Heterologous expression of the honeysuckle R2R3-MYB transcription factor LjMYB106 enhances phenylpropanoid and flavonoid metabolism in Arabidopsis thaliana and Nicotiana benthamiana
Lonicera japonica Thunb. is a traditional medicinal plant rich in bioactive flavonoids, but the transcriptional regulation of flavonoid biosynthesis remains unclear. In this study, we identified LjMYB106, an R2R3-MYB transcription factor associated with flavonoid accumulation, from floral developmental transcriptomes. Sequence and phylogenetic analyses showed that LjMYB106 contains conserved R2 and R3 MYB domains and is closely related to homologous MYB proteins. Heterologous overexpression of LjMYB106 in Arabidopsis thaliana and Nicotiana benthamiana increased total flavonoid and p-coumaric acid contents. Integrated transcriptomic and widely targeted metabolomic analyses in A. thaliana showed that LjMYB106 overexpression was associated with changes in phenylpropanoid and flavonoid biosynthetic pathways. qRT-PCR validation further showed that PAL, C4H, 4CL, CHS, DFR, and ANS homologs were up-regulated, whereas CHI, F3H, and FLS homologs were down-regulated in LjMYB106-overexpressing plants. Subcellular localization and yeast transactivation assays indicated that LjMYB106 is a nuclear protein with transcriptional activation activity. These results suggest that LjMYB106 is a candidate regulator of phenylpropanoid and flavonoid metabolism and provide a basis for further studies of MYB-mediated flavonoid regulation in L. japonica.