Virus Resistance

Question 1

How is infection controlled?

Answer 1

• Spray insecticides
• Delay planting to avoid insects
• Destroy infected crops
• Good field hygiene

Question 2

What does viral nucleic acid encode?

Answer 2

• Enzymes to replicated viral genome
• Proteins to allow transmission from cell to cell
• coat proteins which encapsulates the viral genome

Question 3

What causes viral resistance in plants?

Answer 3

Plants which express coat protein are virus resistant.
- Complete coat protein not required, just part of one
- Frame shift mutations which allow RNA production, but not protein synthesis cause resistance
- Coding regions inserted in reverse cause resistance
- Gene fragments as short as 25bp can cause resistance

Question 4

What is post translational gene silencing (PTGS)?

Answer 4

Expression of high levels of foreign genes can lead to repression of gene expression.
If dsRNA is produced, they are diced into 25 nucleotide RNAs.
This activates sequence specific nuclease, causing the degradation of mRNA

Question 5

How are virus resistant plants made?
Is resistance guaranteed?

Answer 5

• A portion of the viral genome is introduced into the crop, generating dsRNA molecules.
• However, some viruses produce proteins that suppress PTGS, so resistance is not guaranteed.

Question 6

What are the concerns against transgenic virus resistant squash?

Answer 6

• Squash may become weed
• Virus resistant genes may be transferred to weeds
• Recombination of viral genes in plants with other viruses can create new viruses.

Question 7

Why is there an increased probability of viral recombination in transgenic virus resistant plants?

Answer 7

It is unlikely that 2 viruses will infect a cell at the same time and recombine.
However, transgenic plants contain part of the viral genome
Meaning, any virus that infects the plant could recombine with the viral DNA.

Question 8

What is PRSV?

Answer 8

Papaya ring spot virus.
Discovered in Oahu in 1940s,
Papaya production destroyed in 1950s
Papaya production moved to Puna in 1960s
PRSV found in 1992

Question 9

How is transgenic papaya resistant to PRSV made?

Answer 9

Using biolistics containing part of the coat protein of PRSV.

Question 10

What is the potential problem of virus resistant papaya?

Answer 10

Coat protein used to make transgenic papaya might be allergenic.
It contains 6 amino acids shared with an allergen from roundworms
However, in 1997, USDA says it is safe.

Question 11

How is containment of GM plants unsuccessful?

Answer 11

India: Third of cotton is Bt, 80% is unlicensed.
Thailand: GM papaya resistant to PRSV has been found
Hawaii: Trees contain GM transgenes from contaminated pollen

Question 12

Give examples of GM contamination:

Answer 12

2001: GM corn used for animal food found in food products
2002: Traces of corn containing pig vaccine found in soy beans grown on former test plots
2005: Unapproved Bt10 corn found in stocks of approved Bt11 corn
2006: Approved glyphosate resistant rice from US found in EU stocks.