Engineering anthocyanin biosynthesis in plants

Metabolome and Transcriptome Analyses Reveal Flower Color Differentiation Mechanisms in Various Sophora japonica L. Petal Types

Sophora japonica L. is an important landscaping and ornamental tree species throughout southern and northern parts of China. The most common color of S. japonica petals is yellow and white. In this study, S. japonica flower color mutants with yellow and white flag petals and light purple-red wing and keel petals were used for transcriptomics and metabolomics analyses. To investigate the underlying mechanisms of flower color variation in S. japonica 'AM' mutant, 36 anthocyanin metabolites were screened in the anthocyanin-targeting metabolome. The results demonstrated that cyanidins such as cyanidin-3-O-glucoside and cyanidin-3-O-rutinoside in the 'AM' mutant were the key metabolites responsible for the red color of the wing and keel petals. Transcriptome sequencing and differentially expressed gene (DEG) analysis identified the key structural genes and transcription factors related to anthocyanin biosynthesis. Among these, F3'5'H, ANS, UFGT79B1, bHLH, and WRKY expression was significantly correlated with the cyanidin-type anthocyanins (key regulatory factors affecting anthocyanin biosynthesis) in the flag, wing, and keel petals in S. japonica at various flower development stages.

Genus Amorphophallus: A Comprehensive Overview on Phytochemistry, Ethnomedicinal Uses, and Pharmacological Activities

The genus Amorphophallus belongs to the family Araceae. Plants belonging to this genus are available worldwide and have been used in traditional medicines since ancient times, mainly in Ayurveda and Unani medical practices. Amorphophallus species are an abundant source of polyphenolic compounds; these are accountable for their pharmacological properties, such as their analgesic, neuroprotective, hepatoprotective, anti-inflammatory, anticonvulsant, antibacterial, antioxidant, anticancer, antiobesity, and immunomodulatory effects, as well as their ability to prevent gastrointestinal disturbance and reduce blood glucose. Moreover, Amorphophallus species contain numerous other classes of chemical compounds, such as alkaloids, steroids, fats and fixed oils, tannins, proteins, and carbohydrates, each of which contributes to the pharmacological effects for the treatment of acute rheumatism, tumors, lung swelling, asthma, vomiting, abdominal pain, and so on. Additionally, Amorphophallus species have been employed in numerous herbal formulations and pharmaceutical applications. There has been no extensive review conducted on the Amorphophallus genus as of yet, despite the fact that several experimental studies are being published regularly discussing these plants' pharmacological properties. So, this review discusses in detail the pharmacological properties of Amorphophallus species. We also discuss phytochemical constituents in the Amorphophallus species and their ethnomedicinal uses and toxicological profiles.

Natural Sources of Food Colorants as Potential Substitutes for Artificial Additives

In recent years, the demand of healthier food products and products made with natural ingredients has increased overwhelmingly, led by the awareness of human beings of the influence of food on their health, as well as by the evidence of side effects generated by different ingredients such as some additives. This is the case for several artificial colorants, especially azo colorants, which have been related to the development of allergic reactions, attention deficit and hyperactivity disorder. All the above has focused the attention of researchers on obtaining colorants from natural sources that do not present a risk for consumption and, on the contrary, show biological activity. The most representative compounds that present colorant capacity found in nature are anthocyanins, anthraquinones, betalains, carotenoids and chlorophylls. Therefore, the present review summarizes research published in the last 15 years (2008-2023) in different databases (PubMed, Scopus, Web of Science and ScienceDirect) encompassing various natural sources of these colorant compounds, referring to their obtention, identification, some of the efforts made for improvements in their stability and their incorporation in different food matrices. In this way, this review evidences the promising path of development of natural colorants for the replacement of their artificial counterparts.

The Adaptive Role of Carotenoids and Anthocyanins in Solanum lycopersicum Pigment Mutants under High Irradiance

The effects of high-intensity light on the pigment content, photosynthetic rate, and fluorescence parameters of photosystem II in high-pigment tomato mutants (hp 3005) and low-pigment mutants (lp 3617) were investigated. This study also evaluated the dry weight percentage of low molecular weight antioxidant capacity, expression patterns of some photoreceptor-regulated genes, and structural aspects of leaf mesophyll cells. The 3005 mutant displayed increased levels of photosynthetic pigments and anthocyanins, whereas the 3617 mutant demonstrated a heightened content of ultraviolet-absorbing pigments. The photosynthetic rate, photosystem II activity, antioxidant capacity, and carotenoid content were most pronounced in the high-pigment mutant after 72 h exposure to intense light. This mutant also exhibited an increase in leaf thickness and water content when exposed to high-intensity light, suggesting superior physiological adaptability and reduced photoinhibition. Our findings indicate that the enhanced adaptability of the high-pigment mutant might be attributed to increased flavonoid and carotenoid contents, leading to augmented expression of key genes associated with pigment synthesis and light regulation.

Molecular mechanism controlling anthocyanin composition and content in radish plants with different root colors

Radish (Raphanus sativus) roots exhibit various colors that reflect their anthocyanin compositions and contents. However, the details of the mechanism linking the expression of anthocyanin biosynthesis and their transcriptional regulators to anthocyanin composition in radish roots remained unknown. Here, we characterized the role of the anthocyanin biosynthetic enzyme flavonoid 3'-hydroxylase (RsF3'H), together with the R2R3 MYB transcription factor (TF) RsMYB1 and the basic helix-loop-helix (bHLH) TF TRANSPARENT TESTA 8 (RsTT8), in four radish plants with different root colors: white (W), deep red (DR), dark purple (DP), and dark greyish purple (DGP). The DR plant contained heterozygous for RsF3'H with low expression level and accumulated a large amount of pelargonidin, resulting in deep red color. While, the DP and DGP plants accumulated the cyanidin due to the higher expression level of functional RsF3'H. Notably, RsMYB1 and RsTT8 transcripts were abundant in all pigmented roots, but not in white roots. To investigate the differential expression of RsMYB1 and RsTT8, we compared the sequences of their promoter regions among the four radish plants, revealing variations in the numbers of cis-elements and in promoter architecture. Promoter activation assays demonstrated that variation in the RsMYB1 and RsTT8 promoters may contribute to the expression level of these genes, and RsMYB1 can activate its own expression as well as promote the RsTT8 expression. These results suggested that RsF3'H plays a vital role in anthocyanin composition and the expression level of both RsMYB1 and RsTT8 are crucial determinants for anthocyanin content in radish roots. Overall, these findings provide insight into the molecular basis of anthocyanin composition and level in radish roots.

Whole-genome and genome-wide association studies improve key agricultural traits of safflower for industrial and medicinal use

Safflower (Carthamus tinctorius) is widely cultivated around the world for its seeds and flowers. The presence of linoleic acid (LA) in its seeds and hydroxysafflor yellow A (HSYA) in its flowers are the crucial traits that enable safflower to be used for industrial and medicinal purposes. Understanding the genetic control of these traits is essential for optimizing the quality of safflower and its breeding. To further this research, we present a chromosome-scale assembly of the genome of the safflower variety 'Chuanhonghua 1', which was achieved using an integrated strategy combining Illumina, Oxford Nanopore, and Hi-C sequencing. We obtained a 1.17-Gb assembly with a contig N50 of 1.08 Mb, and all assembled sequences were assigned to 12 pseudochromosomes. Safflower's evolution involved the core eudicot γ-triplication event and a whole-genome duplication event, which led to large-scale genomic rearrangements. Extensive genomic shuffling has occurred since the divergence of the ancestor of dicotyledons. We conducted metabolite and transcriptome profiles with time- and part-dependent changes and screened candidate genes that significantly contribute to seed lipid biosynthesis. We also analyzed key gene families that participate in LA and HSYA biosynthesis. Additionally, we re-sequenced 220 safflower lines and carried out a genome-wide association study using high-quality SNP data for eight agronomic traits. We identified SNPs related to important traits in safflower. Besides, the candidate gene HH_034464 (CtCGT1) was shown to be involved in the biosynthesis of HSYA. Overall, we provide a high-quality reference genome and elucidate the genetic basis of LA and HSYA biosynthesis in safflower. This vast amount of data will benefit further research for functional gene mining and breeding in safflower.

