Identification of anthocyanin and other flavonoids from the green-blue petals of Puya alpestris (Bromeliaceae) and a clarification of their coloration mechanism

Genome assembly and multi-omic analyses reveal the mechanisms underlying flower color formation in Torenia fournieri

Torenia fournieri Lind. is an ornamental plant that is popular for its numerous flowers and variety of colors. However, its genomic evolutionary history and the genetic and metabolic bases of flower color formation remain poorly understood. Here, we report the first T. fournieri reference genome, which was resolved to the chromosome scale and was 164.4 Mb in size. Phylogenetic analyses clarified relationships with other plant species, and a comparative genomic analysis indicated that the shared ancestor of T. fournieri and Antirrhinum majus underwent a whole genome duplication event. Joint transcriptomic and metabolomic analyses identified many metabolites related to pelargonidin, peonidin, and naringenin production in rose (TfR)-colored flowers. Samples with blue (TfB) and deep blue (TfD) colors contained numerous derivatives of petunidin, cyanidin, quercetin, and malvidin; differences in the abundances of these metabolites and expression levels of the associated genes were hypothesized to be responsible for variety-specific differences in flower color. Furthermore, the genes encoding flavonoid 3-hydroxylase, anthocyanin synthase, and anthocyanin reductase were differentially expressed between flowers of different colors. Overall, we successfully identified key genes and metabolites involved in T. fournieri flower color formation. The data provided by the chromosome-scale genome assembly establish a basis for understanding the differentiation of this species and will facilitate future genetic studies and genomic-assisted breeding.

Floral pigments and their perception by avian pollinators in three Chilean Puya species

The Chilean Puya species, Puya coerulea var. violacea and P. chilensis bear blue and pale-yellow flowers, respectively, while P. alpestris considered to be their hybrid-derived species has unique turquoise flowers. In this study, the chemical basis underlying the different coloration of the three Puya species was explored. We first isolated and identified three anthocyanins: delphinidin 3,3',5'-tri-O-glucoside, delphinidin 3,3'-di-O-glucoside and delphinidin 3-O-glucoside; seven flavonols: quercetin 3-O-rutinoside-3'-O-glucoside, quercetin 3,3'-di-O-glucoside, quercetin 3-O-rutinoside, isorhamnetin 3-O-rutinoside, myricetin 3,3',5'-tri-O-glucoside, myricetin 3,3'-di-O-glucoside and laricitrin 3,5'-di-O-glucoside; and six flavones: luteolin 4'-O-glucoside, apigenin 4'-O-glucoside, tricetin 4'-O-glucoside, tricetin 3',5'-di-O-glucoside, tricetin 3'-O-glucoside and selagin 5'-O-glucoside, which is a previously undescribed flavone, from their petals. We also compared compositions of floral flavonoid and their aglycone among these species, which suggested that the turquoise species P. alpestris has an essentially intermediate composition between the blue and pale-yellow species. The vacuolar pH was relatively higher in the turquoise (pH 6.2) and pale-yellow (pH 6.2) flower species, while that of blue flower species was usual (pH 5.2). The flower color was reconstructed in vitro using isolated anthocyanin, flavonol and flavone at neutral and acidic pH, and its color was analyzed by reflectance spectra and the visual modeling of their avian pollinators. The modeling demonstrated that the higher pH of the turquoise and pale-yellow species enhances the chromatic contrast and spectral purity. The precise regulation of flower color by flavonoid composition and vacuolar pH may be adapted to the visual perception of their avian pollinator vision.

Analysis of flavonoid metabolism of compounds in succulent fruits and leaves of three different colors of Rosaceae

