trait since it has evolved independently on multiple occasions. Most members of
344-452: Is about 1 millimetre ( 3 ⁄ 64 in) long; the female is slightly larger, about 1.4 millimetres ( 1 ⁄ 16 in) in length. Males are rare, and are always pale yellow, while females vary in color, often by season, from red to yellow to dark brown. Each adult is elongated and thin, with two pairs of long wings. The eggs are oval or kidney-shaped, white, and about 0.2 millimetres ( 1 ⁄ 128 in) long. The nymph
387-685: Is common for their genome to be segmented. Negative-strand RNA viruses constitute the phylum Negarnaviricota , in the kingdom Orthornavirae and realm Riboviria . They are descended from a common ancestor that was a double-stranded RNA (dsRNA) virus , and they are considered to be a sister clade of reoviruses , which are dsRNA viruses. Within the phylum, there are two major branches that form two subphyla: Haploviricotina , whose members are mostly non-segmented and which encode an RdRp that synthesizes caps on mRNA, and Polyploviricotina , whose members are segmented and which encode an RdRp that snatches caps from host mRNAs. A total of six classes in
430-438: Is constructed, the mRNA is released by RdRp. In genomes that encode more than one transcribable portion, RdRp can continue scanning to the next start sequence to continue with transcription. Some −ssRNA viruses are ambisense , meaning that both the negative genomic strand and positive antigenome separately encode different proteins. In order to transcribe ambisense viruses, two rounds of transcription are performed: first, mRNA
473-615: Is disagreement about the degree to which cross-species transmission of arthropod −ssRNA viruses occurs among arthropods. Plant and vertebrate −ssRNA viruses tend to be genetically related to arthropod-infected viruses. Furthermore, most −ssRNA viruses outside of arthropods are found in species that interact with arthropods. Arthropods therefore serve as both key hosts and vectors of transmission of −ssRNA viruses. In terms of transmission, non-arthropod −ssRNA viruses can be distinguished between those that are reliant on arthropods for transmission and those that can circulate among vertebrates without
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#1732858914511516-407: Is important to reduce spread of the virus by vectors. The following species are recognized: Negative-strand RNA virus See text Negative-strand RNA viruses ( −ssRNA viruses ) are a group of related viruses that have negative-sense , single-stranded genomes made of ribonucleic acid (RNA). They have genomes that act as complementary strands from which messenger RNA (mRNA)
559-435: Is known to occur. Most western flower thrips are female and reproduce by arrhenotokous parthenogenesis ; i.e. females can produce males from unfertilized eggs, but females arise only from fertilized eggs. It has been documented to feed on over 500 different species of host plants, including a large number of fruit, vegetable, and ornamental crops including Brassica oleracea ( broccoli , 'Marathon'). The insect damages
602-465: Is produced directly from the genome; second, mRNA is created from the antigenome. All ambisense viruses contain a hairpin loop structure to stop transcription after the protein's mRNA has been transcribed. Negative-strand RNA viruses contain a ribonucleoprotein complex composed of the genome and an RdRp attached to each segment of the genome surrounded by a capsid. The capsid is composed of proteins whose folded structure contains five alpha-helices in
645-436: Is synthesized by the viral enzyme RNA-dependent RNA polymerase (RdRp). During replication of the viral genome, RdRp synthesizes a positive-sense antigenome that it uses as a template to create genomic negative-sense RNA. Negative-strand RNA viruses also share a number of other characteristics: most contain a viral envelope that surrounds the capsid, which encases the viral genome, −ssRNA virus genomes are usually linear, and it
688-497: Is the suffix used for virus subphyla. The subphylum Polyploviricotina follows the same pattern, Polyplo being taken from Ancient Greek πολύπλοκος, meaning complex. All viruses in Negarnaviricota are negative-sense, single-stranded RNA (−ssRNA) viruses. They have genomes made of RNA, which are single instead of double-stranded. Their genomes are negative sense, meaning that messenger RNA (mRNA) can be synthesized directly from
731-429: Is yellowish in color with red eyes. The lifecycle of the western flower thrips varies in length due to temperature, with the adult living from two to five or more weeks, and the nymph stage lasting from five to 20 days. Each female may lay 40 to over 100 eggs in the tissues of the plant, often in the flower, but also in the fruit or foliage. The newly hatched nymph feeds on the plant for two of its instars, then falls off
774-531: The Ebola virus , hantaviruses , influenza viruses , the Lassa fever virus , and the rabies virus . Negarnaviricota takes the first part of its name from Latin nega , meaning negative, the middle part rna refers to RNA, and the final part, viricota , is the suffix used for virus phyla. The subphylum Haploviricotina takes the first part of its name, Haplo , from Ancient Greek ἁπλός, meaning simple, and 'viricotina
817-572: The N-terminal lobe (5-H motif) and three alpha-helices in the C-terminal lobe (3-H motif). Inside the capsid, the genome is sandwiched between these two motifs. Excluding the family Aspiviridae , −ssRNA viruses contain an outer viral envelope , a type of a lipid membrane that surrounds the capsid. The shape of the virus particle, called a virion, of −ssRNA viruses varies and may be filamentous, pleomorphic, spherical, or tubular. Genome segmentation
