Genome-wide identification, characterization and tissue-associated expression analysis of the bZIP transcription factor gene family in winged bean (Psophocarpus tetragonolobus)

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Background Basic leucine zipper ( bZIP ) transcription factors regulate plant growth, development, hormone signaling, and stress responses. Despite their importance, the bZIP gene family has not been comprehensively characterized in winged bean ( Psophocarpus tetragonolobus ). Methods A genome-wide analysis of the bZIP gene family was performed using the winged bean reference genome. PtbZIP genes were characterized based on physicochemical properties, chromosomal distribution, phylogenetic relationships, gene structure, conserved motifs, promoter cis-regulatory elements, gene duplication, Ka/Ks ratios, comparative synteny, and publicly available RNA-seq data from four tissues. Results A total of 50 bZIP genes were identified and designated PtbZIP1–PtbZIP50 . The genes were unevenly distributed across nine chromosomes, with the highest numbers on chromosomes 2 and 5. Exon and intron numbers ranged from 1 to 12 and 0 to 11, respectively. Promoter analysis identified cis-regulatory elements associated with light responsiveness, hormone signaling, growth and development, and stress responses. Gene duplication analysis identified 22 segmentally duplicated pairs and one tandemly duplicated pair. All duplicated pairs with valid Ka/Ks estimates showed ratios below 1, indicating predominant purifying selection. Comparative synteny analysis identified 25, 18, 22, and 18 orthologous bZIP gene pairs with Glycine max , Vigna unguiculata , Phaseolus vulgaris , and Vigna radiata , respectively. RNA-seq analysis provided a preliminary overview of tissue-associated variation in PtbZIP transcript abundance across four tissues. Conclusions The study provides a genomic resource for understanding the evolutionary organization and potential regulatory roles of the bZIP gene family in winged bean and prioritizing candidates PtbZIP gene for future functional studies. However, the expression analysis lacked biological replicates and should therefore be interpreted as a preliminary assessment rather than statistically validated tissue-specific expression. Database registration: Not applicable.