Cucumber Green Mottle Mosaic Virus

Running Head: CUCUMBER GREEN MOTTLE MOSAIC VIRUS 1

Name

Institution

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Cucumber green mottle virus: Tobamovirus genus, Virgaviridae family, class IV, positive

single-stranded RNA genome; 3 tRNA like structure encoding four polypeptides.

The scientific article that first reported on the virus: T. Tian, K. Posis et al. (2014) “First

Report of Cucumber green mottle mosaic virus on Melon in the USA”, Plant disease. Volume

98, pp. 1163

News article: Filmer K. Adkins S, Pongam P D’Elia. (2015) “First complete genome sequence

of a cucumber mottle mosaic virus in North America. American Journal of Plant Sciences.

Interest: What caught your attention about the virus?

The disease “Cucumber green mottle virus” (CGMMV) has an unusually long name that

attracted my attention. The fact that this virus spreads from short distance to long distances so

quickly without a vector makes it attractive to study. I intended to gain a detailed understanding

of the virus aetiology and epidemiology. Furthermore, I was curious to understand the

relationship of the virus and the plants of the family Cucurbitaceae that it infected, how it

manifested itself in host plants, its relationship to other members of the Virgaviridae family,

particularly the genus Tobamovirus.

Discovery: Discuss the methods used to identify the virus in infected plants.

“Cucumber green mottle virus” was first described in England, 1935 infecting cucumber,

making it one of the first plant viruses to be studied. It was discovered that it diminished cucurbit

fruit yields and quality, especially in watermelons. The research was initiated to obtain insights

into its particle, genome characteristics, evolution and epidemiology. It was discovered that the

virus particularly stability and ease of contact transmission, which is common among

tobamovirus genus, explained its complex disease cycle and its ability to spread over long and

short distances without a vector. In the US, July 2013, a melon “Cucumis melo” field in Yolo

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County, California was inspected as part of a phytosanitary inspection for seed production. The

plant leaves exhibited mosaic, dark green on the leaves, blotches and mottled areas of light. The

virus name was derived from these characteristics. Plant sap was examined using a transmission

electron microscope, and rigid rod-shaped particles were observed indicating the presence of the

virus. RNA was analyzed to confirm the presence of the virus by RT-PCR (Reverse

Transcription Polymerase Chain Reaction) using primers designated by PPQ (Plant Protection

and Quarantine) based on 21 genomic sequences of CGMMV found worldwide. The 976-bp

amplicon was sequenced, and BLAST analysis (Basic Local Alignment Search Tool) showed

that the series was 95% identical to MP (Movement protein) and CP (Coat Protein) region of

CGMMV isolates reported in Russia, Spain, Israel, China, Korea, Japan and India. These

confirmed the first case of the Cucumber green mottle virus in the United States. Another

method used to identify the virus is by taking affected plants’ samples, testing them using

double-antibody sandwich with commercial antisera against CGMMV giving positive results of

the presence of the virus.

Prevalence: How many host species does the virus affect? How widespread is the virus

infection? What is the route(s) of transmission? If this virus affects humans, is it zoonotic?

The virus has been realized to have several host species, and it specializes in infecting

plants. It affects cucurbit crops such as cucumber, watermelon, melons, large melon, zucchini,

pumpkin, squash, bitter gourd, bottle gourd and cantaloupe (Chenopodium amaranticolor,

Chenopodium murale, Citrullus lanatus, Citrullus vulgaris, Cucumis sativus, Lagenaria siceraria,

Nicotiana tabacum). Regarding distribution, the virus was first documented in the United

Kingdom, England in 1935, affecting cucumber. From England, it spread to other parts of

Europe, Asia and the Middle East, North America where it was first documented in California

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and Alberta in 2013, and also in Northern Australia. The virus is spread through various means

such as the virus attacks plant cells through invisible plant wounds, and it can be introduced into

crops through contaminated seed and soil, by sap or infected seeds and remain dormant with the

seed coat. Spreading is sped through mechanical transfer where it involves normal handling of

contaminated crops when pruning or staking. Contact of a disinfected crop with an infected plant

is enough to spread the virus. These can occur via contaminated machinery, through root to root

connection, through contact with contaminated clothing or the hands of people who have come

into contact with the infected plants, through recycled packaging materials, and infected

rootstock plants and grafts. It is not spread through a vector. The Detection of this virus to

molecular level can be done using methods such as Enzyme-linked immunosorbent assay

(ELISA) usually in seeds. RT-PCR (Reverse Transcription Polymerase Chain Reaction) is used

to detect other strains of the CGMMV. These have helped realize that the virus does not affect

humans in any way and therefore not zoonotic.

