Carotenoid gene expression explains the difference of carotenoid accumulation in carrot root tissues

Quantitative measurement of internal quality of carrots using hyperspectral imaging and multivariate analysis

The study aimed to measure the carotenoid (Car) and pH contents of carrots using hyperspectral imaging. A total of 300 images were collected using a hyperspectral imaging system, covering 472 wavebands from 400 to 1000 nm. Regions of interest (ROIs) were defined to extract average spectra from the hyperspectral images (HIS). We developed two models: least squares support vector machine (LS-SVM) and partial least squares regression (PLSR) to establish a quantitative analysis between the pigment amounts and spectra. The spectra and pigment contents were predicted and correlated using these models. The selection of EWs for modeling was done using the Successive Projections Algorithm (SPA), regression coefficients (RC) from PLSR models, and LS-SVM. The results demonstrated that hyperspectral imaging could effectively evaluate the internal attributes of carrot cortex and xylem. Moreover, these models accurately predicted the Car and pH contents of the carrot parts. This study provides a valuable approach for variable selection and modeling in hyperspectral imaging studies of carrots.

Response Surface Methodology to Optimize the Extraction of Carotenoids from Horticultural By-Products-A Systematic Review

Response Surface Methodology (RSM) is a widely used mathematical tool for process optimization, setting their main factorial variables. The current research analyzes and summarizes the current knowledge about the RSM in the extraction of carotenoids from fruit and vegetable by-products, following a systematic review protocol (Prisma 2020 Statement). After an identification of manuscripts in Web of Science (September 2023) using inclusion search terms ("carotenoids", "extraction", "response-surface methodology", "ultrasound", "microwave" and "enzyme"), they were screened by titles and abstracts. Finally, 29 manuscripts were selected according to the PRISMA methodology (an evidence-based minimum set of items for reporting in systematic reviews), then, 16 questions related to the quality criteria developed by authors were applied. All studies were classified as having an acceptable level of quality criteria (≤50% "yes answers"), with four of them reaching a moderate level (>50 to ≤70% "yes answers"). No studies were cataloged as complete (>70% "yes answers"). Most studies are mainly focused on ultrasound-assisted extraction, which has been widely developed compared to microwave or enzymatic-assisted extractions. Most evidence shows that it is important to provide information when RSM is applied, such as the rationale for selecting a particular design, the specification of input variables and their potential levels, a discussion on the statistical model's validity, and an explanation of the optimization procedure. In addition, the principles of open science, specifically data availability, should be included in future scientific manuscripts related to RSM and revalorization.

Chemical Composition, Functional and Anticancer Properties of Carrot

Plants are a valuable source of drugs for cancer treatment. Daucus carota has been investigated for its health properties. In particular, Daucus carota L. subsp. Sativus, the common edible carrot root, has been found to be rich in bioactive compounds such as carotenoids and dietary fiber and contains many other functional components with significant health-promoting features, while Daucus carota L. subsp. Carrot (Apiacae), also known as wild carrot, has been usually used for gastric ulcer therapy, diabetes, and muscle pain in Lebanon. Here, we review the chemical composition of Daucus carota L. and the functional properties of both edible and wild carrot subspecies. Then, we focus on compounds with anticancer characteristics identified in both Daucus carota subspecies, and we discuss their potential use in the development of novel anticancer therapeutic strategies.

Lycopene ε-cyclase mediated transition of α-carotene and β-carotene metabolic flow in carrot fleshy root

