Affiliation:
1. Department of Molecular Genetics The Ohio State University Columbus OH 43210 USA
2. Division of Applied Life Science (BK21 Four), Plant Biological Rhythm Research Center (PBRRC), Plant Molecular Biology and Biotechnology Research Center (PMBBRC) Gyeongsang National University Jinju 52828 Korea
Abstract
Summary
Arabidopsis PSEUDORESPONSE REGULATOR7 (PRR7) is a core component of the circadian oscillator which also plays a crucial role in freezing tolerance. PRR7 undergoes proteasome‐dependent degradation to discretely phase maximal expression in early evening. While its repressive activity on downstream genes is integral to cold regulation, the mechanism of the conditional regulation of the PRR7 abundance is unknown.
We used mutant analysis, protein interaction and ubiquitylation assays to establish that the ubiquitin ligase adaptor, HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENE 15 (HOS15), controls the protein accumulation pattern of PRR7 through direct protein–protein interactions at low temperatures. Freezing tolerance and electrolyte leakage assays show that PRR7 enhances cold temperature sensitivity, supported by ChIP‐qPCR at C‐REPEAT BINDING FACTOR1 (CBF1) and COLD‐REGULATED 15A (COR15A) promoters where PRR7 levels were higher in hos15 mutants.
HOS15 mediates PRR7 turnover through enhanced ubiquitylation at low temperature in the dark. Under the same conditions, increased PRR7 association with the promoters of CBFs and COR15A in hos15 correlates with decreased CBF1 and COR15A transcription and enhanced freezing sensitivity.
We propose a novel mechanism whereby HOS15‐mediated degradation of PRR7 provides an intersection between the circadian system and other cold acclimation pathways that lead to increased freezing tolerance.
Funder
Rural Development Administration
National Institute of General Medical Sciences