Red flesh apple (Malus pumila var. medzwetzkyana Dieck), purple leaf plum (Prunus cerasifera Ehrhar f), and purple leaf peach (Prunus persica 'Atropurpurea') are significant ornamental plants within the Rosaceae family. The coloration of their fruits and leaves is crucial in their appearance and nutritional quality. However, qualitative and quantitative studies on flavonoids in the succulent fruits and leaves of multicolored Rosaceae plants are lacking. To unveil the diversity and variety-specificity of flavonoids in these three varieties, we conducted a comparative analysis of flavonoid metabolic components using ultra-high-performance liquid phase mass spectrometry (UPLC-MS/MS). The results revealed the detection of 311 metabolites, including 47 flavonoids, 105 flavonols, 16 chalcones, 37 dihydroflavonoids, 8 dihydroflavonols, 30 anthocyanins, 14 flavonoid carbon glycosides, 23 flavanols, 8 isoflavones, 11 tannins, and 12 proanthocyanidins. Notably, although the purple plum and peach leaves exhibited distinct anthocyanin compounds, paeoniflorin and corythrin glycosides were common but displayed varying glycosylation levels. While the green purple leaf peach fruit (PEF) and red flesh apple leaf (AL) possessed the lowest anthocyanin content, they exhibited the highest total flavonoid content. Conversely, the red flesh apple fruit (AF) displayed the highest anthocyanin content and a diverse range of anthocyanin glycosylation modifications, indicating that anthocyanins predominantly influenced the fruit's color. Purple PLF, PLL, and PEL showcased varying concentrations of anthocyanins, suggesting that their colors result from the co-color interaction between specific types of anthocyanins and secondary metabolites, such as flavonols, flavonoids, and dihydroflavonoids. This study provides novel insights into the variations in tissue metabolites among Rosaceae plants with distinct fruit and leaf colors.

Many different flowers make a bouquet: Lessons from specialized metabolite diversity in plant-pollinator interactions

Flowering plants have evolved extraordinarily diverse metabolites that underpin the floral visual and olfactory signals enabling plant-pollinator interactions. In some cases, these metabolites also provide unusual rewards that specific pollinators depend on. While some metabolites are shared by most flowering plants, many have evolved in restricted lineages in response to the specific selection pressures encountered within different niches. The latter are designated as specialized metabolites. Recent investigations continue to uncover a growing repertoire of unusual specialized metabolites. Increased accessibility to cutting-edge multi-omics technologies (e.g. genome, transcriptome, proteome, metabolome) is now opening new doors to simultaneously uncover the molecular basis of their synthesis and their evolution across diverse plant lineages. Drawing upon the recent literature, this perspective discusses these aspects and, where known, their ecological and evolutionary relevance. A primer on omics-guided approaches to discover the genetic and biochemical basis of functional specialized metabolites is also provided.

Assessment of metabolic, mineral, and cytotoxic profile in pineapple leaves of different commercial varieties: A new eco-friendly and inexpensive source of bioactive compounds

Pineapple is among the most produced and consumed fruits worldwide, and consequently, its agroindustrial production/processing generates high amounts of agricultural waste, which are routinely discarded. Thus, it is crucial to seek alternatives to reuse this agricultural waste that are in high availability. Therefore, this work aims to evaluate the chemical composition of a specific residue (leaves) of seven commercial varieties of pineapples, to attribute high added value uses, and to evaluate its potential as a source of secondary metabolites and minerals. Thereby, twenty-eight metabolites were annotated by UPLC-QTOF-MS^E, including amino acids, organic acids, and phenolic compounds. The following minerals were quantitatively assessed by ICP-OES: Zn (5.30-19.77 mg kg^-1), Cr, Cd, Mn (50.80-113.98 mg kg^-1), Cu (1.05-4.01 mg kg^-1), P (1030.77-6163.63 mg kg^-1) and Fe (9.06-70.17 mg kg^-1). In addition, Cr and Cd (toxic materials) present concentration levels below the limit of quantification of the analytical method (LOQ_Cr and LOQ_Cd = 0.02 mg kg^-1) for all samples. The multivariate analysis was conceived from the chemical profile, through the tools of PCA (principal component analysis) and HCA (hierarchical cluster analysis). The results show that pineapple leaves have similarities and differences concerning their chemical composition. In addition, the cytotoxicity assays of the extracts against tumor and non-tumor strains shows that the extracts were non-toxic. This fact can corroborate and enhance the prospection of new uses and applications of agroindustrial co-products from pineapple, enabling the evaluation and use in different types of industries, such as pharmacological, cosmetic, and food, in addition to the possibility of being a potential source of bioactive compounds.

Different color regulation mechanism in willow barks determined using integrated metabolomics and transcriptomics analyses

BACKGROUND

The rich yellow-orange to vividly deep red bark of willow (Salix spp.) branches have high ornamental and economic value. However, the mechanism underlying the regulation of willow branch color remains unknown. Therefore, we performed metabolomics and transcriptomics analyses of purple, green, and red willow barks to elucidating the mechanisms regulating color development.

