Double Flowers Research Articles

The overall regulatory network and contributions of ABC(D)E model genes in yellowhorn flower development.

Single flowers and double flowers, exhibiting distinct flower morphologies, developmental process and regulatory networks, have garnered significant attention recently. In yellowhorn (Xanthoceras sorbifolium), the cause of double flower variation has been elucidated, yet the differences in regulatory networks between single and double flowers remain unexplored. Here, we investigated transcriptional changes underlying flower development among yellowhorn single- and double-flowered-trees. Transcriptome analysis and weighted gene co-expression network analysis (WGCNA) were applied to identify key genes and reveal the characteristics of single and double flower traits. The involvement of development-specific and flower-type-specific DEGs related to hormone signaling, metabolism, growth and development was identified, and ABC(D)E model genes were found to be closely associated with floral organ development. Overexpression of yellowhorn ABC(D)E model genes in Arabidopsis demonstrated their roles in floral organ development, and the interactions between different pairs of genes were also validated by yeast two-hybrid (Y2H) experiments. Therefore we elucidated differences between yellowhorn single and double flower development, highlighting the roles of yellowhorn ABC(D)E model genes in controlling flower structures, which not only enriches the understanding of yellowhorn flower researches, but also provides insights for studying flower development in other woody species.

Creation of a collection fund and study of cultivars of daylilies in the M. M. Gryshko National Botanical Garden of the National Academy of Sciences of Ukraine

Purpose. Analysis and comparative study of daylily cultivars from the collection fund of the M. M. Gryshko National Botanical Garden of the National Academy of Sciences of Ukraine (NBG), selection of assortment for decorative horticulture and landscaping. Methods. Cultivars from the NBG daylily collection were studied. The cultivars were evaluated in terms of their aesthetic and economic attributes, and were classified according to their coloration and the timing of their flowering. The author of the cultivar, country of origin, year of creation and introduction into the NBG were also identified. The cultivars were also grouped according to these parameters. Results. The NBG daylily collection is the result of 40 years of introduction and 20 years of breeding work with this crop at the NBG. It includes 174 world cultivars, 26 cultivars of Ukrainian breeding and more than 1000 hybrid seedlings. Most of the cultivars (79) were introduced in 2000–2009. The main part of the current structure of the daylily collection consists of cultivars bred in the 1960–1970s. Most of these are hybrids from American breeders: David F. Hall (20 cultivars) and Allen Wild (46 cultivars). A total of 15 new cultivars were developed based on the original collection. These new cultivars feature double flowers, a valuable trait for hybrids in Ukraine. For effective use in ornamental horticulture and landscaping, the cultivars were grouped according to flower colour and flowering time. The yellow­flowered group is the most widely represented. A large number of cultivars with red flowers are inherent in hybrids bred between 1980 and 1999. Cultivars from modern breeding are mostly represented by the purple and pink colour group. Most of the cultivars in the collection are early and medium early. The smallest part is made up of medium­late and late hybrids. Conclusions. The modern daylily collection is representative. The cultivars introduced into the NBG illustrate the main stages of breeding work with the crop and the achievements of breeders from different countries of the world. The collection includes early and medium early, medium, medium late and late flowering cultivars. Varying in colour and flowering time, the collection can be effectively used to extend the flowering period of daylilies by three months (from the second decade of May to the second decade of August) in ornamental gardening in Ukraine and in various landscape compositions.

Biochemical and physiological effects of propagule type and auxin concentration on adventitious root formation in novel Jasmine genotypes

