HOS15-mediated turnover of PRR7 enhances freezing tolerance

Area of Science:

• Plant molecular biology
• Circadian clock regulation
• Cold stress response

Background:

• PSEUDO RESPONSE REGULATOR7 (PRR7) is vital for Arabidopsis circadian rhythms and freezing tolerance.
• PRR7 protein levels are regulated by proteasome-dependent degradation, but the mechanism is unclear.
• Understanding PRR7 regulation is key to deciphering cold acclimation pathways.

Purpose of the Study:

• To elucidate the mechanism controlling PRR7 protein accumulation and its role in cold tolerance.
• To identify proteins interacting with PRR7 and regulating its stability.
• To investigate the link between PRR7, circadian clock, and cold acclimation.

Main Methods:

• Double mutant analysis in Arabidopsis.
• Protein-protein interaction assays.
• Ubiquitylation assays, ChIP-qPCR, freezing tolerance tests, and electrolyte leakage assays.

Main Results:

• HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENE 15 (HOS15) directly interacts with PRR7 and controls its protein levels.
• HOS15 mediates PRR7 turnover via ubiquitylation, particularly at low temperatures in the dark.
• hos15 mutants exhibit altered PRR7 accumulation, leading to increased freezing sensitivity and changes in CBF/COR gene expression.

Conclusions:

• HOS15 acts as a ubiquitin ligase adaptor, regulating PRR7 stability and impacting freezing tolerance.
• This HOS15-PRR7 interaction provides a novel link between the circadian system and cold acclimation pathways.
• PRR7 regulation by HOS15 influences the transcription of key cold-responsive genes like CBF1 and COR15A.