TOC1 clock protein phosphorylation controls complex formation with NF‐YB/C to repress hypocotyl growth

Five specific phosphorylation sites in the core clock protein TOC1 were identified that, when mutated, eliminated detectable phosphorylation.

• The TOC1 phospho-mutant fails to fully restore clock, growth, and flowering features in toc1 mutants.
• This mutant displays an advanced phase, increased degradation rate, and reduced interactions with PIF3 and HDA15.
• Poor binding of the TOC1 phospho-mutant occurs at genes related to pre-dawn hypocotyl growth, resulting in decreased repression of hypocotyl growth.
• NF-YB/C subunits stabilize TOC1 at target promoters, forming a trimeric complex that functions as a transcriptional co-repressor with HDA15.
• Phosphorylation of TOC1 may influence its stability and interactions, thereby regulating the timing of PHG expression and hypocotyl growth.

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