Carotenoid metabolism and regulation in horticultural crops

Molecular mechanisms of neutron radiation dose effects on M1 generation peas

The dose effect of radiation has long been a topic of concern, but the molecular mechanism behind it is still unclear. In this study, dried pea seeds were irradiated with 252Cf fission neutron source. Through analyzing the transcriptome and proteome of M1 generation pea (Pisum sativum L.) leaves, we studied the molecular rule and mechanism of neutron dose effect. Our results showed three important rules of global gene expression in the studied dose range. The rule closely related to the neutron absorbed dose at the transcription and translation levels is: the greater the difference in neutron absorbed dose between two radiation treatment groups, the greater the difference in differential expression between the two groups and the control group. We also obtained important sensitive metabolic pathways of neutron radiation, as well as related key genes. Furthermore, the overall molecular regulation mechanism of dose effect was revealed based on the main functional items obtained. Our research results can be applied to appropriate radiation dose estimation and agricultural production practice.

A novel C2H2-type zinc-finger transcription factor, CitZAT4, regulates ethylene-induced orange coloration in Satsuma mandarin flavedo (Citrus unshiu Marc.)

Ethylene treatment promotes orange coloration in the flavedo of Satsuma mandarin (Citrus unshiu Marc.) fruit, but the corresponding regulatory mechanism is still largely unknown. In this study, we identified a C2H2-type zinc-finger transcription factor, CitZAT4, the expression of which was markedly induced by ethylene. CitZAT4 directly binds to the CitPSY promoter and activates its expression, thereby promoting carotenoid biosynthesis. Transient expression in Satsuma mandarin fruit and stable transformation of citrus calli showed that overexpressing of CitZAT4 inhibited CitLCYE expression, thus inhibiting α-branch yellow carotenoid (lutein) biosynthesis. CitZAT4 overexpression also enhanced the transcript levels of CitLCYB, CitHYD, and CitNCED2, promoting β-branch orange carotenoid accumulation. Molecular biochemical assays, including yeast one-hybrid (Y1H), electrophoretic mobility shift (EMSA), chromatin immunoprecipitation quantitative polymerase chain reaction (ChIP-qPCR), and luciferase (LUC) assays, demonstrated that CitZAT4 directly binds to the promoters of its target genes and regulates their expression. An ethylene response factor, CitERF061, which is induced by ethylene signaling, was found to directly bound to the CitZAT4 promoter and induced its expression, thus positively regulating CitZAT4-mediated orange coloration in citrus fruit. Together, our findings reveal that a CitZAT4-mediated transcriptional cascade is driven by ethylene via CitERF061, linking ethylene signaling to carotenoid metabolism in promoting orange coloration in the flavedo of Satsuma mandarin fruit. The molecular regulatory mechanism revealed here represents a significant step toward developing strategies for improving the quality and economic efficiency of citrus crops.

Biosynthesis and Extraction of Chlorophyll, Carotenoids, Anthocyanins, and Betalaine In Vivo and In Vitro

As natural bioactive compounds, plant pigments play crucial roles not only in plant phenotype, growth, development, and adaptation to stress but also hold unique value in biotechnology, healthcare, and industrial applications. There is growing interest in the biosynthesis and acquisition of plant pigments. Thus, this paper explores emerging extraction methods of natural pigments and elucidates the biosynthesis pathways of four key plant pigments, chlorophylls, carotenoids, anthocyanins, and betalaine in vivo and in vitro. We comprehensively discuss the application of solvent, supercritical fluid [extraction], ultrasonic, and microwave-assisted extraction techniques, as well as introducing key enzymes, precursors, and synthetic pathways involved in pigment synthesis. δ-Aminolevulinic acid represents a pivotal initiating enzyme for chlorophyll synthesis, whereas isopentenylpyrophosphate, (IPP) and dimethylallyl pyrophosphate, (DMAPP) are closely associated with carotenoid biosynthesis. Phenylalanine and tyrosine are critical substances for anthocyanin and betalaine synthesis, respectively. Hence, crucial genes such as chlI, crtB, PGT8, CYP76AD1, and BvDODA can be employed for heterologous biosynthesis in vitro to meet the demand for increased plant pigment amount. As a pivotal determinant of plant coloration, an in-depth exploration into the high-quality acquisition of plant pigments can provide a basis for developing superior pigments and offer new insights into increasing pigment yield.

The abscisic acid-responsive transcriptional regulatory module CsERF110-CsERF53 orchestrates citrus fruit coloration

Carotenoid biosynthesis is closely associated with abscisic acid (ABA) during the ripening process of non-climacteric fruits, but the regulatory mechanism that links ABA signaling to carotenoid metabolism remains largely unclear. Here, we identified two master regulators of ABA-mediated citrus fruit coloration, CsERF110 and CsERF53, which activate the expression of carotenoid metabolism genes (CsGGPPS, CsPSY, CsPDS, CsCRTISO, CsLCYB2, CsLCYE, CsHYD, CsZEP, and CsNCED2) to facilitate carotenoid accumulation. Further investigations showed that CsERF110 not only activates the expression of CsERF53 by binding to its promoter but also interacts with CsERF53 to form the transcriptional regulatory module CsERF110-CsERF53. We also discovered a positive feedback regulatory loop between the ABA signal and carotenoid metabolism regulated by the transcriptional regulatory module CsERF110-CsERF53. Our results reveal that the CsERF110-CsERF53 module responds to ABA signaling, thereby orchestrating citrus fruit coloration. Considering the importance of carotenoid content for citrus and many other carotenoid-rich crops, the revelation of molecular mechanisms that underlie ABA-mediated carotenoid biosynthesis in plants will facilitate the development of transgenic/gene-editing approaches, further contributing to improving the quality of citrus and other carotenoid-rich crops.

Multi-faceted effects of NaCl on salt-tolerant microalgae Golenkinia sp. SDEC-16

The salt-tolerant microalgae are extremely few and salt-tolerance mechanism is unclear, requiring urgent exploration of salt-tolerance mechanism of known microalgae. This study was first to reveal the salt-tolerance mechanism of Golenkinia sp. SDEC-16 by investigating the growth and metabolism under different salinities and high salinity long-term cultivation. SDEC-16 can survive under high salinity and resume normal growth after NaCl removal. Under long-term stress, SDEC-16 had higher lipid content and productivity than BG11. However, the suppressed Fv/Fm (58.4%) and Fv/F0 (84.0%) along with the increased reactive oxygen species (×6.6), and superoxide dismutase (×1.7) during the treatment revealed NaCl-induced photosynthetic inhibition and oxidative stress. RNA sequencing results showed inhibition of the photosynthetic system, and the enhancement of pathways such as nitrogen metabolism, energy metabolism, and lipid synthesis contributed to the good function of chloroplast, energy supply, and metabolic activity of SDEC-16. This study provides theoretical support for large-scale microalgal cultivation in seawater.

Walnut protein isolate based emulsion as a promising delivery system enhanced lutein bioaccessibility

Lutein, a natural pigment with multiple beneficial bioactivities, faces limitations in food processing due to its instability. In this study, we constructed four modified walnut protein isolate (WNPI) based emulsions as emulsion-based delivery systems (EBDS) for lutein fortification. The modification treatments enhanced the encapsulation efficiency of the WNPI-based EBDS on lutein. The modified WNPI-based EBDS exhibited improved storage and digestive stability, as well as increased lutein delivery capability in simulated gastrointestinal conditions. After in vitro digestion, the lutein retention in the modified WNPI-based EBDS was higher than in the untreated WNPI-based EBDS, with a maximum retention of 49.67 ± 1.10 % achieved after ultrasonic modification. Furthermore, the modified WNPI-based EBDS exhibited an elevated lutein bioaccessibility, reaching a maximum value of 40.49 ± 1.29 % after ultrasonic modification, nearly twice as high as the untreated WNPI-based EBDS. Molecular docking analysis indicated a robust affinity between WNPI and lutein, involving hydrogen bonds and hydrophobic interactions. Collectively, this study broadens WNPI's application and provides a foundation for fortifying other fat-soluble bioactive substances.

