Tree peony (Paeonia suffruticosa Andr.) is a popular ornamental plant in China due to its showy and colorful flowers. However, yellow-colored flowers are rare in both wild species and domesticated cultivars. The molecular mechanisms underlying yellow pigmentation remain poorly understood. Here, petal tissues of two tree peony cultivars, “High Noon” (yellow flowers) and “Roufurong” (purple–red flowers), were sampled at five developmental stages (S1–S5) from early flower buds to full blooms. Five petal color indices (brightness, redness, yellowness, chroma, and hue angle) and the contents of ten different flavonoids were determined. Compared to “Roufurong,” which accumulated abundant anthocyanins at S3–S5, the yellow-colored “High Noon” displayed relatively higher contents of tetrahydroxychalcone (THC), flavones, and flavonols but no anthocyanin production. The contents of THC, flavones, and flavonols in “High Noon” peaked at S3 and dropped gradually as the flower bloomed, consistent with the color index patterns. Furthermore, RNA-seq analyses at S3 showed that structural genes such as PsC4Hs, PsDFRs, and PsUFGTs in the flavonoid biosynthesis pathway were downregulated in “High Noon,” whereas most PsFLSs, PsF3Hs, and PsF3’Hs were upregulated. Five transcription factor (TF) genes related to flavonoid biosynthesis were also upregulated in “High Noon.” One of these TFs, PsMYB111, was overexpressed in tobacco, which led to increased flavonols but decreased anthocyanins. Dual-luciferase assays further confirmed that PsMYB111 upregulated PsFLS. These results improve our understanding of yellow pigmentation in tree peony and provide a guide for future molecular-assisted breeding experiments in tree peony with novel flower colors.

Primula vulgaris is an important ornamental plant species with various flower color. To explore the molecular mechanism of its color formation, comparative transcriptome analyses of the petals in red and white cultivars was performed. A total of 4451 differentially expressed genes were identified and annotated into 128 metabolic pathways. Candidate genes FLS, F3 0 H, DFR, ANS and AOMT in the anthocyanin pathway were expressed significantly higher in the red cultivar than the white and may be responsible for the red coloration. In the red petals, a putative transcription factors bHLH (c52273.-graph_c0) was up-regulated about 14-fold, while a R2R3-MYB unigene (c36140.graph_c0) was identified as a repressor involved in anthocyanin regulation and was significantly down-regulated. In addition, the anatomy analyses and pigments composition in the red and white petals were also analyzed. The papillae on the adaxial epidermis of the red petals of P. vulgaris display a triangle-shapes, in contrast with a spherical shape for the white petals. Although flavonoids were detected in both cultivars, anthocyanins could only be identified in the red cultivar. Gossypetin and peonidin/rosinin were the most abundant pigments in red petals. This study shed light on the genetic and biochemistry mechanisms underlying the flower coloration in Primula. Keywords Primula vulgaris Á Red petal Á Anthocyanin biosynthesis Á Flower coloration Á R2R3-MYB Á Epigenetic analysis Abbreviations 3GT Anthocyanin 3-O-glucosyltransferase 5GT Anthocyanin 5-O-glucosyltransferase a*, b* Chromatic components ABP Anthocyanin biosynthetic pathway ANS Anthocyanin synthase AOMT Anthocyanin O-methyltransferase bHLH Basic helix-loop-helix C* Chroma (brightness) CHI Chalcone isomerase CHS Chalcone synthase CIE Three-Dimensional International Commission on Illumination COG Cluster of orthologous groups of proteins database DEGs Differentially expressed genes DFR Dihydroflavonol 4-reductase F3 0 H Flavonoid 3 0-hydroxylase F3H Flavanone 3-hydroxylase FDR False discovery rates FLS Flavonol synthase FPKM Fragments per kilobase per million mapped reads GO Gene ontology database KEGG Kyoto encyclopedia of genes and genomes database KOG EuKaryotic Orthologous Groups database Electronic supplementary material The online version of this article (

