Lily Mottle Virus

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Lily Mottle Virus
Systematics
Classification : Viruses
Area : Riboviria
Empire : Orthornavirae
Phylum : Pisuviricota
Class : Stelpaviricetes
Order : Patatavirales
Family : Potyviridae
Genre : Potyvirus
Type : Lily Mottle Virus
Taxonomic characteristics
Genome : (+) ssRNA linear
Baltimore : Group 4
Symmetry : helical
Cover : no
Scientific name
Lily Mottle Virus
Short name
LMoV
Left
NCBI  Taxonomy: 32624
ICTV Taxon History: 201854634
ICTVdB Virus Code : 00.057.0.01.069

The tulip breaking virus ( LMoV or LiMV ), rarely as Lilienscheckungsvirus called, is a plant virus , the virus family Potyviridae that in plants from the family of the lily plants to asymptomatic carries (Liliaceae) to mild disorders of individual plant parts. A common simultaneous infection with other plant viruses which alone cause only mild or no disease can cause the entire plant to die. This co-infection leads to considerable crop damage when growing lilies and is therefore of great economic importance. The Lily Mottle Virus is spread by aphids and, during vegetative reproduction, by splitting the lily bulbs in horticulture. The LMoV was a synonymous name for a subtype of the tulip-breaking virus (TBV) that occurs in lilies , but has been classified as a closely related, but independent, virus species of the genus Potyvirus since 2005 .

discovery

The symptoms of the plant disease caused by LMoV were known as early as the 19th century. It was not until 1944 that P. Brierley and FF Smith succeeded in demonstrating a co-infection with two viruses as the cause by means of infection experiments on several tulip and lily species. In several species of lily grown in the USA ( Lilium auratum , L. speciosum , L. longiflorum ), which showed streaky lightening ( chlorosis ) or individual necrotic spots on the leaves, they could catch the Lily-symptomless virus (LSV, order Tymovirales : Betaflexiviridae : Carlavirus ), which was always present at the same time as the cucumber mosaic virus or the Lily Mottle virus . They were also able to show that all three viruses are transmitted by aphids of the species Aphis gossypii .

Virus build-up

morphology

Schematic structure of the LMoV capsid (section with eight helix turns ). Conserved areas of the capsid protein (gray), N-terminus (blue) and C-terminus (red)

Virus particles (virions) of the Lily Mottle virus consist of a thread-like capsid with helical symmetry , in which a single-stranded RNA is packaged as a genome ; there is no virus envelope . The capsid is 13 nm thick and about 740 nm long. The length of the capsid increases in the presence of divalent cations (particularly calcium - ion ) in the preparation for and after their binding by the addition of EDTA from. The individual capsomeres of which the capsid is composed require a pitch of 3.4 nm for a helix turn . This pitch is relatively large compared to viruses with rigid rods and a comparable structure (e.g. the tobacco mosaic virus ) and allows flexibility and flexibility of the LMoV capsids. 7.7 capsomeres are required for one turn, so that the entire capsid is composed of around 1700 capsomeres. The individual capsomeres consist of only one molecule of the LMoV capsid protein (CP, coat / capsid protein ) with a length of 274 amino acids (33  kDa ). The CP is folded several times so that the N and C terminus point outwards. These outer ends of the capsid protein are very variable. The protruding N-terminus predominantly determines the specific attachment to the host cell and enables the serological differentiation of different virus isolates . The sections in the middle of the CP (216 amino acids), which are very conserved within the various members of the Potyviridae, point inwards in the capsid and interact with the viral RNA.

The virions are stable to ethanol and only lose their infectivity in the sap after 10 minutes at 65–70 ° C. The LMoV has a density of 1.31 g / ml in density ( cesium chloride ) and a sedimentation 137-160  S .

Genome

As a genome , the LMoV has a linear, single-stranded RNA with positive polarity [(+) ssRNA] and a length of 9644 nucleotides . A viral protein (VPg) is covalently linked to the 5 'end of the RNA. As with cellular messenger RNAs, there is a poly (A) tail of 20 to 160 adenosines at the 3 'end of the virus genome . Between the two non- coding ends (NCR: non-coding region ) is an open reading frame (ORF) for a 3095 amino acids large polyprotein encoded. This polyprotein is split into the individual virus proteins by proteases during translation .