The MdMYB44-MdTPR1 repressive complex inhibits MdCCD4 and MdCYP97A3 expression through histone deacetylation to regulate carotenoid biosynthesis in apple

Carotenoids are photosynthetic pigments and antioxidants that contribute to different plant colors. However, the involvement of TOPLESS (TPL/TPR)-mediated histone deacetylation in the modulation of carotenoid biosynthesis through ethylene-responsive element-binding factor-associated amphiphilic repression (EAR)-containing transcription factors (TFs) in apple (Malus domestica Borkh.) is poorly understood. MdMYB44 is a transcriptional repressor that contains an EAR repression motif. In the present study, we used functional analyses and molecular assays to elucidate the molecular mechanisms through which MdMYB44-MdTPR1-mediated histone deacetylation influences carotenoid biosynthesis in apples. We identified two carotenoid biosynthetic genes, MdCCD4 and MdCYP97A3, that were confirmed to be involved in MdMYB44-mediated carotenoid biosynthesis. MdMYB44 enhanced β-branch carotenoid biosynthesis by repressing MdCCD4 expression, whereas MdMYB44 suppressed lutein level by repressing MdCYP97A3 expression. Moreover, MdMYB44 partially influences carotenoid biosynthesis by interacting with the co-repressor TPR1 through the EAR motif to inhibit MdCCD4 and MdCYP97A3 expression via histone deacetylation. Our findings indicate that the MdTPR1-MdMYB44 repressive cascade regulates carotenoid biosynthesis, providing profound insights into the molecular basis of histone deacetylation-mediated carotenoid biosynthesis in plants. These results also provide evidence that the EAR-harboring TF/TPL repressive complex plays a universal role in histone deacetylation-mediated inhibition of gene expression in various plants.

Abscisic acid activates transcription factor module MdABI5-MdMYBS1 during carotenoid-derived apple fruit coloration

Carotenoids are major pigments contributing to fruit coloration. We previously reported that the apple (Malus domestica Borkh.) mutant fruits of "Beni Shogun" and "Yanfu 3" show a marked difference in fruit coloration. However, the regulatory mechanism underlying this phenomenon remains unclear. In this study, we determined that carotenoid is the main factor influencing fruit flesh color. We identified an R1-type MYB transcription factor (TF), MdMYBS1, which was found to be highly associated with carotenoids and abscisic acid (ABA) contents of apple fruits. Overexpression of MdMYBS1 promoted, and silencing of MdMYBS1 repressed, β-branch carotenoids synthesis and ABA accumulation. MdMYBS1 regulates carotenoid biosynthesis by directly activating the major carotenoid biosynthetic genes encoding phytoene synthase (MdPSY2-1) and lycopene β-cyclase (MdLCYb). 9-cis-epoxycarotenoid dioxygenase 1 (MdNCED1) contributes to ABA biosynthesis, and MdMYBS1 enhances endogenous ABA accumulation by activating the MdNCED1 promoter. In addition, the basic leucine zipper domain TF ABSCISIC ACID-INSENSITIVE5 (MdABI5) was identified as an upstream activator of MdMYBS1, which promotes carotenoid and ABA accumulation. Furthermore, ABA promotes carotenoid biosynthesis and enhances MdMYBS1 and MdABI5 promoter activities. Our findings demonstrate that the MdABI5-MdMYBS1 cascade activated by ABA regulates carotenoid-derived fruit coloration and ABA accumulation in apple, providing avenues in breeding and planting for improvement of fruit coloration and quality.

Integrative Analysis of Metabolome and Transcriptome of Carotenoid Biosynthesis Reveals the Mechanism of Fruit Color Change in Tomato (Solanum lycopersicum)

Tomato fruit ripening is accompanied by carotenoid accumulation and color changes. To elucidate the regulatory mechanisms underlying carotenoid synthesis during fruit ripening, a combined transcriptomic and metabolomic analysis was conducted on red-fruited tomato (WP190) and orange-fruited tomato (ZH108). A total of twenty-nine (29) different carotenoid compounds were identified in tomato fruits at six different stages. The abundance of the majority of the carotenoids was enhanced significantly with fruit ripening, with higher levels of lycopene; (E/Z)-lycopene; and α-, β- and γ-carotenoids detected in the fruits of WP190 at 50 and 60 days post anthesis (DPA). Transcriptome analysis revealed that the fruits of two varieties exhibited the highest number of differentially expressed genes (DEGs) at 50 DPA, and a module of co-expressed genes related to the fruit carotenoid content was established by WGCNA. qRT-PCR analysis validated the transcriptome result with a significantly elevated transcript level of lycopene biosynthesis genes (including SlPSY2, SlZCIS, SlPDS, SlZDS and SlCRTSO2) observed in WP190 at 50 DPA in comparison to ZH108. In addition, during the ripening process, the expression of ethylene biosynthesis (SlACSs and SlACOs) and signaling (SlEIN3 and SlERF1) genes was also increased, and these mechanisms may regulate carotenoid accumulation and fruit ripening in tomato. Differential expression of several key genes in the fruit of two tomato varieties at different stages regulates the accumulation of carotenoids and leads to differences in color between the two varieties of tomato. The results of this study provide a comprehensive understanding of carotenoid accumulation and ethylene biosynthesis and signal transduction pathway regulatory mechanisms during tomato fruit development.

Lactating mothers' perceptions and sensory acceptability of a provitamin A carotenoid-iron-rich composite dish prepared from iron-biofortified common bean and orange-fleshed sweet potato in rural western Uganda

Uganda's lactating mothers are vulnerable to deficiencies of vitamin A and iron because they consume plant-based conventional foods such as white-fleshed sweet potato (WFSP) and non-iron biofortified common bean (NIBCB) that are low in provitamin A (PVA) and iron, respectively. A PVA carotenoid-iron-rich dish was prepared from a combination of orange-fleshed sweet potato (OFSP) and iron-biofortified common bean (IBCB). This study evaluated the perceptions and sensory acceptability of OFSP+IBCB (test food) against WFSP+NIBCB (control food) among lactating mothers in rural Uganda. A total of 94 lactating mothers participated in the study. The sensory attributes (taste, color, aroma, texture, and general acceptability) of test and control foods were rated using a five-point facial hedonic scale (1 = dislike very much, 2 = dislike, 3 = neutral, 4 = like 5 = like very much). An attribute was acceptable if the participant scored from like to like very much. Focus group discussions (FGDs) were conducted to assess participant perceptions about their future consumption of OFSP+IBCB. The chi-square test was used to detect the proportion difference for each sensory attribute between OFSP+IBCB and WFSP+NIBCB, while FGD data were analyzed by thematic analysis. Taste, color, and aroma were acceptable to the mothers and not significantly different between OFSP+IBCB and WFSP+NIBCB (p > .05). Participants had positive perceptions of the taste, aroma, and color of the OFSP+IBCB and negative perceptions about the soft texture of OFSP. The lactating mothers had positive perceptions of consuming OFSP+IBCB provided they were accessible, affordable, and feasible to prepare.

BoaBZR1.1 mediates brassinosteroid-induced carotenoid biosynthesis in Chinese kale

Brassinazole resistant 1 (BZR1), a brassinosteroid (BR) signaling component, plays a pivotal role in regulating numerous specific developmental processes. Our study demonstrated that exogenous treatment with 2,4-epibrassinolide (EBR) significantly enhanced the accumulation of carotenoids and chlorophylls in Chinese kale (Brassica oleracea var. alboglabra). The underlying mechanism was deciphered through yeast one-hybrid (Y1H) and dual-luciferase (LUC) assays, whereby BoaBZR1.1 directly interacts with the promoters of BoaCRTISO and BoaPSY2, activating their expression. This effect was further validated through overexpression of BoaBZR1.1 in Chinese kale calli and plants, both of which exhibited increased carotenoid accumulation. Additionally, qPCR analysis unveiled upregulation of carotenoid and chlorophyll biosynthetic genes in the T1 generation of BoaBZR1.1-overexpressing plants. These findings underscored the significance of BoaBZR1.1-mediated BR signaling in regulating carotenoid accumulation in Chinese kale and suggested the potential for enhancing the nutritional quality of Chinese kale through genetic engineering of BoaBZR1.1.

