ABSTRACT
Cold acclimation is a crucial strategy for plant survival at freezing temperatures. C-REPEAT BINDING FACTOR (CBF) genes are rapidly and transiently induced by low temperature and play important roles in cold acclimation. However, the mechanism underlying the attenuation of CBF expression during the later stages of the cold stress response is obscure. Here, we show that the protein kinase BRASSINOSTEROID-INSENSITIVE2 (BIN2) interacts with and phosphorylates INDUCER OF CBF EXPRESSION1 (ICE1) in Arabidopsis (Arabidopsis thaliana) under prolonged cold stress, facilitating the interaction between ICE1 and the E3 ubiquitin ligase HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENE1 and thereby promoting ICE1 degradation. The kinase activity of BIN2 is inhibited during the early stages of the cold stress response and is subsequently restored, suggesting that BIN2 mainly downregulates ICE1 abundance when CBF expression is attenuated. A loss-of-function mutation of ICE1 partially suppresses the cold-induced expression of CBFs and compromises the enhanced freezing tolerance of bin2-3 bil1 bil2 These findings reveal an important role for BIN2 in fine-tuning CBF expression, and thus in balancing plant growth and the cold stress response.
Subject(s)
Arabidopsis/metabolism , Brassinosteroids/metabolism , Cold-Shock Response , Protein Kinases/metabolism , Transcription Factors/metabolism , Arabidopsis/genetics , Arabidopsis Proteins/genetics , Arabidopsis Proteins/metabolism , Freezing , Gene Expression Regulation, Plant , Genes, Plant/genetics , Intracellular Signaling Peptides and Proteins/metabolism , Nuclear Proteins/metabolism , Phosphorylation , Plants, Genetically Modified , Signal TransductionABSTRACT
Cold stress is a major environmental factor that adversely affects plant growth and development. The C-repeat binding factor/DRE binding factor 1 (CBF/DREB1) transcriptional regulatory cascade has been shown to play important roles in plant response to cold. Here we demonstrate that two key components of brassinosteroid (BR) signaling modulate freezing tolerance of Arabidopsis plants. The loss-of-function mutant of the GSK3-like kinases involved in BR signaling, bin2-3 bil1 bil2, showed increased freezing tolerance, whereas overexpression of BIN2 resulted in hypersensitivity to freezing stress under both non-acclimated and acclimated conditions. By contrast, gain-of-function mutants of the transcription factors BZR1 and BES1 displayed enhanced freezing tolerance, and consistently cold treatment could induce the accumulation of dephosphorylated BZR1. Biochemical and genetic analyses showed that BZR1 acts upstream of CBF1 and CBF2 to directly regulate their expression. Moreover, we found that BZR1 also regulated other COR genes uncoupled with CBFs, such as WKRY6, PYL6, SOC1, JMT, and SAG21, to modulate plant response to cold stress. Consistently, wrky6 mutants showed decreased freezing tolerance. Taken together, our results indicate that BZR1 positively modulates plant freezing tolerance through CBF-dependent and CBF-independent pathways.