Jasmine is primarily propagated through asexual methods, and bio-stimulants can improve soil fertility around plant roots. Some jasmine genotypes are mainly propagated through cuttings; however, the rooting process is slow and inconsistent. Specific jasmine genotypes are primarily propagated through cuttings, but the rooting process is slow and uneven. This study evaluated the regeneration potential of stem cuttings by investigating the effects of auxins and various propagule types on adventitious root formation, along with associated biochemical changes. A field experiment conducted by the Department of Floriculture and Landscaping at TNAU, Coimbatore, Tamil Nadu, from December 2023 to June 2024, during the winter monsoon, investigated the rooting of stem cuttings in three Jasminum genotypes using auxin. Stem cuttings of J. sambac Double Flower type (DF), J. grandiflorum White Flower type (WF) and a new cultivar of J. multiflorum CO.1 Winter Jasmine (CO.1 WJ) were treated with three Indole-3-Butyric Acid (IBA) concentrations (0.5, 1, 1.5 g L-1) and distilled water as control. Utilizing a Factorial, Completely Randomized Design for terminal and semi-hardwood cuttings, the study found that rooting hormone significantly enhanced root formation and stem and shoot growth. Semi-hardwood cuttings of J. sambac (DF) treated with 1g L-1 IBA had the highest rooting rate (88.60%), number of roots (9.34), root length (12.74 cm), shoot length (10.26 cm) and number of leaves (6.60). The highest rooting rate of 48.15% was obtained from the terminal cuttings of J. grandiflorum (WF) that had been treated with 1g L-1 IBA, in addition to other parameters such as number of roots (13.52), root length (12.03 cm), shoot length (14.30 cm), and number of leaves (13.48). On the other hand, J. multiflorum (CO.1 WJ) recorded the highest rooting rate of 72.23%, root number of 16.52, root length of 17.22 cm, shoot length of 14.14 cm and number of leaves, which was pegged at 31.70 when terminal cuttings were treated with 1g L-1 IBA. The current findings indicate that the application of auxins is crucial for promoting early root initiation and achieving higher rooting success, making it advantageous for vegetative propagation.

A single dominant GLOBOSA allele accounts for repeated origins of hose-in-hose flowers in Sinningia (Gesneriaceae).

Plants bearing double flowers have long been cultivated as ornamental plants. Hose-in-hose flowers, bearing 2-whorled corolla tubes in whorls 1 and 2, are uncommon but recur in Sinningia (Gesnerioideae, Gesneriaceae). In this study, we selected 15 hose-in-hose cultivars as materials to explore the underlying molecular and genetic mechanisms of this floral architecture. We found that they originated from different hybridization events within the Dircaea clade. Three B-class MADS-box genes were globally expressed in all floral whorls, but only GLOBOSA1 (GLO1) has accumulated a dominant mutation, i.e., the insertion of a hAT-like miniature inverted-repeat transposable element (MITE) into its promoter, that co-segregated with the hose-in-hose phenotype. In addition, all 15 hose-in-hose cultivars contained the same dominant GLO1 allele. Transient gene expression assays confirmed the role of this MITE insertion in up-regulating the promoter activity of GLO1 by providing several cis-regulatory elements. Genetic transformation in heterologous Chirita pumila (Didymocarpoideae, Gesneriaceae) verified that this dominant GLO1 allele is sufficient to confer the hose-in-hose phenotype. We further demonstrated that both the GLO1 allele and the hAT-like MITE descended from wild S. cardinalis with single flowers. This study highlights the significance of wide hybridization in frequent gains of the dominant GLO1 allele and thereafter repeated occurrence of hose-in-hose flowers in Sinningia.

Haplotype-resolved genome assembly and resequencing provide insights into the origin and breeding of modern rose.

Modern rose (Rosa hybrida) is a recently formed interspecific hybrid and has become one of the most important and widely cultivated ornamentals. Here we report the haplotype-resolved chromosome-scale genome assembly of the tetraploid R. hybrida 'Samantha' ('JACmantha') and a genome variation map of 233 Rosa accessions involving various wild species, and old and modern cultivars. Homologous chromosomes of 'Samantha' exhibit frequent homoeologous exchanges. Population genomic and genomic composition analyses reveal the contributions of wild Rosa species to modern roses and highlight that R. odorata and its derived cultivars are important contributors to modern roses, much like R. chinensis 'Old Blush'. Furthermore, selective sweeps during modern rose breeding associated with major agronomic traits, including continuous and recurrent flowering, double flower, flower senescence and disease resistance, are identified. This study provides insights into the genetic basis of modern rose origin and breeding history, and offers unprecedented genomic resources for rose improvement.

