Disc Florets Research Articles

Lineage‐specific duplication of a CYCLOIDEA2 gene and the diversification of capitula in the tribe Anthemideae (Asteraceae)

AbstractGene duplications have contributed to the innovation of morphological traits during plant evolution. An outstanding example is the role of CYCLOIDEA2 (CYC2) gene duplications in the formation of the complex structure of Asteraceae capitula. Previous studies have shown that Chrysanthemum lavandulifolium (Fischer ex Trautv.) Makino and a few other species of the Asteraceae harbor two copies of CYC2e. Here, we identified a lineage‐specific CYC2e duplication event at the root of the phylogeny of the tribe Anthemideae by analyzing the evolutionary history of CYC2 genes across the Asteraceae. Although the gene expression patterns of CYC2e1 and CYC2e2 were similar in most of floral organs, CYC2e1 promoted ligule elongation by promoting cell expansion, whereas CYC2e2 showed a weak inhibiting effect on the ray‐floret development, and overexpression of CYC2e2 resulted in the maldevelopment of stamens in disc florets. These results indicated differentiated functions of CYC2e1 and CYC2e2 in the capitulum development of the Anthemideae. Given the previous data that identified CYC2g and CYC2d as main regulators in ligule morphogenesis, we comparatively analyzed 10 Asteraceae genomic data, and identified tandem arrays of CYC2g, CYC2d, and CYC2e. We further investigated the regulatory relationships between CYC2g/CYC2d and CYC2e genes, and found that CYC2g can activate the expression of CYC2e1. The findings of this study elucidate the synergistic roles of CYC2 genes in regulating the formation of the Asteraceae capitula and enhance understanding of the mechanism of duplicated gene retention during plant evolution.

Population structure and natural selection across a flower color polymorphism in the desert plant Encelia farinosa.

Clines-or the geographic sorting of phenotypes across continual space-provide an opportunity to understand the interaction of dispersal, selection, and history in structuring polymorphisms. In this study, we combine field-sampling, genetics, climatic analyses, and machine learning to understand a flower color polymorphism in the wide-ranging desert annual Encelia farinosa. We find evidence for replicated transitions in disk floret color from brown to yellow across spatial scales, with the most prominent cline stretching ~100 km from southwestern United States into México. Because population structure across the cline is minimal, selection is more likely than drift to have an important role in determining cline width. Given that the cline aligns with a climatic transition but there is no evidence for pollinator preference for flower color, we hypothesize that floret color likely varies as a function of climatic conditions.

Nocturnal burst emissions of germacrene D from the open disk florets of pyrethrum flowers induce moths to oviposit on a nonhost and improve pollination success.

Recent studies show that nocturnal pollinators may be more important to ecosystem function and food production than is currently appreciated. Here, we describe an agricultural field study of pyrethrum (Tanacetum cinerariifolium) flower pollination. Pyrethrum is genetically self-incompatible and thus is reliant on pollinators for seed set. Our pollinator exclusion experiment showed that nocturnal insects, particularly moths, significantly contribute to seed set and quality. We discovered that the most abundant floral volatile, the sesquiterpene (-)-germacrene D (GD), is key in attracting the noctuid moths Peridroma saucia and Helicoverpa armigera. Germacrene D synthase (GDS) gene expression regulates the specific GD production and accumulation in flowers, which, in contrast to related species, lose the habit of closing at night. We did observe that female moths also oviposited on pyrethrum leaves and flower peduncles, but found that only a small fraction of those eggs hatched. Larvae were severely stunted in development, most likely due to the presence of pyrethrin defense compounds. This example of exploitative mutualism, which blocks the reproductive success of the moth pollinator and depends on nocturnal interactions, is placed into an ecological context to explain why it may have developed.

