The brassinosteroid-responsive transcription factor CmBEEL1 through integrating ICE1 cascade and ROS homeostasis enhances cold tolerance in Chrysanthemum.

Cold stress ranks among the notable abiotic stresses that significantly hinder plant growth and geographical distribution. Brassinosteroids (BRs) have been proven to enhance the cold tolerance of plants across multiple species. However, the involvement of BR and its regulatory mechanism underlying cold tolerance in chrysanthemum has not yet been fully elucidated. In this study, we found that BR treatment alleviated cold stress-induced growth inhibition in chrysanthemum. Based on the transcriptome database of Chrysanthemum in response to cold stress, CmBEEL1, a member of the bHLH family genes, was identified and characterized. Both cold stress and BR treatments upregulated the expression of CmBEEL1. We further generated CmBEEL1-overexpressing (CmBEEL1-OX) lines, and found that CmBEEL1-OX lines exhibited enhanced cold tolerance, characterized by reduced electrolyte leakage and lower reactive oxygen species (ROS) accumulation. Weighted gene co-expression network analysis (WGCNA) and downstream gene analysis indicated that CmBEEL1 primarily modulates cold tolerance by inducing alterations in the expression of the ICE - DREB - COR pathway and ROS metabolism. Moreover, CmBEEL1 was shown to directly bind to the promoter of CmICE1, to activate ICE - DREB - COR cascade. It is concluded that overexpression of CmBEEL1 is sufficient to enhance cold tolerance in chrysanthemum via the ICE1 cascade and ROS homeostasis.