The accumulation of carotenoids, such as xanthophylls, lycopene, and carotenes, is responsible for the color of carrot (Daucus carota subsp. sativus) fleshy roots. The potential role of DcLCYE, encoding a lycopene ε-cyclase associated with carrot root color, was investigated using cultivars with orange and red roots. The expression of DcLCYE in red carrot varieties was significantly lower than that in orange carrots at the mature stage. Furthermore, red carrots accumulated larger amounts of lycopene and lower levels of α-carotene. Sequence comparison and prokaryotic expression analysis revealed that amino acid differences in red carrots did not affect the cyclization function of DcLCYE. Analysis of the catalytic activity of DcLCYE revealed that it mainly formed ε-carotene, while a side activity on α-carotene and γ-carotene was also observed. Comparative analysis of the promoter region sequences indicated that differences in the promoter region may affect the transcription of DcLCYE. DcLCYE was overexpressed in the red carrot 'Benhongjinshi' under the control of the CaMV35S promoter. Lycopene in transgenic carrot roots was cyclized, resulting in the accumulation of higher levels of α-carotene and xanthophylls, while the β-carotene content was significantly decreased. The expression levels of other genes in the carotenoid pathway were simultaneously upregulated. Knockout of DcLCYE in the orange carrot 'Kurodagosun' by CRISPR/Cas9 technology resulted in a decrease in the α-carotene and xanthophyll contents. The relative expression levels of DcPSY1, DcPSY2, and DcCHXE were sharply increased in DcLCYE knockout mutants. The results of this study provide insights into the function of DcLCYE in carrots, which could serve as a basis for creating colorful carrot germplasms.

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.

Unraveling transcriptomics of sorghum grain carotenoids: a step forward for biofortification

BACKGROUND

Sorghum (Sorghum bicolor [L.] Moench) is a promising target for pro-vitamin A biofortification as it is a global staple crop, particularly in regions where vitamin A deficiency is prevalent. As with most cereal grains, carotenoid concentrations are low in sorghum, and breeding could be a feasible strategy to increase pro-vitamin A carotenoids to biologically relevant concentrations. However, there are knowledge gaps in the biosynthesis and regulation of sorghum grain carotenoids, which can limit breeding effectiveness. The aim of this research was to gain an understanding of the transcriptional regulation of a priori candidate genes in carotenoid precursor, biosynthesis, and degradation pathways.

RESULTS

We used RNA sequencing of grain to compare the transcriptional profile of four sorghum accessions with contrasting carotenoid profiles through grain development. Most a priori candidate genes involved in the precursor MEP, carotenoid biosynthesis, and carotenoid degradation pathways were found to be differentially expressed between sorghum grain developmental stages. There was also differential expression of some of the a priori candidate genes between high and low carotenoid content groups at each developmental time point. Among these, we propose geranyl geranyl pyrophosphate synthase (GGPPS), phytoene synthase (PSY), and phytoene desaturase (PDS) as promising targets for pro-vitamin A carotenoid biofortification efforts in sorghum grain.

CONCLUSIONS

A deeper understanding of the controls underlying biosynthesis and degradation of sorghum grain carotenoids is needed to advance biofortification efforts. This study provides the first insights into the regulation of sorghum grain carotenoid biosynthesis and degradation, suggesting potential gene targets to prioritize for molecular breeding.

Influence of Root Color and Tissue on Phytochemical Contents and Antioxidant Activities in Carrot Genotypes

This study monitored changes in major carotenoids (lutein, ⍺-carotene, and β-carotene), free sugars (fructose, glucose, and sucrose), ascorbic acid, vitamin E, phytosterols (campesterol, stigmasterol, and β-sitosterol), fatty acid composition, total phenol content (TPC), total flavonoid content (TFC), total anthocyanin content, and antioxidant activities (AA); ferric-reducing antioxidant power (FRAP) and 2,2'-azino-bis (3-ethylbenzothiazoline-6sulfonic acid) [ABTS] assays, in the inner and outer root tissues of nine carrot genotypes with orange, white, and purple roots. The results showed a differential accumulation of bioactive compounds and antioxidant activities depending on root tissue and color. Carotenoids, free sugars, and total phytosterol contents were higher in genotypes with orange roots than in other genotypes. Ascorbic acid, TPC, TFC, total anthocyanin, and AA were highest in purple-colored carrots while vitamin E content was higher in white/purple carrots. Root color was highly related to the accumulation of individual carotenoids, vitamin E isomers, and total anthocyanin content most prominently among the analyzed bioactive compounds and AA. Free sugar and carotenoid contents were relatively higher in outer tissues than in inner tissues. Furthermore, ascorbic acid, TPC, TFC, and AA were statistically higher or similar in outer tissues when compared to inner tissues in all genotypes. In contrast, trends in vitamin E and phytosterol content were inconsistent between the inner and outer tissues, depending on the genotype. Although fatty acid composition was affected by both root color and tissue, the results were not significant. Thus, the phytochemical profile and content were highly dependent on root color and tissue in carrot genotypes. This may be useful in the food processing and pharmaceutical industries for the extraction of targeted bioactive compounds.

