Sweet potato leaf curl virus

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Sweet potato leaf curl virus
Virus classification OOjs UI icon edit-ltr.svg
(unranked): Virus
Realm: Monodnaviria
Kingdom: Shotokuvirae
Phylum: Cressdnaviricota
Class: Repensiviricetes
Order: Geplafuvirales
Family: Geminiviridae
Genus: Begomovirus
Species:
Sweet potato leaf curl virus
Illustrated image of Geminiviruses (family SPLCV belongs to). Geminiviruses drawing.png
Illustrated image of Geminiviruses (family SPLCV belongs to).

Sweet potato leaf curl virus is commonly abbreviated SPLCV. Select isolates are referred to as SPLCV followed by an abbreviation of where they were isolated. For example, the Brazilian isolate is referred to as SPLCV-Br. [1]

Contents

The sweet potato leaf curl virus is one of more than 20 viruses known to infect the sweet potato. [2] It is part of a group of sweet potato-infecting Begomoviruses generally known as "sweepoviruses". [3] Viruses are common among sweet potatoes because their propagation is commonly dependent on stored roots or stems. Therefore, viruses can build up and have delayed emergence over the years. [4] Viruses in sweet potatoes are problematic because they decrease crop yield and quality of storage roots. [5] This is problematic as sweet potatoes are ranked seventh for global food crops. [4]

Sweet potato leaf curl virus is commonly transmitted from insect to plant by whiteflies ( Bemisia tabaci ). [5] [4] Additionally, it can be transmitted from plant to plant via vegetative propagation, grafting, or the seeds. [4] It is widely speculated that management of the whitefly population is essential to managing the spread of the SPLCV virus between infected and uninfected plants. In one case, the infection spread rapidly between plants within only two years of field planting. [3]

Structure

The virus is short, rod-shaped, and non-enveloped. [6] The nucleocapsid has been measured at 38 nm long and 15-22 nm in diameter. Each nucleocapsid includes 22 capsomeres. Particles are two incomplete icosahedra joined together.

Genome

The genome consists of 2.8 kb of circular single stranded DNA (ssDNA). [7] Unlike the majority of virus genomes in the Begomovirus family which are bipartite, the SPLCV is monopartite. It contains only a single genomic component, which is similar to DNA-A of bipartite viruses. DNA-A typically encodes products for DNA replication, controls gene expression, and controls insect transmission. [8] This suggests it is originally from the Old World. [1] [8] However, SPLCV (and other related sweepoviruses) are phylogenetically distinct from both Old World and New World Begomovirus groups. [3] The genome contains six open reading frames (ORF). Two are located on virion sense strand which runs 3’ to 5’ (V1 and V2). The other four are located on complementary sense strand which runs 5’ to 3’ (C1, C2, C3, and C4). They are separated by an intergenic region (IR) which contains a conserved stem-loop sequence motif. [7] [8] [9]

Replication cycle

Virus particles enter the host cell and then the uncoated viral genome enters the nucleus of that cell. Within the nucleus, the viral genome is amplified and goes through the process of DNA replication. [10]

Entry into cell

At this time, the mechanisms behind the entry of SPLCV into host cells are unclear.

Replication and transcription

One aspect of the replication process of the geminivirus (SPLCV genus) replication cycle includes the conversion of (-) viral ssDNA to (+) dsDNA intermediate. [11] Many mechanisms of (-) DNA replication initiation in the SPLCV have been identified but this first step in the replication process is thought to be catalyzed by host factors. [12] The presence of DNA primase along with polymerase activity has been noted as one method of replication initiation. During replication, (-) viral ssDNA is converted to (+) dsDNA intermediate upon activation of the (-) strand origin of DNA replication. As replication continues, elongation occurs in order to produce dsDNA followed by the production of covalently closed circular dsDNA. [11]

During another aspect of SPLCV replication, supercoiled (ccc)dsDNA is converted into dsDNA and ssDNA by rolling-circle replication. Pivotal viral proteins have various effects on the replication and translation of SPLCV. [11] All geminiviruses encode a REP protein, which is one protein that influences initiation of replication while also allowing for the continuation of replication past that point. The RepA protein contains three RCR conserved motifs and behaves similarly to the REP protein. The REn protein has been identified during this process but its role is currently unknown. Other proteins such as R2 and CP have been hypothesized to participate in the witch from the rolling circle to the ssDNA genomes.