Effects of different light intensity on leaf color changes in a Chinese cabbage yellow cotyledon mutant

Leaf color is one of the most important phenotypic features in horticultural crops and directly related to the contents of photosynthetic pigments. Most leaf color mutants are determined by the altered chlorophyll or carotenoid, which can be affected by light quality and intensity. Our previous study obtained a Chinese cabbage yellow cotyledon mutant that exhibited obvious yellow phenotypes in the cotyledons and the new leaves. However, the underlying mechanisms in the formation of yellow cotyledons and leaves remain unclear. In this study, the Chinese cabbage yellow cotyledon mutant 19YC-2 exhibited obvious difference in leaf color and abnormal chloroplast ultrastructure compared to the normal green cotyledon line 19GC-2. Remarkably, low-intensity light treatment caused turn-green leaves and a significant decrease in carotenoid content in 19YC-2. RNA-seq analysis revealed that the pathways of photosynthesis antenna proteins and carotenoid biosynthesis were significantly enriched during the process of leaf color changes, and many differentially expressed genes related to the two pathways were identified to respond to different light intensities. Remarkably, BrPDS and BrLCYE genes related to carotenoid biosynthesis showed significantly higher expression in 19YC-2 than that in 19GC-2, which was positively related to the higher carotenoid content in 19YC-2. In addition, several differentially expressed transcription factors were also identified and highly correlated to the changes in carotenoid content, suggesting that they may participate in the regulatory pathway of carotenoid biosynthesis. These findings provide insights into the molecular mechanisms of leaf color changes in yellow cotyledon mutant 19YC-2 of Chinese cabbage.

The CrMYB33 transcription factor positively coordinate the regulation of both carotenoid accumulation and chlorophyll degradation in the peel of citrus fruit

Citrus, cultivated extensively across the globe, possesses considerable economic importance and nutritional value. With the degradation of chlorophyll and accumulation of carotenoids, mature citrus fruits develop an orange-yellow peel, enhancing fruit value and consumer preference. MYB transcription factors (TFs) exert a significant role in diverse plant developmental processes and investigating their involvement in fruit coloration is crucial for developing new cultivars. This work aimed to characterize a citrus TF, CrMYB33, whose expression was found to be positively correlated with carotenoid biosynthesis during fruit ripening. The interference of CrMYB33 expression in citrus fruit resulted in inhibition of carotenoid accumulation, down-regulation of carotenoid biosynthetic genes, and a slower rate of chlorophyll degradation. Conversely, overexpression of CrMYB33 in tomato (Solanum lycopersicum) enhanced chlorophyll degradation and carotenoid biosynthesis, resulting in a deeper red coloration of the fruits. Furthermore, the transcription of associated genes was upregulated in CrMYB33-overexpressing tomato fruits. Additional assays reveal that CrMYB33 exhibits direct links and activation of the promoters of lycopene β-cyclase 2 (CrLCYb2), and β-carotene hydroxylases 2 (CrBCH2), both crucial genes in the carotenoid biosynthetic pathway. Additionally, it was found to inhibit chlorophyllase (CrCLH), a gene essential in chlorophyll degradation. These findings provide insight into the observed changes in LCYb2, BCH2, and CLH expression in the transgenic lines under investigation. In conclusion, our study revealed that CrMYB33 modulates carotenoid accumulation and chlorophyll degradation in citrus fruits through transcriptionally activating genes involved in metabolic pathways.

Transcriptome, Plant Hormone, and Metabolome Analysis Reveals the Mechanism of Purple Pericarp Formation in 'Zihui' Papaya (Carica papaya L.)

The color of the pericarp is a crucial characteristic that influences the marketability of papaya fruit. Prior to ripening, normal papaya exhibits a green pericarp, whereas the cultivar 'Zihui' displays purple ring spots on the fruit tip, which significantly affects the fruit's visual appeal. To understand the mechanism behind the formation of purple pericarp, this study performed a thorough examination of the transcriptome, plant hormone, and metabolome. Based on the UPLC-ESI-MS/MS system, a total of 35 anthocyanins and 11 plant hormones were identified, with 27 anthocyanins and two plant hormones exhibiting higher levels of abundance in the purple pericarp. In the purple pericarp, 14 anthocyanin synthesis genes were up-regulated, including CHS, CHI, F3H, F3'5'H, F3'H, ANS, OMT, and CYP73A. Additionally, through co-expression network analysis, three MYBs were identified as potential key regulators of anthocyanin synthesis by controlling genes encoding anthocyanin biosynthesis. As a result, we have identified numerous key genes involved in anthocyanin synthesis and developed new insights into how the purple pericarp of papaya is formed.

Metabolome and Transcriptome Reveal Chlorophyll, Carotenoid, and Anthocyanin Jointly Regulate the Color Formation of Triadica sebifera

The Chinese tallow tree (Triadica sebifera) is an economically important plant on account of its ornamental value and oil-producing seeds. Leaf colour is a key characteristic of T. sebifera, with yellow-, red- and purple-leaved varieties providing visually impressive displays during autumn. In this study, we performed metabolomic and transcriptomic analyses to gain a better understanding of the mechanisms underlying leaf colour development in purple-leaved T. sebifera at three stages during the autumnal colour transition, namely, green, hemi-purple, and purple leaves. We accordingly detected 370 flavonoid metabolites and 10 anthocyanins, among the latter of which, cyanidin-3-xyloside and peonidin-3-O-glucoside were identified as the predominant compounds in hemi-purple and purple leaves. Transcriptomic analysis revealed that structural genes associated with the anthocyanin biosynthetic pathway, chlorophyll synthesis pathway and carotenoid synthesis pathway were significantly differential expressed at the three assessed colour stages. Additionally, transcription factors associated with the MYB-bHLH-WD40 complex, including 22 R2R3-MYBs, 79 bHLHs and 44 WD40 genes, were identified as candidate regulators of the anthocyanin biosynthetic pathway. Moreover, on the basis of the identified differentially accumulated anthocyanins and key genes, we generated genetic and metabolic regulatory networks for anthocyanin biosynthesis in T. sebifera. These findings provide comprehensive information on the leaf transcriptome and three pigments of T. sebifera, thereby shedding new light on the mechanisms underlying the autumnal colouring of the leaves of this tree.

The transcriptional regulatory module CsHB5-CsbZIP44 positively regulates abscisic acid-mediated carotenoid biosynthesis in citrus (Citrus spp.)

Carotenoids contribute to fruit coloration and are valuable sources of provitamin A in the human diet. Abscisic acid (ABA) plays an essential role in fruit coloration during citrus fruit ripening, but little is known about the underlying mechanisms. Here, we identified a novel bZIP transcription activator called CsbZIP44, which serves as a central regulator of ABA-mediated citrus carotenoid biosynthesis. CsbZIP44 directly binds to the promoters of four carotenoid metabolism-related genes (CsDXR, CsGGPPs, CsBCH1 and CsNCED2) and activates their expression. Furthermore, our research indicates that CsHB5, a positive regulator of ABA and carotenoid-driven processes, activates the expression of CsbZIP44 by binding to its promoter. Additionally, CsHB5 interacts with CsbZIP44 to form a transcriptional regulatory module CsHB5-CsbZIP44, which is responsive to ABA induction and promotes carotenoid accumulation in citrus. Interestingly, we also discover a positive feedback regulation loop between the ABA signal and carotenoid biosynthesis mediated by the CsHB5-CsbZIP44 transcriptional regulatory module. Our findings show that CsHB5-CsbZIP44 precisely modulates ABA signal-mediated carotenoid metabolism, providing an effective strategy for quality improvement of citrus fruit and other crops.

Integrated Metabolomic and Transcriptomic Profiles Provide Insights into the Mechanisms of Anthocyanin and Carotenoid Biosynthesis in Petals of Medicago sativa ssp. sativa and Medicago sativa ssp. falcata

The petals of Medicago sativa ssp. sativa and M. sativa ssp. falcata are purple and yellow, respectively. Free hybridization between M. sativa ssp. sativa and M. sativa ssp. falcata has created hybrids with various flower colors in nature. Moreover, the flower colors of alfalfa are closely correlated with yield, nutritional quality, stress tolerance and other agronomic characteristics. To elucidate the underlying mechanisms of flower color formation in M. sativa ssp. sativa and M. sativa ssp. falcata, we conducted an integrative analysis of the transcriptome and metabolome of alfalfa with three different petal colors (purple, yellow and cream). The metabolic profiles suggested that anthocyanins and carotenoids are the crucial pigments in purple and yellow flowers, respectively. A quantitative exploration of the anthocyanin and carotenoid components indicated that the accumulations of cyanidin, delphinidin, peonidin, malvidin, pelargonidin and petunidin derivatives are significantly higher in purple flowers than in cream flowers. In addition, the content of carotenes (phytoene, α-carotene and β-carotene) and xanthophylls (α-cryptoxanthin, lutein, β-cryptoxanthin, zeaxanthin, antheraxanthin and violaxanthin derivatives) was markedly higher in yellow flowers than in cream flowers. Furthermore, we found that delphinidin-3,5-O-diglucoside and lutein were the predominant pigments accumulated in purple and yellow flowers, respectively. The transcriptomic results revealed that twenty-five upregulated structural genes (one C4H, three 4CL, twelve CHS, two CHI, one F3H, one F3'H, one F3'5'H and four DFR) are involved in the accumulation of anthocyanins in purple flowers, and nine structural genes (two PSY, one ZDS, two CRTISO, two BCH, one ZEP and one ECH) exert an effect on the carotenoid biosynthesis pathway in yellow flowers. The findings of this study reveal the underlying mechanisms of anthocyanin and carotenoid biosynthesis in alfalfa with three classic flower colors.

