Genome-wide identification and expression analysis of bZIP transcription factors in sugarcane reveals roles in development, hormone signaling, and stress response

Basic leucine zipper ( bZIP ) transcription factors play central roles in plant development, hormone signaling, and stress adaptation; however, their genome-wide organization in Saccharum officinarum LA-Purple has remained unclear. In this study, 215 SobZIP genes were identified from the LA-Purple genome, indicating substantial expansion of this gene family. The encoded proteins were predominantly hydrophilic and were predicted to localize mainly to the nucleus. Phylogenetic, motif, domain, exon-intron, and comparative analyses with other grasses revealed strong conservation of the core bZIP region alongside extensive structural diversification. These analyses further suggested that the major bZIP lineages were established before monocot divergence and were subsequently amplified during the evolution of the polyploid sugarcane genome. Analysis of the 1.5 kb upstream sequences identified 57 cis -regulatory elements associated with phytohormone responses, development, tissue specificity, and stress responses. RNA-seq profiling under GA and IAA treatments and across developmental tissues revealed marked tissue-, developmental stage-, and time-dependent expression patterns. Among the representative candidates, SobZIP205 and SobZIP209 were consistently highly expressed across multiple tissues and treatments, whereas SobZIP97 showed contrasting GA-responsive expression between stems and leaves at 48 and 96 h. Collectively, these findings provide a solid foundation for future functional validation and molecular breeding aimed at improving sugarcane growth, hormone responsiveness, and stress resilience.