Genome-Wide Analysis of bZIP Transcription Factors and Expression Patterns in Response to Shading Treatment in Taxus yunnanensis

Basic leucine zipper (bZIP) transcription factors are widely involved in plant growth, development, environmental adaptation, and secondary metabolism. However, the bZIP gene family in Taxus yunnanensis has not been systematically characterized, and its potential involvement in shading-responsive regulation of paclitaxel biosynthesis remains unclear. In this study, a genome-wide analysis was performed to identify and characterize the bZIP family in T. yunnanensis. Phylogenetic analysis, conserved motif and domain identification, promoter cis-element analysis, chromosomal localization, and expression profiling were conducted to investigate their structural features and regulatory potential. A total of 18 TyubZIP genes were identified and classified into 10 subfamilies. These genes exhibited variation in physicochemical properties but showed conserved structural features and nuclear localization. Promoter analysis revealed abundant light-responsive, hormone-related, and stress-related cis-elements. Expression profiling indicated tissue-specific expression patterns and diverse responses to shading treatment. WGCNA further identified candidate TyubZIP genes potentially associated with paclitaxel biosynthesis. Among them, TyuHY5 was selected for functional analysis. Subcellular localization and transcriptional assays demonstrated that TyuHY5 can bind to the promoter of TyuDBTNBT and positively regulate its activity. These findings provide the first genome-wide characterization of the bZIP family in T. yunnanensis and identify TyuHY5 as a shading-responsive candidate regulator of paclitaxel biosynthesis, providing insights that may inform the genetic improvement and cultivation strategies of Taxus for enhanced paclitaxel production.