TrAP is a 15-kDa transcriptional activator protein that is also called AC2 or AL2 and is unique to begomoviruses (SPLCV family). [11] C2 is a related protein that was identified in the SPLCV replication and transcription processes but it is unclear what it accomplishes. TrAP is a required activation protein. Truncated mRNAs found in SPLCV cannot be spliced. They are able to be translated into the RepA protein. The RepA protein is necessary in the viral-sense transcription that results in the production of MP and CP. Termination mechanisms for SPLCV replication are present but their exact mechanics have yet to be identified. [13]

Assembly and release

The Rep protein is responsible for termination. It cuts and releases newly synthesized ssDNA in order to create many copies of viral ssDNAs. [14]

Symptoms

Leaf curl virus on Capsicum plant. Physical symptoms are synonymous in sweet potatoes. SequoiaBio Leaf Curl.jpg
Leaf curl virus on Capsicum plant. Physical symptoms are synonymous in sweet potatoes.

The primary symptom of SPLCV includes upward leaf curling. [4] [13] This is primarily seen in young plants with SPLCV. As plants mature, it is common for visual symptoms to dissipate. [4] Additional symptoms of SPLCV include seedling twisting, deformation of floral tissues, and reduction of pollen fertility and seed number. [13] A common method for analyzing symptoms is through the use of PCR (Polymerase chain reaction). [15]

Another symptom is stunted development of the anther and pollen. A C4 protein related to the SPLCV interacts with brassinosteroid-intensive 2 (ABtBIN2) in the plasma membrane of host cells. This results in the C4 protein re-localizing AtBIN2-interacting proteins in the nucleus of the host cell, altering the expression of brassinosteriod (BR)-genes to cause the activation of BR-signaling pathway. This causes the down-regulated expression of key genes that are necessary to the development of the anther and pollen. [13]

SPLCV is most common in sweet potatoes, but symptoms have also been observed in blue morning glory (Ipomoea indica). [16]

Interaction with host

Main vector of SPLCV, the sweet potato whitefly (Bemisia tabaci). Silverleaf whitefly.jpg
Main vector of SPLCV, the sweet potato whitefly ( Bemisia tabaci ).

The sweet potato whitefly ( Bemisia tabaci ) transmits over 100 plant viruses, one of these being SPLCV. Both male and female whiteflies have been shown to transmit SPLCV to a similar efficiency. [15] Furthermore, the whiteflies do not carry the virus for life. Instead, they have been shown to carry it for a maximum of 35 days. [15]

Transmission occurs in a persistent-circulative manner. Persistent refers to how the virus passes through the gut to the haemolymph, and then to the salivary glands. Circulative denotes that the virus cannot replicate in both the parent and the insect. SPLCV is protected inside the whitefly by a chaperone protein produced by symbionts. This protein is called symbionin.

Control and prevention

Insecticides have been tested towards SPLCV prevention. A study in 2014 published in the Journal of Agricultural and Urban Entomology reported that insecticides were ineffective in decreasing whitefly populations, but they had a positive effect in decreasing SPLCV in about half of the sprayed plots. [17]

In order to work toward controlling the spread of SPLCV, it is necessary to know the three conditions that result in insect-transmitted viruses spreading. These conditions include a source of the virus, an insect vector that is present, and an insect that moves about. In many cases, real-time polymerase chain reaction (PCR) techniques are used to determine whether SPLCV has been transmitted. [9]

Whiteflies ( Bemisia tabaci ) have been identified as the vector for the SPLCV and it is hypothesized that the reduction in this population would result in a reduction of the SPLCV cases. It has been determined that decreased feeding or increased flight activity of the whiteflies ( Bemisia tabaci ) could interfere with the spread of SPLCV. This is one reasoning that generally backs up the use of insecticides. [9]

Control of whitefly ( Bemisia tabaci ) vectors with insecticides has met with limited success in preventing the spread of virus diseases. In one study that spanned over two years, only 2 out of 36 plots used represented a decrease in the presence of whiteflies. Insecticides used in this particular study included imidacloprid, pyriproxyfen, acetamiprid, and pymetrozine. Due to the outcomes in this study as well as data gathered from similar studies, the consensus is that insecticides should not be depicted as a possible management approach for insects that infect sweet potatoes. [9]  