Molecular mechanism of different flower color formation of Cymbidium ensifolium

Cymbidium ensifolium is one of the national orchids in China, which has high ornamental value with changeable flower colors. To understand the formation mechanism of different flower colors of C. ensifolium, this research conducted transcriptome and metabolome analyses on four different colored sepals of C. ensifolium. Metabolome analysis detected 204 flavonoid metabolites, including 17 polyphenols, 27 anthocyanins, 75 flavones, 34 flavonols, 25 flavonoids, 18 flavanones, and 8 isoflavones. Among them, purple-red and red sepals contain a lot of anthocyanins, including cyanidin, pelargonin, and paeoniflorin, while yellow-green and white sepals have less anthocyanins detected, and their metabolites are mainly flavonols, flavanones and flavonoids. Transcriptome sequencing analysis showed that the expression levels of the anthocyanin biosynthetic enzyme genes in red and purple-red sepals were significantly higher than those in white and yellow-green sepals of C. ensifolium. The experimental results showed that CeF3'H2, CeDFR, CeANS, CeF3H and CeUFGT1 may be the key genes involved in anthocyanin production in C. ensifolium sepals, and CeMYB104 has been proved to play an important role in the flower color formation of C. ensifolium. The results of transformation showed that the CeMYB104 is involved in the synthesis of anthocyanins and can form a purple-red color in the white perianth of Phalaenopsis. These findings provide a theoretical reference to understand the formation mechanism of flower color in C. ensifolium.

Chromosome-scale genome assembly provides insights into flower coloration mechanisms of Canna indica

Canna indica, which produce conspicuous and colorful flowers, are widely appreciated as ornamental plants. We used Pacific Biosciences sequencing (PacBio) and chromosome conformation capture (Hi-C) genome scaffolding to build a high-quality chromosome-scale genome assembly of C. indica and the genome assembly was 821Mb with a contig N50 of 48Mb assembled into nine chromosomes. The genome of C. indica was predicted to contain 31,130 genes and 30,816 genes were functionally annotated. Genome annotation identified 522 Mb (63.59 %) as repetitive sequences. Genome evolution analysis showed that whole-genome duplication occurred 53.4 million years ago. Transcriptome analysis revealed that petal coloration was linked with the expression of genes encoding enzymes involved in anthocyanin biosynthesis, carotenoid biosynthesis, and the methylerythritol phosphate (MEP) pathway. Furthermore, modules of co-expressed genes and hub genes were identified via weighted gene co-expression network analysis. These results suggested that, in Canna indica, deep red petal coloration was regulated by CHS2 and yellow petal coloration was associated with expression of ARF6 and NAC14. Considered together, the current study revealed a high-quality reference genome which may provide new insights into the molecular basis of flower coloration in Canna indica and help enhance the conservation and breeding of ornamental plants in general.

Deciphering the regulatory network of the NAC transcription factor FvRIF, a key regulator of strawberry (Fragaria vesca) fruit ripening

The NAC transcription factor ripening inducing factor (RIF) was previously reported to be necessary for the ripening of octoploid strawberry (Fragaria × ananassa) fruit, but the mechanistic basis of RIF-mediated transcriptional regulation and how RIF activity is modulated remains elusive. Here, we show that FvRIF in diploid strawberry, Fragaria vesca, is a key regulator in the control of fruit ripening and that knockout mutations of FvRIF result in a complete block of fruit ripening. DNA affinity purification sequencing coupled with transcriptome deep sequencing suggests that 2,080 genes are direct targets of FvRIF-mediated regulation, including those related to various aspects of fruit ripening. We provide evidence that FvRIF modulates anthocyanin biosynthesis and fruit softening by directly regulating the related core genes. Moreover, we demonstrate that FvRIF interacts with and serves as a substrate of MAP kinase 6 (FvMAPK6), which regulates the transcriptional activation function of FvRIF by phosphorylating FvRIF at Thr-310. Our findings uncover the FvRIF-mediated transcriptional regulatory network in controlling strawberry fruit ripening and highlight the physiological significance of phosphorylation modification on FvRIF activity in ripening.

An arginine-to-histidine mutation in flavanone-3-hydroxylase results in pink strawberry fruits

Fruit color is a very important external commodity factor for consumers. Compared to the most typical red octoploid strawberry (Fragaria × ananassa), the pink strawberry often sells for a more expensive price and has a higher economic benefit due to its outstanding color. However, few studies have examined the molecular basis of pink-colored strawberry fruit. Through an EMS mutagenesis of woodland strawberry (Fragaria vesca), we identified a mutant with pink fruits and green petioles. Bulked-segregant analysis sequencing analysis and gene function verification confirmed that the responsible mutation resides in a gene encoding flavanone-3-hydroxylase (F3H) in the anthocyanin synthesis pathway. This nonsynonymous mutation results in an arginine-to-histidine change at position 130 of F3H. Molecular docking experiments showed that the arginine-to-histidine mutation results in a reduction of intermolecular force-hydrogen bonding between the F3H protein and its substrates. Enzymatic experiments showed a greatly reduced ability of the mutated F3H protein to catalyze the conversion of the substrates and hence a blockage of the anthocyanin synthesis pathway. The discovery of a key residue in the F3H gene controlling anthocyanin synthesis provides a clear target of modification for the molecular breeding of strawberry varieties with pink-colored fruits, which may be of great commercial value.

Combined Metabolome and Transcriptome Analysis of Creamy Yellow and Purple Colored Panax notoginseng Roots

Panax notoginseng (Burk.) F.H. Chen is a species of the Araliaceae family that inhabits southwestern China, Burma, and Nepal. It is cultivated on a commercial scale in Yunnan province, China, owing to its significance in traditional Chinese medicine. Panax notoginseng roots are usually yellow-white (HS); however, purple roots (ZS) have also been reported. The majority of P. notoginseng research has concentrated on the identification and production of natural chemicals in HS; however, there is little to no information about the composition of ZS. Using UPLC-MS/MS, we investigated the global metabolome profile of both ZS- and HS-type roots and discovered 834 metabolites from 11 chemical groups. There were 123 differentially accumulated metabolites (DAM) in the HS and ZS roots, which were classified as lipids and lipid-like molecules, polyketides, organoheterocyclic chemicals, and organooxygen compounds. We investigated the associated compounds in the DAMs because of the importance of anthocyanins in color and saponins and ginsenosides in health benefits. In general, we discovered that pigment compounds such as petunidin 3-glucoside, delphinidin 3-glucoside, and peonidin-3-O-beta-galactoside were more abundant in ZS. The saponin (eight compounds) and ginsenoside (26 compounds) content of the two varieties of roots differed as well. Transcriptome sequencing revealed that flavonoid and anthocyanin production genes were more abundant in ZS than in HS. Similarly, we found differences in gene expression in genes involved in terpenoid production and related pathways. Overall, these findings suggest that the purple roots of P. notoginseng contain varying amounts of ginsenosides and anthocyanins compared to roots with a creamy yellow color.

Integrated Metabolome and Transcriptome Analysis of Petal Anthocyanin Accumulation Mechanism in Gloriosa superba 'Rothschildiana' during Different Flower Development Stages

Flower color is a key ornamental trait in plants. The petals of Gloriosa superba 'Rothschildiana' petals undergo a color transformation from yellow to red during their development, but the molecular mechanism of this process remains unexplored. This study examines the anthocyanin profiles and gene expression patterns of 'Rothschildiana' petals across four developmental stages: bud (S1), initial opening (S2), half opening (S3), and full opening stage (S4). A total of 59 anthocyanins were identified with significant increases in cyanidin-3,5-O-diglucoside, cyanidin-3-O-glucoside, pelargonidin-3-O-glucoside, and pelargonidin-3,5-O-diglucoside levels observed during petal maturation. Transcriptome analysis revealed 46 differentially expressed genes implicated in flavonoid and anthocyanin biosynthesis. Additionally, three gene modules were found to be associated with anthocyanin accumulation throughout flower development. Expression levels of genes associated with auxin, abscisic acid, brassinosteroid signaling, and transcription factors such as NACs and WRKYs underwent significant changes and exhibited strong correlations with several flavonoid and anthocyanin biosynthetic genes in these modules. These findings offer novel insights into the molecular underpinnings of flower color variation and lay the groundwork for the improvement of G. superba.

Heterologous Expression of Platycodon grandiflorus PgF3'5'H Modifies Flower Color Pigmentation in Tobacco

Flavonoid-3',5'-hydroxylase (F3'5'H) is the key enzyme for the biosynthesis of delphinidin-based anthocyanins, which are generally required for purple or blue flowers. Previously, we isolated a full-length cDNA of PgF3'5'H from Platycodon grandiflorus, which shared the highest homology with Campanula medium F3'5'H. In this study, PgF3'5'H was subcloned into a plant over-expression vector and transformed into tobacco via Agrobacterium tumefaciens to investigate its catalytic function. Positive transgenic tobacco T0 plants were obtained by hygromycin resistance screening and PCR detection. PgF3'5'H showed a higher expression level in all PgF3'5'H transgenic tobacco plants than in control plants. Under the drive of the cauliflower mosaic virus (CaMV) 35S promoter, the over-expressed PgF3'5'H produced dihydromyricetin (DHM) and some new anthocyanin pigments (including delphinidin, petunidin, peonidin, and malvidin derivatives), and increased dihydrokaempferol (DHK), taxifolin, tridactyl, cyanidin derivatives, and pelargonidin derivatives in PgF3'5'H transgenic tobacco plants by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) analysis, resulting in a dramatic color alteration from light pink to magenta. These results indicate that PgF3'5'H products have F3'5'H enzyme activity. In addition, PgF3'5'H transfer alters flavonoid pigment synthesis and accumulation in tobacco. Thus, PgF3'5'H may be considered a candidate gene for gene engineering to enhance anthocyanin accumulation and the molecular breeding project for blue flowers.

