A Novel R2R3-MYB Transcription Factor PqMYB4 Inhibited Anthocyanin Biosynthesis inPaeonia qiui

Paeonia qiuiis a wild tree peony native to China. Its leaves show a clear purple-red color from the germination to the flowering stage, and it has high leaf-viewing value. A MYB transcription factor gene, designated asPqMYB4, was isolated from leaves ofP. qiuibased on transcriptome datas. The full-length cDNA ofPqMYB4was 693 bp, encoding 230 amino acids. Sequence alignment and phylogenetic analysis revealed that PqMYB4 was a R2R3-MYB transcription factor clustered with AtMYB4 inArabidopsis thaliana. Moreover, it contained a C1 motif, an EAR repression motif and a TLLLFR motif in the C-terminal domains, which were unique in transcription repression MYB. Subcellular location analysis showed that PqMYB4 was located in the cell nucleus.PqMYB4was highly expressed in the late stage of leaf development, and was negatively correlated with the anthocyanin content. The petiole of wild-type Arabidopsis seedlings was deeper in color than the transgenic lines ofPqMYB4and showed a little purple-red color. The seed coat color of Arabidopsis seeds that overexpressedPqMYB4gene was significantly lighter than that of wild-type seeds. In transgenic Arabidopsis, the expression level ofAtCHS,AtCHI,AtDFRandAtANSwere down-regulated significantly. These results showed that PqMYB4 was involved in the negative regulation of anthocyanin biosynthesis in tree peony leaves, which can control the anthocyanin pathway genes. Together, these findings provide a valuable resource with which to further study the regulatory mechanism of anthocyanin biosynthesis in the leaf ofP. qiui. They also benefit the molecular breeding of tree peony cultivars with colored leaf.