860-460: The Rift Valley fever virus and the tomato spotted wilt virus . Among vertebrates, bats and rodents are common vectors for many viruses, including the Ebola virus and the rabies virus , transmitted by bats and other vertebrates, and the Lassa fever virus and hantaviruses , transmitted by rodents. Influenza viruses are common among birds and mammals. Human-specific −ssRNA viruses include
903-498: The Tospovirus genus. These include both food crops (such as peanuts , watermelons , capsicums , tomatoes , zucchinis , et al. ) as well as ornamental species which are important to flower farms ( calla lily , impatiens , chrysanthemums , iris , et al. ). For a more complete list of hosts examine the Tospovirus host list at Kansas State University . Early symptoms of infection are difficult to diagnose. In young infected plants
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#1732858914511946-445: The aid of arthropods. The latter group is likely to have originated from the former, adapting to vertebrate-only transmission. Negarnaviricota belongs to the kingdom Orthornavirae , which encompasses all RNA viruses that encode RdRp, and the realm Riboviria , which includes Orthornavirae as well as all viruses that encode reverse transcriptase in the kingdom Pararnavirae . Negarnaviricota contains two subphyla, which contain
989-401: The antigenome and synthesizes a copy of the genome while using the antigenome as a template. Replication is executed while the genome is inside the nucleocapsid, and RdRp unveils the capsid and translocates along the genome during replication. As new nucleotide sequences are synthesized by RdRp, capsid proteins are assembled and encapsidate the newly replicate viral RNA. Transcribing mRNA from
1032-516: The characteristic symptoms consist of inward cupping of leaves and leaves that develop a bronze cast followed by dark spots. As the infection progresses additional symptoms develop which include dark streaks on the main stem and wilting of the top portion of the plant. Fruit may be deformed, show uneven ripening and often have raised bumps on the surface. Once a plant becomes infected the disease cannot be controlled. Serological and molecular tests are commercially available to diagnose TSWV as well as
1075-402: The disease. Infection with these viruses results in spotting and wilting of the plant, reduced vegetative output, and eventually death. No antiviral cures have been developed for plants infected with a Tospovirus, and infected plants should be removed from a field and destroyed in order to prevent the spread of the disease. A large number of plant families are known to be affected by viruses of
1118-412: The environment. For −ssRNA viruses, this allowed for a large number of invertebrate, and especially arthropod, viruses to be identified, which helped to provide insight into the evolutionary history of −ssRNA viruses. Based on phylogenetic analysis of RdRp showing that −ssRNA viruses were descended from a common ancestor, Negarnaviricota and its two subphyla were established in 2018, and it was placed into
1161-448: The genome by the viral enzyme RNA-dependent RNA polymerase (RdRp), also called RNA replicase, which is encoded by all −ssRNA viruses. Excluding viruses in the genus Tenuivirus and some in the family Chuviridae , all −ssRNA viruses have linear rather than circular genomes, and the genomes may be segmented or non-segmented. All −ssRNA genomes contain terminal inverted repeats , which are palindromic nucleotide sequences at each end of
1204-426: The genome follows the same directional pattern as producing the antigenome. At the leader sequence, RdRp synthesizes a 5-'end (usually pronounced "five prime end") triphosphate-leader RNA and either, in the case of the subphylum Haploviricotina , caps the 5'-end or, in the case of the subphylum Polyploviricotina , snatches a cap from a host mRNA and attaches it to the viral mRNA so that the mRNA can be translated by
1247-452: The genome. Replication of −ssRNA genomes is executed by RdRp, which initiates replication by binding to a leader sequence on the 3'-end (usually pronounced "three prime end") of the genome. RdRp then uses the negative sense genome as a template to synthesize a positive-sense antigenome. When replicating the antigenome, RdRp first binds to the trailer sequence on the 3'-end of the antigenome. Thereafter, RdRp ignores all transcription signals on
1290-621: The genus with more being discovered on a regular basis. Member viruses infect over eight hundred plant species from 82 different families. Tospoviruses have a negative-sense , single-strand RNA genome . The genome resembles that of the genus Phlebovirus . It is linear and is 17.2 kb in size. It is divided into three segments termed S (2.9kb), M (5.4kb), and L (8.9kb). The M and S RNA segments encode for proteins in an ambisense direction. Tospoviruses are arboviruses usually vectored by thrips . At least ten species of thrips belonging to family Thripidae have been confirmed as vectors for
1333-410: The host cell's ribosomes . After capping the mRNA, RdRp initiates transcription at a gene start signal and later terminates transcription upon reaching a gene end signal. At the end of transcription, RdRp synthesizes a polyadenylated tail (poly (A) tail) consisting of hundreds of adenines in the mRNA's 3-end, which may be done by stuttering on a sequence of uracils . After the poly (A) tail