In an attempt control the spread of SPLCV neonicotinoids were introduced. However, this resulted in worldwide resistance due to extensive exposure. In addition to this, there are now many examples of a cross cross resistance with other insecticide classes. Generally, when insecticides are used in an attempt to control the spread of SPLCV, rather than resulting in a decrease in viral infection, the incidence of disease increased. [9]

Despite previous evidence, it has also been reported that the chitin synthesis inhibitor, buprofezin, and the juvenile hormone analog, pyriproxyfen, when used along with neonicotinoids has been successful in managing the spread of SPLCV through whiteflies ( Bemisia tabaci ). [9]

Associated diseases

Sweet potato leaf curl virus is one of 322 species in the genus Begomovirus. It is most closely related to its isolates, distinguished by location. Some of the currently known isolates of SPLCV include:

Additionally, SPLCV is related to other sweepoviruses. Sweepovirus refers to all Begomoviruses isolated from sweet potatoes and other Ipomoea species. [4] Examples include Sweet potato Golden vein associated virus (SPGVaV), Sweet potato mosaic virus, Ipomoea leaf curl virus (ILCV), Sweet potato mild mottle virus (SPMMV). [3] [5]

Tropism

The exact type of cell that SPLCV infects to cause disease is currently unclear.

Related Research Articles

<span class="mw-page-title-main">Whitefly</span> Family of insects

Whiteflies are Hemipterans that typically feed on the undersides of plant leaves. They comprise the family Aleyrodidae, the only family in the superfamily Aleyrodoidea. More than 1550 species have been described.

<i>Geminiviridae</i> Family of viruses

Geminiviridae is a family of plant viruses that encode their genetic information on a circular genome of single-stranded (ss) DNA. There are 520 species in this family, assigned to 14 genera. Diseases associated with this family include: bright yellow mosaic, yellow mosaic, yellow mottle, leaf curling, stunting, streaks, reduced yields. They have single-stranded circular DNA genomes encoding genes that diverge in both directions from a virion strand origin of replication. According to the Baltimore classification they are considered class II viruses. It is the largest known family of single stranded DNA viruses.

<span class="mw-page-title-main">Silverleaf whitefly</span> Species of true bug

The silverleaf whitefly is one of several species of whitefly that are currently important agricultural pests. A review in 2011 concluded that the silverleaf whitefly is actually a species complex containing at least 40 morphologically indistinguishable species.

<i>Begomovirus</i> Genus of viruses

Begomovirus is a genus of viruses, in the family Geminiviridae. They are plant viruses that as a group have a very wide host range, infecting dicotyledonous plants. Worldwide they are responsible for a considerable amount of economic damage to many important crops such as tomatoes, beans, squash, cassava and cotton. There are 445 species in this genus.

<span class="mw-page-title-main">Cassava mosaic virus</span> Genus of viruses

Cassava mosaic virus is the common name used to refer to any of eleven different species of plant pathogenic virus in the genus Begomovirus. African cassava mosaic virus (ACMV), East African cassava mosaic virus (EACMV), and South African cassava mosaic virus (SACMV) are distinct species of circular single-stranded DNA viruses which are transmitted by whiteflies and primarily infect cassava plants; these have thus far only been reported from Africa. Related species of viruses are found in India and neighbouring islands, though cassava is cultivated in Latin America as well as Southeast Asia. Nine species of cassava-infecting geminiviruses have been identified between Africa and India based on genomic sequencing and phylogenetic analysis. This number is likely to grow due to a high rate of natural transformation associated with CMV.

Cotton leaf curl viruses (CLCuV) are a number of plant pathogenic virus species of the family Geminiviridae.

Mungbean yellow mosaic virus (MYMV) is a plant pathogenic virus of the family Geminiviridae. Of the various viral diseases inflicting legume crops, Mungbean Yellow Mosaic disease is one of the most destructive and widely distributed. The disease has been reported from various countries.

