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This research was supported by the Natural Science Foundation of China (No. 31471898) and the Key Technology Research of Oil Peony Industry in Shaanxi Province (2014HXFWYL016) and Special project to Build World‐class Disciplines Of Beijing Forestry University (2019XKJS0324). Determining the factors promoting speciation is a major task in ecological and evolutionary research and can be aided by phylogeographic analysis. The Qinling–Daba Mountains (QDM) located in central China form an important geographic barrier between southern subtropical and northern temperate regions, and exhibit complex topography, climatic, and ecological diversity. Surprisingly, few phylogeographic analyses and studies of plant speciation in this region have been conducted. To address this issue, we investigated the genetic divergence and evolutionary histories of three closely related tree peony species (Paeonia qiui, P. jishanensis, and P. rockii) endemic to the QDM. Forty populations of the three tree peony species were genotyped using 22 nuclear simple sequence repeat markers (nSSRs) and three chloroplast DNA sequences to assess genetic structure and phylogenetic relationships, supplemented by morphological characterization and ecological niche modeling (ENM). Morphological and molecular genetic analyses showed the three species to be clearly differentiated from each other. In addition, coalescent analyses using DIYABC conducted on nSSR variation indicated that the species diverged from each other in the late Pleistocene, while ecological niche modeling (ENM) suggested they occupied a larger area during the Last Glacial Maximum (LGM) than at present. The combined genetic evidence from nuclear and chloroplast DNA and the results of ENM indicate that each species persisted through the late Pleistocene in multiple refugia in the Qinling, Daba, and Taihang Mountains with divergence favored by restricted gene flow caused by geographic isolation, ecological divergence, and limited pollen and seed dispersal. Our study contributes to a growing understanding of the origin and population structure of tree peonies and provides insights into the high level of plant endemism present in the Qinling–Daba Mountains of Central China. Publisher PDF

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Arabidopsis thaliana Flowering locus T (FT) homologs have been shown to be sufficient to trigger flowering and to regulate flowering time in a wide range of plants. However, such a homologue for the perennial ornamental shrub tree peony has not yet been characterized. In this study, we isolated PsFT, which is a closely related FT homolog from reblooming [Paeonia ×lemoinei ‘High Noon’ (HN)] and nonreblooming [P. ×suffruticosa ‘Luo Yang Hong’ (LYH)] cultivars of tree peonies, and identified its potential role in the regulation of flowering time. The PsFT alleles from the two cultivars encode the same protein, which indicates that the polymorphisms observed in the coding region do not contribute to the distinct flowering phenotypes of HN and LYH. Comparative analyses of the PsFT expression patterns in HN and LYH indicated that PsFT might be associated with reblooming. Transgenic A. thaliana plants ectopically expressing PsFT exhibited a phenotype that included significantly early flowering compared with the wild-type (WT) plants. Taken together, our data provide valuable clues for shortening the juvenile periods and extending the flowering periods of perennial woody plants, such as tree peonies.

Paeonia ostii is a traditional ornamental and medicinal species that has attracted considerable interest for its high oil value. To facilitate the effective and rational cultivation and application of P. ostii in China, it is necessary to determine its potential spatial habitat distribution and environmental requirements. Using high-resolution environmental data for current and future climate scenarios, the potential suitable area and climatic requirements of P. ostii were modelled. Among the 11 environmental variables investigated, growing degree days, precipitation of the wettest month, mean temperature of the coldest quarter, global UV-B radiation, annual precipitation, and soil pH played major roles in determining the suitability of a habitat for the cultivation of P. ostii. Under the current environmental conditions in China, a total area of 20.31 × 105 km2 is suitable for growing P. ostii, accounting for 21.16% of the country’s total land area. Under the two future climate scenario/year combinations (i.e., representative concentration pathways [RCPs], RCP2.6 and RCP8.5 in 2050), this species would increase its suitable area at high latitudes while decrease at low latitudes. These results present valuable information and a theoretical reference point for identifying the suitable cultivation areas of P. ostii.