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1376-472: The larval phases of development, as pupation and metamorphosis separate the connection between the salivary glands and the infected muscle tissue of the mid-gut. Adults transmit the virus from infected salivary glands, and uninfected adults will not transmit the virus. Obviously, controlling the infection by limiting transmission from infected plants to larval thrips or by preventing adult dispersal from infected plants are key strategies in preventing an epidemic of
1419-431: The measles virus and the mumps virus . Many diseases caused by −ssRNA viruses have been known throughout history, including hantavirus infection, measles, and rabies. In modern history, some such as Ebola and influenza have caused deadly disease outbreaks. The vesicular stomatitis virus , first isolated in 1925 and one of the first animal viruses to be studied because it could be studied well in cell cultures ,
1462-467: The phylum are recognized. Negative-strand RNA viruses are closely associated with arthropods and can be informally divided between those that are reliant on arthropods for transmission and those that are descended from arthropod viruses but can now replicate in vertebrates without the aid of arthropods. Prominent arthropod-borne −ssRNA viruses include the Rift Valley fever virus and the tomato spotted wilt virus . Notable vertebrate −ssRNA viruses include
1505-403: The plant in several ways. The major damage is caused by the adult ovipositing in the plant tissue. The plant is also injured by feeding, which leaves holes and areas of silvery discoloration when the plant reacts to the insect's saliva. Nymphs feed heavily on new fruit just beginning to develop from the flower. The western flower thrips is also the major vector of tomato spotted wilt virus (TSWV),
1548-468: The plant to complete its other two instar stages. Nymphs feed heavily on new fruit just beginning to develop from the flower. Flower-feeding thrips are routinely attracted to bright floral colors, especially white, blue, and yellow, and will land and attempt to feed. Some flower thrips will "bite" humans wearing clothing with such bright colors, though no species feed on blood. Such biting does not result in any known disease transmission, but skin irritation
1591-460: The subphylum Haploviricotina are nonsegmented, whereas segmentation is universal in Polyploviricotina . Phylogenetic analysis based on RdRp shows that −ssRNA viruses are descended from a common ancestor and that they are likely a sister clade of reoviruses , which are dsRNA viruses. Within the phylum, there are two clear branches, assigned to two subphyla, based on whether RdRp synthesizes
1634-575: The then newly established realm Riboviria . Frankliniella occidentalis The western flower thrips [ Frankliniella occidentalis (Pergande)] is an invasive pest insect in agriculture. This species of thrips is native to the Southwestern United States but has spread to other continents, including Europe , Australia (where it was identified in May 1993 ), and South America via transport of infested plant material. The adult male
1677-501: The thrips are especially attracted, such as jimson weed . The thrips' natural enemies include pirate bugs of genus Orius and Neoseiulus cucumeris , a predatory mite species which is the most commonly used biological control agent against western flower thrips in protected crops including cucumber and strawberry . Other agents show promise as biological pest control , including the entomopathogenic fungi Metarhizium robertsii (syn. M. anisopliae ) and Beauveria bassiana , and
1720-434: The transmission of at least three tospoviruses, but there remains some controversy over its efficiency as a vector. Immunological testing and vector-competence studies suggest that S. dorsalis may represents a non-transmitting carrier for some strains of virus. The success of this virus has also been attributed to the acquisition of a gene in the M segment of the genome which encodes a movement protein . This protein allows
1763-438: The transmission of thirteen or more tospoviruses. The thrips vectors are not closely related, implying an independent origin of infection for each thrips, possibly transmitted horizontally through shared hosts. There may be other species of thrips competent to transmit similar viruses, but they have not been documented on crops of economic significance. Recent research concludes that thrips can only be infected by tospovirus during
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1806-486: The virus to infect a wide range of hosts. The gene encoding this protein was likely acquired by recombination from either a plant host or from another plant virus. Control of these diseases is difficult. One of the reasons for this is that the wide host range allows the viruses to successfully overseason from one crop to the next. To prevent spread of the virus infected plants should be immediately removed away from neighbouring plants. Control of insects, especially thrips,
1849-403: Was identified as an −ssRNA virus, which was unique at the time because other RNA viruses that had been discovered were positive sense. In the early 21st century, the bovine disease rinderpest , caused by −ssRNA rinderpest virus, became the second disease to be eradicated, after smallpox , caused by a DNA virus. In the 21st century, viral metagenomics has become common to identify viruses in
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