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 <i>bZIP</i> gene family in Soapberry (<i>Sapindus mukorossi</i> Gaertn.), a significant tree species for forestry biomass energy, remains unclear. In this study, we conducted a genome-wide analysis of the <i>bZIP</i> 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 <i>SmbZIP</i>s and provided detailed information regarding their physicochemical characteristics, gene structures, protein motifs, phylogenetic relationships, <i>cis-</i>regulatory elements (CREs), and predicted transcriptional regulatory networks. According to our prediction of the <i>SmbZIP</i>-mediated regulatory network and CREs in the promoter region, <i>SmbZIP</i>s 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 <i>SmbZIP</i>s were specific to the graft-healing stages and locations. In conclusion, our study elucidates the potential role of the <i>bZIP</i> gene family in responding to plant wounding stress and facilitating graft healing, thereby providing valuable insights for future functional genomics studies of Soapberry.