Tomato yellow leaf curl virus (TYLCV) is a DNA virus from the genus Begomovirus and the family Geminiviridae. TYLCV causes the most destructive disease of tomato, and it can be found in tropical and subtropical regions causing severe economic losses. This virus is transmitted by an insect vector from the family Aleyrodidae and order Hemiptera, the whitefly Bemisia tabaci, commonly known as the silverleaf whitefly or the sweet potato whitefly. The primary host for TYLCV is the tomato plant, and other plant hosts where TYLCV infection has been found include eggplants, potatoes, tobacco, beans, and peppers. Due to the rapid spread of TYLCV in the last few decades, there is an increased focus in research trying to understand and control this damaging pathogen. Some interesting findings include the virus being sexually transmitted from infected males to non-infected females, and an evidence that TYLCV is transovarially transmitted to offspring for two generations.

<i>Carlavirus</i> Genus of viruses

Carlavirus, formerly known as the "Carnation latent virus group", is a genus of viruses in the order Tymovirales, in the family Betaflexiviridae. Plants serve as natural hosts. There are 53 species in this genus. Diseases associated with this genus include: mosaic and ringspot symptoms.

Cassava brown streak virus disease (CBSD) is a damaging disease of cassava plants, and is especially troublesome in East Africa. It was first identified in 1936 in Tanzania, and has spread to other coastal areas of East Africa, from Kenya to Mozambique. Recently, it was found that two distinct viruses are responsible for the disease: cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV). Both have (+)ss RNA genomes, belong to the genus Ipomovirus in the family Potyviridae, and produce generally similar symptoms in infected plants. Root rot renders the cassava tuber inedible, resulting in severe loss of economic value; therefore, current research focuses on achieving cultivars that do not develop the necrotic rot. This disease is considered to be the biggest threat to food security in coastal East Africa and around the eastern lakes.

Alphasatellites are a single-stranded DNA family of satellite viruses that depend on the presence of another virus to replicate their genomes. As such, they have minimal genomes with very low genomic redundancy. The genome is a single circular single strand DNA molecule. The first alphasatellites were described in 1999 and were associated with cotton leaf curl disease and Ageratum yellow vein disease. As begomoviruses are being characterised at the molecular level an increasing number of alphasatellites are being described.

Ipomovirus is a genus of positive-strand RNA viruses in the family Potyviridae. Member viruses infect plants and are transmitted by whiteflies. The name of the genus is derived from Ipomoea – the generic name of sweet potato. There are seven species in this genus.

Bean calico mosaic virus is a plant virus transmitted by whiteflies that infects bean genera and species within the families Fabaceae, Malvaceae, and Solanaceae. Like other New World begomoviruses, its genome is bipartite, or having two parts. Phylogenetic analysis of its two genome segments, DNA-A and DNA-B, indicate the virus is from Sonora, Mexico, and shares a most recent common ancestor with the Leaf curl virus-E strain and the Texas pepper virus, both also found in the Sonora desert, and the Cabbage leaf curl virus from Florida.

<i>Abutilon mosaic virus</i> Species of virus

Abutilon mosaic virus (AbMV) is a virus of the genus Begomovirus. It infects Abutilon species, notably the flowering maple, Abutilon striatum. The mottled or variegated effect on the leaves of Abutilon striatum is sought after.

Cassava brown streak virus is a species of positive-strand RNA viruses in the genus Ipomovirus and family Potyviridae which infects plants. Member viruses are unique in their induction of pinwheel, or scroll-shaped inclusion bodies in the cytoplasm of infected cells. Cylindrical inclusion bodies include aggregations of virus-encoded helicase proteins. These inclusion bodies are thought to be sites of viral replication and assembly, making then an important factor in the viral lifecycle. Viruses from both the species Cassava brown streak virus and Ugandan cassava brown streak virus (UCBSV), lead to the development of Cassava Brown Streak Disease (CBSD) within cassava plants.

<i>Pepper leaf curl virus</i> Species of virus

Pepper leaf curl virus(PepLCV) is a DNA virus from the genus Begomovirus and the family Geminiviridae. PepLCV causes severe disease especially in pepper (Capsicum spp.). It can be found in tropical and subtropical regions such as Thailand and India, but has also been detected in countries such as the United States and Nigeria. This virus is transmitted by an insect vector from the family Aleyrodidae and order Hemiptera, the whitefly Bemisia tabaci. The primary host for PepLCV are several Capsicum spp.. PepLCV has been responsible for several epidemics and causes severe economic losses. It is the focus of research trying to understand the genetic basis of resistance. Currently, a source of resistance to the virus has been identified in the Bhut Jolokia pepper.