Plastid diversity and chromoplast biogenesis in differently coloured carrots: role of the DcOR3Leu gene

Distinct plastid types and ultrastructural changes are associated with differences in carotenoid pigment profiles in differently coloured carrots, and a variant of the OR gene, DcOR3^Leu is vital for chromoplast biogenesis. Accumulation of different types and amounts of carotenoids in carrots impart different colours to their taproots. In this study, the carotenoid pigment profiles, morphology, and ultrastructure of plastids in 25 carrot varieties with orange, red, yellow, or white taproots were investigated by ultra-high performance liquid chromatography as well as light and transmission electron microscopy. α-/β-Carotene and lycopene were identified as colour-determining carotenoids in orange and red carrots, respectively. In contrast, lutein was identified as the colour-determining carotenoid in almost all tested yellow and white carrots. The latter contained only trace amounts of lutein as a unique detectable carotenoid. Striking differences in plastid types that coincided with distinct carotenoid profiles were observed among the differently coloured carrots. Microscopic analysis of the different carotenoid pigment-loaded plastids revealed abundant crystalloid chromoplasts in the orange and red carrots, whereas amyloplasts were dominant in most of the yellow and white carrots, except for the yellow carrot 'Yellow Stone', where yellow chromoplasts were observed. Plastoglobuli and crystal remnants, the carotenoid sequestering substructures, were identified in crystalloid chromoplasts. Crystal remnants were often associated with a characteristic undulated internal membrane in orange carrots or several undulated membranes in red carrots. No crystal remnants, but some plastoglobuli, were observed in the plastids of all tested yellow and white carrots. In addition, the presence of chromoplast in carrot taproots was found to be associated with DcOR3^Leu, a natural variant of DcOR3, which was previously reported to be co-segregated with carotene content in carrots. Knocking out DcOR3^Leu in the orange carrot 'Kurodagosun' depressed chromoplast biogenesis and led to the generation of yellow carrots. Our results support that DcOR3^Leu is vital but insufficient for chromoplasts biogenesis in carrots, and add to the understanding of the formation of chromoplasts in carrots.

Novel Approaches for the Recovery of Natural Pigments with Potential Health Effects

The current increased industrial food production has led to a significant rise in the amount of food waste generated. These food wastes, especially fruit and vegetable byproducts, are good sources of natural pigments, such as anthocyanins, betalains, carotenoids, and chlorophylls, with both coloring and health-related properties. Therefore, recovery of natural pigments from food wastes is important for both economic and environmental reasons. Conventional methods that are used to extract natural pigments from food wastes are time-consuming, expensive, and unsustainable. In addition, natural pigments are sensitive to high temperatures and prolonged processing times that are applied during conventional treatments. In this sense, the present review provides an elucidation of the latest research on the extraction of pigments from the agri-food industry and how their consumption may improve human health.

