Genome-Wide Identification and Characterization of the MYB Transcription Factor Family in Platycodon grandiflorus and Its Potential Involvement in Flavonoid Biosynthesis Regulation

Background: MYB transcription factors are key regulators of plant growth, development, secondary metabolism, and stress responses. However, this family has not been systematically characterized in the traditional medicinal plant Platycodon grandiflorus, and its roles in flavonoid biosynthesis remain largely unknown. Methods: We performed genome-wide identification of the MYB family using a combined HMMER and BLASTP approach with manual domain validation. Phylogenetic analysis was conducted on conserved MYB domains, followed by synteny, gene structure, conserved motif, and promoter cis-element analyses. Expression patterns under methyl jasmonate (MeJA) treatment were examined via transcriptomics and RT-qPCR. Protein-protein interaction networks were predicted using STRING based on Arabidopsis homologs. Subcellular localization of candidate proteins was tested in Nicotiana benthamiana leaf epidermal cells. Results: A total of 170 PgMYB members were identified, comprising 52.9% 1R-MYB and 44.1% 2R-MYB. They clustered into 26 subgroups (P1–P26), with 1R-MYBs enriched in subgroup P1 (82 members). Synteny analysis revealed 192 collinear blocks between P. grandiflorus and Arabidopsis, and all 26 syntenic gene pairs examined had Ka/Ks < 1, indicating strong purifying selection. Promoter regions were enriched in hormone- (72.9% ABA-responsive) and stress-responsive elements. Nine selected genes showed consistent MeJA-induced expression changes between RNA-seq and RT-qPCR. Integrated analysis of phylogeny, expression correlation, and predicted protein-protein interactions nominated PgMYB47, PgMYB142, and PgMYB151 as candidate regulators of flavonoid biosynthesis. All three proteins localized to the nucleus in N. benthamiana cells. Conclusions: This study provides the first comprehensive characterization of the P. grandiflorus MYB family, highlighting its evolutionary conservation and expression dynamics. The nominated candidates offer a foundation for future functional validation of flavonoid biosynthesis regulation.