Carotenoid Metabolism Research Articles

AgMYB5, an MYB transcription factor from celery, enhanced β-carotene synthesis and promoted drought tolerance in transgenic Arabidopsis

BackgroundWater shortage caused by global warming seriously affects the yield and quality of vegetable crops. β-carotene, the lipid-soluble natural product with important pharmacological value, is abundant in celery. Transcription factor MYB family extensively disperses in plants and plays regulatory roles in carotenoid metabolism and water scarcity response.ResultsHere, the AgMYB5 gene encoding 196 amino acids was amplified from celery cv. ‘Jinnanshiqin’. In celery, the expression of AgMYB5 exhibited transactivation activity, tissue specificity, and drought-condition responsiveness. Further analysis proved that ectopic expression of AgMYB5 increased β-carotene content and promoted drought tolerance in transgenic Arabidopsis thaliana. Moreover, AgMYB5 expression promoted β-carotene biosynthesis by triggering the expression of AtCRTISO and AtLCYB, which in turn increased antioxidant enzyme activities, and led to the decreased contents of H2O2 and MDA, and the inhibition of O2− generation. Meanwhile, β-carotene accumulation promoted endogenous ABA biosynthesis of transgenic Arabidopsis, which resulted in ABA-induced stomatal closing and delayed water loss. In addition, ectopic expression of AgMYB5 increased expression levels of AtERD1, AtP5CS1, AtRD22, and AtRD29.ConclusionsThe findings indicated that AgMYB5 up-regulated β-carotene biosynthesis and drought tolerance of Arabidopsis.

Expression of fatty acid related gene promotes astaxanthin heterologous production in Chlamydomonas reinhardtii.

Natural astaxanthin is a high-value ketone carotenoid mainly derived from Haematococcus pluvialis, which is an excellent antioxidant for human consumption. To study the role of lipids in accumulation of astaxanthin, the H. pluvialis-derived astaxanthin synthesis pathway genes (β-carotene ketolase gene, BKT and β-carotene hydroxylase gene, BCH) and fatty acid elongation gene (mitochondrial trans-2-enoyl-coa reductase gene, MECR) were heterologously co-expressed in C. reinhardtii. Zeaxanthin, the precursor of astaxanthin synthesis, was significantly increased after BKT and BCH were expressed. In contrast, the α-carotene that competes with astaxanthin synthesis for lycopene decreased significantly. This redistribution of carbon flow was conducive to the synthesis of astaxanthin. In addition, the transformant only expressed astaxanthin metabolism related genes (BKT, BCH) would lead to an increase in total lipid, a decrease in monounsaturated fatty acids and an increase in polyunsaturated fatty acids. On this basis, the expression of MECR gene further increased the total lipid, and the relative content of different fatty acids also changed. The astaxanthin content of algal strains transformed with BKT and BCH genes was nearly 50% higher than that of the wild type. On this basis, the astaxanthin content of transformants expressing MECR gene related to long-chain fatty acid synthesis was increased by 227.5%. In this study, an astaxanthin production model similar to H. pluvialis by combining carotenoid metabolism and fatty acid metabolism was constructed in C. reinhardtii. The results suggest that the increase in astaxanthin is indeed linked to the regulation of fatty acid metabolism, and this link may involve the type of fatty acids and the dynamics of astaxanthin ester in cells. The strategy of promoting the synthesis of fatty acids has potential to achieve efficient production of astaxanthin in C. reinhardtii.

