Genome-Wide Survey and Expression Profiling of bZIP Transcription Factors in Juglans mandshurica Reveal Candidate Genes Involved in Floral Development, Light Stress, and Drought/Salt Tolerance

Basic-region leucine zipper (bZIP) transcription factors are crucial for plant stress responses, but their characterization in the wild species Juglans mandshurica remains limited. Here, we identified 80 bZIP genes in the J. mandshurica genome and classified them into 13 subgroups, with notable enrichment in subgroups S, A, D, and I. All subgroup D members contain both bZIP and DELAY OF GERMINATION 1 (DOG1) domains, forming characteristic dual-module fusion proteins. Evolutionary analysis detected three orthologous gene pairs under positive selection since divergence from Juglans regia. Promoter cis-elements, especially MYB and MYC motifs, are abundant in JmbZIP genes. Protein–protein interaction networks suggest potential functional specialization and coordination among JmbZIP members. Expression profiling revealed distinct patterns across subgroups, with S, A, and D showing high activity across various physiological processes and light stress responses. qRT-PCR validated the dynamic expression of six ABA pathway marker genes, the ABRE-rich JmbZIP41 and JmbZIP42 genes, together with the highly expressed JmbZIP12 gene under salt and drought stress. Our genome-wide analysis enabled the functional screening of bZIP members across subgroups. The key genes identified in this study provide valuable genetic resources for stress-resistance breeding in forest trees, with JmABI5 (JmbZIP40) and JmbZIP42 serving as prime candidates for enhancing tree stress tolerance.