Characterization of cassava ORANGE proteins and their capability to increase provitamin A carotenoids accumulation

Cassava (Manihot esculenta Crantz) biofortification with provitamin A carotenoids is an ongoing process that aims to alleviate vitamin A deficiency. The moderate content of provitamin A carotenoids achieved so far limits the contribution to providing adequate dietary vitamin A levels. Strategies to increase carotenoid content focused on genes from the carotenoids biosynthesis pathway. In recent years, special emphasis was given to ORANGE protein (OR), which promotes the accumulation of carotenoids and their stability in several plants. The aim of this work was to identify, characterize and investigate the role of OR in the biosynthesis and stabilization of carotenoids in cassava and its relationship with phytoene synthase (PSY), the rate-limiting enzyme of the carotenoids biosynthesis pathway. Gene and protein characterization of OR, expression levels, protein amounts and carotenoids levels were evaluated in roots of one white (60444) and two yellow cassava cultivars (GM5309-57 and GM3736-37). Four OR variants were found in yellow cassava roots. Although comparable expression was found for three variants, significantly higher OR protein amounts were observed in the yellow varieties. In contrast, cassava PSY1 expression was significantly higher in the yellow cultivars, but PSY protein amount did not vary. Furthermore, we evaluated whether expression of one of the variants, MeOR_X1, affected carotenoid accumulation in cassava Friable Embryogenic Callus (FEC). Overexpression of maize PSY1 alone resulted in carotenoids accumulation and induced crystal formation. Co-expression with MeOR_X1 led to greatly increase of carotenoids although PSY1 expression was high in the co-expressed FEC. Our data suggest that posttranslational mechanisms controlling OR and PSY protein stability contribute to higher carotenoid levels in yellow cassava. Moreover, we showed that cassava FEC can be used to study the efficiency of single and combinatorial gene expression in increasing the carotenoid content prior to its application for the generation of biofortified cassava with enhanced carotenoids levels.

Discoloration investigations of freeze-dried carrot cylinders from physical structure and color-related chemical compositions

BACKGROUND

High carotenoid content always lead to a yellower/redder color in carrots, while a puzzling phenomenon still exists that freeze-dried carrots (FDC) have a higher carotenoid content but a lighter color compared with thermal-dried carrots. It seems that carotenoid is not the only main factor affecting sample color. Hence the discoloration characteristics of freeze-dried carrots were comprehensively analyzed from physical structure and color-related chemical composition profile.

RESULTS

Outcomes of low-field nuclear magnetic resonance and scanning electron microscopy showed that sublimation of immobilized water preserved the intact porous structure of FDC, which kept the volume shrinkage below 30% and led to less accumulations of color-related compositions. Besides, results of correlation and principal component analysis-X model proved that lutein and caffeic acid mainly affected a* value (r = 0.917) and b* value (r = 0.836) of FDC, respectively. Moreover, lipoxygenase indirectly affected sample color by degrading carotenoids, and the lutein content loss for fresh and blanching FDC was 41.56% and 47.14%, respectively.

CONCLUSIONS

The discoloration of FDC was significantly affected by both physical structure and color-related chemical compositions. © 2021 Society of Chemical Industry.

Repression of Carotenoid Accumulation by Nitrogen and NH4+ Supply in Carrot Callus Cells In Vitro

The effect of mineral nutrition on the accumulation of the main health beneficial compounds in carrots, the carotenoid pigments, remains ambiguous; here, a model-based approach was applied to reveal which compounds are responsible for the variation in carotenoid content in carrot cells in vitro. For this purpose, carotenoid-rich callus was cultured on either BI (modified Gamborg B5) or R (modified Murashige and Skoog MS) mineral media or on modified media obtained by exchanging compounds between BI and R. Callus growing on the BI medium had abundant carotene crystals in the cells and a dark orange color in contrast to pale orange callus with sparse crystals on the R medium. The carotenoid content, determined by HPLC and spectrophotometrically after two months of culture, was 5.3 higher on the BI medium. The replacement of media components revealed that only the N concentration and the NO3:NH4 ratio affected carotenoid accumulation. Either the increase of N amount above 27 mM or decrease of NO3:NH4 ratio below 12 resulted in the repression of carotenoid accumulation. An adverse effect of the increased NH4+ level on callus growth was additionally found. Somatic embryos were formed regardless of the level of N supplied. Changes to other media components, i.e., macroelements other than N, microelements, vitamins, growth regulators, and sucrose had no effect on callus growth and carotenoid accumulation. The results obtained from this model system expand the range of factors, such as N availability, composition of N salts, and ratio of nitrate to ammonium N form, that may affect the regulation of carotenoid metabolism.

