Isolation and functional characterization of a R2R3-MYB regulator of Prunus mume anthocyanin biosynthetic pathway

Flower color is an important economic trait of Prunus mume, a famous ornamental plant widely cultivated in East Asia. Anthocyanins, acting as major pigments of flower coloration, are biosynthesized via transcriptional regulation of transcription factors (TFs). Many R2R3-MYB TFs have been identified to regulate anthocyanin biosynthetic pathways. However, very little is known about the role of R2R3-MYB TFs regulating anthocyanin biosynthesis in P. mume. In our study, the first R2R3-MYB TF (PmMYBa1) from P. mume has been isolated and characterized. Sequence analysis revealed that PmMYBa1 contains conserved R2R3 MYB domain and belongs to anthocyanin-related subgroup 6 of R2R3-MYB family. Overexpression of PmMYBa1 in tobacco contributed to anthocyanin accumulation by activating endogenous anthocyanin-relating genes in the flowers and fruits of transgenic lines. Gene expression analysis showed that almost all of the endogenous structural genes of anthocyanin biosynthesis were obviously up-regulated, as well as bHLH TFs An1a and An1b in the flowers and fruits of PmMYBa1-overexpressing tobacco. In contrast, only three structural genes NtCHS, NtF3H, and NtANS were up-regulated in the leaves. In addition, the expression level of PmMYBa1 was higher in the anthocyanin-rich red flowers than in white ones and strongly correlated with anthocyanin content in the developing petals of P. mume. These findings strongly suggest that PmMYBa1 is involved in regulating anthocyanin biosynthesis in P. mume. Moreover, PmDFR and PmANS might be potential target genes regulated by PmMYBa1 in P. mume according to the correlation analysis. Isolation and functional characterization of PmMYBa1 laid a foundation for further exploring the mechanisms of anthocyanin synthesis and provide a potential candidate gene for breeding to manipulate flower colors in P. mume.