Marigold (Tagetes erecta) MADS-Box Genes: A Systematic Analysis and Their Implications for Floral Organ Development

Marigold (Tagetes erecta) has a capitulum with two floret types: sterile ray florets and fertile disc florets. This distinction makes marigold a valuable model for studying floral organ development in Asteraceae, where MADS-box transcription factors play crucial roles. Here, 65 MADS-box genes were identified in the marigold genome, distributed across all 12 chromosomes. These genes were classified into type I (13 genes) and type II (52 genes) according to phylogenetic relationships. The gene structure of type I was simpler than that of type II, with fewer conserved motifs. Type I was further divided into three subclasses, Mα (8 genes), Mβ (2 genes), and Mγ (3 genes), while type II was divided into two groups: MIKCC (50 genes) and MIKC* (2 genes), with MIKCC comprising 13 subfamilies. Many type II MADS-box genes had evolutionarily conserved functions in marigold. Expression analysis of type II genes across different organs revealed organ-specific patterns, identifying 34 genes related to flower organ development. Given the distinct characteristics of the two floret types, four genes were specifically expressed only in the petals of one floret type, while twenty genes were expressed in the stamens of disc florets. These genes might have been related to the formation of different floret types. Our research provided a comprehensive and systematic analysis of the marigold MADS-box genes and laid the foundation for further studies on the roles of MADS-box genes in floral organ development in Asteraceae.

HaMADS3, HaMADS7, and HaMADS8 are involved in petal prolongation and floret symmetry establishment in sunflower (Helianthus annuus L.).

The development of floral organs, crucial for the establishment of floral symmetry and morphology in higher plants, is regulated by MADS-box genes. In sunflower, the capitulum is comprised of ray and disc florets with various floral organs. In the sunflower long petal mutant (lpm), the abnormal disc (ray-like) floret possesses prolongated petals and degenerated stamens, resulting in a transformation from zygomorphic to actinomorphic symmetry. In this study, we investigated the effect of MADS-box genes on floral organs, particularly on petals, using WT and lpm plants as materials. Based on our RNA-seq data, 29 MADS-box candidate genes were identified, and their roles on floral organ development, especially in petals, were explored, by analyzing the expression levels in various tissues in WT and lpm plants through RNA-sequencing and qPCR. The results suggested that HaMADS3, HaMADS7, and HaMADS8 could regulate petal development in sunflower. High levels of HaMADS3 that relieved the inhibition of cell proliferation, together with low levels of HaMADS7 and HaMADS8, promoted petal prolongation and maintained the morphology of ray florets. In contrast, low levels of HaMADS3 and high levels of HaMADS7 and HaMADS8 repressed petal extension and maintained the morphology of disc florets. Their coordination may contribute to the differentiation of disc and ray florets in sunflower and maintain the balance between attracting pollinators and producing offspring. Meanwhile, Pearson correlation analysis between petal length and expression levels of MADS-box genes further indicated their involvement in petal prolongation. Additionally, the analysis of cis-acting elements indicated that these three MADS-box genes may regulate petal development and floral symmetry establishment by regulating the expression activity of HaCYC2c. Our findings can provide some new understanding of the molecular regulatory network of petal development and floral morphology formation, as well as the differentiation of disc and ray florets in sunflower.

The haplotype-resolved genome of diploid Chrysanthemum indicum unveils new acacetin synthases genes and their evolutionary history.

Acacetin, a flavonoid compound, possesses a wide range of pharmacological effects, including antimicrobial, immune regulation, and anticancer effects. Some key steps in its biosynthetic pathway were largely unknown in flowering plants. Here, we present the first haplotype-resolved genome of Chrysanthemum indicum, whose dried flowers contain abundant flavonoids and have been utilized as traditional Chinese medicine. Various phylogenetic analyses revealed almost equal proportion of three tree topologies among three Chrysanthemum species (C. indicum, C. nankingense, and C. lavandulifolium), indicating that frequent gene flow among Chrysanthemum species or incomplete lineage sorting due to rapid speciation might contribute to conflict topologies. The expanded gene families in C. indicum were associated with oxidative functions. Through comprehensive candidate gene screening, we identified five flavonoid O-methyltransferase (FOMT) candidates, which were highly expressed in flowers and whose expressional levels were significantly correlated with the content of acacetin. Further experiments validated two FOMTs (CI02A009970 and CI03A006662) were capable of catalyzing the conversion of apigenin into acacetin, and these two genes are possibly responsible acacetin accumulation in disc florets and young leaves, respectively. Furthermore, combined analyses of ancestral chromosome reconstruction and phylogenetic trees revealed the distinct evolutionary fates of the two validated FOMT genes. Our study provides new insights into the biosynthetic pathway of flavonoid compounds in the Asteraceae family and offers a model for tracing the origin and evolutionary routes of single genes. These findings will facilitate in vitro biosynthetic production of flavonoid compounds through cellular and metabolic engineering and expedite molecular breeding of C. indicum cultivars.

