biology

Tombusviridae

Tombusviridae is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Tombusviridae rather than just read about it. In short: Tombusviridae is a family of single-stranded positive sense RNA plant viruses. The family contains 19 genera in 3 subfamilies.

Key takeaways

Tombusviridae belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Tombusviridae to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Tombusviridae from memory before moving on to harder problems.

Reference excerpt

Tombusviridae is a family of single-stranded positive sense RNA plant viruses. The family contains 19 genera in 3 subfamilies. The name is derived from Tomato bushy stunt virus (TBSV).

Genome

All viruses in the family have a non-segmented (monopartite) linear genome, with the exception of Dianthoviruses, whose genome is bipartite. The genome is approximately 4.6–4.8kb in length, lacks a 5' cap and a poly(A) tail, and it encodes 4–6 ORFs. The polymerase encodes an amber stop codon which is the site of a readthrough event within ORF1, producing two products necessary for replication. There is no helicase encoded by the virus.

Structure The RNA is encapsulated in an icosahedral (T=3) capsid, composed of 180 units of a single coat protein 27–42K in size; the virion measures 28–35 nm in diameter, and it is not enveloped.

Life cycle Viral replication is cytoplasmic, and is lysogenic. Entry into the host cell is achieved by penetration into the host cell. Replication follows the positive stranded RNA virus replication model. Positive stranded RNA virus transcription, using the premature termination model of subgenomic RNA transcription is the method of transcription. Translation takes place by leaky scanning, −1 ribosomal frameshifting, viral initiation, and suppression of termination. The virus exits the host cell by tubule-guided viral movement. Plants serve as the natural host. Transmission routes are mechanical, seed borne, and contact. Viruses in this family are primarily soil-borne, some transmitted by fungal species of the order Chytridiales, others by no known vector. Virions may spread by water, root growth into infected soil, contact between plants, pollen, or seed, depending on the virus species. These viruses may be successfully transmitted by grafting or mechanical inoculation, and both the virion and the genetic material alone are infective.

Replication Members of Tombusviridae replicate in the cytoplasm, by use of negative strand templates. The replication process leaves a surplus of positive sense (+)RNA strands, and it is thought that not only does the viral RNA act as a template for replication, but is also able to manipulate and regulate RNA synthesis. The level of RNA synthesis has been shown to be affected by the cis-acting properties of certain elements on the RNA (such as RNA1 and 2), which include core promoter sequences which regulate the site of initiation for the complementary RNA strand synthesis. This mechanism is thought to be recognised by RNA-dependent RNA polymerase, found encoded within the genome. Viruses in Tombusviridae have been found to co-opt GAPDH, a host metabolic enzyme, for use in the replication center. GAPDH may bind to the (−)RNA strand and keep it in the replicase complex, allowing (+)RNA strands synthesized from it to be exported and accumulate in the host cell. Downregulation of GAPDH reduced viral RNA accumulation, and eliminated the surplus of (+)RNA copies.

Notes Research has shown that infection of plants from tombusviruses contain defective interfering RNAs that are born directly from the viruses RNA genome, and no host genome. Viral DI RNAs with their small size and cis-acting elements are good templates both in vivo and in vitro on which to study RNA replication. Sub-genomic RNA is used in the synthesis of some proteins; they are generated by premature termination of (−)strand synthesis. sgRNAs and sgRNA negative-sense templates are found in infected cells.

Taxonomy The family contains the following subfamilies and genera (-virinae denotes subfamily and -virus denotes genus):

References

External links Viralzone: Tombusviridae ICTV

Illustrations

Worked examples

Example 1 — a first encounter with Tombusviridae

Start with the simplest possible case. Write down what Tombusviridae claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Tombusviridae before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Tombusviridae ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Tombusviridae

In research: Tombusviridae appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Tombusviridae in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Tombusviridae is common in secondary-school and first-year university syllabi. It links to neighbouring topics Riboviria, Tombusviridae, Viral plant pathogens and diseases, so understanding it makes those chapters shorter.
In everyday life: Look for Tombusviridae outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Tombusviridae in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Tombusviridae means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Tombusviridae out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Tombusviridae in simple terms?

Tombusviridae is a family of single-stranded positive sense RNA plant viruses. The family contains 19 genera in 3 subfamilies.

Why does Tombusviridae matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Tombusviridae?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Tombusviridae.