Comparative Transcriptome and Metabolome Profiling Reveal Mechanisms of Red Leaf Color Fading in Populus × euramericana cv. 'Zhonghuahongye'

Anthocyanins are among the flavonoids that serve as the principal pigments affecting the color of plants. During leaf growth, the leaf color of 'Zhonghuahongye' gradually changes from copper-brown to yellow-green. At present, the mechanism of color change at different stages has not yet been discovered. To find this, we compared the color phenotype, metabolome, and transcriptome of the three leaf stages. The results showed that the anthocyanin content of leaves decreased by 62.5% and the chlorophyll content increased by 204.35%, 69.23%, 155.56% and 60%, respectively. Differential metabolites and genes were enriched in the pathway related to the synthesis of 'Zhonghuahongye' flavonoids and anthocyanins and to the biosynthesis of secondary metabolites. Furthermore, 273 flavonoid metabolites were detected, with a total of eight classes. DFR, FLS and ANS downstream of anthocyanin synthesis may be the key structural genes in reducing anthocyanin synthesis and accumulation in the green leaf of 'Zhonghuahongye'. The results of multi-omics analysis showed that the formation of color was primarily affected by anthocyanin regulation and its related synthesis-affected genes. This study preliminarily analyzed the green regression gene and metabolic changes in 'Zhonghuahongye' red leaves and constitutes a reference for the molecular breeding of 'Zhonghuahongye' red leaves.

Family characteristics, phylogenetic reconstruction, and potential applications of the plant BAHD acyltransferase family

The BAHD acyltransferase family is a class of proteins in plants that can acylate a variety of primary and specialized secondary metabolites. The typically acylated products have greatly improved stability, lipid solubility, and bioavailability and thus show significant differences in their physicochemical properties and pharmacological activities. Here, we review the protein structure, catalytic mechanism, and phylogenetic reconstruction of plant BAHD acyltransferases to describe their family characteristics, acylation reactions, and the processes of potential functional differentiation. Moreover, the potential applications of the BAHD family in human activities are discussed from the perspectives of improving the quality of economic plants, enhancing the efficacy of medicinal plants, improving plant biomass for use in biofuel, and promoting stress resistance of land plants. This review provides a reference for the research and production of plant BAHD acyltransferases.

Encapsulation of purple basil leaf extract by electrospraying in double emulsion (W/O/W) filled alginate-carrageenan beads to improve the bioaccessibility of anthocyanins

The purple basil leaf extract (PBLE) was encapsulated in double emulsion (W1/O/W2)-loaded beads (emulgel) by electrospraying. The influence of κ-carrageenan (κ-CG) and cross-linking agents (Ca2+/K+) on the properties of alginate (SA) beads were assessed. In emulgel beads, κ-CG inclusion resulted in larger sizes and more distorted shapes, wrinkles on the surface, and lower gel strength. The encapsulation efficiency of anthocyanins (ACNs) in emulgel beads ranged from 70.73 to 87.89 %, whereas it ranged from 13.50 to 20.67 % in emulsion-free (hydrogel) beads. Fourier transforms infrared (FTIR) revealed the crosslinking of SA and κ-CG with Ca2+ and K+, thermogravimetric analysis (TGA), derivative thermogravimetric (DTG), and differential scanning calorimetry (DSC) thermograms showed emulgel beads yielded higher thermal stability. The emulgel beads elevated the in vitro bioaccessibility of ACNs under simulated digestion. At the gastric phase, 86 % of ACNs in PBLE, and 46 % of loaded ACNs in hydrogel beads were released, whereas no release was occurred in emulgel beads. At the intestinal phase, after 150 min of digestion, no ACNs were detected in PBLE and hydrogel beads, whereas all emulgel beads continued to release ACNs until 300 min. The incorporation of double emulsions in hydrogel beads can be utilized in the development of functional foods.

Effect of drought acclimation on antioxidant system and polyphenolic content of Foxtail Millet (Setaria italica L.)

The impact of climate change-induced drought stress on global food security and environmental sustainability is a serious concern. While previous research has highlighted the potential benefits of drought hardening in improving plants' ability to withstand drought, the exact underlying physiological mechanisms in millet plants (Setaria italica L.) have not been explored. This study aimed to investigate the impact of drought hardening on antioxidant defense and polyphenol accumulation in different millet genotypes ('PI 689680' and 'PI 662292') subjected to different treatments: control (unstressed), drought acclimation (two stress episodes with recovery), and non-acclimation (single stress episode with no recovery). The results showed that drought stress led to higher levels of polyphenols and oxidative damage, as indicated by increased phenolic, flavonoid, and anthocyanin levels. Non-acclimated (NA) plants experienced more severe oxidative damage and inhibition of enzymes associated with the ascorbate glutathione cycle compared to drought-acclimated plants. NA plants also exhibited a significant reduction in photosynthesis and tissue water content. The expression of genes related to antioxidants and polyphenol synthesis was more pronounced in non-acclimated plants. The study demonstrated that drought hardening not only prepared plants for subsequent drought stress but also mitigated damage caused by oxidative stress in plant physiology. Drought-acclimated (DA) plants displayed improved drought tolerance, as evidenced by better growth, photosynthesis, antioxidant defense, polyphenol accumulation, and gene expression related to antioxidants and polyphenol synthesis. In conclusion, the research advocates for the use of drought hardening as an effective strategy to alleviate the negative impacts of drought-induced metabolic disturbances in millet.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01366-w.

New insights into the genetic manipulation of the R2R3-MYB and CHI gene families on anthocyanin pigmentation in Petunia hybrida

Several R2R3-MYB genes control anthocyanin pigmentation in petunia, and ANTHOCYANIN-2 (AN2) is treated as the main player in petal limbs. However, the actual roles of R2R3-MYBs in the coloration of different floral tissues in the so called "darkly-veined" petunias are still not clear. The genetic background and expression of AN2 paralogs from various petunias with different color patterns were identified. All "darkly-veined" genotypes have the identical mutation in the AN2 gene, but express a different functional paralog - ANTHOCYANIN-4 (AN4) - abundantly in flowers. Constitutive overexpression of PhAN4 in this petunia resulted not only in a fully colored flower but also in a clearly visible pigmentation in the green tissue and roots, which can be rapidly increased by stress conditions. Suppression of AN4 gene resulted in discolored petals and whitish anthers. Interestingly, when a similar white flower phenotype was achieved by knockout of an essential structural gene of anthocyanin biosynthesis - CHALCONE ISOMERASE-A (CHI-A) - the plant responded directly by upregulating of another paralogs - DEEP PURPLE (DPL) and PURPLE HAZE (PHZ). Moreover, we also found that CHI-B can partially substitute for CHI-A in anthers, but not in vegetative tissues. Further, no significant effects on the longevity of white or enhanced colored flowers were observed compared with the wild type. We concluded that endogenous up-regulation of AN4 leads to the restoration of petal color in the "darkly-veined" phenotypes as a result of the breeding process under human selection, and CHI-B is a backup for CHI-A acitvity in some floral tissues.

Biomarkers of postharvest resilience: unveiling the role of abscisic acid in table grapes during cold storage

Table grapes are considered non-climacteric fruit, not showing a rapid increase in respiration rate and ethylene production during ripening. Previous research has suggested that abscisic acid (ABA) may have a more crucial role in grape postharvest behaviour. This study aimed to identify biomarkers of postharvest resilience and flavour life of imported table grapes. An experiment was designed to determine i) the role of ABA and catabolites on grape berry senescence; ii) the spatial distribution of these hormones within the grape berry, and iii) the effect of 1-MCP and storage temperature on its postharvest quality. Hence, the use of an ethylene inhibitor, 1-methylcyclopropane (1-MCP), during table grape storage was investigated. Table grapes (Vitis vinifera L.) cv. 'Krissy' were subjected to i) control (untreated); and ii) 1-MCP (1 µL L-1; 12 hours; 15°C) and stored under two scenarios: i) 15 days at 0.5°C, followed by five days at 5.5°C to simulate shelf-life; and ii) 20 days at 5.5°C to simulate a higher storage temperature followed by shelf-life. Physiological (i.e. mould incidence, skin colour, firmness, respiration rate) and biochemical analysis (i.e. individual sugars, organic acids, abscisic acid and catabolites) were performed. Grapes subjected to 5.5°C showed significantly higher mould incidence at the end of the shelf-life compared to 0.5°C storage temperature (12.6% vs. 3.1%). Also, and for the first time, the spatial distribution of ABA during the senescence of table grapes was profiled; the distal section had three times more ABA and metabolites than the proximal. We demonstrated that senescence processes were initiated after a significant increase in respiration rate (from 1 to 2.8 mL CO2 kg-1 h-1), and that ABA could be considered a biomarker for table grapes senescence, since an ABA peak preceded the increase in respiration rate, mould incidence, organic acids, and sucrose hydrolysis during postharvest storage; and coincided with a decrease in berry firmness. These findings are of significant importance for the industry as understanding how ABA regulates both senescence processes and quality changes during postharvest cold storage of tables grapes can improve the consistency and reduce waste and consumer complaints.