LMoV genome organization : P1 ( protease 1 ), HC ( helper component ), P3 ( protease 3 ), CI ( cylindrical inclusions protein ), VPg ( genomic virus protein ), Pro ( protease ), NI ( nuclear inclusions protein ), CP ( capsid / coat protein ). The interfaces of the proteases are shown as wedges.

An IRES structure was suspected in the 5'-NCR of potyviruses , since translation is initiated without a 5'-cap structure . The LMoV neither has a cap structure, nor could an IRES be confirmed from sequence data. The VPg protein bound to the 5 'NCR may serve as a primer for the RNA polymerase to amplify the RNA. The VPg of other potyviruses also interacts directly with the translation initiation factors eIF4E and eIFiso4E. This could represent a previously unspecified, Cap- and IRES-independent translation path.

Virus Proteins and Replication

After infection, the virus enters the plant via the vascular bundles and is absorbed by the cells through membrane vesicles ( endocytosis ). The capsid breaks down in the cytoplasm and the RNA is released. The viral RNA can also very effectively enter the cell via infected neighboring cells through cell contact points ( plasmodesmata ). This direct transport of naked, infectious RNA is controlled by several virus proteins, including the so-called HC ( helper component ), which form a so-called movement complex . As with all (+) ssRNA viruses , the ingested RNA is first translated into protein on the ribosomes , since at least one copy of the viral RNA-dependent RNA polymerase is required for the replication of the RNA. After it has synthesized multiple copies of the viral RNA , the LMoV proteins are produced in large quantities. These bales at the locations of the synthesis Viroplasmas to morphologically visible inclusion bodies ( inclusion bodies together). When infected with LMoV in the cytoplasm, these inclusion bodies have a characteristic cylindrical to spiral shape; the virus protein that predominantly forms these cylinders is therefore also referred to as CI ( cylindrical inclusion ). Amorphous inclusion bodies, which consist of two virus proteins NIa and NIb ( nuclear inclusions ), form in the cell nucleus . Since the virus proteins are always formed in the same ratio during the translation of the RNA and larger amounts of the capsid protein are required compared to other proteins, these proteins that are not required in many copies form inclusion bodies, are broken down or excreted from the cell.

The polyprotein of the LMoV is split into eight individual proteins by viral proteases. The viral protease 1 (P1) splits itself off from the polyprotein at the N terminus. Next is the HC protein, which is important for aphid transmission; however, the mechanism remains unclear. The HC has a papain- like protein domain at the C-terminus , with which the HC also splits off independently from the polyprotein. All other proteins are split off by the NIa protease. This is followed by another protease (P3) with an as yet unexplained function and the CI, from which a small peptide 6K1 is cleaved (possibly for activation). The CI is active as a helicase in RNA replication . Together with a protease component, the VPg forms the NIa. The NIb is the viral RNA polymerase from which the viral capsid protein CP is cleaved. If enough viral (+) ssRNA and CP have been formed, the packaging can take place in the capsid and mature viruses can be released into the plant sap by exocytosis . The much more effective cell-to-cell infection of the naked RNA explains the appearance of spotting lesions on the leaves.

Systematics

The genus Potyvirus is currently the largest group of all plant viruses with 168 virus species. This large number of potyviruses makes it difficult to differentiate and delimit individual species or subtypes , this is particularly true of the Lily-Mottle-Virus and the Tulip-breaking-Virus (TBV), which for a long time were regarded as synonyms of a single species. The LMoV was considered to be the common subtype of TBV in lilies (TBV subtype Lily). This distinction was made even more difficult by the fact that the real species TBV can also cause diseases in lilies. With more and more comparison sequences of the genome of different virus isolates, wrong assignments could be detected so far. In an investigation of 187 complete genome sequences and 1220 partial sequences for the capsid protein of potyviruses, several subgroups within the genus were identified and the criteria for the species limits were redefined for the LMoV and TBV as well. Accordingly, a match in the nucleotide sequence between two complete genomes of more than 76% is considered a species limit (corresponds to 82% match in the amino acid sequence ). The part of the nucleotide sequence coding for the capsid protein CP showed a species limit of 76-77%. The sequence of the CI protein appeared to be the most suitable for differentiation. Several sequences of potyviruses (including TBV and LMoV) published in the international GenBank had to be assigned to other species.