Inhibition of Carotenoid Biosynthesis by CRISPR/Cas9 Triggers Cell Wall Remodelling in Carrot

Recent data indicate that modifications to carotenoid biosynthesis pathway in plants alter the expression of genes affecting chemical composition of the cell wall. Phytoene synthase (PSY) is a rate limiting factor of carotenoid biosynthesis and it may exhibit species-specific and organ-specific roles determined by the presence of psy paralogous genes, the importance of which often remains unrevealed. Thus, the aim of this work was to elaborate the roles of two psy paralogs in a model system and to reveal biochemical changes in the cell wall of psy knockout mutants. For this purpose, Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and CRISPR associated (Cas9) proteins (CRISPR/Cas9) vectors were introduced to carotenoid-rich carrot (Daucus carota) callus cells in order to induce mutations in the psy1 and psy2 genes. Gene sequencing, expression analysis, and carotenoid content analysis revealed that the psy2 gene is critical for carotenoid biosynthesis in this model and its knockout blocks carotenogenesis. The psy2 knockout also decreased the expression of the psy1 paralog. Immunohistochemical staining of the psy2 mutant cells showed altered composition of arabinogalactan proteins, pectins, and extensins in the mutant cell walls. In particular, low-methylesterified pectins were abundantly present in the cell walls of carotenoid-rich callus in contrast to the carotenoid-free psy2 mutant. Transmission electron microscopy revealed altered plastid transition to amyloplasts instead of chromoplasts. The results demonstrate for the first time that the inhibited biosynthesis of carotenoids triggers the cell wall remodelling.

Bioactive Compounds and Antioxidant Capacity in Anthocyanin-Rich Carrots: A Comparison between the Black Carrot and the Apulian Landrace "Polignano" Carrot

The carrot is one of the most cultivated vegetables in the world. Black or purple carrots contain acylated anthocyanins which are of special interest to the food industry for their stability and nutraceutical characteristics. Anthocyanin-rich fruits and vegetables have gained popularity in the last ten years, due to the health benefits they provide. In this paper, the characterizations of the bioactive compounds and antioxidant capacities of different anthocyanin-containing carrots (a black carrot—BC, and a local purple carrot, the “Polignano” carrot—PC), compared to the commercial orange carrot (OC) (lacking of anthocyanins), are reported. The anthocyanin profiles of the polyphenolic extracts of BC and PC were similar, but differences were observed at quantitative levels. The total anthocyanin content in BC was more than twice that in PC (13.84 ± 0.61 vs. 5.64 ± 0.48 mg K Eq. g⁻¹ DW). Phenolic acids (mostly chlorogenic acid) were also present at high level in anthocyanin-rich carrots compared to OC. High polyphenol content accounted also for a high reducing capacity (evaluated by Folin–Ciocalteu reagent, FCR), and antioxidant capacity (evaluated by TEAC and ORAC assays) which were the highest for BC (FCR value: 16.6 ± 1.1 mg GAE. g⁻¹ DW; TEAC: 76.6 ± 10.6 µmol TE. g⁻¹ DW; ORAC: 159.9 ± 3.3 µmol TE. g⁻¹ DW). All carrot genotypes (mostly OC) were rich in carotenoids (BC 0.14 ± 0.024; PC 0.33 ± 0.038; OC 1.29 ± 0.09 mg. g⁻¹ DW), with predominance of α and β-carotene, in OC, and lutein in BC. PC showed the highest malic acid and sugar (glucose plus fructose) content. In conclusion, while BC is remarkable for nutraceutical features, the local genotype (“Polignano” carrot) is worth considering in genetic biodiversity conservation programme.