The E3 ubiquitin ligase SINA1 and the protein kinase BIN2 cooperatively regulate PHR1 in apple anthocyanin biosynthesis

PHR1 (PHOSPHATE STARVATION RESPONSE1) plays key roles in the inorganic phosphate (Pi) starvation response and in Pi deficiency-induced anthocyanin biosynthesis in plants. However, the post-translational regulation of PHR1 is unclear, and the molecular basis of PHR1-mediated anthocyanin biosynthesis remains elusive. In this study, we determined that MdPHR1 was essential for Pi deficiency-induced anthocyanin accumulation in apple (Malus × domestica). MdPHR1 interacted with MdWRKY75, a positive regulator of anthocyanin biosynthesis, to enhance the MdWRKY75-activated transcription of MdMYB1, leading to anthocyanin accumulation. In addition, the E3 ubiquitin ligase SEVEN IN ABSENTIA1 (MdSINA1) negatively regulated MdPHR1-promoted anthocyanin biosynthesis via the ubiquitination-mediated degradation of MdPHR1. Moreover, the protein kinase apple BRASSINOSTEROID INSENSITIVE2 (MdBIN2) phosphorylated MdPHR1 and positively regulated MdPHR1-mediated anthocyanin accumulation by attenuating the MdSINA1-mediated ubiquitination degradation of MdPHR1. Taken together, these findings not only demonstrate the regulatory role of MdPHR1 in Pi starvation induced anthocyanin accumulation, but also provide an insight into the post-translational regulation of PHR1.

Transcriptome analysis reveals important regulatory genes and pathways for tuber color variation in Pinellia ternata (Thunb.) Breit

During the growth of Pinellia ternata (Thunb.) Breit. (P. ternata), the violet-red skin was occasionally produced spontaneously under natural cultivation. However, the specific mechanism leading to the color change is still unclear. This study performed transcriptomes in violet-red and pale-yellow skin and their peeled tubers of P. ternata, and the total flavonoids and anthocyanin contents were also determined. The results showed that the majority of genes involved in anthocyanin production were considerably increased in the violet-red skin of P. ternata tuber compared to the pale-yellow skin. Especially, phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS) showed a remarkable increase in gene expression levels. Notably, shikimate O-hydroxycinnamoyltransferase (HCT), naringenin 3-dioxygenase (F3H), flavanone 4-reductase (DFR), and anthocyanidin synthase (ANS) were explicitly expressed in violet-red skin of P. ternata tuber, while undetectable in pale-yellow skin. The upregulation of these genes may explain the accumulation of anthocyanins, which forms the violet-red skin of P. ternata tuber. The transcription factors, including C2H2, bZIP, ERF, GATA, bHLH, C3H, NAC, MYB-related, and MYB families, might trigger the skin color change in P. ternata. The entire anthocyanin content in the violet-red skin of P. ternata tuber was 71.10 μg/g, and pale-yellow skin was 7.74 μg/g. According to phenotypic and transcriptome results, the elevated expression levels of genes linked to the synthesis of anthocyanins considerably contributed to the violet-red skin alterations in P. ternata tuber. This study provides a new understanding of the formation of the violet-red skin, lays a theoretical foundation for the cultivation of unique varieties of P. ternata, and provides transcriptome data for further study of the differences between different colors of P. ternata.

SnRK1 inhibits anthocyanin biosynthesis through both transcriptional regulation and direct phosphorylation and dissociation of the MYB/bHLH/TTG1 MBW complex

Plants have evolved an extensive specialized secondary metabolism. The colorful flavonoid anthocyanins, for example, not only stimulate flower pollination and seed dispersal, but also protect different tissues against high light, UV and oxidative stress. Their biosynthesis is highly regulated by environmental and developmental cues and induced by high sucrose levels. Expression of the biosynthetic enzymes involved is controlled by a transcriptional MBW complex, comprising (R2R3) MYB- and bHLH-type transcription factors and the WD40 repeat protein TTG1. Anthocyanin biosynthesis is not only useful, but also carbon- and energy-intensive and non-vital. Consistently, the SnRK1 protein kinase, a metabolic sensor activated in carbon- and energy-depleting stress conditions, represses anthocyanin biosynthesis. Here we show that Arabidopsis SnRK1 represses MBW complex activity both at the transcriptional and post-translational level. In addition to repressing expression of the key transcription factor MYB75/PAP1, SnRK1 activity triggers MBW complex dissociation, associated with loss of target promoter binding, MYB75 protein degradation and nuclear export of TTG1. We also provide evidence for direct interaction with and phosphorylation of multiple MBW complex proteins. These results indicate that repression of expensive anthocyanin biosynthesis is an important strategy to save energy and redirect carbon flow to more essential processes for survival in metabolic stress conditions.

Mycorrhizal colonization and Streptomyces viridosporus HH1 synergistically up-regulate the polyphenol biosynthesis genes in wheat against stripe rust

BACKGROUND

Stripe rust is considered one of the most devastating diseases of wheat all over the world, resulting in a high loss in its production. In this study, time-course changes in expression of the polyphenol biosynthesis pathways genes in wheat against stripe rust were investigated. The defense mechanisms triggered by mycorrhizal colonization and/or spraying with Streptomyces viridosporus HH1 against this disease were also investigated.

RESULTS

Results obtained revealed that C3H, which is considered the key gene in lignin biosynthesis, was the most expressed gene. Furthermore, most of the chlorogenic acid and flavonoid biosynthesis genes were also overexpressed. Volcano plots of the studied genes reveal that the dual treatment led to a high significant overexpression of 10 out of the 13 studied genes. Heatmap of these genes showed that the most frequent expressed gene in response to all applied treatments along the study period was DFR, the key gene in the biosynthesis of anthocyanidins. Gene co-expression network of the studied genes showed that HQT was the most central gene with respect to the other genes, followed by AN2 and DFR, respectively. Accumulation of different flavonoids and phenolic acids were detected in response to the dual treatment, in particular, cinnamic acid, coumarin, and esculetin, which recorded the highest elevation level recording 1000, 488.23, and 329.5% respectively. Furthermore, results from the greenhouse experiment showed that application of the dual treatment led to an 82.8% reduction in the disease severity, compared with the control treatment.

CONCLUSIONS

We can conclude that the biosynthesis of lignin, chlorogenic acid, and flavonoids contributed to the synergistic triggering effect of the dual treatment on wheat resistance to stripe rust.

Insight into the Molecular Mechanism of Flower Color Regulation in Rhododendron latoucheae Franch: A Multi-Omics Approach

Rhododendron latoucheae Franch. (R. latoucheae) is a valuable woody plant known for its high ornamental value. While purple flowers are a distinct and attractive variant phenotype of R. latoucheae, the underlying mechanism regulating its flower color is still poorly understood. To investigate the molecular regulatory mechanism responsible for the variation in flower color, we selected plants with white-pink and purple petals as the object and conducted analyses of metabolites, key genes, and transcription factors associated with flower color. A combined metabolome-transcriptome analysis was performed, and the expression of key genes was subsequently verified through qRT-PCR experiments. The results of our study demonstrated a significant enrichment of differential metabolites in the flavonoid metabolic pathway. Changes in anthocyanin content followed the same trend as the observed flower color variations, specifically showing significant correlations with the contents of malvidin-3-O-glucoside, dihydromyricetin, gallocatechin, and peonidin-3-O-glucoside. Furthermore, we identified three key structural genes (F3GT1, LAR, ANR) and four transcription factors (bHLH130, bHLH41, bHLH123, MYB4) that are potentially associated with the biosynthesis of flavonoid compounds, thereby influencing the appearance of purple flower color in R. latoucheae.