MiR-330 targeting BCO2 is involved in carotenoid metabolism to regulate skin pigmentation in rainbow trout (Oncorhynchus mykiss)

BackgroundMicroRNAs (miRNAs) play a critical role in regulating skin pigmentation. As a key economic trait, skin color directly affects the market value of rainbow trout (Oncorhynchus mykiss), however, the regulatory mechanism of most miRNAs in fish skin color is still unclear.ResultsIn this study, the full-length cDNA sequence of β-carotene oxygenase 2 (BCO2, a key regulator of carotenoid metabolism) from the rainbow trout was obtained using rapid-amplification of cDNA ends (RACE) technology, and qRT-PCR was used to investigate the differential expression of miR-330 and BCO2 in 14 developmental stages and 13 tissues between wild-type rainbow trout (WTrt) and yellow mutant rainbow trout (YMrt). Additionally, the function of miR-330 was verified by overexpression and silencing in vitro and in vivo. The results showed that the complete cDNA sequence of BCO2 was 2057 bp with a 1707 bp ORF, encoding a 568 amino acid protein having a molecular weight of 64.07 kD. Sequence alignment revealed that higher conservation of BCO2 protein amongst fishes than amongst other vertebrates, which was further confirmed by phylogenetic analysis. The analysis of spatial and temporal expression patterns suggested that BCO2 and miR-330 were abundantly expressed from fertilized-stage to multi-cell as well as in the dorsal and ventral skin of WTrt and YMrt, and their expression patterns were opposite in most of the same periods and tissues. In vitro, luciferase reporter assay confirmed that BCO2 was a direct target of miR-330, and transfection of miR-330 mimics into rainbow trout liver cells resulted in a decrease in the expression of BCO2; conversely, miR-330 inhibitor had the opposite effect to the miR-330 mimics. In vivo, miR-330 agomir significantly decreased BCO2 expression in dorsal skin, tail fin, and liver. Furthermore, overexpression of miR-330 could suppress cell proliferation and induce apoptosis.ConclusionOur results showed that miR-330 is involved in the regulation of skin pigmentation in rainbow trout by targeting BCO2 and shows its promise as a potential molecular target to assist the selection of rainbow trout with better skin color patterns.

Integrated metabolic and transcriptional analysis reveals the role of carotenoid cleavage dioxygenase 4 (IbCCD4) in carotenoid accumulation in sweetpotato tuberous roots

BackgroundPlant carotenoids are essential for human health, having wide uses in dietary supplements, food colorants, animal feed additives, and cosmetics. With the increasing demand for natural carotenoids, plant carotenoids have gained great interest in both academic and industry research worldwide. Orange-fleshed sweetpotato (Ipomoea batatas) enriched with carotenoids is an ideal feedstock for producing natural carotenoids. However, limited information is available regarding the molecular mechanism responsible for carotenoid metabolism in sweetpotato tuberous roots.ResultsIn this study, metabolic profiling of carotenoids and gene expression analysis were conducted at six tuberous root developmental stages of three sweetpotato varieties with different flesh colors. The correlations between the expression of carotenoid metabolic genes and carotenoid levels suggested that the carotenoid cleavage dioxygenase 4 (IbCCD4) and 9-cis-epoxycarotenoid cleavage dioxygenases 3 (IbNCED3) play important roles in the regulation of carotenoid contents in sweetpotato. Transgenic experiments confirmed that the total carotenoid content decreased in the tuberous roots of IbCCD4-overexpressing sweetpotato. In addition, IbCCD4 may be regulated by two stress-related transcription factors, IbWRKY20 and IbCBF2, implying that the carotenoid accumulation in sweeetpotato is possibly fine-tuned in responses to stress signals.ConclusionsA set of key genes were revealed to be responsible for carotenoid accumulation in sweetpotato, with IbCCD4 acts as a crucial player. Our findings provided new insights into carotenoid metabolism in sweetpotato tuberous roots and insinuated IbCCD4 to be a target gene in the development of new sweetpotato varieties with high carotenoid production.

Testosterone Coordinates Gene Expression Across Different Tissues to Produce Carotenoid-Based Red Ornamentation.

