Jianrang Luo

Floral fragrance is a major trait of ornamental crops and an important economic feature in the floral industry. Although tree peony ( Paeonia suffruticosa ) is a culturally significant and widely cultivated ornamental plant, studies on its floral scent are relatively limited. ‘High Noon’ is characterised by a unique fragrance and high fragrance content, making it a suitable material for the breeding of fragrant tree peony. In this study, we analysed volatile organic compounds (VOCs) across five flowering stages using GC–MS, identifying 57 distinct VOCs. The types and amounts of Monoterpenoid and benzenoid/phenylpropanoid compounds gradually increased, reaching a peak at full blooming, exhibiting a trend consistent with sensory perception. Odour activity value (OAV) analysis identified linalool, geraniol, 2‐hexenal, and α‐citral as key aroma compounds at full blooming stage. Differential metabolite analysis showed upregulation of monoterpenes including linalool, (Z)‐citral, geraniol, and (E)‐citral across developmental stages. Gene expression analysis via qRT‐PCR revealed that PsDXS3 , PsDXR1 , PsMDS1 , and PsHDR1 are key genes in monoterpenoid synthesis with PsTPS5 associated with geraniol synthesis. This study explored the relationship between flowering stages and aroma formation, elucidated the contribution of specific VOCs to the aroma, and highlights candidate genes responsible for floral fragrance, providing valuable insights for the genetic engineering of tree peony floral aroma.

Helleborus orientalis L. is a valuable winter-flowering and understory landscape plant, but its application and breeding are hindered by poor heat tolerance and the lack of a robust germplasm evaluation system. In this study, 51 Helleborus L. hybrid individuals obtained through manual open pollination were evaluated using coefficient of variation (CV), Shannon–Weaver diversity index (H′), correlation analysis, principal component analysis (PCA), and cluster analysis to assess genetic diversity and ornamental value based on 17 phenotypic traits. The results showed rich phenotypic diversity among the hybrids. Quantitative traits showed CV ranging from 9.48% to 37.99% and H′ between 0.77 and 1.51, with flower count and leaf length being the most variable. Qualitative traits had H′ values from 0.52 to 1.55, with sepal color showing the highest diversity. Significant correlations were detected among heat tolerance, pest resistance, leaf and petiole length, as well as plant and flower form. PCA extracted six principal components accounting for 74.50% of cumulative variance. Cluster analysis classified the 51 germplasms into five groups. Using the AHP model, a comprehensive evaluation system was established, and 13 elite individuals were selected for variety rights application and characterization. This study provides a reference for establishing DUS test guidelines and advancing breeding and utilization of Helleborus L.

Anthocyanin and chlorophyll are two compounds responsible for coloration in plants. Plant hormones can influence the accumulation of anthocyanins and chlorophyll. In this study, Paeonia ostii and Paeonia qiui, which exhibit red leaves during their juvenile stage, were selected to explore the effects of different hormones on leaf coloration. Tree peony leaves predominantly contained cyanidin-3,5-O-diglucoside (Cy3G5G) and peonidin-3,5-O-diglucoside (Pn3G5G), with minimal peonidin-3-O-glucoside (Pn3G). Among eight phytohormone treatments, gibberellins (GA3), group maximized anthocyanin accumulation while methyl jasmonate (MeJA) group showed opposite effects. Anthocyanin accumulation was influenced by eight plant hormones, but only MeJA group had a notable effect on chlorophyll production. GA3 group significantly upregulated gibberellin 2-oxidase (GA2ox) expression in two tree peony species, enhancing endogenous GA biosynthesis. Concurrently, GA3 group significantly upregulated the expression of multiple key genes in the anthocyanin biosynthetic pathway in tree peony leaves. Specifically, dihydro flavonol 4-reductase (PoDFR) exhibited the most pronounced upregulation (1.325-fold) in Paeonia ostii leaves, while anthocyanidin synthase (PqANS) showed a remarkable (5.72-fold) increase in expression in Paeonia qiui leaves. MeJA group significantly upregulated the expression of allene oxide synthase (AOS) and allene oxide cyclase (AOC) genes in the jasmonic acid (JA) biosynthesis pathway, consequently enhancing endogenous JA levels in the leaves. High levels of JA stimulated the activation of genes involved in chlorophyll synthesis in plants. However, the expression of most anthocyanin biosynthetic genes in MeJA group was significantly suppressed, with particularly marked downregulation observed in chalcone synthase (CHS) and glucose-flavonoid-3-glucosyltransferase (UFGT). Furthermore, MeJA and GA3 may engage in complex crosstalk with other hormones, potentially exhibiting either synergistic or antagonistic interactions that modulate plant physiological responses. The tree peony leaves treated with GA3, strigolactone analog (rac-GR24), brassinosteroids (BR), and 6-benzyladenine (6-BA) were redder in color, but leaves treated with indole-3-acetic acid (IAA), salicylic acid (SA), abscisic acid (ABA), and MeJA were greener than control (CK) group. This study provides a basis for further research on the mechanism of hormone regulation of leaf color in tree peony.

