Question

Arrange the following events in the correct order
(A). Restoration of Effector Triggered Susceptibility by Pathogen
(B). Effector triggered susceptibility by Pathogen
(C). Effector triggered immunity by Plant
(D). PAMP triggered immunity by Plant

• A. (D), (B), (C), (A)
• B. (A), (B), (C), (D)
• C. (B), (A), (D), (C)
• D. (C), (B), (D), (A)

Hint:

Remember the sequence of the "zigzag" model:
1. PTI (Plant defense)
2. ETS (Pathogen counter-attack)
3. ETI (Plant counter-defense)
4. Restoration of ETS (Pathogen adaptation).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The co-evolutionary interaction between plants and pathogens is described by the "zigzag" model proposed by Jones and Dangl.
This model illustrates the alternating phases of plant defense activation and pathogen evasion.

Step 2: Detailed Explanation:
Let us trace the evolutionary events in their correct sequential order:
1. PAMP-triggered immunity (PTI) (D): In the first phase, plant surface-localized pattern recognition receptors (PRRs) detect conserved pathogen-associated molecular patterns (PAMPs, like flagellin or chitin).
This recognition triggers a basal defense response known as PTI.
2. Effector-triggered susceptibility (ETS) (B): To counter PTI, successful pathogens inject virulent proteins called "effectors" directly into the plant host cell cytoplasm.
These effectors suppress PTI signaling pathways, leading to ETS and disease susceptibility.
3. Effector-triggered immunity (ETI) (C): In response, plants co-evolve intracellular resistance (R) proteins (mostly NB-LRR receptors) that specifically recognize these pathogen effectors or their activities.
This recognition triggers a robust, amplified immune response known as ETI, often culminating in local cell death (hypersensitive response) to stop the pathogen.
4. Restoration of Effector-triggered susceptibility (A): Under ETI selection pressure, the pathogen population evolves to lose the recognized effector, mutate it to avoid detection, or gain novel effectors that suppress the ETI pathway.
This restores susceptibility, allowing the pathogen to bypass host defenses once again.
Therefore, the correct chronological sequence is: (D) \(\rightarrow\) (B) \(\rightarrow\) (C) \(\rightarrow\) (A).

Step 3: Final Answer:
The correct option is (D), (B), (C), (A).