Prunus mume is an important woody plant that has high ornamental and economic value, widely distributed and used in landscape architecture in East Asia. In plants, basic (region) leucine zipper (bZIP) transcription factors play important regulatory roles in growth, development, dormancy and abiotic stress. To date, bZIP transcription factors have not been systematically studied in P. mume. In this study, 49 bZIP genes were first identified in P. mume, and the PmbZIP family was divided into 12 groups according to the grouping principles for the Arabidopsis thaliana bZIP family. For the first time, we constructed a detailed model of the PmbZIP domains (R-x₃N-x₇-R/K-x₂-K-x₆-L-x₆-L-x₆-L). Phylogenetic and synteny analyses showed that PmbZIPs duplication events might have occurred during the large-scale genome duplication events. A relatively short time of speciation and the finding that 91.84% of the bZIP genes formed orthologous pairs between P. mume and Prunus armeniaca provided evidence of a close relationship. Gene expression patterns were analysed in different tissues and periods, indicating that PmbZIP genes with the same motifs exhibited similar expression patterns. The gene expression results showed that PmbZIP31/36/41 genes played a more prominent role in the response to freezing stress than cold stress. The expression level of almost all subset III genes was upregulated under freezing treatment, especially after cold exposure. We analysed the gene expression patterns of PmbZIP12/31/36/41/48 and their responses to low-temperature stress, which provided useful resources for future studies on the cold/freezing-tolerant molecular breeding of P. mume.

Plant dormancy is essential for perennial plant survival. Different genotypes of Prunus mume, including Eumume group and Apricot Mei group, undergo leaf senescence and dormancy at different times. In order to verify the cold resistance of P. mume, freeze resistance evaluation was carried out. Our results showed that Apricot Mei group had a stronger freezing tolerance than Eumume group and that leaf senescence and dormancy of Apricot Mei group occurred at an earlier period before winter. Based on phenotypic data in response to seasonal climate change, the significant candidate regions were selected using GWAS. Furthermore, through KEGG pathway and qRT-PCR analyses, we found that the ethylene-related genes, including PmEIL (Pm002057) and PmERF (Pm004265), were significantly upregulated in ‘Songchun’ Mei (Apricot Mei group) and downregulated in ‘Zaohua Lve’ Mei (Eumume group). Ethylene-related genes expression models showed that ethylene may be indirectly involved in the induction of dormancy. The PmEIL and PmERF genes were the core genes of the ethylene signal transduction pathway and were regulated by the exogenous ACC or PZA compounds. For non-dormant or weekly dormant perennial plants, application of ACC was able to induce plant dormancy and thus enhance cold/freeze tolerance. Overall, the expression of the major ethylene genes played a significant role in dormancy induction and freezing tolerance in P. mume; accordingly, application of ACC and PZA compounds were an effective approach for enhancing cold/freeze of tolerance of woody plant.