Differential hydroxylation efficiency of the two non-heme carotene hydroxylases: DcBCH1, rather than DcBCH2, plays a major role in carrot taproot

Targeted metabolite and molecular profiling of carotenoids in rose petals: A step forward towards functional food applications

Given the increasing consumer demand for natural and functional foods, rose petals offer a promising novel ingredient for food innovation, especially yellow and orange rose petals rich in carotenoids, making them ideal for food processing and color retention. Despite their potential, the metabolic profile of carotenoids in roses has not yet been fully explored. Therefore, the present study aimed to provide a comprehensive analysis of carotenoid metabolism in rose petals during three developmental stages. The results revealed that orange rose petals had the highest carotenoid content of 488.85 μg/g, with xanthophylls being identified as the primary carotenoid constituents (70.40 %) in roses for the first time. Furthermore, two genes, RhBCH1 and RhCCD4, were identified to be involved in the regulation of carotenoid biosynthesis in roses. Overall, this study demonstrates the enormous potential of rose petals as functional food ingredients, providing a theoretical basis for breeding high-carotenoid rose varieties.

Altering Carotene Hydroxylase Activity of DcCYP97C1 Affects Carotenoid Flux and Changes Taproot Colour in Carrot

CYP97C1 as a haem-containing cytochrome P450 hydroxylase (P450-type) is important for carotene hydroxylation and xanthophyll biosynthesis. Research about this type of hydroxylase was mainly reported in several model plant species which have no specialized tissues accumulating massive carotenoids. The function of CYP97C1 in the horticultural plant, like carrots, was not fully studied. In this study, we focused on the role of DcCYP97C1 in carotenoid flux and colour formation in carrot. DcCYP97C1 was found highly expressed in the 'turning stage' of carrot taproot. Using stable transformation and CRISPR/Cas9-mediated gene knockout technology, DcCYP97C1 was confirmed the rate-limiting enzyme for lutein biosynthesis and important for taproot colour formation. Overexpression of DcCYP97C1 in an orange carrot KRD (Kurodagosun) resulted in five times overproduction of lutein accompanied by dramatic reduction of carotenes. Knockout of DcCYP97C1 in orange KRD and yellow carrot QTH (Qitouhuang) reduced all kinds of carotenoids including lutein, α-carotene and β-carotene reflecting the key role of DcCYP97C1 for total carotenoid accumulation in taproot 'turning stage'. Our study demonstrated that manipulation of DcCYP97C1 was sufficient to influence carotenoid flux, change carrot colour and for high lutein production. The uncovered role of DcCYP97C1 may be helpful for understanding plant carotenoid metabolism and breeding colourful carrot cultivars.

Generation of high purity capsanthin and capsorubin through synthetic metabolic engineering in carrot germplasm

Capsanthin and capsorubin are red κ-xanthophylls exclusively found in a handful of other plant species. Currently, capsanthin and capsorubin are extracted from red pepper (Capsicum annuum L.). Here, high purity production of capsanthin and capsorubin was achieved in carrot (Daucus carota L.) taproot by a synthetic metabolic engineering strategy. Expression of a capsanthin-capsorubin synthase gene (CaCCS) from pepper resulted in dominant production of capsanthin, whereas expression of a LiCCS gene from tiger lily (Lilium lancifolium Thunb.) resulted in production of both capsanthin and capsorubin in carrot taproot. The highest content of capsanthin and capsorubin was obtained in LiC-1 carrot taproot hosting the LiCCS gene. Co-expression of DcBCH1 with CCS could improve the purity of capsanthin and capsorubin by eliminating the non-target carotenoids (e.g. α-carotene and β-carotene). The highest purity of capsanthin and capsorubin was obtained in BLiC-1 carrot taproot hosting DcBCH1+LiCCS genes, 91.10% of total carotenoids. The non-native pigments were esterified partially and stored in the globular chromoplast of carrot taproot. Our results demonstrated the use of carrot taproot as green factories for high purity production of capsanthin and capsorubin. The capsanthin/capsorubin carrot germplasms are also valuable materials for breeding colorful carrots cultivars.

Multiomics analysis reveals the involvement of OnDIVARICATA 3 in controlling dynamic flower coloring of Oncidium hybridum

Flower color is one of the main quality and economic traits of ornamental plants, and a large amount of research on flower color mainly focuses on the differences between varieties, while there were few reports on the change of flower color at different developmental stages. In this study, the metabolome and transcriptome of a new strain 'XM-1' with dynamic color changes of Oncidium were analyzed. The results showed that rutin, quercetin and carotenoids metabolism decreased significantly during the change of color from yellow to white. Analyzing the correlation network between metabolites and differential expressed genes, 25 key structural genes were detected and regulated by multiple MYB-related transcription factors. The MYB-related transcription factor Cluster-100966.1_OnDIVARICATA 3 was selected for further analysis. The phylogenetic tree of DIVARICATA in different species of Orchidaceae and Arabidopsis thaliana was constructed and the most closely related members were selected for sequence comparison. The results showed that OnDIVARICATA 3 contained MYB-like conserved domains. Subcellular localization results showed that OnDIVARICATA 3 was located in the nucleus. In overexpressing OnDIVARICATA 3 transgenic hairy roots, the expression of flower color related genes FLS, ZEP, and CHYB were significantly up-regulated. In summary, this study characterized the key metabolic pathways in the formation of the dynamic flower color of Oncidium hybridum, and constructed the regulatory network of the MYB-related. These results laid a theoretical foundation for the subsequent research on flower color and genetic engineering technology breeding of Oncidium hybridum.