Identification of candidate genes associated with double flowers via integrating BSA-seq and RNA-seq in Brassica napus

As a Brassica crop, Brassica napus typically has single flowers that contain four petals. The double-flower phenotype of rapeseed has been a desirable trait in China because of its potential commercial value in ornamental tourism. However, few double-flowered germplasms have been documented in B. napus, and knowledge of the underlying genes is limited. Here, B. napus D376 was characterized as a double-flowered strain that presented an average of 10.92 ± 1.40 petals and other normal floral organs. F1, F2 and BC1 populations were constructed by crossing D376 with a single-flowered line reciprocally. Genetic analysis revealed that the double-flower trait was a recessive trait controlled by multiple genes. To identify the key genes controlling the double-flower trait, bulk segregant analysis sequencing (BSA-seq) and RNA-seq analyses were conducted on F2 individual bulks with opposite extreme phenotypes. Through BSA-seq, one candidate interval was mapped at the region of chromosome C05: 14.56–16.17 Mb. GO and KEGG enrichment analyses revealed that the DEGs were significantly enriched in carbohydrate metabolic processes, notably starch and sucrose metabolism. Interestingly, five and thirty-six DEGs associated with floral development were significantly up- and down-regulated, respectively, in the double-flowered plants. A combined analysis of BSA-seq and RNA-seq data revealed that five genes were candidates associated with the double flower trait, and BnaC05.ERS2 was the most promising gene. These findings provide novel insights into the breeding of double-flowered varieties and lay a theoretical foundation for unveiling the molecular mechanisms of floral development in B. napus.

Aroma formation in single- and double-petal jasmines (Jasminum sambac) during flowering via volatile metabolome and transcriptome

Jasminum sambac (L.) Aiton exists in single-petal (SP), double-petal (DP), and multi-petal (MP) phenotypes, which have a sweet floral scent and release aroma when the flowers open. A total of 103 volatiles were discovered from SP and DP jasmines. 16 volatiles were identified as their key odorants. Caryophyllene, geraniol, linalool, α-farnesene, β-ocimene, methyl anthranilate, methyl salicylate, benzeneacetaldehyde and hexanal may form the overall aroma of those two jasmines during flowering. High-resolution transcriptional profiles of those two jasmines at four flowering stages were generated from our recently reported chromosome-level genome assembly, from which we identified 35 differentially expressed genes (DEGs) involved in terpenoid metabolic pathways and 10 DEGs involved in the phenylpropane/benzene metabolic pathway, which may shape the characteristic aroma of those two jasmines at the molecular level. Through co-expression network analysis of key odorants, we found that bZIP8, bHLH6, MYB4, and AP2/ERF3 may contribute to the regulation of aroma volatiles in those two jasmines. These results offer an important theoretical foundation for studying the regulation of aroma formation for SP and DP jasmines.

Molecular and genetic regulation of petal number variation in plants.

Floral forms with an increased number of petals, also known as double flower (DF) with great agronomic and economic values, have been selected and conserved in many domesticated plants, particularly in ornamentals. The molecular and genetic mechanisms that control this trait are therefore a hot topic, not only for scientists, but also for breeders. In this review, we summarize the current knowledge on the gene regulatory networks of flower initiation and development and known mutations that lead to variation of petal number in many species. Besides the well-accepted miR172/AP2-like module, for which many questions remain unanswered, we also discuss the current knowledge of other pathways in which mutations also lead to extra-petals formation, such as those involved in meristem development, hormones signaling, epigenetic regulations, and responses to environmental signals. We discuss how the concept of "natural mutants" and the recent advances in genomics and genome editing makes it possible to explore the molecular mechanisms underlying the DF formation, and how such knowledge could contribute to the future breeding and selection of this trait in more crops.

Mutations overlying the miR172 target site of TOE-type genes are prime candidate variants for the double-flower trait in mei

Mutations affecting flower shape in many plants have been favored by human selection, and various fruit trees are also grown for ornamental purposes. Mei (Prunus mume) is a dual purpose tree originated in China well known in the Western world for its generous early blooms, often bearing double flowers. Building on the knowledge of its genomic location, a candidate gene approach was used to identify a 49 bp deletion encompassing the miR172 target site of the euAP2 gene pmTOE (PmuVar_Ch1_3490) as a prime variant linked to flower doubleness. Searching within a large dataset of genome sequencing data from Eastern germplasm collections demonstrated a tight variant-trait association, further confirmed in a panel of commercial and non-commercial varieties available in Italy. Moreover, two SNP mutations in the miR172 target site of pmPET (PmuVar_Ch1_1333) were identified in some double flower accessions. The mei orthologue of PETALOSA genes already found responsible for the phenotype in other plants suggests that independent variants may have been selected throughout mei domestication history.