Carotenoid pigments underlie most of the red, orange, and yellow visual signals used in mate choice in vertebrates. However, many of the underlying processes surrounding the production of carotenoid-based traits remain unclear due to the complex nature of carotenoid uptake, metabolism, and deposition across tissues. Here, we leverage the ability to experimentally induce the production of a carotenoid-based red plumage patch in the red-backed fairywren (Malurus melanocephalus), a songbird in which red plumage is an important male sexual signal. We experimentally elevated testosterone in unornamented males lacking red plumage to induce the production of ornamentation and compared gene expression in both the liver and feather follicles between unornamented control males, testosterone-implanted males, and naturally ornamented males. We show that testosterone upregulates the expression of CYP2J19, a gene known to be involved in ketocarotenoid metabolism, and a putative carotenoid processing gene (ELOVL6) in the liver, and also regulates the expression of putative carotenoid transporter genes in red feather follicles on the back, including ABCG1. In black feathers, carotenoid-related genes are downregulated and melanin genes upregulated, but we find that carotenoids are still present in the feathers. This may be due to the activity of the carotenoid-cleaving enzyme BCO2 in black feathers. Our study provides a first working model of a pathway for carotenoid-based trait production in free-living birds, implicates testosterone as a key regulator of carotenoid-associated gene expression, and suggests hormones may coordinate the many processes that underlie the production of these traits across multiple tissues.

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.

The transcription factor CaBBX20 regulates capsanthin accumulation in pepper (Capsicum annuum L.)

Carotenoids are important pigments whose accumulation is regulated by transcription factors such as those from the MADS-box and MYB families. BBXs are a kind of zinc finger transcription factors with one or two B-box domains, which were identified involved in photomorphogenesis. However, little is known about the function of CaBBX in the pigmentation of pepper fruit (Capsicum annuum). Here, we selected two red-fruited pepper cultivars to investigate carotenoid contents at three developmental stages (Mg: mature green stage, Tf: turning stage, and Rf: ripen stage) during fruit ripening (30, 45 and 60 days after flowering). Our results showed that carotenoid accumulation in pepper fruits begins at turning stage (Tf) and peaks in ripen stage (Rf), which was reflected in the fruit color change (from green to brown, and then to red). The expression of CaBBX20 was upregulated with the pigmentation during fruit ripening. Silencing CaBBX20 led to reduced carotenoid accumulation, as well as downregulated expression of CaCCS, suggesting a positive role of CaBBX20 in carotenoid metabolism of pepper fruit. Our study thus provides basic insight into carotenoid biosynthesis during pepper fruit pigmentation.

Recent Advancements and Biotechnological Implications of Carotenoid Metabolism of Brassica

Carotenoids were synthesized in the plant cells involved in photosynthesis and photo-protection. In humans, carotenoids are essential as dietary antioxidants and vitamin A precursors. Brassica crops are the major sources of nutritionally important dietary carotenoids. Recent studies have unraveled the major genetic components in the carotenoid metabolic pathway in Brassica, including the identification of key factors that directly participate or regulate carotenoid biosynthesis. However, recent genetic advances and the complexity of the mechanism and regulation of Brassica carotenoid accumulation have not been reviewed. Herein, we reviewed the recent progress regarding Brassica carotenoids from the perspective of forward genetics, discussed biotechnological implications and provided new perspectives on how to transfer the knowledge of carotenoid research in Brassica to the crop breeding process.

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.

Regulation of carotenoid and flavonoid biosynthetic pathways in Lactuca sativa var capitate L. in protected cultivation.

