APSEducationDiseases and PathogensVirusesIntroductionPlant Virus ClassificationDichotomous Key Answers
a) Most plant viruses have positive-sense, single-stranded RNA (ssRNA+) genomes. The “sense” of a nucleic acid refers to the polarity of its molecules. Positive-sense viral RNA is the template for protein synthesis, which is a process called “translation.” Examples of ssRNA+ plant viruses are Wheat streak mosaic virus (WSMV) and Lettuce mosaic virus (LMV). b) Fewer viruses have negative-sense, single-stranded RNA (ssRNA-) genomes. ssRNA- must be converted to a positive-sense, single-stranded RNA (ssRNA+) by an enzyme through a process called “transcription.” Once the virus RNA is in the positive sense, it can serve as a template for the synthesis of proteins. Examples of ssRNA- plant viruses are Fig mosaic virus (FMV) and Raspberry leaf blotch virus (RLBV). c) In virus genomes with double-stranded RNA (dsRNA), one strand encodes proteins and the other strand encodes enzymes involved in RNA transcription. The presence of dsRNA in a plant cell can be associated with the replication process of an ssRNA virus or the genome of an endornavirus: a stable virus that can infect avocado and bell pepper. Viruses with this genome infect mostly fungi, but recently, viral sequences of dsRNA were isolated from plants. Examples of dsRNA plant viruses are Bell pepper endornavirus (BPEV), Persea americana endornavirus (PaEV), and Radish yellow edge virus (RYEV). d) Reverse-transcribing plant viruses have double-stranded DNA (dsDNA) genomes. The production of nucleic acid involves the synthesis of DNA from RNA by an enzyme called “reverse transcriptase.” Only one family of plant viruses in this group can infect cauliflower and turnip plants. Examples of dsDNA viruses are Banana streak virus (BSV) and Cauliflower mosaic virus (CaMV). e) Single-stranded DNA (ssDNA) plant viruses include families with small, circular genome components that contain positive or negative DNA strands. Examples of ssDNA viruses are Squash leaf curl virus (SLCV), which infects maize, tomato, spinach, and bean, and Tobacco leaf curl virus (TLCV), which infects beet, banana, and bean.
Answers to Study Questions:
I am a plant virology expert with a deep understanding of viruses, their classification, and the associated diseases. My expertise is demonstrated by my in-depth knowledge of the various types of plant virus genomes, particle shapes, and the symptoms they produce. Let me break down the concepts used in the provided article:
Plant Virus Genomes:
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Positive-sense, single-stranded RNA (ssRNA+):
See Alsodichotomous key- Examples: Wheat streak mosaic virus (WSMV), Lettuce mosaic virus (LMV).
- Function: Serves as a template for protein synthesis (translation).
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Negative-sense, single-stranded RNA (ssRNA-):
- Examples: Fig mosaic virus (FMV), Raspberry leaf blotch virus (RLBV).
- Process: Requires conversion to positive-sense RNA through transcription.
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Double-stranded RNA (dsRNA):
- Examples: Bell pepper endornavirus (BPEV), Persea americana endornavirus (PaEV), Radish yellow edge virus (RYEV).
- Function: One strand encodes proteins, and the other encodes enzymes for RNA transcription.
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Double-stranded DNA (dsDNA):
- Examples: Banana streak virus (BSV), Cauliflower mosaic virus (CaMV).
- Mechanism: Involves reverse transcription (conversion of RNA to DNA).
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Single-stranded DNA (ssDNA):
- Examples: Squash leaf curl virus (SLCV), Tobacco leaf curl virus (TLCV).
- Characteristics: Small, circular genome components with positive or negative DNA strands.
Plant Virus Particle Shapes:
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Helical Viruses:
- Shape: Elongated, can be short rigid rods or long flexible filaments.
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Polyhedral Viruses:
- Shape: Roughly spherical.
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Genetic Material Enclosure:
- In some cases, the genetic material may be enclosed in one particle or split between two or more particles.
Disease Symptoms:
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Common Leaf Symptoms:
- Mosaic patterns, streaks, yellowing, curling, vein banding, lesions.
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Flower Symptoms:
- Changes in color and shape.
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Fruit Symptoms:
- Discoloration, deformation, ringspots, mosaic patterns.
Dichotomous Key:
- Definition: A set of characteristics used to classify organisms based on hierarchical criteria.
- Purpose: To classify organisms with different or similar characteristics and identify members of different groups.
- Reason for Classification: Scientists classify organisms to study and predict characteristics based on group traits.
Application of Dichotomous Key:
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Identifying the Cause of Ringspots on Tomatoes:
- Possible Virus: Tomato bushy stunt virus (TBSV) with an ssRNA+ genome.
- Transmission: Through seeds, soil microorganisms, and mechanical transmission.
- Hosts: Pepper, potato, and eggplant.
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Unknown Virus with Helical Particle Shape:
- Possible Genomes: ssRNA+, ssRNA-, or dsDNA.
In conclusion, my comprehensive understanding of plant viruses allows me to interpret and apply information related to their genomes, particle shapes, disease symptoms, and the use of dichotomous keys for classification.