Comparative assessment of anti-ulcer effects: Hydro-ethanolic extract from air-dried ray and disc florets vs essential oil of traditional Tagetes erecta (Asteraceae) in Swiss Albino rats

The Tagetes erecta Linn (family: Asteraceae) herb possesses medicinal and antioxidants value. The herb is traditionally used to treat various ailments, including ulcers. In order to investigate antiulcer activity of T. erecta herb, experimental study was performed between ray and disc florets extracted with 30 parts of water and 70 parts of ethanol solvents using Soxhlet apparatus and leaf's essential oil extracted in Clevenger apparatus by steam distillation method. Two doses of the hydroethanolic extract (400 and 800 mg/kg, Per os) and single dose of essential oil (10 ml/Kg, Per os) were administered for five consecutive days. Rat's pyloric ligation and aspirin (200 mg/kg, Per os) were used to induce acute and chronic gastric ulcers respectively. Antiulcer activity of both the herb's parts was compared on gastric juice parameters (pH, free acidity, total acidity) ulcer-index and ulcer percent protection. The p value of less than 0.05 was considered significant in statistical analysis. Elevation in pH, reduction in free acidity, total acidity and ulcer-index in both the ulcer models confirm that the test drug showed the ulcer-protective activity in rats. Dose-dependent effects were observed in the antiulcer activity of the hydroethanolic extract. However, the leaf's essential oil showed 94 % and 96.93 % ulcer protection in the pyloric ligation and aspirin-induced gastric ulcer models respectively. The hydroethanolic extract and the essential oil may be capable in part, regulating gastric acid secretion pathways or stimulating the cytoprotective secretion of bicarbonate, mucus and prostaglandins. Histological studies supported the observed antiulcer activity of the herb. The essential oil has more potent and significant anti-ulcer activity than hydro-ethanolic extract and respective standard drugs: ranitidine (50 mg/kg, Per os) & pantoprazole (20 mg/kg, Per os). The herb exhibits antiulcer activity, which could be due to the presence of lead phytochemicals: Quercetin-3-methyl ether, quercetin-7-methyl-ether & kaempferol flavonoids in the extract and limonene & terpinolene in leaf's essential oil and, thus, confirmed the traditional uses of T. erecta in the treatment of ulcers. The herb may cure acid pepsin disorders.

Reduction of CO2 emissions through the co-combustion of lignite with biomass residues: Renewable and non-renewable CO2 per produced megajoule and fuel characterization

Accumulation of unmanaged agricultural wastes is related to increased environmental concern, as they usually are left unexploited and/or burned uncontrolled in the fields. The reduction/utilization of these wastes by turning them into solid biofuels for energy production is a viable solution for addressing the related environmental issues. In this study, twelve alternative solid biofuels of biomass residues and lignite (sunflower husk - BSH, stem, disk florets and seeds biodiesel sunflower wastes -BSW, corn husk -HKC, corn stalk and husk -SHC) were mixed with lignite in several proportions and assessed by using energy content analysis, proximate analysis, and ultimate analysis. Empirical chemical formulas were also determined. Furthermore, it introduces a novel concept to separate and quantify the renewable CO2 emissions, from the non-renewable emissions resulting from biomass co-combustion with lignite (alternative solid composite biofuels). The renewable and non-renewable CO2 emissions were expressed per produced megajoule (MJ) and per kilogram (Kg). The non-renewable CO2 emissions per produced MJ of the blends were compared to lignite emissions. The results showed that blends with 70 wt%, 50 wt% and 30 wt% biomass in blend could reduce about 75 %, 57 % and 34 % the non-renewable CO2 emissions per produced MJ, respectively. The present work suggests that blends of agricultural residues with lignite not only could be used as alternative solid biofuels (with better combustion characteristics than lignite sample, e.g. better energy content, less ash content, less Sulphur content, and similar Nitrogen content), but also could help to reduce carbon emissions via the co-combustion process.