The Y locus encodes a REPRESSOR OF PHOTOSYNTHETIC GENES protein that represses carotenoid biosynthesis via interaction with APRR2 in carrot

Little is known about the factors regulating carotenoid biosynthesis in roots. In this study, we characterized DCAR_032551, the candidate gene of the Y locus responsible for the transition of root color from ancestral white to yellow during carrot (Daucus carota) domestication. We show that DCAR_032551 encodes a REPRESSOR OF PHOTOSYNTHETIC GENES (RPGE) protein, named DcRPGE1. DcRPGE1 from wild carrot (DcRPGE1W) is a repressor of carotenoid biosynthesis. Specifically, DcRPGE1W physically interacts with DcAPRR2, an ARABIDOPSIS PSEUDO-RESPONSE REGULATOR2 (APRR2)-like transcription factor. Through this interaction, DcRPGE1W suppresses DcAPRR2-mediated transcriptional activation of the key carotenogenic genes phytoene synthase 1 (DcPSY1), DcPSY2, and lycopene ε-cyclase (DcLCYE), which strongly decreases carotenoid biosynthesis. We also demonstrate that the DcRPGE1W-DcAPRR2 interaction prevents DcAPRR2 from binding to the RGATTY elements in the promoter regions of DcPSY1, DcPSY2, and DcLCYE. Additionally, we identified a mutation in the DcRPGE1 coding region of yellow and orange carrots that leads to the generation of alternatively spliced transcripts encoding truncated DcRPGE1 proteins unable to interact with DcAPRR2, thereby failing to suppress carotenoid biosynthesis. These findings provide insights into the transcriptional regulation of carotenoid biosynthesis and offer potential target genes for enhancing carotenoid accumulation in crop plants.

De Novo Biosynthesis of Lutein in Yarrowia lipolytica

Lutein is a high-value tetraterpenoid carotenoid that is widely used in feed, cosmetics, food, and drugs. Microbial synthesis of lutein is an important method for green and sustainable production, serving as an alternative to plant extraction methods. However, an inadequate precursor supply and low catalytic efficiency of key pathway enzymes are the main reasons for the low efficacy of microbial synthesis of lutein. In this study, some strategies, such as enhancing the MVA pathway and localizing α-carotene synthase OluLCY within the subcellular organelles in Yarrowia lipolytica, were adopted to enhance the synthesis of precursor α-carotene, which resulted in a 10.50-fold increase in α-carotene titer, reaching 38.50 mg/L. Subsequently, by improving hydroxylase activity with truncated N-terminal transport peptide and locating hydroxylases to subcellular organelles, the final strain L9 producing 75.25 mg/L lutein was obtained. Eventually, a lutein titer of 675.40 mg/L (6.13 mg/g DCW) was achieved in a 5 L bioreactor by adding the antioxidant 2,6-ditert-butyl-4-methylphenol. This study realizes de novo synthesis of lutein in Y. lipolytica for the first time and achieves the highest lutein titer reported so far.

Chromosome Doubling Enhances Biomass and Carotenoid Content in Lycium chinense

Lycium chinense, a type of medicinal and edible plant, is rich in bioactive compounds beneficial to human health. In order to meet the market requirements for the yield and quality of L. chinense, polyploid induction is usually an effective way to increase plant biomass and improve the content of bioactive components. This study established the most effective tetraploid induction protocol by assessing various preculture durations, colchicine concentrations, and exposure times. The peak tetraploid induction efficacy, 18.2%, was achieved with a 12-day preculture and 24-h exposure to 50 mg L-1 colchicine. Compared to diploids, tetraploids exhibited potentially advantageous characteristics such as larger leaves, more robust stems, and faster growth rates. Physiologically, tetraploids demonstrated increased stomatal size and chloroplast count in stomata but reduced stomatal density. Nutrient analysis revealed a substantial increase in polysaccharides, calcium, iron, and zinc in tetraploid leaves. In addition, seventeen carotenoids were identified in the leaves of L. chinense. Compared to the diploid, lutein, β-carotene, neoxanthin, violaxanthin, and (E/Z)-phytoene exhibited higher levels in tetraploid strains T39 and T1, with T39 demonstrating a greater accumulation than T1. The findings suggest that the generated tetraploids harbor potential for further exploitation and lay the foundation for the selection and breeding of novel genetic resources of Lycium.

