Active BR signalling adjusts the subcellular localisation of BES1/HSP90 complex formation

Area of Science:

• Plant molecular biology
• Cellular signaling pathways
• Protein-protein interactions

Background:

• Heat shock proteins 90 (HSP90) are crucial for cellular adaptation and involved in plant hormone signaling, including brassinosteroids (BR).
• The BES1 transcription factor is activated by BR and regulates BR-responsive genes, playing a key role in plant growth.
• Understanding the regulation of BES1 by HSP90 is vital for deciphering BR signaling.

Purpose of the Study:

• To investigate the interaction between BES1 and HSP90 in plant cells.
• To determine the role of HSP90 in BR signaling and BES1 activity.
• To assess the effect of HSP90 inhibition on plant development.

Main Methods:

• Genetic and physiological analyses
• Fluorescence live-cell imaging
• Molecular and biochemical assays including co-immunoprecipitation, yeast-two hybrid, and Bimolecular fluorescence complementation (BiFC)
• Phenotypic analysis of plant mutants
• Pharmacological inhibition of HSP90 ATPase activity

Main Results:

• HSP90 interacts with BES1 in both the nucleus and cytoplasm of plant cells.
• During active BR signaling, nuclear HSP90/BES1 complexes diminish, while cytoplasmic complexes become prominent.
• Pharmacological inhibition of HSP90 ATPase activity with geldanamycin (GDA) significantly reduces hypocotyl elongation in the bes1-D mutant.
• Active BR signaling cannot rescue the GDA-induced inhibition of hypocotyl elongation in the bes1-D mutant, indicating hypersensitivity to GDA.

Conclusions:

• HSP90 facilitates a nuclear metastable conformation of BES1, crucial for regulating BR-dependent gene expression.
• HSP90 plays a role in the compartmentalized cycle of BES1 during active BR signaling.
• The constitutively active BES1 mutant (bes1-D) is hypersensitive to the inhibition of HSP90 ATPase activity.