Crassothonna moniliformis (Asteraceae, Senecioneae), a new species from the Albany Centre of floristic endemism, South Africa

Crassothonna moniliformis is described as a new species from the Eastern Cape province, South Africa. The species is a prostrate, succulent-leaved perennial herb distinguished from Crassothonna capensis in having slender, weak, trailing, distantly branched stems, with nodal adventitious roots developing precociously, forming diffuse patches to ±50 cm diam., with erect to ascending, usually red-purple, globose-obovoid to obovoid to subclavate leaves 10–25 mm long, and a more slender synflorescence bearing fewer capitula (1–4 per flowering shoot) with fewer ray florets (7–9) and functionally staminate peripheral disc florets. The species is geographically localised, with the known Extent of Occurrence and Area of Occupancy <10 km2, and is habitat-restricted, growing in shallow sandy sediments overlying exposed sandstone pavements among coastal thicket. The single known population is threatened by sand mining and informal housing encroachment. Based on the IUCN Red List categories and criteria, a conservation assessment of Vulnerable (VU – D2) is recommended.

Marigold Like Structure from Methionine Mediated Growth of Positively Charged Gold Nanorod

AbstractDuring morphological evolution of gold nanoparticles, amino acids play a vital role in tuning shape, introducing chirality and inducing facet selective reactivity. Herein, we report the synthesis of unique marigold like structure (MGS) via growth reaction of methionine (Met) incubated positively charged anisotropic gold nanorod (GNR). Varying three important parameters such as growth time, concentration of Met and Au3+ reveals the combination of freshly generated small nucleated particles (fNPs) and GNR towards fabricating the unique MGS containing disk and ray floret parts. Strong interaction between Met and (111) plane of Au0 controls the orientation of (111) plane parallel to the direction of growth. This preferential interaction directs the assembly of gold nanostructures through Au (200) plane and results in merging of fNPs with concave GNR (cGNR) to fabricate the external arrangement of ray floret structure. The structural selectivity is attributed to the electron donating capacity of thioether functional group of Met(S) to Au+, generated prior to secondary nucleation. As confirmed by XPS and ζ‐potential analysis, the above interaction controls the Met concentration dependent inhibition of further Au+→Au0 reduction. The growth strategy of GNR has been further validated with a Met enriched peptide to produce disk and ray florets.

Cla-miR164-NO APICAL MERISTEM (ClNAM) regulates the inflorescence architecture development of Chrysanthemum lavandulifolium.

Chrysanthemum × morifolium has great ornamental and economic value on account of its exquisite capitulum. However, previous studies have mainly focused on the corolla morphology of the capitulum. Such an approach cannot explain the variable inflorescence architecture of the chrysanthemum. Previous research from our group has shown that NO APICAL MERISTEM (ClNAM) is likely to function as a hub gene in capitulum architecture in the early development stage. In the present study, ClNAM was used to investigate the function of these boundary genes in the capitulum architecture of Chrysanthemum lavandulifolium, a closely related species of C. × morifolium in the genus. Modification of ClNAM in C. lavandulifolium resulted in an advanced initiation of the floral primordium at the capitulum. As a result, the receptacle morphology was altered and the number of florets decreased. The ray floret corolla was shortened, but the disc floret was elongated. The number of capitula increased significantly, arranged in more densely compounded corymbose synflorescences. The yeast and luciferase reporter system revealed that ClAP1, ClRCD2, and ClLBD18 target and activate ClNAM. Subsequently, ClNAM targets and activates ClCUC2a/c, which regulates the initiation of floral and inflorescence in C. lavandulifolium. ClNAM was also targeted and cleaved by cla-miR164 in this process. In conclusion, this study established a boundary gene regulatory network with cla-miR164-ClNAM as the hub. This network not only influences the architecture of capitulum, but also affects compound corymbose synflorescences of the C. lavandulifolium. These results provide new insights into the mechanisms regulating inflorescence architecture in chrysanthemum.