Differential content of leaf and fruit pigment in tomatoes culminate in a complex metabolic reprogramming without growth impacts

Although significant efforts to produce carotenoid-enriched foods either by biotechnology or traditional breeding strategies have been carried out, our understanding of how changes in the carotenoid biosynthesis might affect overall plant performance remains limited. Here, we investigate how the metabolic machinery of well characterized tomato carotenoid mutant plants [namely crimson (old gold-og), Delta carotene (Del) and tangerine (t)] adjusts itself to varying carotenoid biosynthesis and whether these adjustments are supported by a reprogramming of photosynthetic and central metabolism in the source organs (leaves). We observed that mutations og, Del and t did not greatly affect vegetative growth, leaf anatomy and gas exchange parameters. However, an exquisite metabolic reprogramming was recorded on the leaves, with an increase in levels of amino acids and reduction of organic acids. Taken together, our results show that despite minor impacts on growth and gas exchange, carbon flux is extensively affected, leading to adjustments in tomato leaves metabolism to support changes in carotenoid biosynthesis on fruits (sinks). We discuss these data in the context of our current understanding of metabolic adjustments and carotenoid biosynthesis as well as regarding to improving human nutrition.

15-cis-Phytoene Desaturase and 15-cis-Phytoene Synthase Can Catalyze the Synthesis of β-Carotene and Influence the Color of Apricot Pulp

Fruit color affects its commercial value. β-carotene is the pigment that provides color for many fruits and vegetables. However, the molecular mechanism of β-carotene metabolism during apricot ripening is largely unknown. Here, we investigated whether β-carotene content affects apricot fruit color. First, the differences in β-carotene content between orange apricot 'JTY' and white apricot 'X15' during nine developmental stages (S1-S9) were compared. β-carotene contents highly significantly differed between 'JTY' and 'X15' from S5 (color transition stage) onwards. Whole-transcriptome analysis showed that the β-carotene synthesis genes 15-cis-phytoene desaturase (PaPDS) and 15-cis-phytoene synthase (PaPSY) significantly differed between the two cultivars during the color transition stage. There was a 5 bp deletion in exon 11 of PaPDS in 'X15', which led to early termination of amino acid translation. Gene overexpression and virus-induced silencing analysis showed that truncated PaPDS disrupted the β-carotene biosynthesis pathway in apricot pulp, resulting in decreased β-carotene content and a white phenotype. Furthermore, virus-induced silencing analysis showed that PaPSY was also a key gene in β-carotene biosynthesis. These findings provide new insights into the molecular regulation of apricot carotenoids and provide a theoretical reference for breeding new cultivars of apricot.

Transcriptome Characterization of Pigment-Related Genes in Jujube (Ziziphus Jujuba Mill.) Peel at Different Growth Stages

One of the most important qualities of jujube fruit is its color. Chlorophyll, carotenoid, and anthocyanin all play important roles in the coloring of jujube fruit. However, few studies have focused on the pigment molecular mechanism. In the present study, jujube peels of 'Sanbianhong' in three growth stages were evaluated for their gene expression characteristics and gene regulation related to pigment formation using the transcriptome sequencing analysis. A total of 84.86 Gb of clean data were obtained in the analysis. In the FS1 vs. FS3, FS1 vs. FS5, and FS3 vs. FS5, 4,530, 11,012, and 9,072 differentially expressed genes (DEGs) were identified, respectively. The inter-group screening among the three comparisons yielded 1430 common DEGs. Among these DEGs, 27, 16, and 28 genes were enriched in chlorophyll, carotenoid, and anthocyanin metabolic pathways, respectively. Twelve genes were chosen at random, and the accuracy of the transcriptome data were confirmed using qRT-PCR. The molecular mechanism underlying the pigmentation of jujube fruit was elucidated at the transcriptome level, which would provide a scientific basis for the subsequent functional studies on the color-regulating genes of jujube fruits.

Prospects of chloroplast metabolic engineering for developing nutrient-dense food crops

Addressing nutritional deficiencies in food crops through biofortification is a sustainable approach to tackling malnutrition. Biofortification is continuously being attempted through conventional breeding as well as through various plant biotechnological interventions, ranging from molecular breeding to genetic engineering and genome editing for enriching crops with various health-promoting metabolites. Genetic engineering is used for the rational incorporation of desired nutritional traits in food crops and predominantly operates through nuclear and chloroplast genome engineering. In the recent past, chloroplast engineering has been deployed as a strategic tool to develop model plants with enhanced nutritional traits due to the various advantages it offers over nuclear genome engineering. However, this approach needs to be extended for the nutritional enhancement of major food crops. Further, this platform could be combined with strategies, such as synthetic biology, chloroplast editing, nanoparticle-mediated rapid chloroplast transformation, and horizontal gene transfer through grafting for targeting endogenous metabolic pathways for overproducing native nutraceuticals, production of biopharmaceuticals, and biosynthesis of designer nutritional compounds. This review focuses on exploring various features of chloroplast genome engineering for nutritional enhancement of food crops by enhancing the levels of existing metabolites, restoring the metabolites lost during crop domestication, and introducing novel metabolites and phytonutrients needed for a healthy daily diet.

NtMYB1 and NtNCED1/2 control abscisic acid biosynthesis and tepal senescence in Chinese narcissus (Narcissus tazetta)

Chinese narcissus (Narcissus tazetta var. chinensis cv. 'Jinzhanyintai') is one of the 10 most famous traditional flowers of China, having a beautiful and highly ornamental flower with a rich fragrance. However, the flower longevity affects its commercial appeal. While petal senescence in Narcissus is ethylene-independent and abscisic acid-dependent, the regulatory mechanism has yet to be determined. In this study, we identified a R2R3-MYB gene (NtMYB1) from Narcissus tazetta and generated oeNtMYB1 and Ntmyb1 RNA interference mutants in Narcissus as well as an oeNtMYB1 construct in Arabidopsis. Overexpressing NtMYB1 in Narcissus or Arabidopsis led to premature leaf yellowing, an elevated level of total carotenoid, a reduced level of chlorophyll b, and a decrease in photosystem II fluorescence (Fv/Fm). A dual-luciferase assay and chromatin immunoprecipitation-quantitative PCR revealed that NtMYB1 directly binds to the promoter of NtNCED1 or NtNCED2 and activates NtNCED1/2 gene expression both in vitro and in vivo. Moreover, overexpressing NtMYB1 accelerated abscisic acid biosynthesis, up-regulated the content of zeatin and abscisic acid, and down-regulated the level of β-carotene and gibberellin A1, leading to petal senescence and leaf yellowing in Narcissus. This study revealed a regulatory process that is fundamentally different between non-photosynthetic organs and leaves.

Exploring Plants with Flowers: From Therapeutic Nutritional Benefits to Innovative Sustainable Uses

Flowers have played a significant role in society, focusing on their aesthetic value rather than their food potential. This study's goal was to look into flowering plants for everything from health benefits to other possible applications. This review presents detailed information on 119 species of flowers with agri-food and health relevance. Data were collected on their family, species, common name, commonly used plant part, bioremediation applications, main chemical compounds, medicinal and gastronomic uses, and concentration of bioactive compounds such as carotenoids and phenolic compounds. In this respect, 87% of the floral species studied contain some toxic compounds, sometimes making them inedible, but specific molecules from these species have been used in medicine. Seventy-six percent can be consumed in low doses by infusion. In addition, 97% of the species studied are reported to have medicinal uses (32% immune system), and 63% could be used in the bioremediation of contaminated environments. Significantly, more than 50% of the species were only analysed for total concentrations of carotenoids and phenolic compounds, indicating a significant gap in identifying specific molecules of these bioactive compounds. These potential sources of bioactive compounds could transform the health and nutraceutical industries, offering innovative approaches to combat oxidative stress and promote optimal well-being.

