Genome-Wide Analysis of bZIP Transcription Factor Family and Its Expression in Graft Healing of Soapberry (Sapindus mukorossi Gaertn.).

The Basic Leucine Zipper (bZIP) transcription factors play a vital role in plant responses to abiotic stress. Despite being studied in various plant species, the function of the bZIP gene family in Soapberry (Sapindus mukorossi Gaertn.), a significant tree species for forestry biomass energy, remains unclear. In this study, we conducted a genome-wide analysis of the bZIP gene family in Soapberry, based on the observation that bZIP transcription factors were enriched in the transcriptome data of Soapberry-grafted stem segments, as revealed by both GO and KEGG analyses. For the first time, we identified 31 SmbZIPs and provided detailed information regarding their physicochemical characteristics, gene structures, protein motifs, phylogenetic relationships, cis-regulatory elements (CREs), and predicted transcriptional regulatory networks. According to our prediction of the SmbZIP-mediated regulatory network and CREs in the promoter region, SmbZIPs may be associated with plant growth and development as well as responses to mechanical wounding stress. By integrating RT-qPCR and RNA-seq analyses, we determined that the expression patterns of SmbZIPs were specific to the graft-healing stages and locations. In conclusion, our study elucidates the potential role of the bZIP gene family in responding to plant wounding stress and facilitating graft healing, thereby providing valuable insights for future functional genomics studies of Soapberry.