Map-based cloning and CRISPR/Cas9-based editing uncover BoNA1 as the causal gene for the no-anthocyanin-accumulation phenotype in curly kale (Brassica oleracea var. sabellica)

Brassica oleracea comprises several important vegetable and ornamental crops, including curly kale, ornamental kale, cabbage, broccoli, and others. The accumulation of anthocyanins, important secondary metabolites valuable to human health, in these plants varies widely and is responsible for their pink to dark purple colors. Some curly kale varieties lack anthocyanins, making these plants completely green. The genetic basis of this trait is still unknown. We crossed the curly kale inbred line BK2019 (without anthocyanins) with the cabbage inbred line YL1 (with anthocyanins) and the Chinese kale inbred line TO1000 (with anthocyanins) to generate segregating populations. The no-anthocyanin trait was genetically controlled by a recessive gene, bona1. We generated a linkage map and mapped bona1 to a 256-kb interval on C09. We identified one candidate gene, Bo9g058630, in the target genomic region; this gene is homologous to AT5G42800, which encodes a dihydroflavonol-4-reductase-like (DFR-like) protein in Arabidopsis. In BK2019, a 1-bp insertion was observed in the second exon of Bo9g058630 and directly produced a stop codon. To verify the candidate gene function, CRISPR/Cas9 gene editing technology was applied to knock out Bo9g058630. We generated three bona1 mutants, two of which were completely green with no anthocyanins, confirming that Bo9g058630 corresponds to BoNA1. Different insertion/deletion mutations in BoNA1 exons were found in all six of the other no-anthocyanin kale varieties examined, supporting that independent disruption of BoNA1 resulted in no-anthocyanin varieties of B. oleracea. This study improves the understanding of the regulation mechanism of anthocyanin accumulation in B. oleracea subspecies.

A 43 Bp-Deletion in the F3'H Gene Reducing Anthocyanins Is Responsible for Keeping Buds Green at Low Temperatures in Broccoli

Most broccoli cultivars or accessions exhibit green buds under appropriate growth conditions, which turn purple at cold temperatures. However, certain cultivars consistently maintain green buds both during normal growth and at cold temperatures. In this study, we used BSA-seq (bulked segregation analysis-sequencing), along with fine mapping and transcriptome analysis to identify a candidate gene (flavonoid 3'-hydroxylase, F3'H) responsible for reducing anthocyanin accumulation in the mutant GS and HX-16 broccoli (Brassica oleracea L. var. italica), which could retain green buds even at low temperatures. A 43-bp deletion was detected in the coding sequence (CDS) of the F3'H gene in HX-16 and the mutant GS, which significantly decreased F3'H expression and the accumulation of cyanidin and delphinidin in the mutant GS. Furthermore, the expression of F3'H was upregulated at low temperatures in the wild line PS. Our results demonstrated the efficacy of utilizing the 43-bp InDel (Insertion-Deletion) in predicting whether buds in B. oleracea L. will turn purple or remain green at cold temperatures across forty-two germplasm materials. This study provides critical genetic and molecular insights for the molecular breeding of B. oleracea and sheds light on the molecular mechanisms underlying the effect of low temperatures on bud color in broccoli.

When Cannabis sativa L. Turns Purple: Biosynthesis and Accumulation of Anthocyanins

Environmental cues elicit anthocyanin synthesis in plant vegetative and reproductive tissues. Their accumulation in different organs accounts for their diverse biological functions, mainly related to their antioxidant properties, and it depends on a temporally and spatially regulated mechanism controlled by the action of a well-known multi-transcription factor complex. Despite the highly recognizable value of Cannabis sativa L. as a natural biorefinery of phytochemicals, very little information is known on anthocyanin pigmentation in this species. In this work, a targeted quantification of anthocyanins via HPLC-MS/MS, combined with the transcriptional profile via RT-qPCR of genes encoding for structural and decorating enzymes and regulatory transcription factors in different C. sativa tissues, help gain insights into the anthocyanin pathway in this species. To the best of our knowledge, this is the first report on the identification of cyanidin-3-rutinoside (keracyanin) as the major anthocyanin in C. sativa vegetative and floral tissues. Keracyanin amounts were higher than in small berries, suggesting that Cannabis biomass is a valuable source of colored antioxidants to be exploited in diverse applications. Furthermore, a gene putatively encoding for an anthocyanin DTX35 type transporter and CsTTG1 were identified in silico and their transcriptional levels were assessed via RT-qPCR. The results allow us to provide the first model of anthocyanin regulation in C. sativa, opening a new research scenario in this species for both breeding purposes and phytochemical exploitation.

Phenolic Composition of Brazilian BRS Carmem (Muscat Belly A × BRS Rúbea) Grapes: Evaluation of Their Potential Use as Bioingredients

The BRS Carmem grape was developed as an alternative for processing juices and wines. This study aimed to determine the phenolic compounds (PC) in the edible parts of this grape from two harvests-one harvested at ideal maturation time and another when the grapes were still immature-using HPLC-DAD-ESI-MS/MS. Student's t-test was used (α = 0.05) to evaluate differences in the PC content between the edible parts and between the harvests. Both skins showed a predominance of flavonols, anthocyanins, hydroxycinnamic acids derivatives (HCAD) and stilbenes, with higher concentrations for harvest 1 than harvest 2. For both harvests (harvest 1 and harvest 2), the HCAD (mg of caftaric acid•kg fruit^-1) was higher in whole grapes (383.98 and 67.09) than in their skins (173.95 and 21.74), with a predominance of trans-caffeic acid for all samples; the flavan-3-ols and proanthocyanidins (mg of (+)-catechin•kg fruit^-1) presented higher concentrations in the seeds (flavan-3-ols: 203.20 and 182.71, proanthocyanidins: 453.57 and 299.86) than in the skins (flavan-3-ols: 1.90 and 4.56, proanthocyanidins: 37.58 and 98.92); the stilbenes concentration (µg 3-glc-resveratrol•kg fruit^-1) was higher for the seeds from harvest 2 (896.25) than those from harvest 1 (48.67). BRS Carmem grapes contain a phenolic composition complex, and still have a relevant concentration of flavonols, anthocyanins and stilbenes, even when immature.

Why do plants blush when they are hungry?

Foliar anthocyanins, as well as other secondary metabolites, accumulate transiently under nutritional stress. A misconception that only nitrogen or phosphorus deficiency induces leaf purpling/reddening has led to overuse of fertilizers that burden the environment. Here, we emphasize that several other nutritional imbalances induce anthocyanin accumulation, and nutrient-specific differences in this response have been reported for some deficiencies. A range of ecophysiological functions have been attributed to anthocyanins. We discuss the proposed functions and signalling pathways that elicit anthocyanin synthesis in nutrient-stressed leaves. Knowledge from the fields of genetics, molecular biology, ecophysiology and plant nutrition is combined to deduce how and why anthocyanins accumulate under nutritional stress. Future research to fully understand the mechanisms and nuances of foliar anthocyanin accumulation in nutrient-stressed crops could be utilized to allow these leaf pigments to act as bioindicators for demand-oriented application of fertilizers. This would benefit the environment, being timely due to the increasing impact of the climate crisis on crop performance.

Anthocyanins and reactive oxygen species: a team of rivals regulating plant development?

Anthocyanins are a family of water-soluble vacuolar pigments present in almost all flowering plants. The chemistry, biosynthesis and functions of these flavonoids have been intensively studied, in part due to their benefit for human health. Given that they are efficient antioxidants, intense research has been devoted to studying their possible roles against damage caused by reactive oxygen species (ROS). However, the redox homeostasis established between antioxidants and ROS is important for plant growth and development. On the one hand, high levels of ROS can damage DNA, proteins, and lipids, on the other, they are also required for cell signaling, plant development and stress responses. Thus, a balance is needed in which antioxidants can remove excessive ROS, while not precluding ROS from triggering important cellular signaling cascades. In this article, we discuss how anthocyanins and ROS interact and how a deeper understanding of the balance between them could help improve plant productivity, nutritional value, and resistance to stress, while simultaneously maintaining proper cellular function and plant growth.

The health-promoting anthocyanin petanin in Lycium ruthenicum fruit: a promising natural colorant

Acylated anthocyanins derived from dietary sources have gained significant attention due to their health-promoting properties and potential as natural colorants with high stability. However, exploration of the functional food products using acylated anthocyanins enriched in fruits and vegetables remains largely delayed in food industries. The black goji (Lycium ruthencium) fruit (LRF) is a functional food that is extensively used due to its exceptionally high levels of acylated anthocyanins, including petanin. This review provides a comprehensive summary of the functional properties and anthocyanin components of LRF. The stability, bioaccessibility, bioavailability, and bioactivities of petanin, the major anthocyanin component, are compared with those of LRF anthocyanin extracts and other food sources. Furthermore, the biosynthetic pathway and regulatory network of petanin in LRF are proposed and constructed, respectively. The key genes that could be potentially used for metabolic engineering to produce petanin are predicted. Finally, the potential application of petanin derivatives in the food industry is also discussed. This review presents comprehensive and systematic information about the dual-function of petanin as a bioactive component and a promising natural colorant for future food industrial applications.