Secretory Tissues and Volatile Components of Disc Florets in Several Wild Helianthus L. Species

Although flower pollinator interactions are known to be mediated by floral traits, not enough attention has been paid to the research of secretory tissues and volatile components of sunflower disc florets as potentially important parameters in breeding programs. (1) To our knowledge, this is the first integrated study aimed at better understanding the attractiveness of sunflower capitula to insects. In the study, we have made a very detailed comparative analysis of secretory tissues and the characterization of the volatile components (VOCs) of disc florets in 10 wild perennial Helianthus species. (2) For anatomical analyses, cross-sections were obtained from the nectary zone of disc florets using a cryotechnique procedure. Micromorphological observation and morphological and anatomical analysis of disc florets were performed using light and scanning electron microscopy. For VOCs, we applied headspace, GC-FID, and GC/MS analyses. (3) The obtained results indicate that there is a difference between the analyzed traits among studied species. H. eggertii, H. hirsutus, H. mollis, H. resinosus, and H. tuberosus had high disc diameter values, a high cross-section area and disc floret corolla length, as well as the largest cross-section area and thickness of the disc florets nectary. In the analyzed VOCs, 30 different compounds were detected. The highest yield and quantity of α-Pinene was observed in H. mollis. (4) Inflorescence features, such as receptacle diameter, corolla and secretory tissue properties, and floret VOCs production and characterization, provided valuable information that can be used as guidelines in sunflower breeding programs to maximize pollinator attractiveness and increase seed yield.

Ultrasound-Assisted Extraction of L-Tryptophan from Chamomile Flower: Method Development and Application for Flower Parts Characterization and Varietal Difference

Chamomile has been widely used as a functional tea due to its effects on several neurohormones, some of which are related to tryptophan. An analytical ultrasound-assisted extraction (UAE) technique was successfully optimized and validated to determine tryptophan levels in chamomile flowers. A Box-Behnken design, in conjunction with response surface methodology, was conducted based on 3 factors and 3 levels: Temperature (x1; 30, 50, and 70 °C), solvent composition (x2; 0, 40, and 80% methanol in water), and ultrasonic power (x3; 20, 60, and 100%). The main (x2) and quadratic effect of solvent (x2x2); quadratic of temperature (x1x1) and ultrasonic power (x3x3); also, the interaction of solvent-ultrasonic power (x2x3) and temperature-ultrasonic power (x1x3), significantly affected (p < 0.05) the level of L-tryptophan in the extracts. Optimum extraction conditions were achieved by applying a temperature of 54 °C for 15 min using 17% methanol in water and 69% ultrasonic power. A high recovery (94.26%) was achieved with 2 extraction cycles. The coefficient of variation (CV) demonstrated that the developed method had a satisfactory level of precision (CV < 5%) for repeatability and intermediate precision. To check the applicability of the method, the parts of 2 types of chamomile flowers (German and Roman) were evaluated. This method was successfully applied to characterize chamomile flowers based on L-tryptophan levels. HIGHLIGHTS A novel ultrasound-assisted extraction method was successfully optimized and validated for extracting L-tryptophan from chamomile flowers Solvent composition was the most influential factor in extracting L-tryptophan from chamomile flowers The level of L-tryptophan in ray and disc florets part of Roman dan German chamomile was revealed for the first time GRAPHICAL ABSTRACT

Artemisia kargilensis (Asteraceae), a new species from Ladakh (Trans-Himalaya), India

A new species, Artemisia kargilensis, is described here from Ladakh (Trans-Himalaya), India. The new species can be distinguished from its allied congeners Artemisia salsoloides Willd. and A. saposhnikovii Krasch. ex Poljakov in having leaves sessile, leaf rachis winged, leaf segments linear to linear-lanceolate, capitula globose and upright, pedicel 2–5 mm long, bracteole linear, margins flat, apices acuminate, involucre 3-seriate, outermost phyllary ovate, innermost phyllary broadly obovate, number of marginal female florets 8–18, number of disc florets 16–28, and achenes obovoid.

