Genome-Wide Identification and Characterization of the bZIP Gene Family in Elephant Grass (Cenchrus purpureus) and Its Response to Cold Stress

Elephant grass (Cenchrus purpureus) is a globally important C4 perennial forage crop valued for its high biomass yield and tolerance to heat and drought. However, its poor cold tolerance severely limits its cultivation in temperate regions. The bZIP (basic region-leucine zipper) transcription factors are known to regulate abiotic stress responses; however, their role in elephant grass’s cold response is unclear. This study aimed to identify and characterize the CpbZIP gene family on a genome-wide scale and analyze its expression patterns under low-temperature stress. Through phylogenetic analysis, we classified 158 putative CpbZIP genes into 13 subgroups, a classification supported by conserved gene structures and motifs. The family expanded primarily through segmental duplication and has been shaped by strong purifying selection. Promoter analysis revealed numerous cis-acting elements associated with hormone signaling and abiotic stress, including low temperature, suggesting the family’s potential role in stress adaptation. Subsequent expression analysis and RT-qPCR validation identified six cold-induced genes. Of these, CpbZIP38 and CpbZIP86 exhibited high basal expression in roots and were significantly upregulated under cold stress. These findings identify promising candidate genes for the cold tolerance regulatory network in elephant grass and lay the groundwork for breeding cold-tolerant varieties.