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Leaf spot disease caused by Alternaria pathogens seriously threatens peony production. The physiological mechanism of peony resistance to the pathogen is little reported. This study aimed to reveal the defensive mechanism of peonies in response to the pathogen Alternaria tenuissima. The disease-resistant (R) variety 'Zi Fengyu' and susceptible (S) variety 'Heihai Botao' were employed, and some parameters in the leaves were analyzed after inoculation with A. tenuissima, mainly including the hypersensitive response (HR), activity of defensive enzymes, and expression of disease-resistance genes. The results showed that compared with the responses in the S genotype, HR occurred more rapidly in the R genotype. Meanwhile, the activity of antioxidant enzymes (superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase) and other two defense enzymes (polyphenol oxidase and phenylalanine ammonia-lyase) increased more significantly, and the expression of pathogenesis-related (PR) genes (PlPR1, PlPR2, PlPR4B, PlPR5, and PlPR10) and two WRKY genes (PlWRKY13 and PlWRKY65) was more strongly induced. These responses collectively contributed to the disease resistance of the R genotype. These findings provided a theoretical basis for understanding the intrinsic mechanism of peony resistance to Alternaria leaf spot disease and breeding the disease-resistant peony varieties using a molecular approach. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Paeonia lactiflora Pall. is an important ornamental plant with high economic and medicinal value, which has considerable development prospects worldwide. The lack of efficient tissue culture techniques and genetic transformation systems has become a master obstacle for P. lactiflora research. The purpose of the present study focuses on obtaining an efficient and stable genetic transformation method using callus as the receptor and exploring an efficient protocol for callus induction and proliferation associated with P. lactiflora. Callus induction and proliferation were performed using MS medium with various concentrations of 2,4-Dichlorophenoxyacetic acid (2,4-D), 1-Naphthaleneacetic acid (NAA), 6- Benzylaminopurine (6-BA) and thidiazuron (TDZ). The sensitivity of callus to kanamycin and cefotaxime was determined. Several parameters such as Agrobacterium cell density, infection time and co-culture duration were studied to optimize transformation efficiency. Agrobacterium strains EHA105 and pBI121 binary vector harboring the b-glucuronidase (GUS) gene were used for transformation. Expression of the GUS reporter gene was detected by GUS assay, polymerase chain reaction (PCR) and Quantitative Real-time PCR (RTqPCR). The MS medium containing 1.0 mg·L-1 NAA, 0.5 mg·L-1 2,4-D and 0.5 mg·L-1 TDZ was optimal for callus induction and MS medium containing 0.5 mg·L-1 NAA, 1.0 mg·L-1 2,4-D and 0.5 mg·L-1 TDZ was the best for callus proliferation. The concentrations of kanamycin and cefotaxime used for screening positive callus were 125 mg·L-1 and 200 mg·L-1, respectively. Among various combinations analyzed, the best transformation result was obtained via the 25 min of infection of Agrobacterium at 0.6 OD600 and 3 d of co-culture. Overall, this study provided technical support and theoretical guidance for improving the callus induction and proliferation efficiency and the study of gene function in P. lactiflora. [ABSTRACT FROM AUTHOR]

Leaf spot disease caused by Alternaria pathogens seriously threatens peony production. The physiological mechanism of peony resistance to the pathogen is little reported. This study aimed to reveal the defensive mechanism of peonies in response to the pathogen Alternaria tenuissima. The disease-resistant (R) variety ‘Zi Fengyu’ and susceptible (S) variety ‘Heihai Botao’ were employed, and some parameters in the leaves were analyzed after inoculation with A. tenuissima, mainly including the hypersensitive response (HR), activity of defensive enzymes, and expression of disease-resistance genes. The results showed that compared with the responses in the S genotype, HR occurred more rapidly in the R genotype. Meanwhile, the activity of antioxidant enzymes (superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase) and other two defense enzymes (polyphenol oxidase and phenylalanine ammonia-lyase) increased more significantly, and the expression of pathogenesis-related (PR) genes (PlPR1, PlPR2, PlPR4B, PlPR5, and PlPR10) and two WRKY genes (PlWRKY13 and PlWRKY65) was more strongly induced. These responses collectively contributed to the disease resistance of the R genotype. These findings provided a theoretical basis for understanding the intrinsic mechanism of peony resistance to Alternaria leaf spot disease and breeding the disease-resistant peony varieties using a molecular approach.