The taxonomy established by the " International Committee on Taxonomy of Viruses " and the assignment of the subtypes of the LMoV, which has been valid since 2005, includes subtypes previously classified as TBV:

  • Family Potyviridae
  • Genus Potyvirus
  • Species Lily mottle virus ( en.Lily mottle virus , LMoV)
  • Lily mild mottle virus subtype
  • Lily mottle virus subtype
  • Subtype Tulip band-breaking virus
  • Subtype Mild tulip breaking virus (MTBV)
  • Subtype Severe tulip breaking virus (STBV)

Infection and disease from LMoV

About two weeks after the infection with LMoV, a light green mottle appears on young leaves . The lightening can also appear streaked along the leaf veins. In the course of a few days, the leaf becomes thinner in the light spots and the plant cells can die in these areas if the disease is severe; the irregularly delimited spots now appear dark brown and dried out. All new shoots and flowers that sprout after infection are reduced in size and often deformed.

This expression of the disease symptoms is very different in different lily species and hybrids . Even the disease of identical species in a single growing area has different degrees of severity. This phenomenon can be explained by the influence of the growth phase at the time of infection, the entry point and the infection dose of the virus. The Easter lily ( L. longiflorum ) does not regularly develop any disease, although the virus multiplies in the plant. The tiger lily ( L. lancifolium ) only has a very light, light green spotting. In some LMoV infections, only a slight increase in length and smaller flowers and bulbs can be found. The economically important species L. formosanum always falls ill after an LMoV infection, this also applies to the wild varieties found in Taiwan . Only the specially selected variety Lilium formosanum "Little Snow White" has an increased virus resistance . The hybrid "Enchantment" bred by Jan de Graaff in 1941 and all of its derived varieties such as the cultivar Lilium Asia , which is widespread in Asia, is very susceptible to the LMoV and other plant viruses occurring in lilies . Hybrid cv. Enchantment .

Infection with LMoV alone never leads to the death of the entire plant, but remains locally limited to a few parts of the plant. However, a co-infection of the LMoV with the Lily-symptomless virus , which alone does not cause any symptoms of the disease, but only a reduced plant growth, is particularly common . If a plant is infected by both viruses, the disease is much more severe and faster. After the initial typical symptoms of a pronounced LMoV infection, larger vascular bundles such as the entire phloem are infected , which ultimately causes the entire plant to die. A doubly infected lily bulb can be severely damaged while it is being stored, lose its ability to sprout and die.

Transmission and dissemination

transmission

Aphids tube in the absorption of plant sap

The Lily-Mottle-Virus is transmitted by green aphids (Aphididae) during the sucking act . The aphids ingest the virus, which occurs in high concentrations in the plant sap, during the sucking act and can infect other plants with a delay of a few hours. The virus cannot reproduce in the aphid itself. After the plant sap has been absorbed into the midgut of the aphid, the virus is distributed in the bloodstream and reaches the saliva of the suction apparatus; a new plant can now be infected with the next act of sucking. Those aphid species that mainly transmit the LMoV are Aphis gossypii , Myzus persicae , Macrosiphum euphorbiae and Doralis fabae . Stored bulbs can also be infected with the virus by Anuraphis (Yezabura) tulipae . Winged specimens of the aphid population allow transmission over great distances.
When the plants are grown, the virus is transmitted when the plants are cut and injured with contaminated knives and scissors. This route of infection is used experimentally by specifically scratching the plants. The splitting of the lily bulbs during vegetative reproduction spreads the virus to all daughter plants. The same applies to vegetative propagation by cuttings in tissue cultures, which is very common in industrial horticulture. The virus is not spread through seeds ; if a new plant germinates from the seed of an LMoV-infected plant, it is not infected.

distribution

Onion of a Lilium sp.

