Plant Acquired Immunity

Question 1

What is acquired immunity?

Answer 1

A defence regulatory system that enables genetically susceptible individuals to acquire long-lasting and / or systemic resistance upon recovery of a primary exposure to biotic stress (pests or pathogens)

Question 2

How is acquired immunity in plants different to that in vertebrates?

Answer 2

• Does not involve dedicated immune cells
• Less specific than in humans
• Often referred to as induced resistance (IR)
• Augments basal (quantitative resistance)

Question 3

What can induce long-lasting resistance in plants?

Answer 3

• Selected environmental stresses/stimuli
  e.g.
• Pathogen attack
• Herbivore attack, including volatiles
• Beneficial soil microbes
• Selected chemicals

Question 4

What is systemic acquired resistance? (SAR)

Answer 4

Provides long-lasting, broad-spectrum protection against a range of pathogens after an initial localized infection
- Induced by localised pathogens and MAMPs
- Requires SA and NPR1
- Mostly effective against biotrophic pathogens

Question 5

What is volatile organic compound-induced resistance (VOC-IR)>

Answer 5

Volatile organic compounds can induce resistance in plants against both biotic (like pathogens and herbivores) and abiotic (like environmental stress) threats
Plants release VOCs as a warning to other plants or to attract beneficial organisms, including those that can defend against the attack

Question 6

What is induced systemic resistance (ISR)?

Answer 6

Exposure to a non-pathogenic stimulus (e.g. rhizobacteria, Pseudomonas / Bacillus) primes the plant to resist a subsequent pathogen attack
Requires intact JA and ET signalling
Mostly effective against necrotrophic pathogens and insects

Question 7

What is B-amino-butyric acid (BABA)-induced resistance (BABA-IR)?

Answer 7

• Primes basal defence mechanisms, making them more efficient and quicker to respond to stress
• Induced by the non-protein amino acid BABA
• Effective against a broad range of pathogens, insects and abiotic stresses
• BABA produced by plants under stress conditions and recognised by receptor IBI1

Question 8

Why is immune priming beneficial?

Answer 8

• Inducible defence mechanisms (expressions of innate immunity) are very costly
• Immune priming means defence mechanisms are not upregulated, but primed to go, so not expressed unless the plant is exposed to the pathogen / pest
• Allows plants to act faster and stronger later in the life cycle for the same stimulus

Question 9

What are some of the ways a plant can be primed?

Answer 9

• Pathogens: priming of SA dependent defences
• Herbivores: priming of JA dependent defences
• Beneficial soil microbes: priming of JA dependent defences
• Chemicals: priming of callose and SA dependent defences

Question 10

Why aren’t plants constitutively primed?

Answer 10

• Costs of priming are outweighed by benefits under disease pressure
• Maintaining a constantly primed state would divert resources from growth and reproduction