BSA-seq identified candidate genes and diagnostic KASP markers for anemone type flower in chrysanthemum

Chrysanthemum is one of the most leading commercial flower crops well-known for its flower shape diversity. Anemone type chrysanthemums receive increasing market attention that are distinguished by their pigmented and elongated disk florets. However, there are few reports on quantitative trait loci (QTL) mapping and the identification genes for anemone in chrysanthemum. In this study, bulked segregant analysis coupled with whole-genome sequencing (BSA-seq) approach was employed to detect candidate genomic regions controlling anemone type flower. Two mixed DNA pools composed of 28 anemone type and 20 non-anemone type F1 lines derived from a cross between ‘Nannong Xuefeng’ and ‘Monalisa’ together with two parents were used for high-throughput sequencing. A total of 42 consistent QTLs covering 30.00 Mb were simultaneously identified by |△(SNP/InDel-index)| and Euclidean distance (ED) algorithms based on 15,783,313 SNPs (single-nucleotide polymorphisms) and 1,546,200 small InDels (insertions and deletions). Twenty-two key candidate genes were screened out by a combination of gene functional annotation and transcriptome analysis, in which evm.model.scaffold_915.436 (CBF5), evm.model.scaffold_24.208 (U2AF65A), and a uncharacterized gene evm.model.scaffold_260.201 were highlighted by qRT-PCR. Furtherly, four associations were successfully converted to KASP (kompetitive allele specific PCR) markers, among them, the KASP markers developed for SNP locus Chr6__33961007 and Chr6__179207697 were proven to efficiently discriminate anemone and non-anemone type chrysanthemums being a couple of diagnostic markers in two populations. The results presented herein provide insights for further research on elucidating the formation mechanism of anemone type flower, and the anemone-specific KASP marker will be highly useful for applying MAS to accelerate breeding improvement of chrysanthemum.

Morphological Characteristics and Expression Patterns of CmCYC2c of Different Flower Shapes in Chrysanthemum morifolium

The chrysanthemum is widely used as a cut flower, potted flower, and garden flower worldwide and has high ornamental, edible, and medicinal value. The flower heads, composed of ray florets and disc florets, are the most diverse in terms of morphology among ornamental plants. Here, we compared and analyzed the developmental processes of different capitulum types as well as ray florets and disc florets. Morphological differentiation of the two florets occurred on the dorsal domain of the petals at stage Ⅳ of flower development, and differences in stamen development occurred at stage Ⅴ. The dorsal domain of the ray florets and the early stage of flower development were also an essential site and period, respectively, for the differences among capitulum types. In situ hybridization revealed that CmCYC2c, whose homologs are involved in the specification of floret identity in Asteraceae, was expressed in both the dorsal and ventral domains of the ray petals in the tubular-type chrysanthemum, whereas, it was differentially transcribed in the ray petals of flat- and spoon-type chrysanthemum cultivars and had lower or no expression in the dorsal domain and higher expression in the ventral domain at stage Ⅳ. Our study indicates that the expression pattern of CmCYC2c on the dorsal domain of the ray floret at stage Ⅳ contributes to the formation of diverse flower head types in chrysanthemums.

An updated synopsis of Neurolaena (Neurolaeneae, Asteraceae) with a new species from the Colombian Andes

Neurolaena is a genus native to the Americas and occurring from Mexico to Bolivia, including the Caribbean Islands. It includes shrubs or small trees with alternate leaves, paniculiform capitulescence, discoid or radiate capitula, 3–7-seriate involucre, and pappus with 25–70 bristles. Based on recent taxonomic studies in Neurolaeneae, we provide updates for the infrageneric classification of Neurolaena and recognize the occurrence of disc florets not associated with paleae for the first time in the genus. Furthermore, we describe a new species, N. curtipalea, which is the second species of the genus found in South America and the only species endemic to the Colombian Andes. It can be distinguished from the widespread N. lobata, occurring from Mexico to Bolivia and across the Caribbean Islands, by eucamptodromous (vs. penninervous) venation, radiate (vs. discoid) capitula, 5-seriate (vs. 6-seriate) involucre, paleae shorter (vs. longer) than corolla disc, and disc florets with white (vs. yellow) corollas. The new species is described, illustrated, and mapped, its taxonomic affinities are discussed, and a key to the infrageneric taxa and species belonging to Neurolaena is provided.