Herbaceous peony (Paeonia lactiflora Pall.) is an ornamental plant with huge potential in the international flower market. Similar to the flowers of most other ornamental plants, the top sellers of P. lactiflora are those with red or pink flowers. However, most studies on flower colors have focused on the novel colors and have neglected the most common red flowers. In this study, a red cultivar of P. lactiflora ('Dafugui') and a pink cultivar ('Qingwen') were selected in order to study the discrepancy in the red color of the flowers. The results demonstrate that these two cultivars have the same compositions as anthocyanins, flavones, and flavonols but different contents. 'Dafugui' was found to have a high accumulation of upstream substances due to the higher expression of the early genes encoding phenylalanine ammonialyase (PlPAL) and flavonoid 3′-hydroxylase (PlF3′H). Moreover, the anthocyanidin synthase gene (PlANS) and UDP-glucose flavonoid 3-O-glucosyltransferase gene (PlUF3GT) encoding enzymes catalyze these upstream substances into anthocyanins, resulting in more redness in 'Dafugui' than in 'Qingwen'. Our study thus provides a better understanding of the anthocyanin accumulation and coloring mechanism of P. lactiflora and can serve as a theoretical basis for breeding more red flowers using genetic engineering techniques to cater to consumers' preferences. [ABSTRACT FROM AUTHOR]

Petaloid stamens in Paeonia lactiflora constitute an important developmental phenomenon that explain double flower formation. Although research on stamen development in model plants has progressed considerably, the underlying molecular mechanism in P. lactiflora petaloid stamens is still unclear. In this study, acomparative transcriptomic analysis was performed on two cultivars of P. lactiflora ('Fen Yu Nu' and 'Lian Tai') with different stamen developmental patterns. Following transcriptome sequencing, 89,393 unigenes were identified in P. lactiflora. Trend analysis and weighted gene co-expression network analysis (WGCNA) indicated that 18 candidate genes were likely involved in the formation and development of petaloid stamens, including seven MADS-box genes, PlAP3, PlDEFA, PlPI2, PlAG-1, PlSEP3, PlSEP1-1, and PlSEP1-2, and 11 other transcription factors (TFs), PlTCP2, PlTCP4, PlTCP9, PlbHLH36, PlICE1, PlLBD38, PlNAC083, PlBLH11, PlPDF2, PlGBF1, and PlIIIA. Using these 18 selected candidate genes, we propose ahypothetical model of gene expression network that regulates the development of petaloid stamens. Our results provide acollection of candidate genes that are useful for the analysis of P. lactiflora petaloid stamens, allowing for in-depth studies of the development pattern of P. lactiflora flower organs, and providing atheoretical basis for related research on petaloid stamens of flowers in other herbaceous plants. [ABSTRACT FROM AUTHOR]