Chilli leaf curl virus(ChiLCV) is a DNA virus from the genus Begomovirus and the family Geminiviridae. ChiLCV causes severe disease especially in pepper (Capsicum spp.), but also affects other crops such as tomato (Solanum lycopersicum). It can be found in tropical and subtropical regions primarily in India, but has also been detected in countries such as Indonesia and Sri Lanka. This virus is transmitted by an insect vector from the family Aleyrodidae and order Hemiptera, the whitefly Bemisia tabaci. The primary host for ChiLCV are several Capsicum spp., but host species also include tomato and amaranth. ChiLCV has been responsible for several epidemics and causes severe economic losses. It is the focus of research trying to understand the genetic basis of resistance. Currently, a few sources of resistance have been discovered and used to breed resistant varieties.

Papaya leaf curl virus(PaLCuV) is a DNA virus from the genus Begomovirus and the family Geminiviridae. PaLCuV causes severe disease in papaya (Carica papaya), but can sometimes infect other crops such as tobacco or tomato. It can be found in tropical and subtropical regions primarily in India, but closely related species have also been detected in countries such as China, Malaysia, Nigeria and South Korea. This virus is transmitted by an insect vector from the family Aleyrodidae and order Hemiptera, the whitefly Bemisia tabaci. PaLCuV has been responsible for several epidemics and causes severe economic losses. Because of the broad diversity of these viruses, their characterization and control remains difficult.

Tomato yellow leaf curl China virus (TYLCCNV) is a virus which contains 25 isolates. It infects plants as different as tobacco and tomato, as well as genetically modified plants. Petunias can be infected, but show no symptoms. The microbiology of the virus has been studied in the Chinese province of Yunnan. Tomato yellow leaf curl China virus belongs to the genus Begomovirus, which also contains the tomato leaf curl China virus.