In the face of a growing world population and limited land, there is an urgent demand for higher productivity of food crops, and cultivation systems must be adapted to future needs. Sustainable crop production should aim for not only high yields, but also high nutritional values. In particular, the consumption of bioactive compounds such as carotenoids and flavonoids is associated with a reduced incidence of non-transmissible diseases. Modulating environmental conditions by improving cultivation systems can lead to the adaption of plant metabolisms and the accumulation of bioactive compounds. The present study investigates the regulation of carotenoid and flavonoid metabolisms in lettuce (Lactuca sativa var capitate L.) grown in a protected environment (polytunnels) compared to plants grown without polytunnels. Carotenoid, flavonoid and phytohormone (ABA) contents were determined using HPLC-MS and transcript levels of key metabolic genes were analyzed by RT-qPCR. In this study, we observed inverse contents of flavonoids and carotenoids in lettuce grown without or under polytunnels. Flavonoid contents on a total and individual level were significantly lower, while total carotenoid content was higher in lettuce plants grown under polytunnels compared to without. However, the adaptation was specific to the level of individual carotenoids. For instance, the accumulation of the main carotenoids lutein and neoxanthin was induced while the β-carotene content remained unchanged. In addition, our findings suggest that the flavonoid content of lettuce depends on transcript levels of the key biosynthetic enzyme, which is modulated by UV light. A regulatory influence can be assumed based on the relation between the concentration of the phytohormone ABA and the flavonoid content in lettuce. In contrast, the carotenoid content is not reflected in transcript levels of the key enzyme of either the biosynthetic or the degradation pathway. Nevertheless, the carotenoid metabolic flux determined using norflurazon was higher in lettuce grown under polytunnels, suggesting posttranscriptional regulation of carotenoid accumulation, which should be an integral part of future studies. Therefore, a balance needs to be found between the individual environmental factors, including light and temperature, in order to optimize the carotenoid or flavonoid contents and to obtain nutritionally highly valuable crops in protected cultivation.

CRISPR/Cas9-mediated SNAC9 mutants reveal the positive regulation of tomato ripening by SNAC9 and the mechanism of carotenoid metabolism regulation.

NAC transcriptional regulators are crucial for tomato ripening. Virus-induced gene silencing (VIGS) of SNAC9 (SlNAC19, Gene ID: 101248665) affects tomato ripening, and SNAC9 is involved in ethylene and abscisic acid (ABA) metabolic pathways. However, the function of SNAC9 in pigment metabolism in tomatoes remains unclear. This work seeks to discover the mechanism of SNAC9 involvement in pigment metabolism during tomato ripening by establishing a SNAC9 knockout model using CRISPR/Cas9 technology. The results indicated that fruit ripening was delayed in knockout (KO) mutants, and SNAC9 mutation significantly affected carotenoid metabolism. The chlorophyll (Chl) degradation rate, total carotenoid content, and lycopene content decreased significantly in the mutants. The transformation rate of chloroplasts to chromoplasts in mutants was slower, which was related to the carotenoid content. Furthermore, SNAC9 changed the expression of critical genes (PSY1, PDS, CRTISO, Z-ISO, SGR1, DXS2, LCYE, LCYB, and CrtR-b2) involved in pigment metabolism in tomato ripening. SNAC9 knockout also altered the expression levels of critical genes involved in the biosynthesis of ethylene and ABA. Accordingly, SNAC9 regulated carotenoid metabolism by directly regulating PSY1, DXS2, SGR1, and CrtR-b2. This research provides a foundation for developing the tomato ripening network and precise tomato ripening regulation.

Combined analysis of chromatin accessibility and gene expression profiles provide insight into Fucoxanthin biosynthesis in Isochrysis galbana under green light.

Isochrysis galbana, as a potential accumulator of fucoxanthin, has become a valuable material to develop functional foods for humans. Our previous research revealed that green light effectively promotes the accumulation of fucoxanthin in I. galbana, but there is little research on chromatin accessibility in the process of transcriptional regulation. This study was conducted to reveal the mechanism of fucoxanthin biosynthesis in I. galbana under green light by analyzing promoter accessibility and gene expression profiles. Differentially accessible chromatin regions (DARs)-associated genes were enriched in carotenoid biosynthesis and photosynthesis-antenna protein formation, including IgLHCA1, IgLHCA4, IgPDS, IgZ-ISO, IglcyB, IgZEP, and IgVDE. The motifs for the MYB family were also identified as candidates controlling metabolic regulation responses to green light culture of I. galbana, including IgMYB1, IgMYB2, IgMYB33, IgMYB42, IgMYB98, IgMYB118, and IgMYB119. The results of differential expression analysis and WGCNA showed that several genes or transcription factors (TFs) related to carotenoid metabolism and photosynthesis exhibited a higher expression level and were significantly upregulated in A-G5d compared with A-0d and A-W5d, including IgMYB98, IgLHCA1, IgLHCX2, IgLHCB4, and IgLHCB5. This suggests that upregulation of these genes by green light may be the key factor leading to fucoxanthin accumulation by regulating the photosynthesis-antenna protein pathway. An integrated analysis of ATAC-seq and RNA-seq showed that 3 (IgphoA, IgPKN1, IgOTC) of 34 DARs-associated genes displayed obvious changes in their chromatin regions in ATAC-seq data, suggesting that these genes specific for green light may play a key role in fucoxanthin biosynthesis in I. galbana through a complex regulatory network of multiple metabolic pathways interacting with each other. These findings will facilitate in-depth understanding the molecular regulation mechanisms of fucoxanthin in I. galbana and its role in response to green light regulation, providing technical support for the construction of high fucoxanthin content strains.