Virology: description of the main features of the virion, cell receptor (if known) and entry

mechanism, genome and genetic content, mechanism of genome replication, viral gene

expression, and virion assembly and release. The List of the cell types that allow for viral

replication. You may use analogies to viruses in the same family for a general description.

The virions of the cucumber green mottle mosaic virus are straight, rod-shaped, with a

length of 300nm, 15nm wide and have a size of 6.5 kb. The genome contains 5% nucleic acid,

95% protein. It has tRNA-like activity, accepts histidine and RNA are sequenced. The Non-

genomic nucleic acid found in the virion is subgenomic mRNA. The genome is made up of

linear single-stranded RNA with nucleotide base ratios G25, A26, C19 and comprises four

proteins; 186K, 129K, 29K (movement protein) and 17.3K (coat protein). After virus entry

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through the exposed plant foliage, the virus replicates in all plant tissues including pollen. The

virion’s coat protein play the role of replication, virion formation, cell to cell movement, vector

transmission, genome activation, symptom modulation and its coding region is the assembly

initiation site. Finally, it identifies assembly initiation site located in the genomic RNA in the

initial steps of virion assembly. The virus contains genes that encode movement proteins which

facilitate the movement of released virus particles between cells via the plasmodesmata and also

through the xylem and phloem to other plant tissues. Infectivity decreased when deproteinised

with proteases and retained when deproteinized with phenol or detergent. They virion replicate in

plant leaves, mesophyll, epidermis, vascular parenchyma, xylem, phloem, companion cells, in

cytoplasm and cell vacuoles, just like another virus in the same family.

Infection of the host(s): Describe the general features of contamination of the susceptible

host species.

The host plant species are usually infected through the leaves, stems, roots or any other

outer tissue that can come into contact with an infected plant, hand or machinery( Park et

al.,2005). Also, open cuts make them susceptible to infection. The infected species look

bleached; the plants may be stunted, they exhibit symptoms such as fruit abortion, uneven

ripening, internal yellowing, and breakdown of the flesh, being severely spotted, streaked and

distorted, fruit malformation and even dirty red flesh discoloration. Vein crumpling, vein

clearing may be apparent on young leaves, and the mature leaves have mosaic-like mottling

patterns, look pale, yellow or bleached.

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Exciting things that came up during the preparation of this report: briefly describe 2 to 4

items that you found to be novel or unusual about the virus.

1. Based on this research, the ease of spread and infection mechanisms of the virus in

the farm over long distances have made it and other virus non its genus to be hazardous and one

of the most feared by farmers worldwide.

2. Preventing infection is a hectic process, a farmer should inspect their crops often for

signs of disease if there is any; the plants should be contained to avoid the infection from

spreading. It involves; Plant seeds purchased should be tested by ELISA (Enzyme Linked

Immuno Sorbent Assay), removal of weeds that may harbour viruses in and around cucurbit

crops. Developing a biosecurity plan for your farm, disposal on site of suspected plants and crop

residues by burning or deep burial and sterilization of vehicles, equipment, tools, plant trays and

footwear with potassium peroxymonosulfate or freshly prepared 1% sodium hypochlorite

(NaOCI) bleach.

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References

Park, S. M., Lee, J. S., Jegal, S., Jeon, B. Y., Jung, M., Park, Y. S., ... & Lee, M. Y. (2005).

Transgenic watermelon rootstock resistant to CGMMV (cucumber green mottle mosaic

virus) infection. Plant cell reports, 24(6), 350-356.

Tian, T., Posis, K., Maroon-Lango, C. J., Mavrodieva, V., Haymes, S., Pitman, T. L., & Falk, B.

W. (2014). First report of Cucumber green mottle mosaic virus on melon in the United

States. Plant Disease, 98(8), 1163-1163.

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