Effects of simulated drought stress on carotenoid contents and expression of related genes in carrot taproots

Carotenoids are liposoluble pigments found in plant chromoplasts that are responsible for the yellow, orange, and red colors of carrot taproots. Drought is one of the main stress factors affecting carrot growth. Carotenoids play important roles in drought resistance in higher plants. In the present work, the carotenoid contents in three different-colored carrot cultivars, 'Kurodagosun' (orange), 'Benhongjinshi' (red), and 'Qitouhuang' (yellow), were determined by ultra-high-performance liquid chromatography (UPLC) after 15% polyethylene glycol (PEG) 6000 treatment. Real-time fluorescence quantitative PCR (RT-qPCR) was then used to determine the expression levels of carotenoid synthesis- and degradation-related genes. Increases in β-carotene content in 'Qitouhuang' taproots under drought stress were found to be related to the expression levels of DcPSY2 and DcLCYB. Increases in lutein and decreases in α-carotene content in 'Qitouhuang' and 'Kurodagosun' under PEG treatment may be related to the expression levels of DcCYP97A3, DcCHXE, and DcCHXB1. The expression levels of DcNCED1 and DcNCED2 in the three cultivars significantly increased, thus suggesting that NCED genes could respond to drought stress. Analysis of the growth status and carotenoid contents of carrots under PEG treatment indicated that the orange cultivar 'Kurodagosun' has better adaptability to drought stress than the other cultivars and that β-carotene and lutein may be involved in the stress resistance process of carrot.

Overexpression of the Golden SNP-Carrying Orange Gene Enhances Carotenoid Accumulation and Heat Stress Tolerance in Sweetpotato Plants

Carotenoids function as photosynthetic accessory pigments, antioxidants, and vitamin A precursors. We recently showed that transgenic sweetpotato calli overexpressing the mutant sweetpotato (Ipomoea batatas [L.] Lam) Orange gene (IbOr-R96H), which carries a single nucleotide polymorphism responsible for Arg to His substitution at amino acid position 96, exhibited dramatically higher carotenoid content and abiotic stress tolerance than calli overexpressing the wild-type IbOr gene (IbOr-WT). In this study, we generated transgenic sweetpotato plants overexpressing IbOr-R96H under the control of the cauliflower mosaic virus (CaMV) 35S promoter via Agrobacterium-mediated transformation. The total carotenoid contents of IbOr-R96H storage roots (light-orange flesh) and IbOr-WT storage roots (light-yellow flesh) were 5.4-19.6 and 3.2-fold higher, respectively, than those of non-transgenic (NT) storage roots (white flesh). The β-carotene content of IbOr-R96H storage roots was up to 186.2-fold higher than that of NT storage roots. In addition, IbOr-R96H plants showed greater tolerance to heat stress (47 °C) than NT and IbOr-WT plants, possibly because of higher DPPH radical scavenging activity and ABA contents. These results indicate that IbOr-R96H is a promising strategy for developing new sweetpotato cultivars with improved carotenoid contents and heat stress tolerance.

Carrot Genotypes Contrasted by Root Color and Grown under Different Conditions Displayed Differential Pharmacological Profiles in Vascular and Metabolic Cells

Carrots' genotype and growing conditions influence their potential properties to fight against cardiovascular and metabolic diseases. The present study evaluated the influence of carrot genotypes contrasted by root color (Bolero, Presto, Karotan, Deep Purple, Kintoki and Blanche des Vosges) growing under standard, water-restricted, biotic stress (Alternaria dauci inoculation), and combined stress conditions (water restriction and A.dauci inoculation). The effect of carrots' polyphenol and carotenoid content was assessed on endothelial and smooth muscle cells, hepatocytes, adipocytes and macrophages functions (oxidative stress, apoptosis, proliferation, lipid accumulation and inflammation). Independently of varieties or growing conditions, all carrot extracts affected vascular cells' oxidative stress and apoptosis, and metabolic cells' oxidative stress and lipid accumulation. Three clusters were revealed and displayed beneficial properties mostly for adipocytes function, smooth muscle cells and hepatocytes, and endothelial cells and hepatocytes, respectively. Karotan and Presto varieties exhibited endothelial tropism while Blanche des Vosges targeted adipocytes. Carrots under biotic stress are more efficient in inducing beneficial effects, with the Bolero variety being the most effective. However, extracts from carrots which grew under combined stress conditions had limited beneficial effects. This report underscores the use of certain carrot extracts as potential effective nutraceutical supplements for metabolic diseases.