The E3 ubiquitin ligases SINA1 and SINA2 integrate with the protein kinase CIPK20 to regulate the stability of RGL2a, a positive regulator of anthocyanin biosynthesis

Although DELLA protein destabilization mediated by post-translational modifications is essential for gibberellin (GA) signal transduction and GA-regulated anthocyanin biosynthesis, the related mechanisms remain largely unknown. In this study, we report the ubiquitination and phosphorylation of an apple DELLA protein MdRGL2a in response to GA signaling and its regulatory role in anthocyanin biosynthesis. MdRGL2a could interact with MdWRKY75 to enhance the MdWRKY75-activated transcription of anthocyanin activator MdMYB1 and interfere with the interaction between anthocyanin repressor MdMYB308 and MdbHLH3 or MdbHLH33, thereby promoting anthocyanin accumulation. A protein kinase MdCIPK20 was found to phosphorylate and protect MdRGL2a from degradation, and it was essential for MdRGL2a-promoting anthocyanin accumulation. However, MdRGL2a and MdCIPK20 were ubiquitinated and degraded by E3 ubiquitin ligases MdSINA1 and MdSINA2, respectively, both of which were activated in the presence of GA. Our results display the integration of SINA1/2 with CIPK20 to dynamically regulate GA signaling and will be helpful toward understanding the mechanism of GA signal transduction and GA-inhibited anthocyanin biosynthesis. The discovery of extensive interactions between DELLA and SINA and CIPK proteins in apple will provide reference for the study of ubiquitination and phosphorylation of DELLA proteins in other species.

Engineered production of bioactive polyphenolic O-glycosides

Polyphenolic compounds (such as quercetin and resveratrol) possess potential medicinal values due to their various bioactivities, but poor water solubility hinders their health benefits to humankind. Glycosylation is a well-known post-modification method to biosynthesize natural product glycosides with improved hydrophilicity. Glycosylation has profound effects on decreasing toxicity, increasing bioavailability and stability, together with changing bioactivity of polyphenolic compounds. Therefore, polyphenolic glycosides can be used as food additives, therapeutics, and nutraceuticals. Engineered biosynthesis provides an environmentally friendly and cost-effective approach to generate polyphenolic glycosides through the use of various glycosyltransferases (GTs) and sugar biosynthetic enzymes. GTs transfer the sugar moieties from nucleotide-activated diphosphate sugar (NDP-sugar) donors to sugar acceptors such as polyphenolic compounds. In this review, we systematically review and summarize the representative polyphenolic O-glycosides with various bioactivities and their engineered biosynthesis in microbes with different biotechnological strategies. We also review the major routes towards NDP-sugar formation in microbes, which is significant for producing unusual or novel glycosides. Finally, we discuss the trends in NDP-sugar based glycosylation research to promote the development of prodrugs that positively impact human health and wellness.

A fast breeding strategy creates fragrance- and anthocyanin-enriched rice lines by marker-free gene-editing and hybridization

As rice is a staple food for nearly half of the world's population, rice varieties with excellent agronomic traits as well as high flavor and nutritional quality such as fragrant rice and purple rice are naturally favored by the market. In the current study, we adopt a fast breeding strategy to improve the aroma and anthocyanin content in the excellent rice inbred line, F25. The strategy skillfully used the advantages of obtaining editing pure lines in T0 generation of CRISPR/Cas9 editing system and easy observation of purple character and grain shape, integrated the subsequent screening of non-transgenic lines, and the elimination of undesirable edited variants from gene-editing and cross-breeding at the same time as the separation of the progeny from the purple cross, thus expediting the breeding process. Compared with conventional breeding strategies, this strategy saves about 6-8 generations and reduces breeding costs. Firstly, we edited the OsBADH2 gene associated with rice flavor using an Agrobacterium-mediated CRISPR/Cas9 system to improve the aroma of F25. In the T0 generation, a homozygous OsBADH2-edited F25 line (F25B) containing more of the scented substance 2-AP was obtained. Then, we crossed F25B (♀) with a purple rice inbred line, P351 (♂), with high anthocyanin enrichment to improve the anthocyanin content of F25. After nearly 2.5 years of screening and identification over five generations, the undesirable variation characteristics caused by gene-editing and hybridization and the transgenic components were screened out. Finally, the improved F25 line with highly stable aroma component, 2-AP, increased anthocyanin content and no exogenous transgenic components were obtained. This study not only provides high-quality aromatic anthocyanin rice lines that meet the market demand, but also offers a reference for the comprehensive use of CRISPR/Cas9 editing technology, hybridization, and marker-assisted selection to accelerate multi-trait improvement and breeding process.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-023-01369-1.

Identification of CaPs locus involving in purple stripe formation on unripe fruit, reveals allelic variation and alternative splicing of R2R3-MYB transcription factor in pepper (Capsicum annuum L.)

The purple color of unripe pepper fruit is attributed to the accumulation of anthocyanins. Only a few genes controlling the biosynthesis and regulation of anthocyanins have been cloned in Capsicum. In this study, we performed a bulked segregant analysis of the purple striped trait using an F² population derived from a cross between the immature purple striped fruit line Chen12-4-1-1-1-1 and the normal green fruit line Zhongxian101-M-F⁹. We mapped the CaPs locus to an 841.39 kb region between markers M-CA690-Xba and MCA710-03 on chromosome 10. CA10g11690 encodes an R2R3-MYB transcription factor that is involved in the biosynthesis of anthocyanins as the best candidate gene. Overexpression and silencing in transformed tobacco (Nicotiana tabacum) lines indicated that CA10g11690 is involved in the formation of purple stripes in the exocarp. A comparison of parental sequences identified an insertion fragment of 1,926 bp in the second intron region of Chen12-4, and eight SNPs were detected between the two parents. Additionally, there were 49 single nucleotide polymorphic variations, two sequence deletions, and four sequence insertions in the promoter region. We found that CA10g11690 undergoes alternative splicing and generates different transcripts. Thus, the functional transcript of CA10g11690 appeared to be primarily involved in the development of purple phenotype in the exocarp. Our data provide new insight into the mechanism of anthocyanin biosynthesis and a theoretical basis for the future breeding of purple striped pepper varieties.

Fine mapping of genes controlling pigment accumulation in oilseed rape (Brassica napus L.)

Purple/red appearance is one of the common phenotypic variations in leaves, stems, and siliques of oilseed rape (Brassica napus L.) but very rare in flowers. In this study, the causal genes for the purple/red traits in stems and flowers in two accessions of oilseed rape (DH_PR and DH_GC001, respectively) derived from the wide hybridization were fine mapped, and candidate genes were determined by methods combined with bulked segregant analysis (BSA) and RNA-seq analysis. Both traits of purple stem and red flowers were mapped to the locus as AtPAP2 homologous genes (BnaPAP2.C6a and BnaPAP2.A7b, respectively) belonging to the R2R3-MYB family. Sequence comparisons of full-length allelic genes revealed several InDels and SNPs in intron 1 as well as exons, and completely different promoter region of BnaPAP2.C6a and a 211 bp insertion was identified in the promoter region of BnaPAP2.A7b of DH_GC001. Our results not only contribute to a better understanding of anthocyanin inheritance in B. napus, but also provide a useful toolbox for future breeding of cultivars with purple/red traits through the combination of different functional alleles and homologs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-023-01365-5.

Metabolic engineering of the anthocyanin biosynthetic pathway in Artemisia annua and relation to the expression of the artemisinin biosynthetic pathway

Four types of cells were engineered from Artemisia annua to produce approximately 17 anthocyanins, four of which were elucidated structurally. All of them expressed the artemisinin pathway. Artemisia annua is the only medicinal crop to produce artemisinin for the treatment of malignant malaria. Unfortunately, hundreds of thousands of people still lose their life every year due to the lack of sufficient artemisinin. Artemisinin is considered to result from the spontaneous autoxidation of dihydroartemisinic acid in the presence of reactive oxygen species (ROS) in an oxidative condition of glandular trichomes (GTs); however, whether increasing antioxidative compounds can inhibit artemisinin biosynthesis in plant cells is unknown. Anthocyanins are potent antioxidants that can remove ROS in plant cells. To date, no anthocyanins have been structurally elucidated from A. annua. In this study, we had two goals: (1) to engineer anthocyanins in A. annua cells and (2) to understand the artemisinin biosynthesis in anthocyanin-producing cells. Arabidopsis Production of Anthocyanin Pigment 1 was used to engineer four types of transgenic anthocyanin-producing A. annua (TAPA1-4) cells. Three wild-type cell types were developed as controls. TAPA1 cells produced the highest contents of total anthocyanins. LC-MS analysis detected 17 anthocyanin or anthocyanidin compounds. Crystallization, LC/MS/MS, and NMR analyses identified cyanidin, pelargonidin, one cyanin, and one pelargonin. An integrative analysis characterized that four types of TAPA cells expressed the artemisinin pathway and TAPA1 cells produced the highest artemisinin and artemisinic acid. The contents of arteannuin B were similar in seven cell types. These data showed that the engineering of anthocyanins does not eliminate the biosynthesis of artemisinin in cells. These data allow us to propose a new hypothesis that enzymes catalyze the formation of artemisinin from dihydroartemisinic acid in non-GT cells. These findings show a new platform to increase artemisinin production via non-GT cells of A. annua.