Construction of a high-density genetic map and mapping of double flower genes in petunia

Double flower (DF) is one of the important ornamental traits of horticultural plants, but the molecular mechanism of its formation is still unclear. In this study, forward genetic approaches were applied to explore the key genes involved in the DF formation in petunia. We developed a total of 17 SCAR markers linked to DF, and initially mapped the DF genes onto 9 scaffolds (totally 13.3 Mb) in the genome of the DF petunia. We also constructed a genetic linkage map of petunia, which contained 4474 SNP markers, with a total genetic distance of 2022.786 cM and an average genetic distance of 0.758 cM. In QTL analysis, a QTL associated with DF trait was detected. The LOD value of the marker was 3.82–12.71, and the contribution rate was 16.0 %–44.0 %. To further shorten the mapping interval of the DF genes, we constructed a near-isogenic line (NIL) population containing 2757 plants, and used these 17 SCAR markers to screen the recombinant plants, and located the DF genes within a 2.2 Mb interval. Combined with Bacterial Artificial Chromosome (BAC) library screening, the mapping interval of the DF genes was ultimately shortened from 2.2 Mb to 1.82 Mb. Presently, research on the DF trait of petunia mainly focused on the ABC(D)E model. The fine mapping results of petunia DF genes obtained in this study provide a new idea for revealing the molecular mechanism of DF formation in petunia.

Phenotypic Variation in Flower Color and Morphology in the Gerbera (Gerbera hybrida) F1 Hybrid Population and Their Association with EST-SSR Markers.

Gerbera (Gerbera hybrida) is a widely cultivated ornamental plant. However, its genetic improvement is limited by the lack of genetic analysis and molecular markers for traits. In this study, we analyzed the phenotypic and genotypic variation of 140 F1 progeny from two gerbera varieties with different flower types and colors. We evaluated the flower's morphology, color, and pigment content of the F1 population and performed cluster principal component analysis (PCA) and correlation analysis. The results showed that the main ornamental traits of the hybrid progeny varied greatly. The segregation ratios of single and double flowers and ligulate and split ray florets were both 1:1. The flower colors of the F1 progeny were mainly red and purple-red, similar to the male parent's color. Furthermore, we conducted a genetic analysis of the hybrid progeny using EST-SSR markers and performed association analysis with phenotypic traits. We identified 2, 2, 3, 1, and 2 loci to be associated with peduncle length (PL), ray floret length (RFL), and outer ray floret; the level of apex relative to the top of involucre (LAI); outer corolla lips (OCL); and the b* of ray floret color, respectively. Our results reveal the genetic patterns of important ornamental traits and provide a theoretical basis and practical tools for gerbera genetic breeding.

A 49-bp deletion of PmAP2L results in a double flower phenotype in Prunus mume.

The double flower is an important trait with substantial ornamental value. While mutations in PETALOSA TOE-type or AG (AGAMOUS) genes play a crucial role in enhancing petal number in ornamental plants, the complete mechanism underlying the formation of double flowers remains to be fully elucidated. Through the application of bulked segregant analysis (BSA), we identified a novel gene, APETALA2-like (PmAP2L), characterized by a 49-bp deletion in double-flowered Prunus mume. β-Glucuronidase (GUS) staining and luciferase reporter assays confirmed that the 49-bp deletion in PmAP2L reduced its binding with Pmu-miRNA172a. Phylogenetic analysis and microsynteny analysis suggested that PmAP2L was not a PETALOSA TOE-type gene, and it might be a new gene controlling the formation of double flower in P. mume. Subsequently, overexpression of PmAP2L-D in tobacco led to a significant rise in the number of stamens and the conversion of stamens to petals. Furthermore, silencing of the homologue of RC5G0530900 in rose significantly reduced the number of petals. Using transient gene expression in P. mume flower buds, we determined the functional differences between PmAP2L-D and PmAP2-S in controlling flower development. Meanwhile, DNA-affinity purification sequencing (DAP-seq), yeast hybrid assays and luciferase reporter assays indicated that PmAP2L negatively regulated the floral organ identity genes by forming a repressor complex with PmTPL and PmHDA6/19. Overall, these findings indicate that the variation in PmAP2L is associated with differences in the regulation of genes responsible for floral organ identity, providing new insights into the double-flower trait and double-flower breeding in plants.