Multiomics analysis provides new insights into the regulatory mechanism of carotenoid biosynthesis in yellow peach peel

Carotenoids, as natural tetraterpenes, play a pivotal role in the yellow coloration of peaches and contribute to human dietary health. Despite a relatively clear understanding of the carotenoid biosynthesis pathway, the regulatory mechanism of miRNAs involved in carotenoid synthesis in yellow peaches remain poorly elucidated. This study investigated a total of 14 carotenoids and 40 xanthophyll lipids, including six differentially accumulated carotenoids: violaxanthin, neoxanthin, lutein, zeaxanthin, cryptoxanthin, and (E/Z)-phytoene. An integrated analysis of RNA-seq, miRNA-seq and degradome sequencing revealed that miRNAs could modulate structural genes such as PSY2, CRTISO, ZDS1, CHYB, VDE, ZEP, NCED1, NCED3 and the transcription factors NAC, ARF, WRKY, MYB, and bZIP, thereby participating in carotenoid biosynthesis and metabolism. The authenticity of miRNAs and target gene was corroborated through quantitative real-time PCR. Moreover, through weighted gene coexpression network analysis and a phylogenetic evolutionary study, coexpressed genes and MYB transcription factors potentially implicated in carotenoid synthesis were identified. The results of transient expression experiments indicated that mdm-miR858 inhibited the expression of PpMYB9 through targeted cleavage. Building upon these findings, a regulatory network governing miRNA-mediated carotenoid synthesis was proposed. In summary, this study comprehensively identified miRNAs engaged in carotenoid biosynthesis and their putative target genes, thus enhancing the understanding of carotenoid accumulation and regulatory mechanism in yellow peach peel and expanding the gene regulatory network of carotenoid synthesis.

Transcription factor CsTT8 promotes fruit coloration by positively regulating the methylerythritol 4-phosphate pathway and carotenoid biosynthesis pathway in citrus (Citrus spp.)

Carotenoids directly influence citrus fruit color and nutritional value, which is critical to consumer acceptance. Elucidating the potential molecular mechanism underlying carotenoid metabolism is of great importance for improving fruit quality. Despite the well-established carotenoid biosynthetic pathways, the molecular regulatory mechanism underlying carotenoid metabolism remains poorly understood. Our previous studies have reported that the Myc-type basic helix-loop-helix (bHLH) transcription factor (TF) regulates citrus proanthocyanidin biosynthesis. Transgenic analyses further showed that overexpression of CsTT8 could significantly promote carotenoid accumulation in transgenic citrus calli, but its regulatory mechanism is still unclear. In the present study, we found that overexpression of CsTT8 enhances carotenoid content in citrus fruit and calli by increasing the expression of CsDXR, CsHDS, CsHDR, CsPDS, CsLCYE, CsZEP, and CsNCED2, which was accompanied by changes in the contents of abscisic acid and gibberellin. The in vitro and in vivo assays indicated that CsTT8 directly bound to the promoters of CsDXR, CsHDS, and CsHDR, the key metabolic enzymes of the methylerythritol 4-phosphate (MEP) pathway, thus providing precursors for carotenoid biosynthesis and transcriptionally activating the expression of these three genes. In addition, CsTT8 activated the promoters of four key carotenoid biosynthesis pathway genes, CsPDS, CsLCYE, CsZEP, and CsNCED2, directly promoting carotenoid biosynthesis. This study reveals a novel network of carotenoid metabolism regulated by CsTT8. Our findings will contribute to manipulating carotenoid metabolic engineering to improve the quality of citrus fruit and other crops.

Multiomics Analysis Reveals the Chemical and Genetic Bases of Pigmented Potato Tuber

Anthocyanins and carotenoids determine the diversity of potato tuber flesh pigmentation; here, the underlying chemical and genetic bases were elucidated by multiomics analyses. A total of 31 anthocyanins and 30 carotenoids were quantified in five differently pigmented tubers. Cyanidin and pelargonidin derivatives determined the redness, while malvidin, petunidin, and delphinidin derivatives contributed to purpleness. Violaxanthin derivatives determined the light-yellow color, while zeaxanthin and antheraxanthin derivatives further enhanced the deep-yellow deposition. Integrated transcriptome and proteome analyses identified that F3'5'H highly enhanced anthocyanin biosynthesis in purple flesh and was responsible for metabolic divergence between red and purple samples. BCH2 significantly enhanced carotenoid biosynthesis in yellow samples and along with ZEP, NCED1, and CCD1 genes determined metabolic divergence between light and deep-yellow samples. The weighted correlation network analysis constructed a regulatory network revealing the central role of AN1 in regulating anthocyanin biosynthesis, and 10 new transcription factors related to anthocyanin and carotenoid metabolism regulation were identified. Our findings provide targeted genes controlling tuber pigmentation, which will be meaningful for the genetic manipulation of tuber quality improvement.

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.

Cucumber abscisic acid 8'-hydroxylase Csyf2 regulates yellow flesh by modulating carotenoid biosynthesis

Cucumber (Cucumis sativus L.) flesh is typically colorless or pale green. Flesh with yellow or orange pigment, determined mainly by carotenoid content and composition, is mostly found in semi-wild Xishuangbanna cucumber, which has a very narrow genetic background. Here, we identified a spontaneous cucumber mutant with yellow flesh (yf-343), which accumulated more β-cryptoxanthin and less lutein than regular cultivated European glasshouse-type cucumbers. Genetic analysis revealed that the yellow flesh phenotype was controlled by a single recessive gene. Through fine mapping and gene sequencing, we identified the candidate gene C. sativus yellow flesh 2 (Csyf2), encoding an abscisic acid (ABA) 8'-hydroxylase. Overexpression and RNAi-silencing of Csyf2 in cucumber hairy roots produced lower and higher ABA contents than in non-transgenic controls, respectively. Further, RNA-seq analysis suggested that genes related to ABA signal transduction were differentially expressed in fruit flesh between yf-343 and its wild type, BY, with white flesh. The carotenoid biosynthesis pathway was specifically enriched in fruit flesh at 30 days after pollination when yf-343 fruit flesh turns yellow. Our findings highlight a promising target for gene editing to increase carotenoid content, expanding our genetic resources for pigmented cucumber flesh breeding for improving the nutritional quality of cucumber.

Combined transcriptome and metabolome analysis reveal that the white and yellow mango pulp colors are associated with carotenoid and flavonoid accumulation, and phytohormone signaling

Mango (Mangifera indica L.) is a widely appreciated tropical fruit for its rich color and nutrition. However, knowledge on the molecular basis of color variation is limited. Here, we studied HY3 (yellowish-white pulp) and YX4 (yellow pulp), reaped with 24 h gap from the standard harvesting time. The carotenoids and total flavonoids increased with the advance of harvest time (YX4 > HY34). Transcriptome sequencing showed that higher expressions of the core carotenoid biosynthesis genes and flavonoid biosynthesis genes are correlated to their respective contents. The endogenous indole-3-acetic acid and jasmonic acid contents decreased but abscisic acid and ethylene contents increased with an increase in harvesting time (YX4 > HY34). Similar trends were observed for the corresponding genes. Our results indicate that the color differences are related to carotenoid and flavonoid contents, which in turn are influenced by phytohormone accumulation and signaling.

Research Progress on Anthocyanin-Mediated Regulation of 'Black' Phenotypes of Plant Organs

The color pattern is one of the most important characteristics of plants. Black stands out among the vibrant colors due to its rare and distinctive nature. While some plant organs appear black, they are, in fact, dark purple. Anthocyanins are the key compounds responsible for the diverse hues in plant organs. Cyanidin plays an important role in the deposition of black pigments in various plant organs, such as flower, leaf, and fruit. A number of structural genes and transcription factors are involved in the metabolism of anthocyanins in black organs. It has been shown that the high expression of R2R3-MYB transcription factors, such as PeMYB7, PeMYB11, and CsMYB90, regulates black pigmentation in plants. This review provides a comprehensive overview of the anthocyanin pathways that are involved in the regulation of black pigments in plant organs, including flower, leaf, and fruit. It is a great starting point for further investigation into the molecular regulation mechanism of plant color and the development of novel cultivars with black plant organs.