Two genes, ANS and UFGT2, from Vaccinium spp. are key steps for modulating anthocyanin production

Anthocyanins are a major group of red to blue spectrum plant pigments with many consumer health benefits. Anthocyanins are derived from the flavonoid pathway and diversified by glycosylation and methylation, involving the concerted action of specific enzymes. Blueberry and bilberry (Vaccinium spp.) are regarded as 'superfruits' owing to their high content of flavonoids, especially anthocyanins. While ripening-related anthocyanin production in bilberry (V. myrtillus) and blueberry (V. corymbosum) is regulated by the transcriptional activator MYBA1, the role of specific structural genes in determining the concentration and composition of anthocyanins has not been functionally elucidated. We isolated three candidate genes, CHALCONE SYNTHASE (VmCHS1), ANTHOCYANIDIN SYNTHASE (VmANS) and UDP-GLUCOSE : FLAVONOID-3-O-GLYCOSYLTRANSFERASE (VcUFGT2), from Vaccinium, which were predominantly expressed in pigmented fruit skin tissue and showed high homology between bilberry and blueberry. Agrobacterium-mediated transient expression of Nicotiana benthamiana showed that overexpression of VcMYBA1 in combination with VmANS significantly increased anthocyanin concentration (3-fold). Overexpression of VmCHS1 showed no effect above that induced by VcMYBA1, while VcUFGT2 modulated anthocyanin composition to produce delphinidin-3-galactosylrhamnoside, not naturally produced in tobacco. In strawberry (Fragaria × ananassa), combined transient overexpression of VcUFGT2 with a FLAVONOID 3´,5´-HYDROXYLASE from kiwifruit (Actinidia melanandra) modulated the anthocyanin profile to include galactosides and arabinosides of delphinidin and cyanidin, major anthocyanins in blueberry and bilberry. These findings provide insight into the role of the final steps of biosynthesis in modulating anthocyanin production in Vaccinium and may contribute to the targeted breeding of new cultivars with improved nutritional properties.

The mechanism leading to color differences between purple-red and green partridge tea leaves

BACKGROUND

Partridge tea (Mallotus oblongifolius) is used as an important beverage and medical plant in Hainan province of China. Although some information about the morphology, cytology, and genetics of partridge tea has been reported in the literature, knowledge about this plant is still very limited. The leaves are the most important part for every tea plant, with a major role in nutrition and other functions. The leaves of different cultivars of partridge tea are different in colors and functions. The molecular mechanism of color formation of partridge tea leaf is still unclear. We reveal the molecular mechanism of the color difference between purple-red and green partridge tea leaves through metabolome and transcriptome analysis.

RESULTS

We identified 665 compounds in the two partridge tea cultivars through metabolome analysis. Among these compounds, the content of 324 differed between the two cultivars. We also annotated 50 042 unigenes in the two cultivars by transcriptome analysis; 9665 unigenes were expressed differently between the two cultivars. Using an integrated analysis of the metabolome and transcriptome data, we found that the compounds and genes involved in anthocyanin biosynthesis were up-regulated in the purple-red leaves, compared with the green leaves.

CONCLUSION

Our results showed that the anthocyanin biosynthesis pathway genes were up-regulated, which resulted in the up-regulation of the anthocyanin, making the leaf color purple-red. Our study reveals the molecular mechanism of the color difference between purple-red and green partridge tea, and lays a foundation for the genetic breeding of partridge tea genetic and the utilization of its volatile components. © 2022 Society of Chemical Industry.

Anthocyanin/Honey-Incorporated Alginate Hydrogel as a Bio-Based pH-Responsive/Antibacterial/Antioxidant Wound Dressing

Infection is a major problem that increases the normal pH of the wound bed and interferes with wound healing. Natural biomaterials can serve as a suitable environment to acquire a great practical effect on the healing process. In this context, anthocyanin-rich red cabbage (Brassica oleracea var. capitata F. rubra) extract and honey-loaded alginate hydrogel was fabricated using calcium chloride as a crosslinking agent. The pH sensitivity of anthocyanins can be used as an indicator to monitor possible infection of the wound, while honey would promote the healing process by its intrinsic properties. The mechanical properties of the hydrogel film samples showed that honey acts as a plasticizer and that increasing the incorporation from 200% to 400% enhances the tensile strength from 3.22 to 6.15 MPa and elongation at break from 0.69% to 4.75%. Moreover, a water absorption and retention study showed that the hydrogel film is able to absorb about 250% water after 50 min and retain 40% of its absorbed water after 12 h. The disk diffusion test showed favorable antibacterial activity of the honey-loaded hydrogel against both Gram-positive and Gram-negative Staphylococcus aureus and Escherichia coli, respectively. In addition, the incorporation of honey significantly improved the mechanical properties of the hydrogel. 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay proved the antioxidant activity of the honey and anthocyanin-containing hydrogel samples with more than 95% DPPH scavenging efficiency after 3 h. The pH-dependent property of the samples was investigated and recorded by observing the color change at different pH values of 4, 7, and 9 using different buffers. The result revealed a promising color change from red at pH = 4 to blue at pH = 7 and purple at pH = 9. An in vitro cell culture study of the samples using L929 mouse fibroblast cells showed excellent biocompatibility with significant increase in cell proliferation. Overall, this study provides a promising start and an antibacterial/antioxidant hydrogel with great potential to meet wound-dressing requirements.

Molecular and Metabolic Insights into Anthocyanin Biosynthesis for Spot Formation on Lilium leichtlinii var. maximowiczii Flower Petals

Plants exhibit remarkable diversity in their petal colors through biosynthesis and the accumulation of various pigments. Lilium, an important cut and potted flower, has many coloring pattern variations, including bicolors and spots. To elucidate the mechanisms regulating spot formation in Lilium leichtlinii var. maximowiczii petals, we used multiple approaches to investigate the changes in petal carotenoids, spot anthocyanins, and gene expression dynamics. This included green petals without spots (D1-Pe and D1-Sp), yellow-green petals with purple spots (D2-Pe and D2-Sp), light-orange petals with dark-purple spots (D3-Pe and D3-Sp), and orange petals with dark-purple spots (D4-Pe and D4-Sp). D3-Pe and D4-Pe contained large amounts of capsanthin and capsorubin and small amounts of zeaxanthin and violaxanthin, which contributed to the orange color. In addition to cyanidin-3-O-glucoside, pelargonidin-3-O-rutinoside, cyanidin-3-O-rutinoside, and peonidin-3-O-rutinoside may also contribute to L. leichtlinii var. maximowiczii's petal spot colors. KEGs involved in flavonoid biosyntheses, such as CHS, DFR, and MYB12, were significantly upregulated in D2-Sp and D3-Sp, compared with D1-Sp, as well as in spots, compared with petals. Upregulated anthocyanin concentrations and biosynthesis-related genes promoted spot formation and color transition. Our results provide global insight into pigment accumulation and the regulatory mechanisms underlying spot formation during flower development in L. leichtlinii var. maximowiczii.

Flavonoid Production: Current Trends in Plant Metabolic Engineering and De Novo Microbial Production

Flavonoids are secondary metabolites that represent a heterogeneous family of plant polyphenolic compounds. Recent research has determined that the health benefits of fruits and vegetables, as well as the therapeutic potential of medicinal plants, are based on the presence of various bioactive natural products, including a high proportion of flavonoids. With current trends in plant metabolite research, flavonoids have become the center of attention due to their significant bioactivity associated with anti-cancer, antioxidant, anti-inflammatory, and anti-microbial activities. However, the use of traditional approaches, widely associated with the production of flavonoids, including plant extraction and chemical synthesis, has not been able to establish a scalable route for large-scale production on an industrial level. The renovation of biosynthetic pathways in plants and industrially significant microbes using advanced genetic engineering tools offers substantial promise for the exploration and scalable production of flavonoids. Recently, the co-culture engineering approach has emerged to prevail over the constraints and limitations of the conventional monoculture approach by harnessing the power of two or more strains of engineered microbes to reconstruct the target biosynthetic pathway. In this review, current perspectives on the biosynthesis and metabolic engineering of flavonoids in plants have been summarized. Special emphasis is placed on the most recent developments in the microbial production of major classes of flavonoids. Finally, we describe the recent achievements in genetic engineering for the combinatorial biosynthesis of flavonoids by reconstructing synthesis pathways in microorganisms via a co-culture strategy to obtain high amounts of specific bioactive compounds.

