Explain how gibberellin activates genes by causing the breakdown of DELLA protein repressors, which normally inhibit factors that promote transcription

Sourav PanNovember 1, 2024

Answered

Gibberellins (GAs) are a class of plant hormones that play a crucial role in promoting growth and development, including stem elongation, seed germination, and flowering. One of the key mechanisms by which gibberellins activate gene expression involves the regulation of DELLA proteins, which act as repressors of transcription. Here’s how this process works:

Overview of DELLA Proteins

• DELLA Proteins: DELLA proteins are a family of growth-repressing proteins that inhibit the expression of genes involved in promoting growth and development. They function primarily by interacting with transcription factors that promote the expression of growth-related genes.
• In the absence of gibberellins, DELLA proteins accumulate in the cell and bind to specific transcription factors, preventing them from activating target genes. This results in the repression of growth-promoting processes.

Mechanism of Gibberellin Action

1. Gibberellin Perception:
   • Gibberellins are perceived by specific receptors in the cell, known as Gibberellin Receptors (such as GID1).
   • When gibberellins bind to these receptors, it induces a conformational change in the receptor, allowing it to interact with DELLA proteins.
2. DELLA Protein Degradation:
   • The binding of the gibberellin-receptor complex to DELLA proteins triggers a signaling cascade that leads to the ubiquitination of the DELLA proteins.
   • Ubiquitination is a process where small protein molecules called ubiquitins are attached to a target protein, marking it for degradation by the proteasome, a cellular structure responsible for degrading unneeded or damaged proteins.
   • As a result, the DELLA proteins are targeted for degradation, leading to a decrease in their concentration in the cell.
3. Release of Transcription Factors:
   • With DELLA proteins degraded, the transcription factors that were previously inhibited by DELLA are now free to act.
   • This includes the release of key transcription factors like GAMYB (Gibberellic Acid-Responsive Maturing Factor) and others that are crucial for the expression of growth-promoting genes.
4. Activation of Gene Expression:
   • The liberated transcription factors can now bind to the promoter regions of target genes, leading to an increase in transcription.
   • These target genes often encode enzymes and proteins that promote cell elongation, division, and other processes that enhance growth and development, such as enzymes involved in the breakdown of starches to sugars for energy.