Plant Innate Immune System

Question 1

What are the stages of induced plant defence?

Answer 1

1. Pre-invasive penetration defence: stomatal closure
2. Post-invasive early defence: ROS
3. Post-invasive late defence: Hormone induced defences

Question 2

What is salicylic acid (SA) efficient against?

Answer 2

Efficient against biotrophic pathogens

Question 3

What is jasmonic acid efficient agaisnt?

Answer 3

Efiicient agains necrotrophic pathogens and insects.

Question 4

What is ethylene efficient against?

Answer 4

Works with JA for necrtotrophic pathogens and with SA for biotrophic pathogens.

Question 5

When is ABA activated?

Answer 5

Activated when herbivory causes water loss (drought). Also aids JA.

Question 6

Outline what happens in the jasmonic acid dependent immune system.

Answer 6

Against necrotrophic pathogens
0-10 mins:
- PRR binds to DAMPs
- Transcription factors activated, synthesis of JA.
10 mins - 3 hrs:
- JA and isoleucine complex acts as a label for degradation of JAZ.
- Activates MYC2 which activates defence genes

Question 7

What is a PRR?

Answer 7

Pattern recognition receptor

Question 8

What are DAMPs?

Answer 8

Damage associated molecular patterns.

Question 9

What are PAMPs?

Answer 9

Pathogen associated molecular patterns.

Question 10

What are MAMPs?

Answer 10

Microbe associated molecular patterns.

Question 11

Outline the Salicylic acid dependent immune system.

Answer 11

Against necrotrophic pathogens, slower to be undetected.
0-2 hrs:
- PRR binds to PAMPs
- Activates transcription factors, SA is synthesised.
2 -48 hrs:
- Reaches critical threshold and throws off redox state.
- NPR1 is reduced and enters the nucleus, switching on defence genes.

Question 12

What is NPR1?

Answer 12

Transcription factor that activates defence genes.

Question 13

What does the spatiotemporal model consist of?

Answer 13

• Non host resistance
• Basal resistance
• Race specific resistance (gene for gene resistance)

Question 14

What is non-host resistance?

Answer 14

Passive: host is not suitable environment for pathogen
Active: host activates defence response.
e.g. powdery mildew on Arabidopsis, screen for pen mutants

Question 15

What did screening for pen mutants show in powdery mildew infected Arabidopsis?

Answer 15

Pen = penetration
Pen1: syntaxin- localised to membrane and vesicles
Pen2: glycoside hydrolase- localised to peroxisomes and vesicles
Pen3: abc transporter- localised to membrane at infected sites.

Question 16

What is basal resistance?

Answer 16

Similar to host resistance but weaker.
e.g. Pseudomonas syringae on Arabidopsis: colonized the plant and it was visibly diseased.

Question 17

What is gene for gene resistance?

Answer 17

Specific R gene in plant is combined with corresponding Avr gene in pathogen

Question 18

What happens if Avr genes do not bind to the specific R protein?

Answer 18

Avr gene is actually a virulence gene unless it is recognised by the specific R protein.

Question 19

Outline the evolutionary model of the plant immune system.

Answer 19

MAMPs (low defence)
Evolution of PRRs -> non-host resistance (increase defence)
Evolution of Avr proteins (decreases defence -> basal resistance)
Evolution of R proteins -> race specific resistance (increases defence)
Evolution of 2nd gen effector protein (reduces defence -> basal resistance)
Evolution of 2nd gen R proteins (increases defence -> race specific resistance)