Geraniol contributes significantly to the floral scent of herbaceous peony (Paeonia lactiflora) and is abundant in fragrant cultivars. However, the regulatory mechanism of geraniol biosynthesis in herbaceous peony remains unclear. In this study, we identified a transcriptional regulatory complex (PlMYB73–PlMYB70–PlMYB108) that cooperatively regulated geraniol biosynthesis in herbaceous peony. The three MYB members were identified through correlation analysis between geraniol content and gene expression profiles in 17 herbaceous peony cultivars. Transient overexpression and gene silencing experiments revealed that PlMYB73, PlMYB108, and PlMYB70 positively regulated PlTPS1 expression and geraniol accumulation. PlMYB108 and PlMYB70 directly upregulate PlTPS1 by binding to the TAACCA and CAACTG motifs, respectively, as demonstrated by yeast one-hybrid, dual-luciferase, and electrophoretic mobility shift assays. Although PlMYB73 did not directly bind to the PlTPS1 promoter, yeast two-hybrid, bimolecular fluorescence complementation, luciferase complementation imaging, and dual-luciferase assays revealed its interaction with PlMYB70 in the nucleus, resulting in synergistic activation of PlTPS1. PlMYB108 was also found to interact with PlMYB70. The three MYB transcription factors formed the PlMYB73–PlMYB70–PlMYB108 complex. Gene co-overexpression and co-silencing experiments demonstrated that the complex significantly enhanced geraniol biosynthesis. In conclusion, our research provides novel insights into the molecular mechanism by which transcription factors cooperatively regulate geraniol biosynthesis.

In addition to flower color, the red new leaves of tree peonies in spring are also ornamental, with the leaf color of Paeonia qiui being the most typical. This study aimed to explore the formation mechanism of P. qiui leaf and flower color by quantitative evaluation and correlating the factors affecting the coloration of leaves and petals. Leaves from eight developmental stages, and petals from five developmental stages of P. qiui were collected for determination of color parameter, cellular pH, anthocyanin, anthoxanthin, chlorophyll, and carotenoid contents, and it was found that anthocyanins and chlorophylls were closely related to leaf coloration, with anthocyanins being the determinant of leaf red color, while anthocyanidins and anthoxanthins affect the petal coloration, with anthocyanins being more influential. High-performance liquid chromatography (HPLC) analysis showed that leaves contain peonidin-3,5-di-O-glucoside (Pn3G5G), peonidin-3-O-glucoside (Pn3G), and cyanidin-3,5-di-O-glucoside (Cy3G5G), and petals contain Pn3G5G, Pn3G, Cy3G5G, and pelargonidin-3,5-di-O-glucoside (Pg3G5G), with Pn3G5G being the most abundant in both leaves and petals. qRT-PCR analysis revealed that PqDFR, PqANS, and PqMYB113 significantly and positively correlated with anthocyanin accumulation in leaves, and PqF3H promoted anthocyanin accumulation to a greater extent in petals. The findings of this study can provide a theoretical reference for the cultivation of new tree peony varieties and germplasm innovation.

