Genome-wide identification and characterization of the bZIP gene family in Siberian apricot (Prunus sibirica) and their role under cold stress

The basic leucine zipper (bZIP) transcription factor functions not only as a key regulator of plant ontogeny but also as a critical mediator of cold stress responses. Currently, bZIPs have been subjected to genome-wide identification and functional annotation in multiple species; however, systematic characterization and mechanistic studies of this family remain lacking in the ecologically and economically important forest tree species Prunus sibirica . This study identified 41 PsbZIPs across the entire genome of P. sibirica , divided into 12 subfamilies. Exon–intron architecture and motif composition were largely conserved among PsbZIPs clustered within the same subfamily. No tandem duplication events were detected among the PsbZIPs . Instead, eight segmental duplication-derived gene pairs were identified. Protein–protein interaction analysis indicated potential interactions among most PsbZIPs. Further quantitative real-time PCR (qRT-PCR) analysis indicated that most PsbZIPs were highly expressed in petals, leaves, and stems. Under cold stress, unique expression profiles arose among PsbZIPs , with PsbZIP28 showing significant upregulation during the late stage of cold stress. Transient overexpression of PsbZIP28 in Populus ussuriensis markedly enhanced cold tolerance in the recipient plants. Subcellular localization analysis revealed that PsbZIP28 is localized in the nucleus, and yeast self-activation assays demonstrated that the C-terminus of PsbZIP28 possesses transcriptional activation activity. These results provide a conceptual basis for further elucidating the molecular basis underlying cold tolerance in woody plants and establish a valuable genetic resource for future stress- tolerance breeding and the development of novel cold-tolerant germplasm based on the bZIP gene family.