Identification and characterization of the bZIP transcription factor family in yellowhorn

The basic leucine zipper (bZIP) transcription factor family is one of the largest and most diverse families in plants, regulating plant growth and development and playing an essential role in response to abiotic and biotic stresses. However, little is known about the biological functions of bZIP proteins in yellowhorn (Xanthoceras sorbifolium). Recently, 64 XsbZIP genes were identified in the yellowhorn genome and found to be disproportionately distributed in linkage groups. The XsbZIP proteins clustered into 11 groups based on their phylogenetic relationships with AtbZIP, ZmbZIP and GmbZIP proteins. Five intron patterns in the basic and hinge regions and additional conserved motifs were defined, both supporting the group classification and possibly contributing to their functional diversity. Compared to tandem duplication, the segment duplication greatly contributed to the expansion of yellowhorn bZIP genes. In addition, most XsbZIP genes harbor several stress responsive cis-elements in their promoter regions. Moreover, the RNA-seq and qRT-PCR data indicated XsbZIP genes were extensively involved in response to various stresses, including salt (NaCl), cold and abscisic acid, with possibly different molecular mechanisms. These results provide a new understanding of the biological functions of bZIP transcription factors in yellowhorn.