Transcriptome Profiling of Flower Development Reveals Key Genes Mediating Yellow Formation in Tree Peony

Abstract

Tree peony cultivars with yellow flowers are rare and valuable, but the molecular mechanism of pigment accumulation is not clear. In this study, the petal transcriptome of three developmental stages were sequenced to determine the differentially expressed genes (DEGs) regulating yellow flowers color. The results showed that 10,842 and 12,022 DEGs were screened in stage 1 vs. stage 2 and in stage 2 vs. stage 3, respectively. Through analysis of flavonoid structural genes (FSGs), we found that the transcription level of DFR was very low in the three developmental stages. In a small group of cultivars, the DFR transcription level of red flowers was 862 times higher than that of yellow flowers. These data suggested that the flavonoid pathway is interrupted in the later stage due to the low transcriptional level of DFR, which limits the biosynthesis of anthocyanins in yellow flowers. The transcription levels of F3’H and FLS were upregulated from stage 1 to stage 2, while those of CHI and FLS were downregulated from stage 2 to stage 3. In addition, 67 MYBs and 44 bHLHs showed similar transcription profiles with different members of FSGs. The results deepen our understanding of the molecular mechanism of yellow pigment accumulation in tree peony.