Anomalous peony (<i>Paeonia anomala</i> L.) In the Urals and contiguous landsAnomalous peony (<i>Paeonia anomala</i> L.) In the Urals and contiguous lands

Modern varieties of flowering ornamental plants have high economic and social significance. Prominent representatives of active long-term plant breeding are various varieties of peonies, which are actively used in landscaping botanical gardens, urban landscapes and smallholdings. With the development of molecular genetics, the selection of ornamental varieties of flowering plants has received a new impetus in its development. Researchers have identified markers that determine important decorative and economic qualities, such as flower shape, leaf color, corolla color, variety of double flower, aroma, which allows to intensify plant breeding, and also, which is quite important, to certify new varieties. In this article, we have given an overview of the results of longterm studies of representatives of the genus Paeonia in the Urals and contiguous lands, since the mid-twentieth century to the present, both domestic and foreign scientific schools. The article presents data on the locations of the anomalous peony along the Ural mountain range, the morphology and ecology of the growth of representatives of this species, medicinal properties, the results of molecular genetic typing of various marker systems. The points requiring more detailed study are indicated: there is no complete up-to-date information on the distribution of the anomalous peony in the Urals, there is no up-to-date data on the population size, there is no information about the molecular genetic structure of the species as a whole. The anomalous peony is a red book species that has a high level of decorativeness, as well as resistance to diseases that can be used not only in pharmacology, but also in modern plant selection. It is known that the number of populations of anomalous peony is low, in places of meetings it is noted singly, less often in small groups, which is connected with the active use of this species in folk medicine. Vegetative and root systems contain a large number of biologically active components with different properties. To develop measures for the protection and rational use of representatives of Paeonia anomala growing in the Urals, it is necessary to study the species more closely in order to preserve it in nature and further use in breeding and hybridization as a source of genes that will help significantly improve the plant breeding potential of modern varieties.

New mutations of flower shape in Nigella damascena L., its pleiotropic effects and patterns of inheritance

Two mutants with short sepals were identified after ethyl methanesulfonate treatment of Nigella damascena seeds. In one of them (“shs1” gene = short sepal 1), isolated from the line with double flowers, the sepals, in addition to reduced size, were divided into several rounded lobes, which granted the flower an original rose-like appearance of ornamental value. Another mutant with reduced sepals (“shs2” gene = short sepal 2) was isolated from the line with simple flowers. The allelism test showed that these two genes were non-allelic. Both mutants as pollen parents were crossed with the same line with single flowers. In a dihybrid cross, simple flower, non-reduced sepals (wild type) × double flower, reduced sepals (“shs1” gene) F1 hybrids demonstrated a wild phenotype. F2 progeny, in addition to two parental classes, showed two recombinant classes in a 9:3:3:1 ratio, indicating that flower shape and sepal size were inherited monogenously and independently, and the plant with rose-like flowers was a double recessive homozygote. Reduced sepals (“shs2” gene) in crosses with the single flower line of wild type were inherited as a monogenic recessive trait, showing a 3:1 segregation ratio in F2. Both mutant genes had a number of similar pleiotropic effects, which, however, were different in strength. Thus, both mutant genes shortened leaf segments, divided the cotyledon leaves into several lobes, and caused disturbances in the female generative sphere, leading to a lack of seed setting. At the same time, the identification of mutants as early as at the cotyledon stage, due to the pleiotropic effect, makes it possible to select and maintain them, especially with regard to the mutant with rose-like flowers, which is highly decorative.

Two haplotype-resolved genomes reveal important flower traits in bigleaf hydrangea (Hydrangea macrophylla) and insights into Asterid evolution.

The Hydrangea genus belongs to the Hydrangeaceae family, in the Cornales order of flowering plants, which early diverged among the Asterids, and includes several species that are commonly used ornamental plants. Of them, Hydrangea macrophylla is one of the most valuable species in the nursery trade, yet few genomic resources are available for this crop or closely related Asterid species. Two high-quality haplotype-resolved reference genomes of hydrangea cultivars 'Veitchii' and 'Endless Summer' [highest quality at 2.22 gigabase pairs (Gb), 396 contigs, N50 22.8megabase pairs (Mb)] were assembled and scaffolded into the expected 18 pseudochromosomes. Utilizing the newly developed high-quality reference genomes along with high-quality genomes of other related flowering plants, nuclear data were found to support a single divergence point in the Asterids clade where both the Cornales and Ericales diverged from the euasterids. Genetic mapping with an F1 hybrid population demonstrated the power of linkage mapping combined with the new genomic resources to identify the gene for inflorescence shape, CYP78A5 located on chromosome 4, and a novel gene, BAM3 located on chromosome 17, for causing double flower. Resources developed in this study will not only help to accelerate hydrangea genetic improvement but also contribute to understanding the largest group of flowering plants, the Asterids.