Herbaceous peony (Paeonia lactiflora Pall.) is one of the color-leaved ornamental spring plants, with graceful appearance and splendid color. However, the underlying mechanism of this coloration variation from purple to green has not been studied in P. lactiflora. In th study, the leaves in purple, purple–green, and green stages were compared in terms of anatomical, physiological, and molecular. We found that the variation of leaf color from purple to green was mainly determined by the change in pigments distributed in the leaf surface. Physiological experiments showed a significant increase in chlorophyll contents and a notable reduction in anthocyanin contents in leaves from the purple to green stages. We further found that the anthocyanin biosynthesis-related dihydroflavonol 4-reductase (DFR) gene and anthocyanin synthase (ANS) gene as well as chlorophyll biosynthesis-related glutamyl-tRNA reductase (HEMA) gene showed a decreased trend in leaves from purple to green stages, whereas the chlorophyll degradation-related chlorophyll b reductase (NYC) gene showed a rising trend. Alteration of DFR and ANS gene expression might reduce anthocyanin accumulation, whereas increased HEMA gene expression would enhance chlorophyll biosynthesis and reduced NYC gene expression would inhibit chlorophyll degradation. Consequently, reduction in anthocyanins and enhanced deposition of chlorophylls resulted in leaf coloration variation from purple to green in P. lactiflora, which could improve our understanding of its mechanism for further studies. [ABSTRACT FROM AUTHOR]

Herbaceous peony (Paeonia lactiflora Pall.) is a famous flower with medicinal values, and its flowers have a number of medicinal constituents, especially flavonoids. In this study, a P. lactiflora cultivar with double colors including white outer-petal and yellow inner-petal was used as the experimental materials to perform the qualitative and quantitative analysis of flavonoids by high-performance liquid chromatograph-electrospray ionization-mass spectrometry (HPLC-ESI-MSn) and investigate the expression patterns of flavonoid biosynthetic genes using real-time quantitative polymerase chain reaction (Q-PCR). The results showed that the colors of both petals gradually weakened with flower development. Moreover, one main anthocyanin composition (peonidin 3,5-di-O-glucoside) and five main anthoxanthin compositions (kaempferol di-hexo-side, kaempferol-3-O-malonylglucoside-7-O-glucoside, quercetin-3-O-galactoside, luteolin-7-O-glucoside and isorhamnetin-3-O-glucoside) were found in the both, differing significantly in their peak areas only. Total anthocyanin, anthoxanthin and flavonoid contents in white outer-petal and yellow inner-petal gradually decreased during flower development, and were consistently higher in white outer-petal. Furthermore, the expression patterns of nine structural genes in P. lactiflora flavonoid biosynthetic pathway showed that the expression levels of phenylalanine ammonialyase gene (PIPAL), chalcone synthase gene (PICHS), flavanone 3-hydroxylase gene (PIF3H), anthocyanidin synthase gene (PIANS) and UDP-glucoside: flavonoid 5-O-glucosyltransferase gene (PIF5GT) in two petals basically presented declined tendencies, and transcription levels of PIPAL, PICHS, PIANS, PIF3GT and PIF5GT also tended to be higher in white outer-petal, which was correlated with their flavonoid contents. These results would lay a solid foundation for the exploration and utilization of flavonoid resources in P. lactiflora flowers.

Prohexadione-calcium (Pro-Ca), originally developed as a plant growth retardant, has recently been discovered it could modify floral color in several ornamental plants like petunia and rose. However, the underlying mechanism of Pro-Ca on the regulation of floral color is still elusive. In this study, a purple-red herbaceous peony (Paeonia lactiflora Pall.) cultivar with control and Pro-Ca treatment was used as the material. Their color indices were measured, flavonoid compositions and contents as well as its biosynthetic genes expression were analyzed. After Pro-Ca treatment, a remarkable rise in the color parameter lightness (L*) value along with an obvious fall in the color parameter red/green (a*) value indicated that the loss of red color was occurred. In addition, total anthocyanin, anthoxanthin and flavonoid contents were all decreased significantly after Pro-Ca treatment, which was in accordance with the color indices. Furthermore, the expression patterns of most relative genes in flavonoid biosynthetic pathway expressed an overall decline after Pro-Ca treatment. Among the 2-oxoglutaric aciddependent dioxygenase genes involved in the pathway, flavanone 3-hydroxylase gene (F3H) and anthocyanidin synthase gene (ANS) had the highest levels of expression, suggesting that the loss of red color might be the reason of the synergistic inhibitory effect of these enzymes especially F3H and ANS in response to Pro-Ca. These results would contribute to a theoretical foundation for the regulation of floral color in field P. lactiflora by Pro-Ca treatment. [ABSTRACT FROM AUTHOR]