Herbaceous peony (Paeonia lactiflora) is a globally important ornamental plant. Spontaneous floral mutations occur frequently during cultivation, and are selected as a way to release new cultivars, but the underlying evolutionary developmental genetics remain largely elusive. Here, we investigated a collection of spontaneous corolla mutational plants (SCMPs) whose other floral organs were virtually unaffected. Unlike the corolla in normal plants (NPs) that withered soon after fertilization, the transformed corolla (petals) in SCMPs was greenish and persistent similar to the calyx (sepals). Epidermal cellular morphology of the SCMP corolla was also similar to that of calyx cells, further suggesting a sepaloid corolla in SCMPs. Ten floral MADS-box genes from these Paeonia plants were comparatively characterized with respect to sequence and expression. Codogenic sequence variation of these MADS-box genes was not linked to corolla changes in SCMPs. However, we found that both APETALA3 (AP3) and PISTILLATA (PI) lineages of B-class MADS-box genes were duplicated, and subsequent selective expression alterations of these genes were closely associated with the origin of SCMPs. AP3-PI obligate heterodimerization, essential for organ identity of corolla and stamens, was robustly detected. However, selective down-regulation of these duplicated genes might result in a reduction of this obligate heterodimer concentration in a corolla-specific manner, leading to the sepaloid corolla in SCMPs, thus representing a new sepaloid corolla model taking advantage of gene duplication. Our work suggests that modifying floral MADS-box genes could facilitate the breeding of novel cultivars with distinct floral morphology in ornamental plants, and also provides new insights into the functional evolution of the MADS-box genes in plants.

In Paeonia, hybridization is an important path for both the development of new cultivars and species formation in nature, but the characterization of hybrids has long been a problem. To establish the relationship among Paeonia yananensis, P. jishanensis, and P. rockii, we sampled 159 individuals from 11 populations around the core population of P. yananensis. Samples were subjected to morphological analysis of 22 characters and molecular analysis of three chloroplast DNA (cpDNA) fragments and 14 microsatellites. Paeonia yananensis was distinguishable from the other two species on the basis of morphological characteristics. The phylogenetic tree based on three intergenic spacers in the chloroplast genome (petB‐petD, rps16‐trnQ, and psbA‐trnH) demonstrated that P. yananensis was very closely related to P. jishanensis. However, analysis of 14 microsatellite loci revealed that P. yananensis shared a considerable number of alleles with both P. jishanensis and P. rockii. These results demonstrated that P. yanan...

Genetic linkage maps, permitting the elucidation of genome structure, are one of most powerful genomic tools to accelerate marker-assisted breeding. However, due to a lack of sufficient user-friendly molecular markers, no genetic linkage map has been developed for tree peonies (Paeonia Sect. Moutan), a group of important horticultural plants worldwide. Specific-locus amplified fragment sequencing (SLAF-seq) is a recent molecular marker development technology that enable the large-scale discovery and genotyping of sequence-based marker in genome-wide. In this study, we performed SLAF sequencing of an F1 population, derived from the cross P. ostti ‘FenDanBai’ × P. × suffruticosa ‘HongQiao’, to identify sufficient high-quality markers for the construction of high-density genetic linkage map in tree peonies. After SLAF sequencing, a total of 78 Gb sequencing data and 285,403,225 pair-end reads were generated. We detected 309,198 high-quality SLAFs from these data, of which 85,124 (27.5%) were polymorphic. Subsequently, 3518 of the polymorphic markers, which were successfully encoded in to Mendelian segregation types, and were in conformity with the criteria of high-quality markers, were defined as effective markers and used for genetic linkage mapping. Finally, we constructed an integrated genetic map, which comprised 1189 markers on the five linkage groups, and spanned 920.699 centiMorgans (cM) with an average inter-marker distance of 0.774 cM. There were 1115 ‘SNP-only’ markers, 18 ‘InDel-only’ markers, and 56 ‘SNP&InDel’ markers on the map. Among these markers, 450 (37.85%) showed significant segregation distortion (P < 0.05). In conclusion, this investigation reported the first large-scale marker development and high-density linkage map construction for tree peony. The results of this study will serve as a solid foundation not only for marker-assisted breeding, but also for genome sequence assembly for tree peony.

 Premise of the study : Microsatellite (simple sequence repeat, SSR) primers were developed for the Chinese peony, P. lactifl ora , to investigate the diversity within Chinese peony germplasm resources.  Methods and Results : Using an SSR-enriched genomic library, a set of 10 unique polymorphic genomic SSRs was developed and characterized. The primers amplifi ed 61 alleles in all 10 loci, including di-, tri-, and tetranucleotide repeats. The primers were also effective for P. veitchii and P. obovata .  Conclusions : The new primers will be useful for genetic research of the Chinese peony and extend the repertoire of SSR markers available to study the herbaceous taxa in Paeonia .

