The bZIP transcription factor BcbZIP72 positively regulates cold tolerance through CBF-dependent pathways in...

Cold stress significantly limits the growth and yield of non-heading Chinese cabbage (NHCC, Brassica campestris (syn. Brassica rapa) ssp. Chinensis). The basic leucine zipper (bZIP) transcription factor family plays an essential role in plant responses to cold stress, yet the functions of group G bZIP members in NHCC remain poorly understood. In this study, 150 BcbZIP genes were identified, among which BcbZIP72 (group G) showed strong induction under cold stress. BcbZIP72 encodes a 462-amino acid protein with a 1389-bp open reading frame. Subcellular localization and transcriptional activation assays demonstrated that BcbZIP72 is localized in the nucleus and displays transcriptional activation activity. GUS staining experiments revealed that BcbZIP72 is expressed in the roots, stems, leaves, flowers, and seed pods of NHCC, with its expression significantly upregulated following cold treatment at 4 °C. Overexpression of BcbZIP72 in Arabidopsis and transient overexpression in NHCC both led to upregulation of CBFs and COR genes, thereby enhancing plant tolerance to cold stress. In contrast, VIGS-mediated silencing of BcbZIP72 resulted in a cold-sensitive phenotype. Further analyses confirmed that BcbZIP72 directly binds to a G-box element (-285 to -291 bp) in the BcCBF1 promoter to activate transcription, establishing BcbZIP72 as an upstream regulator of BcCBF1. Notably, cold-induced expression of BcbZIP72 is independent of abscisic acid (ABA). Collectively, these findings identify BcbZIP72 as a key regulator of cold tolerance in NHCC through a CBF-dependent pathway, providing a theoretical basis for cold-tolerance breeding in this crop.