Magnesium accelerates changes in the fruit ripening and carotenoid accumulation in Satsuma Mandarin pulp

This study aims to further examine the effect of Magnesium (Mg) application on fruit quality and carotenoid metabolism in Satsuma mandarin pulp. For this, a field experiment was using 20-year-old Satsuma mandarin (C. unshiu Marc.) for two treatment; (1) CK treatment (without Mg), (2) Mg fertilizer treatment (200 g MgO plant-1). Compared with CK, Mg treatment substantially raised the Mg content in pulp at 90 to 150 DAF (the fruit expansion period), increasing by 15.69%-21.74%. Mg treatment also increased fruit TSS content by 15.84% and 9.88%, decreased fruit TA content in by 34.25% and 33.26% at 195 DAF and 210 DAF (the fruit ripening period). Moreover, at 120 to 195 DAF, Mg treatment significantly increased the levels of lutein, β-cryptoxanthin, zeaxanthin and violaxanthin in the pulp. This can be explained by the increased expression of important biosynthetic genes, including CitPSY, CitPDS, CitLCYb1, CitLCYb2, CitLCYe, CitHYb, and CitZEP, that played a role in altering the carotenoid composition. The findings of this research offer a novel approach for augmenting both the economic and nutritional worth of citrus fruits.

Effect of betanin synthesis on photosynthesis and tyrosine metabolism in transgenic carrot

BACKGROUND

Betalain is a natural pigment with important nutritional value and broad application prospects. Previously, we produced betanin biosynthesis transgenic carrots via expressing optimized genes CYP76AD1S, cDOPA5GTS and DODA1S. Betanin can accumulate throughout the whole transgenic carrots. But the effects of betanin accumulation on the metabolism of transgenic plants and whether it produces unexpected effects are still unclear.

RESULTS

The accumulation of betanin in leaves can significantly improve its antioxidant capacity and induce a decrease of chlorophyll content. Transcriptome and metabolomics analysis showed that 14.0% of genes and 33.1% of metabolites were significantly different, and metabolic pathways related to photosynthesis and tyrosine metabolism were markedly altered. Combined analysis showed that phenylpropane biosynthesis pathway significantly enriched the differentially expressed genes and significantly altered metabolites.

CONCLUSIONS

Results showed that the metabolic status was significantly altered between transgenic and non-transgenic carrots, especially the photosynthesis and tyrosine metabolism. The extra consumption of tyrosine and accumulation of betanin might be the leading causes.

Telomere-to-telomere carrot (Daucus carota) genome assembly reveals carotenoid characteristics

Carrot (Daucus carota) is an Apiaceae plant with multi-colored fleshy roots that provides a model system for carotenoid research. In this study, we assembled a 430.40 Mb high-quality gapless genome to the telomere-to-telomere (T2T) level of "Kurodagosun" carrot. In total, 36 268 genes were identified and 34 961 of them were functionally annotated. The proportion of repeat sequences in the genome was 55.3%, mainly long terminal repeats. Depending on the coverage of the repeats, 14 telomeres and 9 centromeric regions on the chromosomes were predicted. A phylogenetic analysis showed that carrots evolved early in the family Apiaceae. Based on the T2T genome, we reconstructed the carotenoid metabolic pathway and identified the structural genes that regulate carotenoid biosynthesis. Among the 65 genes that were screened, 9 were newly identified. Additionally, some gene sequences overlapped with transposons, suggesting replication and functional differentiation of carotenoid-related genes during carrot evolution. Given that some gene copies were barely expressed during development, they might be functionally redundant. Comparison of 24 cytochrome P450 genes associated with carotenoid biosynthesis revealed the tandem or proximal duplication resulting in expansion of CYP gene family. These results provided molecular information for carrot carotenoid accumulation and contributed to a new genetic resource.

Generating colorful carrot germplasm through metabolic engineering of betalains pigments

Betalains are tyrosine-derived plant pigments exclusively found in the Caryophyllales order and some higher fungi and generally classified into two groups: red-violet betacyanins and yellow-orange betaxanthins. Betalains attract great scientific and economic interest because of their relatively simple biosynthesis pathway, attractive colors and health-promoting properties. Co-expressing two core genes BvCYP76AD1 and BvDODA1 with or without a glycosyltransferase gene MjcDOPA5GT allowed the engineering of carrot (an important taproot vegetable) to produce a palette of unique colors. The highest total betalains content, 943.2 μg·g-1 DW, was obtained in carrot taproot transformed with p35S:RUBY which produces all of the necessary enzymes for betalains synthesis. Root-specific production of betalains slightly relieved tyrosine consumption revealing the possible bottleneck in betalains production. Furthermore, a unique volcano-like phenotype in carrot taproot cross-section was created by vascular cambium-specific production of betalains. The betalains-fortified carrot in this study is thus anticipated to be used as functional vegetable and colorful carrot germplasm in breeding to promote health.