Genome-wide identification and expression analysis of the bZIP gene family in apple (Malus domestica)

The basic leucine zipper (bZIP) family is one of the largest transcription factor (TF) families in plants, which play crucial roles in plant growth and development. bZIP proteins are involved in multiple biological processes, as well as responses to various biotic/abiotic stresses. Although genome-wide analysis of the bZIP gene family has been conducted in several plant species, only few comprehensive characterization of this gene family has been reported in apple (Malus domestica), an important tree fruit in the Rosaceae family. In this study, we identified 114 bZIP genes from the apple genome, which were divided into 10 subgroups based on their sequences. We further characterized these MdbZIP genes in terms of gene structure, protein model, and chromosomal distribution. Genome-wide expression profile of MdbZIP genes indicated that 14 MdbZIPs were highly expressed during apple fruit development, and 17 MdbZIPs showed differential expression in leaves and mature apple fruit. Analysis of the expression of 16 MdbZIPs under drought and salt stresses in apple leaves and roots using quantitative real-time PCR (qRT-PCR) indicated that they all exhibited differential transcript levels in both treatments, suggesting that MdbZIP genes are involved in abiotic stress responses. The genome-wide identification, characterization, and expression analysis of apple bZIP genes provide new insights into the roles of the bZIP TF family and lay a solid foundation for future cloning and functional analysis of this gene family, which may be used to manipulate apple growth and development and improve its stress tolerance.