RESULTS

Seven anthocyanins were isolated; pelargonidin, petunidin 3-O-rutinoside, and cyanin chloride were the most abundant in red bark, whereas pelargonin chloride was most abundant in purple bark. The green bark contained the highest level of malvidin; however, the malvidin level was not significantly higher than in the red bark. The purple bark contained the largest amount of canthaxanthin, a carotenoid pigment. The integrated pathways of flavonoid biosynthesis, carotenoid biosynthesis, and porphyrin and chlorophyll metabolism were constructed for the willow barks. Among the three barks, the expression of the structural genes ANS, ANR, and BZ1, which are involved in anthocyanin synthesis, was the highest in red bark, likely causing anthocyanin accumulation. The expression of CrtZ, which participates in the carotenoid pathway, was the highest in purple bark, likely leading to canthaxanthin accumulation. The high expression of DVR, POR, and CRD1 may be associated with green pigment synthesis in the chlorophyll biosynthesis pathway.

CONCLUSIONS

Purple bark color is co-regulated by anthocyanins and carotenoids, whereas red bark is characterized by anthocyanin accumulation and chlorophyll degradation. The green pigment is regulated by maintaining chlorophyll synthesis. BZ1 and CrtZ are candidate genes regulating anthocyanin and canthaxanthin accumulation in red and purple barks respectively. Collectively, our results may facilitate the genetic breeding and cultivation of colorful willows with improved color and luster.

Flavonoids and phenylethanoids from the flowers and leaves of Aeschynanthus species and cultivars (Gesneriaceae)

Forty-one flavones, each one of flavonol, chalcone and dihydroflavonol, two flavanones, and four phenylethanoids were isolated from corollas, calyces and leaves of two Aeschynanthus species, A. fulgens and A. pulcher, and six cultivars, 'Mahligai', 'Mona Lisa', SoeKa', 'Redona', 'Freshya' and 'Bravera'. Flavonoids were mainly the glucuronides and/or methylglucuronides based on hispidulin, nepetin, pectolinarigenin, 6-hydroxyluteolin, scutellarein, apigenin and luteolin, and identified by UV spectra, HR-MS, LC-MS, acid hydrolysis, NMR, and/or HPLC and TLC comparisons with authentic samples. Of these flavonoids, twelve, i.e. hispidulin 7,4'-di-O-glucuronide, 7,4'-di-O-methylglucuronide, 7-O-methylglucuronide-4'-O-glucuronide, 7-O-glucuronide-4'-O-methylglucuronide, 7-O-glucosyl-(1 → 2)-glucuronide and 8-C-glucoside, nepetin 7,4'-di-O-glucuronide, 7-O-glucuronide-4'-O-methylglucuronide and 7-O-methylglucuronide-4'-O-glucuronide, pectolinarigenin 7-O-glucosyl-(1 → 2)-glucuronide and 7-O-xylosyl-(1 → 2)-(6″-malonylglucoside), and 6-hydroxyluteolin 7,4'-di-O-glucuronide, were previously undescribed.

Glycosylation of luteolin in hydrophilic organic solvents and structure–antioxidant relationships of luteolin glycosides

An effective approach was developed to biotransform luteolin glycosides in hydrophilic organic solvents. Bacillus cereus A46 cells showed high activity and stability in 5–20% (v/v) DMSO with 90–98% conversion rates of luteolin glycosides. Five glycosides of luteolin 7-O-β-glucoside, luteolin 4′-O-β-glucoside, luteolin 3′-O-β-glucoside, luteolin 7,3′-di-O-β-glucoside and luteolin 7,4′-di-O-β-glucoside were obtained. The addition of DMSO greatly promoted the solubility of luteolin and further regulated the formation of the main products from five luteolin glycosides to luteolin 7-O-β-glucoside (931.2 μM). Fourteen flavonoids and anthraquinones were used as tentative substrates. Glycosylation positions were located at the C-7, C-3′ or C4′ hydroxyl groups of flavonoids and C-5 hydroxyl group of anthraquinones. The 3′,4′-dihydroxy arrangement played the key role for the antioxidant activity of luteolin.

Efficient glycosylation of luteolin in organic solvents and the structure–antioxidant relationships of luteolin glycosides were reported for the first time.