Carotenoid sequestration protein FIBRILLIN participates in CmOR-regulated β-carotene accumulation in melon

Chromoplasts are plant organelles with a unique ability to sequester and store massive carotenoids. Chromoplasts have been hypothesized to enable high levels of carotenoid accumulation due to enhanced sequestration ability or sequestration substructure formation. However, the regulators that control the substructure component accumulation and substructure formation in chromoplasts remain unknown. In melon (Cucumis melo) fruit, β-carotene accumulation in chromoplasts is governed by ORANGE (OR), a key regulator for carotenoid accumulation in chromoplasts. By using comparative proteomic analysis of a high β-carotene melon variety and its isogenic line low-β mutant that is defective in CmOr with impaired chromoplast formation, we identified carotenoid sequestration protein FIBRILLIN1 (CmFBN1) as differentially expressed. CmFBN1 expresses highly in melon fruit tissue. Overexpression of CmFBN1 in transgenic Arabidopsis (Arabidopsis thaliana) containing ORHis that genetically mimics CmOr significantly enhances carotenoid accumulation, demonstrating its involvement in CmOR-induced carotenoid accumulation. Both in vitro and in vivo evidence showed that CmOR physically interacts with CmFBN1. Such an interaction occurs in plastoglobules and results in promoting CmFBN1 accumulation. CmOR greatly stabilizes CmFBN1, which stimulates plastoglobule proliferation and subsequently carotenoid accumulation in chromoplasts. Our findings show that CmOR directly regulates CmFBN1 protein levels and suggest a fundamental role of CmFBN1 in facilitating plastoglobule proliferation for carotenoid sequestration. This study also reveals an important genetic tool to further enhance OR-induced carotenoid accumulation in chromoplasts in crops.

CYCLOIDEA-like genes control floral symmetry, floral orientation, and nectar guide patterning

Actinomorphic flowers usually orient vertically (relative to the horizon) and possess symmetric nectar guides, while zygomorphic flowers often face horizontally and have asymmetric nectar guides, indicating that floral symmetry, floral orientation, and nectar guide patterning are correlated. The origin of floral zygomorphy is dependent on the dorsoventrally asymmetric expression of CYCLOIDEA (CYC)-like genes. However, how horizontal orientation and asymmetric nectar guides are achieved remains poorly understood. Here, we selected Chirita pumila (Gesneriaceae) as a model plant to explore the molecular bases for these traits. By analyzing gene expression patterns, protein-DNA and protein-protein interactions, and encoded protein functions, we identified multiple roles and functional divergence of 2 CYC-like genes, i.e. CpCYC1 and CpCYC2, in controlling floral symmetry, floral orientation, and nectar guide patterning. CpCYC1 positively regulates its own expression, whereas CpCYC2 does not regulate itself. In addition, CpCYC2 upregulates CpCYC1, while CpCYC1 downregulates CpCYC2. This asymmetric auto-regulation and cross-regulation mechanism might explain the high expression levels of only 1 of these genes. We show that CpCYC1 and CpCYC2 determine asymmetric nectar guide formation, likely by directly repressing the flavonoid synthesis-related gene CpF3'5'H. We further suggest that CYC-like genes play multiple conserved roles in Gesneriaceae. These findings shed light on the repeated origins of zygomorphic flowers in angiosperms.

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.

Transcriptomics and Metabolomics Reveal the Critical Genes of Carotenoid Biosynthesis and Color Formation of Goji (Lycium barbarum L.) Fruit Ripening

Carotenoids in goji (Lycium barbarum L.) have excellent health benefits, but the underlying mechanism of carotenoid synthesis and color formation in goji fruit ripening is still unclear. The present study uses transcriptomics and metabolomics to investigate carotenoid biosynthesis and color formation differences in N1 (red fruit) and N1Y (yellow fruit) at three stages of ripening. Twenty-seven carotenoids were identified in N1 and N1Y fruits during the M1, M2, and M3 periods, with the M2 and M3 periods being critical for the difference in carotenoid and color between N1 and N1Y fruit. Weighted gene co-expression network analysis (WGCNA), gene trend analysis, and correlation analysis suggest that PSY1 and ZDS16 may be important players in the synthesis of carotenoids during goji fruit ripening. Meanwhile, 63 transcription factors (TFs) were identified related to goji fruit carotenoid biosynthesis. Among them, four TFs (CMB1-1, WRKY22-1, WRKY22-3, and RAP2-13-like) may have potential regulatory relationships with PSY1 and ZDS16. This work sheds light on the molecular network of carotenoid synthesis and explains the differences in carotenoid accumulation in different colored goji fruits.

Comparative Analysis of Carotenoid Profiles and Biosynthetic Gene Expressions among Ten Plum Cultivars

Plums are good sources of various bioactive phytochemical compounds such as vitamins, anthocyanins, and carotenoids, whereby all of which are noted for multiple potential health benefits. However, knowledge regarding plum carotenoid profiles remains limited. Hence, the total and individual carotenoids in the edible parts (skin and flesh) of ten plum cultivars were determined using a spectrophotometer and high-performance liquid chromatography-diode array detection, respectively. Total and individual carotenoid contents in skin were significantly higher (p < 0.05) than those in flesh among all plum cultivars tested. The cultivars with the highest content of total carotenoids in skin were Naili (36.73 μg/g FW), followed by Yinhongli (21.81 μg/g FW) and Yuhuangli (19.70 μg/g FW), with the lowest in Angeleno (8.97 μg/g FW). Lutein, zeaxanthine, β-cryptoxanthin, α-carotene, and β-carotene were the major types of carotenoids detected, with lutein and β-carotene being the predominant constituents of the skin and flesh tissues, respectively. Lutein, zeaxanthine, and total carotenoid contents were positively correlated with the expressions of PSY, LCYB, and LCYE, and negatively correlated with the expressions of PDS and CRTISO. Characterizing the carotenoid profiles and investigating variations in carotenoid biosynthetic gene expressions among plum cultivars are crucial for advancing genetic improvements in plums.

ETHYLENE-INSENSITIVE 3-LIKE 2 regulates β-carotene and ascorbic acid accumulation in tomatoes during ripening

ETHYLENE-INSENSITIVE 3/ETHYLENE-INSENSITIVE 3-LIKEs (EIN3/EILs) are important ethylene response factors during fruit ripening. Here, we discovered that EIL2 controls carotenoid metabolism and ascorbic acid (AsA) biosynthesis in tomato (Solanum lycopersicum). In contrast to the red fruits presented in the wild type (WT) 45 d after pollination, the fruits of CRISPR/Cas9 eil2 mutants and SlEIL2 RNA interference lines (ERIs) showed yellow or orange fruits. Correlation analysis of transcriptome and metabolome data for the ERI and WT ripe fruits revealed that SlEIL2 is involved in β-carotene and AsA accumulation. ETHYLENE RESPONSE FACTORs (ERFs) are the typical components downstream of EIN3 in the ethylene response pathway. Through a comprehensive screening of ERF family members, we determined that SlEIL2 directly regulates the expression of 4 SlERFs. Two of these, SlERF.H30 and SlERF.G6, encode proteins that participate in the regulation of LYCOPENE-β-CYCLASE 2 (SlLCYB2), encoding an enzyme that mediates the conversion of lycopene to carotene in fruits. In addition, SlEIL2 transcriptionally repressed L-GALACTOSE 1-PHOSPHATE PHOSPHATASE 3 (SlGPP3) and MYO-INOSITOL OXYGENASE 1 (SlMIOX1) expression, which resulted in a 1.62-fold increase of AsA via both the L-galactose and myoinositol pathways. Overall, we demonstrated that SlEIL2 functions in controlling β-carotene and AsA levels, providing a potential strategy for genetic engineering to improve the nutritional value and quality of tomato fruit.

Nutritional Composition of Hass Avocado Pulp

Avocados (Persea americana) are a unique fruit that can provide health benefits when included in a healthy diet. As health care moves towards precision health and targeted therapies or preventative medicine, it is critical to understand foods and their dietary components. The nutritional composition and plant physiology of the Hass avocado is strikingly different from other fruits. This paper reviews the nutrient and bioactive composition of the edible portion of the Hass avocado (pulp) reported in the literature and from commercial lab analyses of the current market supply of fresh Hass avocados. These results provide comprehensive data on what nutrients and bioactives are in avocado and the quantity of these nutrients. We discuss the reasons for nutrient composition variations and review some potential health benefits of bioactive compounds found in Hass avocados.