References

  1. 1 2 3 Pardina, P. Rodríguez; Luque, A.; Nome, C.; Colomba, E. López; Delgado, S. Fuentes; Di Feo, L. (2012-12-01). "First report of Sweet potato leaf curl virus infecting sweet potato in Argentina". Australasian Plant Disease Notes. 7 (1): 157–160. doi: 10.1007/s13314-012-0073-7 . ISSN   1833-928X. S2CID   17275755.
  2. ↑ Loebenstein, Gad; Thottappilly, George (2009). The Sweetpotato. Dordrecht, Netherlands: Springer. ISBN   978-1-4020-9475-0.
  3. 1 2 3 4 5 6 7 8 9 10 11 Clark, Christopher A.; Davis, Jeffrey A.; Abad, Jorge A.; Cuellar, Wilmer J.; Fuentes, Segundo; Kreuze, Jan F.; Gibson, Richard William; Mukasa, Settumba B.; Tugume, Arthur K. (2012). "Sweetpotato Viruses: 15 Years of Progress on Understanding and Managing Complex Diseases". Plant Disease. 96 (2): 168–185. doi:10.1094/PDIS-07-11-0550. ISSN   0191-2917. PMID   30731810.
  4. 1 2 3 4 5 6 7 Kim, J.; Kil, E.-J.; Kim, S.; Seo, H.; Byun, H.-S.; Park, J.; Chung, M.-N.; Kwak, H.-R.; Kim, M.-K. (2015). "Seed transmission of Sweet potato leaf curl virus in sweet potato (Ipomoea batatas)". Plant Pathology. 64 (6): 1284–1291. doi: 10.1111/ppa.12366 . ISSN   1365-3059.
  5. 1 2 3 Valverde, Rodrigo A.; Sim, Jeonggu; Lotrakul, Pongtharin (2004). "Whitefly transmission of sweet potato viruses". Virus Research. 100 (1): 123–128. doi:10.1016/j.virusres.2003.12.020. ISSN   0168-1702. PMID   15036843.
  6. ↑ "Sweetpotato leaf curl virus". keys.lucidcentral.org. Retrieved 2019-03-12.
  7. 1 2 "Lotrakul & Valverde Cloning of a DNA-A-like genomic component of sweet potato leaf curl virus : nucleotide sequence and phylogenetic relationships". www.bspp.org.uk. Retrieved 2019-03-12.
  8. 1 2 3 Luan, Yu Shi; Zhang, Juan; Liu, Dan Mei; Li, Wen Li (2007-10-01). "Molecular characterization of sweet potato leaf curl virus isolate from China (SPLCV-CN) and its phylogenetic relationship with other members of the Geminiviridae". Virus Genes. 35 (2): 379–385. doi:10.1007/s11262-007-0084-1. ISSN   1572-994X. PMID   17318425. S2CID   24131024.
  9. 1 2 3 4 5 6 Harrison, Howard F.; Simmons, Alvin M.; Ling, Kai-Shu; Jackson, D. Michael (2014). "Management of Sweet Potato Leaf Curl Virus in Sweetpotatoes Using Insecticides1,2". Journal of Agricultural and Urban Entomology. 30 (1): 82–95. doi:10.3954/JAUE12-13.1. ISSN   1523-5475. S2CID   84270881.
  10. ↑ Gutierrez, C. (1999-10-01). "Geminivirus DNA replication". Cellular and Molecular Life Sciences. 56 (3): 313–329. doi:10.1007/s000180050433. ISSN   1420-9071. PMID   11212359. S2CID   5821240.
  11. 1 2 3 4 Zhang, Shuo Cheng; Ling, Kai-Shu (2011-06-01). "Genetic diversity of sweet potato begomoviruses in the United States and identification of a natural recombinant between sweet potato leaf curl virus and sweet potato leaf curl Georgia virus". Archives of Virology. 156 (6): 955–968. doi:10.1007/s00705-011-0930-2. ISSN   1432-8798. PMID   21302123. S2CID   25480865.
  12. ↑ Fondong, Vincent N. (2013). "Geminivirus protein structure and function: Geminivirus proteins". Molecular Plant Pathology. 14 (6): 635–649. doi:10.1111/mpp.12032. PMC   6638828 . PMID   23615043.
  13. 1 2 3 4 Bi, Huiping; Fan, Weijuan; Zhang, Peng (2017-09-27). "C4 Protein of Sweet Potato Leaf Curl Virus Regulates Brassinosteroid Signaling Pathway through Interaction with AtBIN2 and Affects Male Fertility in Arabidopsis". Frontiers in Plant Science. 8: 1689. doi: 10.3389/fpls.2017.01689 . ISSN   1664-462X. PMC   5623726 . PMID   29021807.
  14. ↑ "Molecular Biology of Geminivirus DNA Replication". ResearchGate. Retrieved 2019-03-12.
  15. 1 2 3 Simmons, Alvin M.; Ling, Kai-Shu; Harrison, Howard F.; Jackson, D. Michael (2009). "Sweet potato leaf curl virus: Efficiency of acquisition, retention, and transmission by Bemisia tabaci (Hemiptera: Aleyrodidae)". Crop Protection. 28 (11): 1007–1011. doi:10.1016/j.cropro.2009.06.011 – via ScienceDirect.
  16. ↑ Fiallo-Olivé, E.; Lapeira, D.; Louro, D.; Navas-Castillo, J. (2017-11-22). "First Report of Sweet potato leaf curl virus and Sweet potato leaf curl deltasatellite 1 Infecting Blue Morning Glory in Portugal". Plant Disease. 102 (5): 1043. doi: 10.1094/PDIS-10-17-1667-PDN . ISSN   0191-2917.
  17. ↑ Harrison, Howard F.; Simmons, Alvin M.; Ling, Kai-Shu; Jackson, D. Michael (2014). "Management of Sweet Potato Leaf Curl Virus in Sweetpotatoes Using Insecticides1,2". Journal of Agricultural and Urban Entomology. 30 (1): 82–95. doi:10.3954/JAUE12-13.1. ISSN   1523-5475. S2CID   84270881.
  18. ↑ Wasswa, P.; Otto, B.; Maruthi, M. N.; Mukasa, S. B.; Monger, W.; Gibson, R. W. (2011). "First identification of a sweet potato begomovirus (sweepovirus) in Uganda: characterization, detection and distribution". Plant Pathology. 60 (6): 1030–1039. doi: 10.1111/j.1365-3059.2011.02464.x . ISSN   1365-3059.
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