The natural geographical distribution of the virus is not known, since when it was discovered in the USA in 1944, it was already anthropogenic through the worldwide flower and bulb trade. By growing lilies in large greenhouses and fields as a monoculture , the transmission is particularly favored compared to the natural occurrence of wild plants. The virus is spread worldwide and endemic in countries with significant lily cultivation . In addition to the United States, this also applies to the Netherlands , Poland , North and South Korea , Japan , Taiwan, China and Israel . The Lily Mild Mottle Virus as a subtype of LMoV was detected in an examination of 185 lily samples from South Korean cultures in 26.3% of all plants, a co-infection of LMoV and the Tomato Ringspot virus was found in a further 23.2% observed.

In the Netherlands, the LMoV could be detected several times in all plants of individual lily fields of the cultivar "Enchantment" . Often there was also an infection with the Lily symptomless virus . In the plantations affected in this way , necrosis of the trunk and leaves is increasingly observed, which is usually followed by the death of the plant. If all the lilies in a plantation are only infected with the LMoV, this usually does not result in a loss of the entire flower harvest; scaled-down flowers or plants with short stature are then offered at lower prices.

The LMoV could be detected in all about 340 large lily cultivars grown. The undetected spread through worldwide transport is given in particular by those lily species that show little or no infection symptoms but can multiply the virus, such as the Easter lily and the tiger lily. The virus has a wider host range than previously assumed. The LMoV could also be detected in the winter endivia ( C. endivia L. var. Latifolium Lam. ).

Infection prevention

The spread of the LMoV in industrial production is mainly prevented by controlling aphids as a vector . Mostly in June and July, less in May and August, the virus is transmitted by the spreading aphid populations. A weekly control of the insects from May and every two weeks in August and September is carried out on an industrial scale. The lilies are most commonly treated with paraffin oil or pyrethroids as aerosols .

For the prevention of infection, it is important to avoid spreading through seed bulbs and the global plant trade. Those types of lily that have no or only mild symptoms are a particular source of outbreaks of infection, as the infection here remains undetected. For this reason, breeding resistant and susceptible lily varieties at the same time is often avoided, as the virus can spread unnoticed in the resistant varieties without developing symptoms of the disease. These form a constant reservoir for infection of susceptible strains. With a monoculture of susceptible varieties, infected plants can be sorted out and the spread of the virus can be controlled to a certain extent. Since the virus is not transmitted by seeds like other members of the genus Potyvirus , a culture can be freed from an infection with the LMoV by more complex, re-growing from seeds.

The transport and trade of parts of plants such as flowers, cuttings or bulbs from growing areas in which the LMoV has been proven is subject to legal restrictions or an import ban in many countries. In particular, the plant parts traded for propagation and rearing have to be tested for LMoV in Germany since 1998 in accordance with an implementation of several EU directives . To detect LMoV, immunological tests for LMoV virus proteins ( ELISA ) and, rarely, detection of the virus genome by PCR are used. Both the leaves ( “leaf test” ) and the harvested onions ( “bulb test” ) are used as test samples for diagnostics. Newer methods for the simultaneous detection of several plant viruses from a sample by DNA hybridization ( macroarray ) are currently being tested.

swell

literature

  • Gerhart Drews , Günter Adam, Cornelia Heinze: Molecular Plant Virology . Berlin 2004; ISBN 3-540-00661-3
  • Sondra D. Lazarowitz: Plant Viruses . In: David M. Knipe, Peter M. Howley (Red.): Fields' Virology . 5th edition. 2 volumes, Philadelphia 2007, pp. 641-705; ISBN 0-7817-6060-7
  • Kenneth M. Smith: A Textbook of Plant Virus Diseases . 3. Edition. Edinburgh 1972
  • PH Berger et al. : Family Potyviridae . In: CM Fauquet, MA Mayo et al. : Eighth Report of the International Committee on Taxonomy of Viruses . London, San Diego 2005, pp. 819-841; ISBN 0-12-249951-4
  • Juan José López-Moya, Juan Antonio García: Potyviruses . In: Allan Granoff, Robert G. Webster (Eds.): Encyclopedia of Virology . Volume 3, Academic Press, San Diego 1999, pp. 1369-1375; ISBN 0-12-227030-4

