| Tree peony (Paeonia suffruticosa) is a kind of important ornamental plant. Flower color is one of the most important ornamental characters of tree peony. The studies about the molecular basis of the flower color of tree peony are lacking. This may restrict the innovation of color germplasm in tree peony. This study used tree peony with white flowers and its variants with different intensities of pink flowers in Paeonia ostii’FengDan Group’ as the research objects. By using high performance liquid chromatography (HPLC) and quantitative real-time polymerase chain reaction (qRT-PCR), we mesaured the pigment composition and the expression of flavonoid biosynthesis pathway genes. This study provides valuable information for further underatanding of the molecular basis of the flower color of tree peony.The main research results are as follows:1.According to the CIE color system, the flower color of Paeonia ostii with different color intensity were well described. As the color of petals deepened, L* and b* got lower, while a* and C* increased. Obvious correlations were detected among L*, a*, b* and C*.2.The anthocyanins and the flavonoids composition in the petals of Paeonia ostii of different colors at full-bloom stage were analyzed through HPLC. The results demonstrated that the type and the content of anthocyanins in the petals were the main reasons for the different flower color of Paeonia ostii. The white petals doesn’t contain anthocyanins. Only Pn3G5G was detected in the petals of Pinkl. Both Pn3G5G and Cy3G5G were detected in the petals of Pink2 and Pink3 with the content of Pn3G5G was far more than Cy3G5G. In this study, no obvious correlation was detected among the content of total flavonoids and the different color of petals.3.Expression stability of 22 endogenous candidate genes including 16 new candidate reference genes form transcriptome data of tree peony and 6 traditional housekeeping genes(ARP2, IWSI, GAPDH, TUBC, TUA5 and UBC28) were assessed by qRT-PCR in a diverse set of 33 tissue samples representing different floral development stages of Paeonia ostii ’Feng Dan Bai’,Paeonia suffruticosa Xi Shi’and Paeonia suffruticosa ’Que Hao’, different color of Paeonia ostii, different samples (stems, leaves, sepals and flowers), different development stages of seeds. The most stable reference genes were selected respectively under four kinds of experimental conditions for qRT-PCR. Moreover, four new reference genes are more stable internal genes when compared with the traditional housekeeping genes.They are DUF1639, MBF1A, PP2C and RPS9.4. The expression analysises of CHS, CHI, F3H, F3’H, DFR, LDOX, MATE and ABC in petals of Paeonia ostii with different flower color intensities were carried out by qRT-PCR. The results indicated that all of these structural and transporter genes were associated with the synthesis and accumulation of anthocyanins in the petals. Except of CHS, the expression levels of these genes in petals of pink flowers were higher than white flowers. All the expression of CHS in petals of different flower color intensities were at high levels. With the color of petals deepened, the expression levels of DFR, LDOX, MATE and MRP increased. They had a obvious correlation with the synthesis and accumulation of anthocyanins in the petals.By comparing the expression levels of flavonoid biosynthesis pathway genes, we got that the late biosynthetic genes and anthocyanin transporter genes played greater role in the accumulation of the anthocyanins than early biosynthetic genes. The results of this study will be helpfull to understand the molecular mechanism of color diversity in Paeonia ostii. It provides valuable informations for further understanding of how these genes effects the color of flowers. |
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