Low ambient temperatures regulate Arabidopsis abscisic acid signaling and seed germination via CBFs–ABI3/ABI5–ICE1 interactions

Seed germination is profoundly influenced by diverse environmental stimuli (e.g., temperatures), but the associated underlying molecular mechanisms remain largely uncharacterized. In this study, we demonstrated that low ambient temperatures, such as 16°C, suppress Arabidopsis thaliana seed germination, with endogenous abscisic acid (ABA) signaling revealed as a critical part of the underlying mechanism. The germination suppression and ABA response regulation by low ambient temperatures require ABSCISIC ACID INSENSITIVE3 (ABI3) and ABI5, two indispensable transcriptional activators in the ABA signaling pathway. In-depth analyses demonstrated physical associations between ABI3/ABI5 and low-temperature-responsive C-REPEAT BINDING FACTOR1 (CBF1), CBF2, and CBF3 (i.e., CBFs). Genetic evidence confirms that CBFs are essential for low-temperature- and ABA-mediated germination repression. Furthermore, CBFs and ABI3/ABI5 synergistically mediate the inhibitory effects of both low temperatures and ABA on germination. Mechanistically, these factors reciprocally enhance each other's transcriptional activities and promoter enrichment at downstream target genes. Notably, CBFs also directly bind INDUCER OF CBF EXPRESSION1 (ICE1), establishing an antagonistic regulatory axis with ABI5. Collectively, our findings underscore the critical modulatory effects of low ambient temperatures on ABA signaling and seed germination, thereby elucidating the mechanism by which the CBFs-ABI3/ABI5-ICE1 module functions as a signal transducer that converts environmental stimuli into endogenous hormone signals.