Small RNA profiling reveals that an ovule-specific microRNA, cja-miR5179, targets a B-class MADS-box gene in Camellia japonica.

The functional specialization of microRNA and its target genes is often an important factor in the establishment of spatiotemporal patterns of gene expression that are essential to plant development and growth. In different plant lineages, understanding the functional conservation and divergence of microRNAs remains to be explored. To identify small regulatory RNAs underlying floral patterning, we performed a tissue-specific profiling of small RNAs in various floral organs from single and double flower varieties (flowers characterized by multiple layers of petals) in Camellia japonica. We identified cja-miR5179, which belongs to a deeply conserved microRNA family that is conserved between angiosperms and basal plants but frequently lost in eudicots. We characterized the molecular function of cja-miR5179 and its target - a B-function MADS-box gene - through gene expression analysis and transient expression assays. We showed that cja-miR5179 is exclusively expressed in ovule tissues at the early stage of floral development. We found that cja-miR5179 targets the coding sequences of a DEFICIENS-like B-class gene (CjDEF) mRNA, which is located in the K motif of the MADS-box domain; and the target sites of miR5179/MADS-box were consistent in Camellia and orchids. Furthermore, through a petal transient-expression assay, we showed that the BASIC PENTACYSTEINE proteins bind to the GA-rich motifs in the cja-miR5179 promoter region and suppresses its expression. We propose that the regulation between miR5179 and a B-class MADS-box gene in C. japonica has a deep evolutionary origin before the separation of monocots and dicots. During floral development of C. japonica, cja-miR5179 is specifically expressed in the ovule, which may be required for the inhibition of CjDEF function. This work highlights the evolutionary conservation as well as functional divergence of small RNAs in floral development.

Efficient double-flowered gentian plant production using the CRISPR/Cas9 system.

Japanese cultivated gentians are highly valued ornamental flowers in Japan, but the flower shape is mostly limited to the single-flower type, unlike other flowers such as roses and carnations. To overcome this limitation, we used the CRISPR/Cas9 genome editing system to increase double-flowered genetic resources in gentians. Our approach targeted an AGAMOUS (AG) floral homeotic gene (AG1), which is responsible for the natural mutation that causes double flowers in gentians. We designed two targets in exon 1 of AG1 for genome editing and found that 9 of 12 herbicide-resistant shoots had biallelic mutations in the target regions of AG1. These nine lines all produced double flowers, with stamens converted into petaloid organs, similar to the natural mutant. We also analyzed the off-target effects of AG2, which is homologous to AG1, and found that such effects occurred in gentian genome editing but with low frequency. Furthermore, we successfully produced transgene-free genome-edited plants (null segregants) by crossing with wild-type pollen. F1 seedlings were subjected to PCR analysis to determine whether foreign DNA sequences, two partial regions of the CaMV35S promoter and Cas9 gene, were present in the genome. As a result, foreign genes were segregated at a 1 : 1 ratio, indicating successful null segregant production. Using PCR analysis, we confirmed that four representative null segregants did not contain transfer DNA. In summary, our study demonstrates that the CRISPR/Cas9 system can efficiently produce double-flowered gentians, and null segregants can also be obtained. These genome-edited plants are valuable genetic resources for future gentian breeding programs.

Genome-Wide Identified MADS-Box Genes in Prunus campanulata 'Plena' and Theirs Roles in Double-Flower Development.

