Plants fine-tune growth hormone response with a molecular dimmer switch
Huang X, Chen H, Reser L, Reyes AV, Xu SL
Plant Signaling
The same growth hormone pathway that tells your tomato seedlings when to stretch toward light and your bulbs when to send up spring shoots turns out to have a built-in dimmer switch, not just an on/off toggle, which helps explain why plant growth responses can be so precisely timed.
Plants use a hormone called gibberellin to control growth, and it works by getting rid of a protein called DELLA that normally holds growth in check. Researchers found that plants have a second, quicker way to quiet down DELLA: a molecular tag added to a specific spot on the protein that weakens its grip on the cellular machinery needed to turn genes on, without destroying the protein itself. It's like a dimmer switch working alongside an on-off switch, giving the plant finer control over exactly how much it grows and when.
Key Findings
CDK8, part of the Mediator complex's kinase module, phosphorylates the Arabidopsis DELLA protein RGA at a specific site (Ser170) in a disordered region of the protein.
This phosphorylation doesn't change RGA's stability, location, or its interactions with transcription factors or histone H2A, but it does weaken RGA's binding to the Mediator subunit MED15, reducing DELLA's ability to activate transcription.
Plants lacking functional CDK8 (cdk8 mutants) show impaired gibberellin responses and delayed developmental phase transitions, and these defects are partially rescued when DELLA function is also removed.
chevron_right Technical Summary
Scientists discovered a molecular 'volume knob' that fine-tunes how plants respond to a key growth hormone, without having to destroy the protein that controls it. This gives plants a faster, more precise way to adjust their growth in response to changing conditions.
Abstract Preview
Original paper
CDK8 phosphorylation of DELLA limits Mediator recruitment in gibberellin signaling.
Gibberellin (GA) promotes plant growth primarily by triggering degradation of DELLA transcription regulators, yet how DELLA activity is fine-tuned dynamically by phosphorylation independently of pr...
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