Genetic Engineering for Global Food Security: Photosynthesis and Biofortification

Increasing demands for food and resources are challenging existing markets, driving a need to continually investigate and establish crop varieties with improved yields and health benefits. By the later part of the century, current estimates indicate that a >50% increase in the yield of most of the important food crops including wheat, rice and barley will be needed to maintain food supplies and improve nutritional quality to tackle what has become known as 'hidden hunger'. Improving the nutritional quality of crops has become a target for providing the micronutrients required in remote communities where dietary variation is often limited. A number of methods to achieve this have been investigated over recent years, from improving photosynthesis through genetic engineering, to breeding new higher yielding varieties. Recent research has shown that growing plants under elevated [CO2] can lead to an increase in Vitamin C due to changes in gene expression, demonstrating one potential route for plant biofortification. In this review, we discuss the current research being undertaken to improve photosynthesis and biofortify key crops to secure future food supplies and the potential links between improved photosynthesis and nutritional quality.

Phytochemicals in Daucus carota and Their Health Benefits-Review Article

Carrots are a multi-nutritional food source. They are an important root vegetable, rich in natural bioactive compounds, which are recognised for their nutraceutical effects and health benefits. This review summarises the occurrence, biosynthesis, factors affecting concentration, and health benefits of phytochemicals found in Daucus carota. Two hundred and fifty-five articles including original research papers, books, and book chapters were analysed, of which one hundred and thirty articles (most relevant to the topic) were selected for writing the review article. The four types of phytochemicals found in carrots, namely phenolics, carotenoids, polyacetylenes, and ascorbic acid, were summarised. These chemicals aid in the risk reduction of cancer and cardiovascular diseases due to their antioxidant, anti-inflammatory, plasma lipid modification, and anti-tumour properties. Numerous factors influence the amount and type of phytochemicals present in carrots. Genotype (colour differences) plays an important role; high contents of α and β-carotene are present in orange carrots, lutein in yellow carrots, lycopene in red carrots, anthocyanins in the root of purple carrots, and phenolic compounds abound in black carrots. Carotenoids range between 3.2 mg/kg and 170 mg/kg, while vitamin C varies from 21 mg/kg to 775 mg/kg between cultivars. Growth temperatures of carrots influence the level of the sugars, carotenoids, and volatile compounds, so that growing in cool conditions results in a higher yield and quality of carrots, while higher temperatures would increase terpene synthesis, resulting in carrots with a bitter taste. It is worthwhile to investigate the cultivation of different genotypes under various environmental conditions to increase levels of phytochemicals and enhance the nutritional value of carrot, along with the valorisation of carrot by-products.

Advances in research on the carrot, an important root vegetable in the Apiaceae family

Carrots (Daucus carota L.), among the most important root vegetables in the Apiaceae family, are cultivated worldwide. The storage root is widely utilized due to its richness in carotenoids, anthocyanins, dietary fiber, vitamins and other nutrients. Carrot extracts, which serve as sources of antioxidants, have important functions in preventing many diseases. The biosynthesis, metabolism, and medicinal properties of carotenoids in carrots have been widely studied. Research on hormone regulation in the growth and development of carrots has also been widely performed. Recently, with the development of high-throughput sequencing technology, many efficient tools have been adopted in carrot research. A large amount of sequence data has been produced and applied to improve carrot breeding. A genome editing system based on CRISPR/Cas9 was also constructed for carrot research. In this review, we will briefly summarize the origins, genetic breeding, resistance breeding, genome editing, omics research, hormone regulation, and nutritional composition of carrots. Perspectives about future research work on carrots are also briefly provided.

