164. Which one of the following statements is correct during gibberellic acid (GA) signal transduction in plants?
1. DELLA protein stimulates GA response
2. GID1 does not make complex with DELLA protein
3. Degradation of DELLA protein by 26S proteasomal pathway
4. GID1 proteins get degraded by 26S proteasomal pathway

Gibberellic Acid (GA) Signal Transduction in Plants

Gibberellic acid (GA) is a crucial plant hormone that regulates several aspects of plant growth, including seed germination, stem elongation, and flowering. Its signaling mechanism is tightly controlled by DELLA proteins, which act as negative regulators of GA responses.

Key Components in GA Signaling

1. DELLA Proteins

   • Repress growth and other GA-induced processes.

   • In the absence of GA, they accumulate and inhibit transcription of GA-responsive genes.

2. GID1 (GA-Insensitive Dwarf1) Receptor

   • A soluble GA receptor that binds gibberellin (GA).

   • Forms a complex with DELLA proteins in the presence of GA.

3. 26S Proteasome

   • Once the GID1-GA-DELLA complex forms, DELLA proteins are ubiquitinated and degraded via the 26S proteasomal pathway.

   • This degradation releases repression, allowing GA responses to proceed.

Explanation of Options

1. DELLA protein stimulates GA response
   → Incorrect. DELLA inhibits GA responses. Its removal stimulates GA effects.

2. GID1 does not make complex with DELLA protein
   → Incorrect. GID1 does form a complex with DELLA in the presence of GA.

3. Degradation of DELLA protein by 26S proteasomal pathway
   → Correct. This is the central mechanism for activating GA responses.

4. GID1 proteins get degraded by 26S proteasomal pathway
   → Incorrect. It is the DELLA protein, not GID1, that gets degraded.

Correct Answer:

3. Degradation of DELLA protein by 26S proteasomal pathway

This degradation is essential for activating GA-mediated responses, and highlights the role of ubiquitin-proteasome pathway in plant hormone signaling.