CDK8 phosphorylation of DELLA limits Mediator recruitment in gibberellin signaling.

Authors

Xu Huang, Hongyi Chen, Larry Reser, Andres V Reyes, Shou-Ling Xu, Jeffrey Shabanowitz, Donald F Hunt, Tai-Ping Sun

Published in

Proceedings of the National Academy of Sciences of the United States of America. Volume 123. Issue 36. Pages e2619939123. Sep 08, 2026. Epub Aug 31, 2026.

Abstract

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 proteolysis remains poorly understood. Here, we show that the CDK8 kinase module of the Mediator complex attenuates activity of the Arabidopsis DELLA protein REPRESSOR OF ga1-3 (RGA) by modulating coactivator recruitment. Using TurboID-based proximity labeling, biochemical and genetic analyses, we identify CDK8 as an in planta kinase that phosphorylates RGA at Ser170 within its disordered PolyS/T region. This phosphorylation does not affect RGA stability, localization, or interactions with transcription factors or histone H2A, but selectively weakens RGA association with the Mediator subunit MED15, thereby reducing DELLA-dependent transcription activation. Consistently, cdk8 mutants show impaired GA-responses and delayed developmental phase transitions that are partially rescued by loss of DELLA function. Our findings uncover a phosphorylation-dependent mechanism by which the Mediator kinase module fine-tunes hormone-responsive transcription through selective control of DELLA-coactivator interactions.

PMID:
42673446
Bibliographic data and abstract were imported from PubMed on 01 Sep 2026.

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