iTRAQ-Based Quantitative Proteomics and Transcriptomics Provide Insights Into the Importance of Expansins During Root Development in Carrot

Carrot is an important root vegetable crop with a variety of nutrients. As the main product of carrots, the growth and development of fleshy roots directly determine the yield and quality of carrots. However, molecular mechanism underlying the carrot root formation and expansion is still limited. In our study, isobaric tags for relative and absolute quantification (iTRAQ) was utilized to explore the differentially expressed proteins (DEPs) during different developmental stages of carrot roots. Overall, 2,845 proteins were detected, of which 118 were significantly expressed in all three stages. DEPs that participated in several growth metabolisms were identified, including energy metabolism, defense metabolism, cell growth and shape regulation. Among them, two expansin proteins were obtained. A total of 30 expansin genes were identified based on the carrot genome database. Structure analysis showed that carrot expansin gene family was relatively conserved. Based on the expression analysis, we found that the expression profile of expansins genes was up-regulated during the vigorous growing period of carrot root. Furthermore, there was a consistent relationship between the expression patterns of mRNA and protein. The results indicated that expansin proteins might play important roles during root development in carrot. Our work provided useful information for understanding molecular mechanism of carrot root development.

Unique chromoplast organisation and carotenoid gene expression in carotenoid-rich carrot callus

MAIN CONCLUSION

The new model orange callus line, similar to carrot root, was rich in carotenoids due to altered expression of some carotenogenesis-associated genes and possessed unique diversity of chromoplast ultrastructure. Callus induced from carrot root segments cultured in vitro is usually pale yellow (p-y) and poor in carotenoids. A unique, non-engineered callus line of dark orange (d-o) colour was developed in this work. The content of carotenoid pigments in d-o callus was at the same level as in an orange carrot storage root and nine-fold higher than in p-y callus. Carotenoids accumulated mainly in abundant crystalline chromoplasts that are also common in carrot root but not in p-y callus. Using transmission electron microscopy, other types of chromoplasts were also found in d-o callus, including membranous chromoplasts rarely identified in plants and not observed in carrot root until now. At the transcriptional level, most carotenogenesis-associated genes were upregulated in d-o callus in comparison to p-y callus, but their expression was downregulated or unchanged when compared to root tissue. Two pathway steps were critical and could explain the massive carotenoid accumulation in this tissue. The geranylgeranyl diphosphate synthase gene involved in the biosynthesis of carotenoid precursors was highly expressed, while the β-carotene hydroxylase gene involved in β-carotene conversion to downstream xanthophylls was highly repressed. Additionally, paralogues of these genes and phytoene synthase were differentially expressed, indicating their tissue-specific roles in carotenoid biosynthesis and metabolism. The established system may serve as a novel model for elucidating plastid biogenesis that coincides with carotenogenesis.

Significance of Genetic, Environmental, and Pre- and Postharvest Factors Affecting Carotenoid Contents in Crops: A Review

Carotenoids are a diverse group of tetraterpenoid pigments that play indispensable roles in plants and animals. The biosynthesis of carotenoids in plants is strictly regulated at the transcriptional and post-transcriptional levels in accordance with inherited genetic signals and developmental requirements and in response to external environmental stimulants. The alteration in the biosynthesis of carotenoids under the influence of external environmental stimulants, such as high light, drought, salinity, and chilling stresses, has been shown to significantly influence the nutritional value of crop plants. In addition to these stimulants, several pre- and postharvesting cultivation practices significantly influence carotenoid compositions and contents. Thus, this review discusses how various environmental stimulants and pre- and postharvesting factors can be positively modulated for the enhanced biosynthesis and accumulation of carotenoids in the edible parts of crop plants, such as the leaves, roots, tubers, flowers, fruit, and seeds. In addition, future research directions in this context are identified.