Regulation of Carotenoid Biosynthesis and Degradation in Lettuce (Lactuca sativa L.) from Seedlings to Harvest

Lettuce (Lactuca sativa L.) is one of the commercially important leafy vegetables worldwide. However, lettuce cultivars vary widely in their carotenoid concentrations at the time of harvest. While the carotenoid content of lettuce can depend on transcript levels of key biosynthetic enzymes, genes that can act as biomarkers for carotenoid accumulation at early stages of plant growth have not been identified. Transcriptomic and metabolomic analysis was performed on the inner and outer leaves of the six cultivars at different developmental stages to identify gene-to-metabolite networks affecting the accumulation of two key carotenoids, β-carotene and lutein. Statistical analysis, including principal component analysis, was used to better understand variations in carotenoid concentration between leaf age and cultivars. Our results demonstrate that key enzymes of carotenoid biosynthesis pathway can alter lutein and β-carotene biosynthesis across commercial cultivars. To ensure high carotenoids content in leaves, the metabolites sink from β-carotene and lutein to zeaxanthin, and subsequently, abscisic acid needs to be regulated. Based on 2-3-fold carotenoids increase at 40 days after sowing (DAS) as compared to the seedling stage, and 1.5-2-fold decline at commercial stage (60 DAS) compared to the 40 DAS stage, we conclude that the value of lettuce for human nutrition would be improved by use of less mature plants, as the widely-used commercial stage is already at plant senescence stage where carotenoids and other essential metabolites are undergoing degradation.

Characterization of Carotenoid Cleavage Oxygenase Genes in Cerasus humilis and Functional Analysis of ChCCD1

Carotenoid cleavage oxygenases (CCOs) are key enzymes that function in degrading carotenoids into a variety of apocarotenoids and some other compounds. In this study, we performed genome-wide identification and characterization analysis of CCO genes in Cerasus humilis. Totally, nine CCO genes could be classified into six subfamilies, including carotenoid cleavage dioxygenase 1 (CCD1), CCD4, CCD7, CCD8, CCD-like and nine-cis-epoxycarotenoid dioxygenase (NCED), were identified. Results of gene expression analysis showed that ChCCOs exhibited diverse expression patterns in different organs and in fruits at different ripening stages. To investigate the roles of ChCCOs in carotenoids degradation, enzyme assays of the ChCCD1 and ChCCD4 were performed in Escerichia coli BL21(DE3) that can accumulate lycopene, β-carotene and zeaxanthin. The prokaryotic expressed ChCCD1 resulted in obvious degradation of lycopene, β-carotene and zeaxanthin, but ChCCD4 did not show similar functions. To further determine the cleaved volatile apocarotenoids of these two proteins, headspace gas chromatography/mass spectrometer analysis was performed. Results showed that ChCCD1 could cleave lycopene at 5, 6 and 5', 6' positions to produce 6-methy-5-hepten-2-one and could catalyze β-carotene at 9, 10 and 9', 10' positions to generate β-ionone. Our study will be helpful for clarifying the roles of CCO genes especially ChCCD1 in regulating carotenoid degradation and apocarotenoid production in C. humilis.

The Estimation of Chemical Properties of Pepper Treated with Natural Fertilizers Based on Image Texture Parameters

The cultivar and fertilization can affect the physicochemical properties of pepper fruit. This study aimed at estimating the content of α-carotene, β-carotene, total carotenoids, and the total sugars of unfertilized pepper and samples treated with natural fertilizers based on texture parameters determined using image analysis. Pearson's correlation coefficients, scatter plots, regression equations, and coefficients of determination were determined. For red pepper Sprinter F₁, the correlation coefficient (R) reached 0.9999 for a texture from color channel B and -0.9999 for a texture from channel Y for the content of α-carotene, -0.9998 (channel a) for β-carotene, 0.9999 (channel a) and -0.9999 (channel L) for total carotenoids, as well as 0.9998 (channel R) and -0.9998 (channel a) for total sugars. The image textures of yellow pepper Devito F₁ were correlated with the content of total carotenoids and total sugars with the correlation coefficient reaching -0.9993 (channel b) and 0.9999 (channel Y), respectively. The coefficient of determination (R²) of up to 0.9999 for α-carotene content and the texture from color channel Y for pepper Sprinter F₁ and 0.9998 for total sugars and the texture from color channel Y for pepper Devito F₁ were found. Furthermore, very high coefficients of correlation and determination, as well as successful regression equations regardless of the cultivar were determined.

AcMADS32 positively regulates carotenoid biosynthesis in kiwifruit by activating AcBCH1/2 expression

Fruits provide abundant carotenoid nutrients for humans, whereas the understanding of the transcriptional regulatory mechanisms of carotenoids in fruits is still limited. Here, we identified a transcription factor AcMADS32 in kiwifruit, which was highly expressed in the fruit, correlated with carotenoid content and localized in the nucleus. The silencing expression of AcMADS32 significantly reduced the content of β-carotene and zeaxanthin and expression of β-carotene hydroxylase gene AcBCH1/2 in kiwifruit, while transient overexpression increased the accumulation of zeaxanthin, suggesting that AcMADS32 was an activator involved in the transcriptional regulation of carotenoid in fruit. When AcMADS32 was further stably transformed into kiwifruit, the content of total carotenoid and components in the leaves of transgenic lines significantly increased, and the expression level of carotenogenic genes was up-regulated. Moreover, Y1H and dual luciferase reporter experiments confirmed that AcMADS32 directly bound the AcBCH1/2 promoter and activated its expression. Through Y2H assays, AcMADS32 can interact with other MADS transcription factor AcMADS30, AcMADS64 and AcMADS70. These findings will contribute to our understanding of the transcriptional regulation mechanisms underlying carotenoid biosynthesis in plants.

The mechanism of white flower formation in Brassica rapa is distinct from that in other Brassica species

KEY MESSAGE

A single nucleotide (G) deletion in the third exon of BraA02.PES2-2 (Bra032957) leads to the conversion of flower color from yellow to white in B. rapa, and knockout mutants of its orthologous genes in B. napus showed white or pale yellow flowers. Brassica rapa (2n = 20, AA) is grown worldwide as an important crop for edible oil and vegetables. The bright yellow flower color and long-lasting flowering period give it aesthetic qualities appealing to countryside tourists. However, the mechanism controlling the accumulation of yellow pigments in B. rapa has not yet been completely revealed. In this study, we characterized the mechanism of white flower formation using a white-flowered natural B. rapa mutant W01. Compared to the petals of yellow-flowered P3246, the petals of W01 have significantly reduced content of yellowish carotenoids. Furthermore, the chromoplasts in white petals of W01 are abnormal with irregularly structured plastoglobules. Genetic analysis indicated that the white flower was controlled by a single recessive gene. By combining BSA-seq with fine mapping, we identified the target gene BraA02.PES2-2 (Bra032957) homologous to AtPES2, which has a single nucleotide (G) deletion in the third exon. Seven homologous PES2 genes including BnaA02.PES2-2 (BnaA02g28340D) and BnaC02.PES2-2 (BnaC02g36410D) were identified in B. napus (2n = 38, AACC), an allotetraploid derived from B. rapa and B. oleracea (2n = 18, CC). Knockout mutants of either one or two of BnaA02.PES2-2 and BnaC02.PES2-2 in the yellow-flowered B. napus cv. Westar by the CRISPR/Cas9 system showed pale-yellow or white flowers. The knock-out mutants of BnaA02.PES2-2 and BnaC02.PES2-2 had fewer esterified carotenoids. These results demonstrated that BraA02.PES2-2 in B. rapa, and BnaA02.PES2-2 and BnaC02.PES2-2 in B. napus play important roles in carotenoids esterification in chromoplasts that contributes to the accumulation of carotenoids in flower petals.

Chrysanthemum morifolium β-carotene hydroxylase overexpression promotes Arabidopsis thaliana tolerance to high light stress

The β-carotene hydroxylase gene (BCH) regulates zeaxanthin production in response to high light levels ro protect Chrysanthemum morifolium plants against light-induced damage. In this study, the Chrysanthemum morifolium CmBCH1 and CmBCH2 genes were cloned and their functional importance was assessed by overexpressing them in Arabidopsis thaliana. These transgenic plants were evaluated for gene-related changes in phenotypic characteristics, photosynthetic activity, fluorescence properties, carotenoid biosynthesis, aboveground/belowground biomass, pigment content, and the expression of light-regulated genes under conditions of high light stress relative to wild-type (WT) plants. When exposed to high light stress, WT A. thaliana leaves turned yellow and the overall biomass was reduced compared to that of the transgenic plants. WT plants exposed to high light stress also exhibited significant reductions in the net photosynthetic rate, stomatal conductance, Fv/Fm, qP, and ETR, whereas these changes were not observed in the transgenic CmBCH1 and CmBCH2 plants. Lutein and zaxanthin levels were significantly increased in the transgenic CmBCH1 and CmBCH2 lines, with progressive induction with prolonged light exposure, whereas no significant changes were observed in light-exposed WT plants. The transgenic plants also expressed higher levels of most carotenoid biosynthesis pathway genes, including phytoene synthase (AtPSY), phytoene desaturase (AtPDS), lycopene-β-cyclase (AtLYCB), and ζ-carotene desaturase (AtZDS). The elongated hypocotyl 5 (HY5) and succinate dehydrogenase (SDH) genes were significantly induced following exposure to high light conditions for 12h, whereas phytochrome-interacting factor 7 (PIF7) was significantly downregulated in these plants.

