Transcriptome sequencing of Paeonia suffruticosa 'Shima Nishiki' to identify differentially expressed genes mediating double-color formation.

Paeonia suffruticosa 'Shima Nishiki' is one of extremely rare double-color cultivars in the world. It usually shows the two beautiful colors of red and white in the same flower, and this trait undoubtedly makes the flowers more charming for the ornamental market. However, few studies have been done to unravel the molecular mechanisms of double-color formation in P. suffruticosa 'Shima Nishiki'. In this study, we measured the anthocyanin composition and concentration, and sequenced the transcriptomes of the red and white petals. We found that the total content of Pg-based glycosides was at a significantly higher level in the red petals. Furthermore, we assembled and annotated 92,671 unigenes. Comparative analyses of the two transcriptomes showed 227 differentially expressed genes (DEGs), among which 57 were up-regulated, and 170 were down-regulated in the red petals. Subsequently, we identified 3 DEGs and the other 6 structural genes in the anthocyanin biosynthetic pathway including PsCHS, PsCHI, PsF3H, PsF3'H, PsDFR, PsANS, PsAOMT, PsMYB, and PsWD40. Among them, PsDFR and PsMYB expressed at a significantly higher level and showed positive correlations between their expression and anthocyanin concentration in the red petals. However, PsWD40 expressed at a significantly lower level and exhibited an inverse relationship in the red petals. Furthermore, we further confirmed the relative expression of the 9 candidate genes using quantitative real-time PCR. Based on the above results, we concluded that the significant differential expression of PsDFR, PsMYB and PsWD40 may play a key role in anthocyanin concentration in the red and white petals, thereby mediating double-color formation. These data will provide a valuable resource to better understand the molecular mechanisms of double-color formation of P. suffruticosa 'Shima Nishiki'.