Individual evidence

  1. ↑ a b c d e ICTV: ICTV Taxonomy history: Lily mottle virus , EC 51, Berlin, Germany, July 2019; Email ratification March 2020 (MSL # 35)
  2. ^ A b P. Brierley and FF Smith: Studies on lily virus diseases: the necrotic fleck complex of Lilium longiflorum . Phytopathology (1944) 34, pp. 529-555.
  3. ↑ Kenneth M. Smith: Virus diseases of farm & garden , 1946, pp. 82-83
  4. ↑ EL Dekker EL et al .: Characterization of potyviruses from tulip and lily which cause flower-breaking . Journal of General Virology (1993) 74 (5), pp. 881-887; PMID 8492092 .
  5. ↑ Drews (2004) p. 149.
  6. ↑ DD Shukla and CW Ward: Structure of potyvirus coat proteins and its application in the taxonomy of the potyvirus group . Adv. Virus Research (1989) 36, pp. 273-314 (review); PMID 2472047 .
  7. ↑ Berger (2005) p. 819.
  8. ↑ DR Gallie: Cap-independent translation conferred by the 5 'leader of tobacco etch virus is eukaryotic initiation factor 4G dependent . Journal of Virology (2001) 75 (24), pp. 12141-12152; PMID 11711605 .
  9. ^ S. Wittmann et al .: Interaction of the viral protein genome linked of turnip mosaic potyvirus with the translational eukaryotic initiation factor (iso) 4E of Arabidopsis thaliana using the yeast two-hybrid system . Virology (1997) 234, pp. 84-92; PMID 9234949 .
  10. ^ S. Léonard et al .: Complex formation between potyvirus VPg and translation eukaryotic initiation factor 4E correlates with virus infectivity . Journal of Virology (2000) 74 (17), pp. 7730-7737; PMID 10933678 .
  11. ↑ ICTV : Master Species List 2018a v1 MSL including all taxa updates since the 2017 release. Fall 2018 (MSL # 33)
  12. ↑ a b Y. Yamaji, L. Xiaoyun et al .: Molecular evidence that a lily-infecting strain of Tulip breaking virus from Japan is a strain of lily mottle virus . European Journal of Plant Pathology (2001) 107, 8, pp. 833-837 (abstract)
  13. ↑ MJ Adams, JFAntoniw and CW Fauquet: Molecular criteria for genus and species discrimination within the family Potyviridae . Archives of Virology (2005) 150 (3), pp. 459-479; PMID 15592889 .
  14. ↑ PH Berger (2005) pp. 824 and 827.
  15. ↑ a b Brunt, AA, Crabtree, K., Dallwitz, MJ, Gibbs, AJ, Watson, L. and Zurcher, EJ (Eds.): Tulip breaking potyvirus , on: Plant Viruses Online: Descriptions and Lists from the VIDE Database (1996 onwards). Version: 16th January 1997
  16. ^ Smith (1972), p. 552.
  17. ↑ K. Lee et al. : Virus disease of lilies in Korea . Acta Horticulturae (ISHS), International Symposium on the Genus Lilium (1996) 414, pp. 195-202.
  18. ↑ Allan Granoff, Robert G. Webster (eds.): Encyclopedia of Virology , San Diego (Academic Press) 1999, Volume 2, p. 1321; ISBN 0-12-227030-4 .
  19. ↑ a b C. J. Asjes: Control of aphid-borne Lily symptomless virus and Lily mottle virus in Lilium in the Netherlands . Virus Research (2000) 71 (1-2), pp. 23-32; PMID 11137159 (review).
  20. ^ V. Lisa, HJ Vetten, D.-E. Lesemann, P. Gotta: Occurrence of Lily mottle virus in escarole . Plant Disease (2002) 86, p. 329.
  21. ↑ Ordinance on the placing on the market of cultivation material for vegetables, fruit and ornamental plants as well as repealing the ordinance to combat viral diseases in fruit growing (June 16, 1998), ( Federal Law Gazette I p. 1322 )
  22. ↑ S. Sugiyama et al. : A simple, sensitive, specific detection of mixed infection of multiple plant viruses using macroarray and microtube hybridization. J. Virol. Methods. (2008) Sep 12. (Epub) PMID 18760308

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