Transcriptome and chemical analysis reveal putative genes involved in flower color change in Paeonia 'Coral Sunset'.

The flower color of Paeonia 'Coral Sunset' and 'Pink Hawaiian Coral' changes from coral to pink to pale yellow during flowering, which confers high ornamental value to these two cultivars. However, the molecular mechanism underlying flower color change is still unclear. In this study, flavonoids in petals of Paeonia 'Coral Sunset' and 'Pink Hawaiian Coral' at seven flowering stages were analyzed to explore the effects of the flavonoid component on changes in flower color. In addition, four cDNA libraries of 'Coral Sunset' during the critical blooming stages were constructed and the transcriptome was sequenced to investigate the molecular mechanism underlying changes to flower color. Two anthocyanins (cyanidin-3,5-di-O-glucoside and peonidin-3,5-di-O-glucoside) were detected in both cultivars. Total anthocyanin content in both cultivars accumulated continuously from stages 1-3 and then decreased sharply. Correlation analysis showed that the change in flower color from coral to pink to pale yellow is due to a significant decrease in anthocyanin content. A total of 91,583 Unigenes were obtained in 'Coral Sunset', 33,962 (37.08%) of which were annotated to major databases. Based on the enrichment analysis of differentially expressed genes, eight structural genes (CHS, F3H, F3'H, FLS, DRF, ANS, ANR and UFGT) and 13 transcription factors (five MYB, three bHLH, one WD40, one HY5, one PIF3, one COP1 and two PHY) related to flavonoid biosynthesis were screened. The qRT-PCR results were generally consistent with the high-throughput sequencing results. This research will provide a foundation to clarify the mechanisms underlying changes in flower color of herbaceous peony.