Tree peony (Paeonia sp.) is a popular traditional ornamental plant in China. Among the nine wild species, Paeonia rockii displays wide-ranging, deep purple variegation at the base of the petals, whereas Paeonia ostii exhibits purely white petals. Overall, the posttranscriptional regulation involved in tree peony flower opening and pigmentation remains unclear. To identify potential microRNAs (miRNAs) involved in flower variegation, six small RNA libraries of P. ostii and P. rockii petals at three different opening stages were constructed and sequenced. Using Illumina-based sequencing, 22 conserved miRNAs and 27 novel miRNAs were identified in P. rockii and P. ostii petals. Seventeen miRNAs were differentially expressed during flower development, and several putative target genes of these miRNAs belonged to transcription factor families, such as Myb domain (MYB), and basic helix-loop-helix (bHLH) transcription factors. Furthermore, an integrative analysis of the expression profiles of miRNAs and their corresponding target genes revealed that variegation formation might be regulated by miR159c, miR168, miR396a, and novel_miR_05, which target the MYB transcription factors, chalcone synthase (CHS), and ABC transporter. Our preliminary study is the first report of miRNAs involved in Paeonia flower pigmentation. It provides insight regarding the molecular mechanisms underlying the regulation of flower pigmentation in tree peony.

Paeonia veitchii has been widely distributed in China under different ecological types. Its roots contain diverse phytochemical constituents, which possess very high bioactivities. However, the influence of ecological factors on activities and ingredients of P. veitchii roots still remains unknown. The purpose of this research was to analyze the variation in bioactivities and phytochemical composition of P. veitchii roots upon exposure to various ecological factors. Seven P. veitchii populations collected from different regions in China were evaluated. The results of correlation analysis suggested that four major ecological factors, including average annual temperature, elevation, total potassium, and organic matter, had a strong correlation with the bioactivities of P. veitchii roots. Further, the major ecological factors were also highly correlated with the contents of naringin, gallic acid, benzoylpaeoniflorin, and paeoniflorin. The principal component analysis results supported four major metabolites as the main contributing ingredients. All populations were classified into three groups, G1, G2, and G3, through hierarchical cluster analysis. G1 showed more significant advantages in the above-mentioned four ecological factors, four active ingredients, and bioactivities compared to the other two groups. P. veitchii roots growing at lower average annual temperature, high elevation, rich total potassium and organic matter in the soils were presumed to have relatively higher bioactivities. These data expand the study on the bioactivities and phytochemical composition of P. veitchii roots and have a guiding significance for the ecological factor selection during the cultivation process of this herbaceous peony species.

In recent years, more and more attention has been paid to the natural floral volatiles in tree peony and the fragrance components have been widely used in the fields of health care, perfumes, and cosmetics. However, there is little research on the identification of fragrance components of wild tree peony species. In present study, volatile components in petals of nine wild tree peony species were analyzed using a headspace solid‐phase microextraction (SPME) technique coupled with gas chromatography–mass spectrometry (GC‐MS). A total of 124 volatile components were identified and clustered into five major chemical classes: terpenoids, alkanes, alcohols, aldehydes, and ketones. Overall, combined with the sensory evaluation of nine wild tree peony species, Paeonia. ostii (P2) performed herbal and waxy attributes, mainly dominated by hexanal and pentadecane, respectively. P rockii (P1), P qiui (P3), P jishanensis (P4), and P decomposita (P5) all possessed sweet attribute, which was positively correlated with geraniol and citronellol. P delavayi (P9), P lutea (P7), P ludlowii (P8), and P potanini (P6) performed intense floral attribute dominated by linalool and trans‐linalool oxide. Moreover, the results of principal component analysis (PCA) and hierarchical clustering analysis (HCA) showed P decomposita (P5), P qiui (P3), P rockii (P1), P jishanensis (P4), and P ostii (P2) in the Subsect. Vagiatae were mixed to form one cluster while P lutea (P7), P delavayi (P9), P ludlowii (P8), and P potanini (P6) in the Subsect. Delavayanae formed the other cluster. In terms of geographical distribution, the two clusters are consistent with the distribution of wild tree peony species. The present study clarified the relationship between fragrance and components and further revealed the phylogenetic relationship of nine wild tree peony species, thus providing a theoretical basis for their development and utilization.