A simple, cost effective and novel method of establishment of seeds of wild species and interspecific crosses of niger

In niger, seeds of wild species are smaller than cultivated niger but, flowers of Guizotia scabra are large with more number of ray and disc florets. Seeds of wild species planted directly in the field often fail to establish and plantlet recovery is very low. To overcome these limitations, seeds are planted in different containers with various kinds of potting mixes. A simple method has been developed for raising the wild species of niger using peat pellets. Using this procedure, there was 100% germination as well as 100% plant establishment was observed. This procedure can be successfully be used for all the crops with such difficulties in initial establishment of the plants.

The CmCYC2 factors regulated the different biosynthesis and distribution of phenolic compounds in the capitulum of Chrysanthemum morifolium ‘Hangju’

Chrysanthemum morifolium Ramat. is an important industrial crop with a high medicinal value, whose capitulum consists of ray and disc florets containing numerous bioactive components, such as flavonoids and phenolic acids. However, the distribution and accumulations of the bioactive metabolites in florets of Chrysanthemum morifolium were unclear. Herein, the ray and disc florets of Chrysanthemum morifolium were separated for comparing the bioactive metabolites. The contents of phenolic compounds and antioxidant activities were significantly different between the two florets. The metabolomic analysis identified 203 and 241 differential metabolites between ray and disc florets at two flowering stages. The derivatives of quercetin, isorhamnetin, tricin, and caffeoylquinic acid were enriched in the disc florets, while apigenin, kaempferol, acacetin, and their glycosides mainly accumulated in the ray florets. Besides, the results of transcriptome and qRT-PCR suggested that the F3H, F3′H, and FLS genes highly expressed in disc florets, while the FNS gene was well expressed in ray florets, which explained the different distribution of phenolic compounds between ray and disc florets. Furthermore, the expression of CmCYC2 genes was found to be significantly related to the distribution of flavones by correlation analysis. It was proved by the luciferase reporter assay that CmCYC2a and CmCYC2d factors could bind and activate the CmFNS promoter to regulate the flavones biosynthesis in ray florets. These results revealed the significant difference of metabolite contents and gene expression profiles between ray and disc floret in Chrysanthemum morifolium and demonstrated that the quality of Chrysanthemum morifolium ‘Hangju’ was closely relevant to its flower morphology.

Genome-wide identification of the TCP gene family in Chrysanthemum lavandulifolium and its homologs expression patterns during flower development in different Chrysanthemum species.

TCP proteins, part of the transcription factors specific to plants, are recognized for their involvement in various aspects of plant growth and development. Nevertheless, a thorough investigation of TCPs in Chrysanthemum lavandulifolium, a prominent ancestral species of cultivated chrysanthemum and an excellent model material for investigating ray floret (RF) and disc floret (DF) development in Chrysanthemum, remains unexplored yet. Herein, a comprehensive study was performed to analyze the genome-wide distribution of TCPs in C. lavandulifolium. In total, 39 TCPs in C. lavandulifolium were identified, showing uneven distribution on 8 chromosomes. Phylogenetic and gene structural analyses revealed that ClTCPs were grouped into classes I and II. The class II genes were subdivided into two subclades, the CIN and CYC/TB1 subclades, with members of each clade having similar conserved motifs and gene structures. Four CIN subclade genes (ClTCP24, ClTCP25, ClTCP26, and ClTCP27) contained the potential miR319 target sites. Promoter analysis revealed that ClTCPs had numerous cis-regulatory elements associated with phytohormone responses, stress responses, and plant growth/development. The expression patterns of ClTCPs during capitulum development and in two different florets were determined using RNA-seq and qRT-PCR. The expression levels of TCPs varied in six development stages of capitula; 25 out of the 36 TCPs genes were specifically expressed in flowers. Additionally, we identified six key ClCYC2 genes, which belong to the class II TCP subclade, with markedly upregulated expression in RFs compared with DFs, and these genes exhibited similar expression patterns in the two florets of Chrysanthemum species. It is speculated that they may be responsible for RFs and DFs development. Subcellular localization and transactivation activity analyses of six candidate genes demonstrated that all of them were localized in the nucleus, while three exhibited self-activation activities. This research provided a better understanding of TCPs in C. lavandulifolium and laid a foundation for unraveling the mechanism by which important TCPs involved in the capitulum development.