The MADS-box gene family plays key roles in flower induction, floral initiation, and floral morphogenesis in flowering plants. To understand their functions in the double-flower formation of Prunus campanulata 'Plena' (hereafter referred to as PCP), which is an excellent flowering cherry cultivar, we performed genome-wide identification of the MADS-box gene family. In this study, 71 MADS-box genes were identified and grouped into the Mα, Mβ, Mγ and MIKC subfamilies according to their structures and phylogenetic relationships. All 71 MADS-box genes were located on eight chromosomes of PCP. Analysis of the cis-acting elements in the promoter region of MADS-box genes indicated that they were associated mainly with auxin, abscisic acid, gibberellin, MeJA (methyl jasmonate), and salicylic acid responsiveness, which may be involved in floral development and differentiation. By observing the floral organ phenotype, we found that the double-flower phenotype of PCP originated from petaloid stamens. The analysis of MIKC-type MADS-box genes in PCP vegetative and floral organs by qRT-PCR revealed six upregulated genes involved in petal development and three downregulated genes participating in stamen identity. Comparative analysis of petaloid stamens and normal stamens also indicated that the expression level of the AG gene (PcMADS40) was significantly reduced. Thus, we speculated that these upregulated and downregulated genes, especially PcMADS40, may lead to petaloid stamen formation and thus double flowers. This study lays a theoretical foundation for MADS-box gene identification and classification and studying the molecular mechanism underlying double flowers in other ornamental plants.

Pedigree-based QTL analysis of flower size traits in two multi-parental diploid rose populations.

Rose (Rosa spp.) is one of the most economically important ornamental species worldwide. Flower diameter, flower weight, and the number of petals and petaloids are key flower-size parameters and attractive targets for DNA-informed breeding. Pedigree-based analysis (PBA) using FlexQTL software was conducted using two sets of multi-parental diploid rose populations. Phenotypic data for flower diameter (Diam), flower weight (fresh (FWT)/dry (DWT)), number of petals (NP), and number of petaloids (PD) were collected over six environments (seasons) at two locations in Texas. The objectives of this study were to 1) identify new and/or validate previously reported QTL(s); 2) identify SNP haplotypes associated with QTL alleles (Q-/q-) of a trait and their sources; and 3) determine QTL genotypes for important rose breeding parents. Several new and previously reported QTLs for NP and Diam traits were identified. In addition, QTLs associated with flower weight and PD were identified for the first time. Two major QTLs with large effects were mapped for all traits. The first QTL was at the distal end of LG1 (60.44-60.95 Mbp) and was associated with Diam and DWT in the TX2WOB populations. The second QTL was consistently mapped in the middle region on LG3 (30.15-39.34 Mbp) and associated with NP, PD, and flower weight across two multi-parent populations (TX2WOB and TX2WSE). Haplotype results revealed a series of QTL alleles with differing effects at important loci for most traits. This work is distinct from previous studies by conducting co-factor analysis to account for the DOUBLE FLOWER locus while mapping QTL for NP. Sources of high-value (Q) alleles were identified, namely, 'Old Blush' and Rosa wichuraiana from J14-3 for Diam, while 'Violette' and PP-J14-3 were sources for other traits. In addition, the source of the low-value (q) alleles for Diam was 'Little Chief', and Rosa wichuraiana through J14-3 was the source for the remaining traits. Hence, our results can potentially inform parental/seedling selections as means to improve ornamental quality in roses and a step towards implementing DNA-informed techniques for use in rose breeding programs.

Transcriptomic and proteomic analyses reveal changes in the metabolic pathways of Paeonia lactiflora petaloid stamens

Paeonia lactiflora or herbaceous peony, a famous traditional Chinese flower, is popular around the world for its cut flowers. Petaloid stamens are a common form of double flowers, but their underlying molecular mechanisms during development are still unclear. In this study, using the petaloid stamens of P. lactiflora ‘Lian Tai’ as research material, transcriptomic and proteomic analyses of flower buds at three developmental stages (stamen primordium, stamen primordium partly petaloid, and stamen primordium completely petaloid) were performed. A total of 81,971 unigenes were identified in the transcriptome, 8,288 proteins were identified in the proteome, and 8,152 genes and proteins were jointly identified in the transcriptome and proteome. GO annotation and KEGG enrichment analysis of differentially expressed proteins indicated that the metabolic pathways related to polysaccharides, carbohydrates, starch, sucrose, fructose, mannose, and photosynthesis were significantly enriched in petaloid stamens. After removing duplicates, 85 differentially expressed genes/proteins were identified in these metabolic pathways. These significantly enriched metabolic pathways and differentially expressed genes/proteins may play an important role in physiological and developmental processes associated with P. lactiflora petaloid stamens. This study provides additional transcriptomic and proteomic reference points for further exploring the molecular mechanisms during the development of P. lactiflora petaloid stamens.