Analysis of Floral Color Differences between Different Ecological Conditions of Clematis tangutica (Maxim.) Korsh

The Clematis tangutica (Maxim.) Korsh. is a wild flowering plant that is most widely distributed on the Qinghai-Tibet Plateau, with beautiful, brightly colored flowers and good ornamental properties and adaptability. In diverse natural environments, the blossom color of C. tangutica (Maxim.) Korsh. varies greatly, although it is unclear what causes this diversity. It was examined using UPLC-MS/MS and transcriptome sequencing for the investigation of various compounds, differentially expressed genes (DEGs), and flavonoid biosynthesis-related pathways in two flowers in two ecological settings. The results showed that a total of 992 metabolites were detected, of which 425 were differential metabolites, mainly flavonoid metabolites associated with its floral color. The most abundant flavonoids, flavonols and anthocyanin metabolites in the G type were cynaroside, isoquercitrin and peonidin-3-O-glucoside, respectively. Flavonoids that differed in multiplicity in G type and N type were rhoifolin, naringin, delphinidin-3-O-rutinoside, chrysoeriol and catechin. Rhoifolin and chrysoeriol, produced in flavone and flavonol biosynthesis, two flavonoid compounds of C. tangutica (Maxim.) Korsh. with the largest difference in floral composition in two ecological environments. In two ecological environments of flower color components, combined transcriptome and metabolome analyses revealed that BZ1-1 and FG3-1 are key genes for delphinidin-3-O-rutinoside in anthocyanin biosynthesis, and HCT-5 and FG3-3 are key genes for rhoifolin and naringin in flavonoid biosynthesis and flavone and flavonol. Key genes for chlorogenic acid in flavonoid biosynthesis include HCT-6, CHS-1 and IF7MAT-1. In summary, differences in flavonoids and their content are the main factors responsible for the differences in the floral color composition of C. tangutica (Maxim.) Korsh. in the two ecological environments, and are associated with differential expression of genes related to flavonoid synthesis.

Two independent loss-of-function mutations in anthocyanidin synthase homeologous genes are responsible for the all-green phenotype of sweet basil

Sweet basil, Ocimum basilicum L., is an important culinary herb grown worldwide. Although basil is green, many landraces, breeding lines, and exotic cultivars have purple stems and flowers. This anthocyanin pigmentation is unacceptable in traditional Italian basil used for Pesto sauce production. In the current study, we aimed to resolve the genetics that underlines the different colors. We used the recently published sweet basil genome to map quantitative trait loci (QTL) for flower and stem color in a bi-parental F₂ population. It was found that the pigmentation is governed by a single QTL, harboring an anthocyanidin synthase (ANS) gene (EC 1.14.20.4). Further analysis revealed that the basil genome harbors two homeologous ANS genes, each carrying a loss-of-function mutation. ObANS1 carries a single base pair insertion resulting in a frameshift, and ObANS2 carries a missense mutation within the active site. In the purple-flower parent, ANS1 is functional, and ANS2 carries a nonsense mutation. The functionality of the ObANS1 active allele was validated by complementation assay in an Arabidopsis ANS mutant. Moreover, we have restored the functionality of the missense-mutated ObANS2 using site-directed activation. We found that the non-functional alleles were expressed to similar levels as the functional allele, suggesting polyploids invest futile effort in expressing non-functional genes, offsetting their advantageous redundancy. This work demonstrated the usefulness of the genomics and genetics of basil to understand the basic mechanism of metabolic traits and raise fundamental questions in polyploid plant biology.

An extensive review of marine pigments: sources, biotechnological applications, and sustainability

The global demand for food and healthcare products based on natural compounds means that the industrial and scientific sectors are on a continuous search for natural colored compounds that can contribute to the replacement of synthetic colors. Natural pigments are a heterogeneous group of chemical molecules, widely distributed in nature. Recently, the interest in marine organisms has increased as they represent the most varied environment in the world and provide a wide range of colored compounds with bioactive properties and biotechnological applications in areas such as the food, pharmaceutical, cosmetic, and textile industries. The use of marine-derived pigments has increased during the last two decades because they are environmentally safe and healthy compounds. This article provides a comprehensive review of the current knowledge of sources, applications, and sustainability of the most important marine pigments. In addition, alternatives to protect these compounds from environmental conditions and their applications in the industrial sector are reviewed.

Accumulation of Anthocyanins in Detached Leaves of Kalanchoë blossfeldiana: Relevance to the Effect of Methyl Jasmonate on This Process

Accumulation of anthocyanins in detached leaves and in excised stems of Kalanchoë blossfeldiana kept under natural light conditions in the presence or absence of methyl jasmonate (JA-Me) was investigated. When the abaxial surface of detached leaves was held lower than the adaxial surface (the normal or natural position) under natural light conditions, anthocyanins were not accumulated on the abaxial side of the leaves. In contrast, when the adaxial surface of detached leaves was held lower than the abaxial surface (inverted position), anthocyanins were highly accumulated on the abaxial side of the leaves. These phenomena were independent of the growth stage of K. blossfeldiana as well as photoperiod. Application of JA-Me in lanolin paste significantly inhibited anthocyanin accumulation induced on the abaxial side of detached leaves held in an inverted position in a dose-dependent manner. Anthocyanin accumulation in the excised stem in response to natural light was also significantly inhibited by JA-Me in lanolin paste. Possible mechanisms of anthocyanin accumulation on the abaxial side of detached K. blossfeldiana leaves held in an inverted position under natural light conditions and the inhibitory effect of JA-Me on this process are described. The accompanying changes in the content of primary metabolites and histological analyses were also described.

Syringa oblata genome provides new insights into molecular mechanism of flower color differences among individuals and biosynthesis of its flower volatiles

Syringa oblata is a high ornamental value tree owing to its elegant colors, unique aromas and wide adaptability, however, studies on the molecular mechanism underlying the formation of its ornamental traits are still lacking. Here, we presented a chromosome-scale genome assembly of S. oblata and the final genome size was 1.11 Gb with a contig N50 of 4.75 Mb, anchored on 23 chromosomes and was a better reference for S. oblata transcriptome assembly. Further by integrating transcriptomic and metabolic data, it was concluded that F3H, F3'H, 4CL and PAL, especially the F3'H, were important candidates involved in the formation of floral color differences among S. oblata individuals. Genome-wide identification and analysis revealed that the TPS-b subfamily was the most abundant subfamily of TPS family in S. oblata, which together with the CYP76 family genes determined the formation of the major floral volatiles of S. oblata. Overall, our results provide an important reference for mechanistic studies on the main ornamental traits and molecular breeding in S. oblata.

Behind the Scenes of Anthocyanins-From the Health Benefits to Potential Applications in Food, Pharmaceutical and Cosmetic Fields

Anthocyanins are widespread and biologically active water-soluble phenolic pigments responsible for a wide range of vivid colours, from red (acidic conditions) to purplish blue (basic conditions), present in fruits, vegetables, and coloured grains. The pigments' stability and colours are influenced mainly by pH but also by structure, temperature, and light. The colour-stabilizing mechanisms of plants are determined by inter- and intramolecular co-pigmentation and metal complexation, driven by van der Waals, π-π stacking, hydrogen bonding, and metal-ligand interactions. This group of flavonoids is well-known to have potent anti-inflammatory and antioxidant effects, which explains the biological effects associated with them. Therefore, this review provides an overview of the role of anthocyanins as natural colorants, showing they are less harmful than conventional colorants, with several technological potential applications in different industrial fields, namely in the textile and food industries, as well as in the development of photosensitizers for dye-sensitized solar cells, as new photosensitizers in photodynamic therapy, pharmaceuticals, and in the cosmetic industry, mainly on the formulation of skin care formulations, sunscreen filters, nail colorants, skin & hair cleansing products, amongst others. In addition, we will unveil some of the latest studies about the health benefits of anthocyanins, mainly focusing on the protection against the most prevalent human diseases mediated by oxidative stress, namely cardiovascular and neurodegenerative diseases, cancer, and diabetes. The contribution of anthocyanins to visual health is also very relevant and will be briefly explored.