BCH1 expression pattern contributes to the fruit carotenoid diversity between peach and apricot

Peach (Prunus persica L. Batsch) and apricot (Prunus armeniaca L.) are two species of economic importance for fruit production in the genus Prunus. Peach and apricot fruits exhibit significant differences in carotenoid levels and profiles. HPLC-PAD analysis showed that a greater content of β-carotene in mature apricot fruits is primarily responsible for orange color, while peach fruits showed a prominent accumulation of xanthophylls (violaxanthin and cryptoxanthin) with yellow color. There are two β-carotene hydroxylase genes in both peach and apricot genomes. Transcriptional analysis revealed that BCH1 expresses highly in peach but lowly in apricot fruit, showing a correlation with peach and apricot fruit carotenoid profiles. By using a carotenoid engineered bacterial system, it was demonstrated that there was no difference in the BCH1 enzymatic activity between peach and apricot. Comparative analysis about the putative cis-acting regulatory elements between peach and apricot BCH1 promoters provided important information for our understanding of the differences in promoter activity of the BCH1 genes in peach and apricot. Therefore, we investigated the promoter activity of BCH1 gene through a GUS detection system, and confirmed that the difference in the transcription level of the BCH1 gene resulted from the difference of the promoter function. This study provides important perspective to understanding the diversity of carotenoid accumulation in Prunus fruits such as peach and apricot. In particular, BCH1 gene is proposed as a main predictor for β-carotene content in peach and apricot fruits during the ripening process.

A carotenoid cleavage dioxygenase 4 from Paulownia tomentosa determines visual and aroma signals in flowers

Paulownia tomentosa is an economically important fast-growing tree, and its flowers and fruits are a rich source of biologically active secondary metabolites. In addition, the flowers of P. tomentosa are distinguished by a strong aroma and are also excellent nectariferous plants. The flowers are pale lilac and characterized by the presence of yellow nectar guides, whose color changes during the development of the flower, representing reliable signals to pollinators while enhancing reproductive success. The chemical analyses of the nectar guides revealed the presence of carotenoids as the pigments responsible for the observed coloration, with β-carotene levels determining the color changes observed after anthesis, with a reduction at anthesis and further increase and accumulation in post anthesis. To understand how β-carotene accumulation was controlled in the nectar guides, the expression of genes related to carotenoid biosynthesis and metabolism was analyzed. Carotenogenic gene expression was not associated with the observed changes in β-carotene during flower development. However, the expression of a gene encoding a carotenoid cleavage dioxygenase, CCD4-4, was co-related with the levels of β-carotene in the nectar guides. In addition, CCD4-4 cleavage β-carotene at C9-C10 and C9'-C10' positions, resulting in the generation of β-ionone, which was detected in flowers at anthesis. The obtained results indicated a developmental stage specific regulation of apocarotenoid formation through β-carotene cleavage, resulting in color changes and volatile production as key traits for plant-pollinator interactions. DATA AVAILABILITY: Data will be made available on request.

Jasmonate activates a CsMPK6-CsMYC2 module that regulates the expression of β-citraurin biosynthetic genes and fruit coloration in orange (Citrus sinensis)

Carotenoids are natural pigments that influence the color of citrus fruit. The red-colored carotenoid β-citraurin is responsible for the peel color in "Newhall" orange (Citrus sinensis). Although jasmonates are known to regulate the biosynthesis and accumulation of carotenoids, their effects on β-citraurin biosynthesis in citrus fruit remain unclear. Here, we determined that treatment with methyl jasmonate (MeJA) significantly promotes fruit coloration and β-citraurin production in "Newhall" orange. A MeJA treatment induced the expression of CsMYC2, which encodes a transcription factor that serves as a master regulator of jasmonate responses. CsMYC2 bound the promoter of the gene that encodes carotenoid cleavage dioxygenase 4b (CsCCD4b), the key gene for β-citraurin biosynthesis, and the promoters of genes that encode phytoene synthase (CsPSY), lycopene β-cyclase (CsLCYb), and β-carotene hydroxylase (CsBCH) and induced their expression. In addition, CsMYC2 promoted CsMPK6 expression. Notably, we found that CsMPK6 interacted with CsMYC2 and that this interaction decreased the stability and DNA-binding activity of CsMYC2. Thus, we conclude that negative feedback regulation attenuates JA signaling during the jasmonate-induced coloration of citrus fruit. Together, our findings indicate that jasmonates induce β-citraurin biosynthesis in citrus by activating a CsMPK6-CsMYC2 cascade, thereby affecting fruit coloration.

Transcriptome analysis reveals association of carotenoid metabolism pathway with fruit color in melon

Flesh color is an important quality of melon (Cucumis melo L.) and is determined mainly by carotenoid content, awarding them with colors, aromas, and nutrients. enhancing the nutritional and health benefits of fruits and vegetables for humans. In this study, we performed transcriptomic analysis of two melon inbred line “B-14” (orange-flesh) and “B-6” (white-flesh) at three developmental stages. We observed that the β-carotene content of inbred line “B-6” (14.232 μg/g) was significantly lower than that of inbred line “B-14” (0.534 μg/g). RNA-sequencing and quantitative reverse transcription PCR analyses were performed to identify differentially expressed genes (DEGs) between the two inbred lines at different stages; the DEGs were analyzed using the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes databases (KEGG). We identified 33 structural DEGs in different developmental periods of the two lines that were related to carotenoid metabolism. Among them, PSY, Z-ISO, ZDS, CRTISO, CCD4, VDE1, and NCED2 were highly correlated with carotenoid content. Thus, this study provides a basis for molecular mechanism of carotenoid biosynthesis and flesh color in melon fruit.

Genetic and molecular basis of carotenoid metabolism in cereals

Carotenoids are vital pigments for higher plants and play a crucial function in photosynthesis and photoprotection. Carotenoids are precursors of vitamin A synthesis and contribute to human nutrition and health. However, cereal grain endosperm contains a minor carotenoid measure and a scarce supply of provitamin A content. Therefore, improving the carotenoids in cereal grain is of major importance. Carotenoid content is governed by multiple candidate genes with their additive effects. Studies on genes related to carotenoid metabolism in cereals would increase the knowledge of potential metabolic steps of carotenoids and enhance the quality of crop plants. Recognizing the metabolism and carotenoid accumulation in various staple cereal crops over the last few decades has broadened our perspective on the interdisciplinary regulation of carotenogenesis. Meanwhile, the amelioration in metabolic engineering approaches has been exploited to step up the level of carotenoid and valuable industrial metabolites in many crops, but wheat is still considerable in this matter. In this study, we present a comprehensive overview of the consequences of biosynthetic and catabolic genes on carotenoid biosynthesis, current improvements in regulatory disciplines of carotenogenesis, and metabolic engineering of carotenoids. A panoptic and deeper understanding of the regulatory mechanisms of carotenoid metabolism and genetic manipulation (genome selection and gene editing) will be useful in improving the carotenoid content of cereals.

Abscisic-Acid-Regulated Responses to Alleviate Cadmium Toxicity in Plants

High levels of cadmium (Cd) in soil can cause crop yield reduction or death. Cadmium accumulation in crops affects human and animal health as it passes through the food chain. Therefore, a strategy is needed to enhance the tolerance of crops to this heavy metal or reduce its accumulation in crops. Abscisic acid (ABA) plays an active role in plants' response to abiotic stress. The application of exogenous ABA can reduce Cd accumulation in shoots of some plants and enhance the tolerance of plants to Cd; therefore, ABA may have good application prospects. In this paper, we reviewed the synthesis and decomposition of ABA, ABA-mediated signal transduction, and ABA-mediated regulation of Cd-responsive genes in plants. We also introduced physiological mechanism underlying Cd tolerance because of ABA. Specifically, ABA affects metal ion uptake and transport by influencing transpiration and antioxidant systems, as well as by affecting the expression of metal transporter and metal chelator protein genes. This study may provide a reference for further research on the physiological mechanism of heavy metal tolerance in plants.