Petunia bZIP transcription factor PhbZIP3 is involved in floral volatile benzenoid/phenylpropanoid biosynthesis through regulating the expression of PhPAL2 and PhBSMT

Floral volatile benzenoid/phenylpropanoid compounds (FVBPs) are essential plant secondary metabolites and play a pivotal role in plant reproduction and development. However, the knowledge of transcriptional regulation of its biosynthesis pathway remains limited. Although extensively implicated in the regulation of plant secondary metabolisms, the basic leucine zipper (bZIP) family has not been reported to regulate FVBP biosynthesis. This study aimed to screen out important bZIP transcription factor members in the transcriptional regulation of FVBP biosynthesis in petunia. The entirety of bZIP genes throughout the petunia genome was ascertained and in-depth investigations into their phylogenetic relationships, structural characteristics, expression patterns, and potential interactions with structural genes related to FVBP biosynthesis were conducted. Outcomes showed that 77 bZIP genes of petunia could be categorized into 11 groups. The significant quantitative differences of introns and conserved motifs among the petunia bZIP members, along with the variety of cis-acting elements, reflected the structure diversity of petunia bZIPs. Seven candidate bZIP genes for regulating FVBP biosynthesis were selected because of their up-regulated expression level after flower opening according to RNA sequencing data. Based on the qPCR and the subcellular localization analysis, one nuclear-localized member, PhbZIP3 was screened out. PhbZIP3 was mainly expressed in the corolla, and its expression level increased significantly during the anthesis period. Dual luciferase assay revealed that PhbZIP3 could enhance the expression of PhPAL2 and PhBSMT. The findings from the yeast one-hybrid assay further corroborated the interaction between PhbZIP3 and the promoters of PhPAL2 and PhBSMT. Taken together, these results suggest that PhbZIP3 play a pivotal role in the regulatory mechanism of FVBP biosynthesis in petunia.