Network Layer — How Cells Resolve Conflicting Signals
Inside every cell, multiple pathways operate simultaneously, often giving conflicting orders.
How does a cell decide which signal to follow?
The network layer is a protocol that governs signal integration, conflict resolution, and priority management.
Example 1: JA-SA Cross-talk in Plant Immunity — A Protocol for Conflict Resolution
Plants face a constant growth-defense tradeoff:
- Jasmonic Acid (JA) fights necrotrophic pathogens and herbivores.
- Salicylic Acid (SA) fights biotrophic pathogens.
Activating both pathways together would waste energy and create conflicts — hence priority negotiation is required.
Protocol Breakdown (Conflict Resolution):
| Step | Action |
|---|---|
| Recognition | PAMPs trigger both JA and SA pathways. |
| Negotiation | NPR1 evaluates context, prioritizing SA or JA. |
| Execution | Defense genes activated based on chosen pathway. |
| Feedback | SA upregulates NPR1 — reinforcing the decision. |
| Error handling | Non-priority pathway suppressed — preventing conflict. |
Failure Example:
- Overactive JA response during normal growth leads to stunted development — mismanaged protocol.
Example 2: Hormone Network for Growth vs. Defense — Dynamic Prioritization
Plants must balance growth hormones (like auxin, gibberellin) and defense hormones (SA, JA):
- DELLA proteins act as protocol switches, suppressing growth when defense is needed.
Protocol Dynamics:
- Recognition: Pathogen detected — defense signals initiated.
- Negotiation: DELLA accumulates to block growth hormones.
- Execution: Defense genes take priority.
- Error handling: DELLA degraded when threat is gone — growth resumes.
Failure Example:
- If DELLA fails to accumulate, plants may continue to grow but remain vulnerable to infection — protocol failure.
Key Takeaways for Network Layer
- Cells receive multiple, often conflicting signals — internal negotiation determines priority.
- Network protocols prevent chaos, ensuring the right response happens at the right time.
- Feedback loops and suppression mechanisms serve as internal “negotiation tools”.
- Protocol failure leads to disease — stunted growth, failed defense, or chronic inflammation.
- Thinking in protocols shows how cells “think” through multiple inputs, and why this system sometimes fails under stress.