Morphological development of forced tree peony (Paeonia suffruticosa) was observed in 17 Chinese and 3 Japanese cultivars (cvs) and the effects of pre-chilling on the growth and development in the Chinese and Japanese cv groups were compared. The development from bud swelling to flowering was divided into 8 stages. The leaves, stem and flower buds mainly grew during stages IV-VII, and stage VI was the longest showing the most vigorous growth. Stages III, IV and V were very complicated in morphology and varied with the cv, but could be identified easily by the leaf development. The pre-chilling promoted the growth and advanced the flowering, but the stage sensitive to the chilling in the Chinese cvs differed from that in Japanese cvs, which indicated the existence of different growth mechanisms. The pre-chilling was effective at the early stages in the Chinese cvs, but at the later stages in the Japanese cvs. The Chinese cvs grew more rapidly and responded to low temperature at an earlier stage, but their cut flower quality was inferior to the Japanese cvs. These results corresponded to a smaller requirement of cumulative temperature for flowering in the Chinese cvs. The pre-chilling decreased the stem length and foliage extension, but promoted the flower size and advanced the flowering date. Non-flowering cvs had normal leaves developed a normal stem and responded to pre-chilling as well as did the flowering cv. These results suggested that the vegetative growth is somewhat independent of the generative growth.

Endosperm in blotched tree peony (P. rockii cvs.) was nuclear type and of three successive development stages: free nuclear stage lasting from 4 to 29 days after anthesis (d.a.a.) , cellularization stage from 29 to 48 d.a.a. and growth and mature stage finished before 85 d.a.a. Free endosperm nuclei multiplied to 200-500 or more and the cellularization of endosperm proceeded from the micropyle to chalazal end. As endosperm developed, the cells of outer integument adjacent to endosperm degenerated to form an evident degenerated zone through which nutrients were transferred into endosperm from integument. Firstly reserved substances were mostly starch gains in the cells, and, however, were gradually reserved into the cell walls so that matured endosperm was oleaginous. Endosperm and embryo corresponded with each other in certain stages and the relationship between them was helpful for the identification of embryo development by endosperm.

This paper dealt with the ovule ontogenesis and development, the megasporogenesis and the embryo sac development in Paeonia rockii cvs. The ovule, originated from the tri-zonate primordium, was anatropous, bitegmic and crassinucellate. And the nucellus consisted of different cytohistological zones and differentiated by a particular way in which the derivative cells from both parietal and sporogeneous cells were contributed to the nucellar tissue. During the megasporogenesis and before the 4-nuclear embryo sac, the megasporocytes successively entered meiosis or commenced to degenerate. Generally a linear tetrad formed after meiosis and the chalazal megaspore was functional and developed into embryo sac by Polygonum type. Multicelled archesporium and multiple megasporocytes in an ovule resulted in 1-3 embryo sacs, which developed to mature within several days after anthesis. Belated mature of embryo sacs supplies a device to guarantee the cross-pollination. The characteristics about ovule and embryo sac of peonies were more primitive and imply the primitive of Paeoniaceae in phylogeny

Background Tree peonies are great ornamental plants associated with a rich ethnobotanical history in Chinese culture and have recently been used as an evolutionary model. The Qinling Mountains represent a significant geographic barrier in Asia, dividing mainland China into northern (temperate) and southern (semi–tropical) regions; however, their flora has not been well analyzed. In this study, the genetic differentiation and genetic structure of Paeonia rockii and the role of the Qinling Mountains as a barrier that has driven intraspecific fragmentation were evaluated using 14 microsatellite markers. Methodology/Principal Findings Twenty wild populations were sampled from the distributional range of P. rockii. Significant population differentiation was suggested (FST value of 0.302). Moderate genetic diversity at the population level (HS of 0.516) and high population diversity at the species level (HT of 0.749) were detected. Significant excess homozygosity (FIS of 0.076) and recent population bottlenecks were detected in three populations. Bayesian clusters, population genetic trees and principal coordinate analysis all classified the P. rockii populations into three genetic groups and one admixed Wenxian population. An isolation-by-distance model for P. rockii was suggested by Mantel tests (r = 0.6074, P