Herbaceous peony (Paeonia lactiflora) is a well-known ornamental plant in China, celebrated for its beautiful flowers that can emit fragrances. However, exact molecular mechanisms governing synthesis of floral volatiles within herbaceous peony remain unclear. To address this gap in knowledge, our study focused on analyzing the transcriptome and the levels of floral volatile compounds in P. lactiflora ‘Wu Hua Long Yu’ at different stages of flower development. Using gas chromatography-mass spectrometry (GC-MS), we obtained eighteen major volatile compounds, with monoterpenes being the dominant components among them. Our transcriptome analysis, based on pooled sequencing data, revealed the most differentially expressed genes (DEGs) existed between stages S1 and S3 of flower development. Among these DEGs, we identified 89 functional genes associated with the synthesis of volatile monoterpenes, with 28 of these genes showing a positive correlation with the release of monoterpenes. Specifically, key regulators of monoterpene synthesis in herbaceous peony appear to be 1-deoxy-D-xylulose 5-phosphate synthase (DXS), geranyl pyrophosphate synthase (GPPS), and terpene synthase (TPS). Additionally, our study identified some transcription factors (TFs) that may be involved in the biosynthesis of monoterpenes. These discoveries offer invaluable illumination into the intricate molecular underpinnings orchestrating the generation of floral fragrances in herbaceous peonies, and they offer a foundation for further research to identify and utilize candidate gene resources for this purpose.

Flower scent is one of the main ornamental characteristics of herbaceous peony, and the improvement of flower fragrance is a vital objective of herbaceous peony breeding. In this study, 87 herbaceous peony cultivars were divided into three groups (no/light fragrance, medium fragrance, and strong fragrance) based on their sensory evaluation scores, and 16 strong fragrance cultivars and one no fragrance cultivar were selected for subsequent analysis. Sixty-eight volatile components were detected in these 17 cultivars based on solid-phase microextraction (SPME) and gas chromatography/mass spectrometry (GC/MS), and 26 types were identified as important scent components. They were composed of terpenoids, benzenoids/phenylpropanoids, and fatty acid derivatives. According to the content and odor threshold of these main aroma components, the characteristic aroma substances of herbaceous peony were identified, including linalool, geraniol, citronellol, and phenylethyl alcohol (2-PE). The cultivars of strong scented herbaceous peony were divided into three types: rose scent, lily scent, and mixed scent. We explored the possible key genes of characteristic aroma substances in herbaceous peony petals with different odors through the qRT-PCR. The key genes encoding monoterpene biosynthesis were found to be PlDXS2, PlDXR1, PlMDS1, PlHDR1, PlGPPS3, and PlGPPS4. In addition, the linalool synthase (LIS) gene and the geraniol synthase (GES) gene were also found. PlAADC1, PlPAR1, and PlMAO1, related to the biosynthesis of 2-PE were detected, and the synthetic pathway of 2-PE was speculated. In conclusion, these findings revealed that the difference in gene expression of monoterpene and 2-PE synthesis pathway was related to the difference in the fragrance of herbaceous peony. This study explored the releasing pathway of herbaceous peony characteristic aroma substances and provided key genetic resources for fragrance improvement.

Tree peony is a “spring colored-leaf” plant which has red leaves in early spring, and the red color of the leaves usually fades in late spring. Flavonols are one subgroup of flavonoids, and they affect the plant organs’ color as co-pigments of anthocyanins. To investigate the color variation mechanism of leaves in tree peony, PqMYBF1, one flavonol biosynthesis-related MYB gene was isolated from Paeonia qiui and characterized. PqMYBF1 contained the SG7 and SG7-2 motifs which are unique in flavonol-specific MYB regulators. Subcellular localization and transactivation assay showed that PqMYBF1 localized to the nucleus and acted as a transcriptional activator. The ectopic expression of PqMYBF1 in transgenic tobacco caused an observable increase in flavonol level and the anthocyanin accumulation was decreased significantly, resulting in pale pink flowers. Dual-luciferase reporter assays showed that PqMYBF1 could activate the promoters of PqCHS, PqF3H, and PqFLS. These results suggested that PqMYBF1 could promote flavonol biosynthesis by activating PqCHS, PqF3H, and PqFLS expression, which leads metabolic flux from anthocyanin to flavonol pathway, resulting in more flavonol accumulation. These findings provide a new train of thought for the molecular mechanism of leaf color variation in tree peony in spring, which will be helpful for the molecular breeding of tree peony with colored foliage.