Abstract: Herbaceous peony (Paeonia lactiflora Pall.) is an excellent landscape plant because of its great ornamental values. The objective of this study was to determine if plant growth and flower quality of P. lactiflora were affected by extreme pH in irrigation water. Compared with the control (pH 7.0), P. lactiflora exhibited a decrease in all morphological parameters except leaf number when irrigated with pH 4.0 and 10.0 waters. Physiological indices including chlorophyll a, chlorophyll b, chlorophyll a+b, soluble protein, malondialdehyde (MDA), soluble sugar, hydrogen peroxide (H2O2) and free proline were increased in response to irrigation with waters at pH 4.0 and 10.0, while the decline was occurred in chlorophyll a/b. Moreover, activities of three protective enzymes were also decreased in response to pH 4.0 and 10.0 treatments. These results indicated that the growth of P. lactiflora was significantly affected by extreme pH in irrigation water, and the most serious stress to P. lactiflora was caused under pH 10.0 treatment. Compared with plants irrigated with water at pH 7.0, 26.78% and 27.82% reduction were found in flower diameter and flower fresh weight of plants irrigated with water at pH 4.0. Likely, flower color fade under pH 4.0 treatment was attributed to decreased anthocyanin content and increased pH value of petal, which were coordinately regulated by nine anthocyanin biosynthetic genes and a vacuolar Na+/H+ antiporter1 gene (NHX1), respectively. The results would provide a theoretical guidance for the use of irrigation water in practical production of P. lactiflora. [Copyright &y& Elsevier]

Melatonin is a bioactive, edible ingredient that promotes human health and exists widely in plants, but little is known about its biosynthetic routes and underlying molecular mechanisms in the herbaceous peony. In this contribution, we found that herbaceous peony flowers are rich in melatonin that is found in the greatest quantities in the white series, followed by the ink series, the red series and then the pink series. On this basis, the melatonin content fluctuates during flower development and peaks during the bloom stage. Moreover, it is apparent that sun exposure and blue light induce melatonin production whereas green light restrains it during a 24-h light/dark cycle of melatonin content, as there were ‘dual peaks’ at 2 p.m. and 2 a.m. Additionally, the corresponding expression pattern of the herbaceous peony tryptophan decarboxylase gene (TDC) was positively related with melatonin production. These results suggest that color series, development stage and light play an important role in melatonin accumulation, and that TDC is a rate-limiting gene in melatonin biosynthesis. [ABSTRACT FROM AUTHOR]

Daminozide is a plant growth retardant that inhibits 2-oxoglutarate-dependent dioxygenase activity in the gibberellin biosynthesis pathway, but few studies have focused on its effect on the flavonoid biosynthesis pathway involved in flower color. In the present study, the effect of daminozide on the regulation of flower color was investigated. An herbaceous peony (Paeonia lactiflora Pall.) cultivar ‘Fenzhu Pan’ was used as the material and treated with daminozide. Color parameters of petals were measured; flavonoid composition and content as well as flavonoid biosynthetic gene expression were monitored. The results showed that daminozide treatment caused less red coloration in herbaceous peony. The content of total anthocyanins was decreased by 23%, and the content of total anthoxanthins was increased by 8%; thus, it appeared that less red coloration in daminozide-treated flowers was associated with restricted anthocyanin accumulation. Furthermore, the gene expression patterns of flavonoid 3′-hydroxylase, dihydroflavonol 4-reductase and anthocyanidin synthase were lower after daminozide treatment, which could decrease anthocyanin accumulation and lead to less red coloration in flowers. These findings would improve our understanding of daminozide regulation of flower color in herbaceous peony. [ABSTRACT FROM AUTHOR]