Stromal Ascorbate Peroxidase (OsAPX7) Modulates Drought Stress Tolerance in Rice (Oryza sativa)

Chloroplast ascorbate peroxidases exert an important role in the maintenance of hydrogen peroxide levels in chloroplasts by using ascorbate as the specific electron donor. In this work, we performed a functional study of the stromal APX in rice (OsAPX7) and demonstrated that silencing of OsAPX7 did not impact plant growth, redox state, or photosynthesis parameters. Nevertheless, when subjected to drought stress, silenced plants (APX7i) show a higher capacity to maintain stomata aperture and photosynthesis performance, resulting in a higher tolerance when compared to non-transformed plants. RNA-seq analyses indicate that the silencing of OsAPX7 did not lead to changes in the global expression of genes related to reactive oxygen species metabolism. In addition, the drought-mediated induction of several genes related to the proteasome pathway and the down-regulation of genes related to nitrogen and carotenoid metabolism was impaired in APX7i plants. During drought stress, APX7i showed an up-regulation of genes encoding flavonoid and tyrosine metabolism enzymes and a down-regulation of genes related to phytohormones signal transduction and nicotinate and nicotinamide metabolism. Our results demonstrate that OsAPX7 might be involved in signaling transduction pathways related to drought stress response, contributing to the understanding of the physiological role of chloroplast APX isoforms in rice.

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 availabilityData will be made available on request.

Engineering the β-Carotene Metabolic Pathway of Microalgae Dunaliella To Confirm Its Carotenoid Synthesis Pattern in Comparison To Bacteria and Plants.

Dunaliella salina is the most salt-tolerant eukaryote and has the highest β-carotene content, but its carotenoid synthesis pathway is still unclear, especially the synthesis of lycopene, the upstream product of β-carotene. In this study, DsGGPS, DsPSY, DsPDS, DsZISO, DsZDS, DsCRTISO, and DsLYCB genes were cloned from D. salina and expressed in Escherichia coli. A series of carotenoid engineering E. coli strains from phytoene to β-carotene were obtained. ZISO was first identified from Chlorophyta, while CRTISO was first isolated from algae. It was found that DsZISO and DsCRTISO were essential for isomerization of carotenoids in photosynthetic organisms and could not be replaced by photoisomerization, unlike some plants. DsZDS was found to have weak beta cyclization abilities, and DsLYCB was able to catalyze 7,7',9,9'-tetra-cis-lycopene to generate 7,7',9,9'-tetra-cis-β-carotene, which had not been reported before. A new carotenoid 7,7',9,9'-tetra-cis-β-carotene, the beta cyclization product of prolycopene, was discovered. Compared with the bacterial-derived carotenoid synthesis pathway, there is higher specificity and greater efficiency of the carotenoid synthesis pathway in algae. This research experimentally confirmed that the conversion of phytoene to lycopene in D. salina was similar to that of plants and different from bacteria and provided a new possibility for the metabolic engineering of β-carotene. IMPORTANCE The synthesis mode of all trans-lycopene in bacteria and plants is clear, but there are still doubts in microalgae. Dunaliella is the organism with the highest β-carotene content, and plant-type and bacterial-type enzyme genes have been found in its carotenoid metabolism pathway. In this study, the entire plant-type enzyme gene was completely cloned into Escherichia coli, and high-efficiency expression was obtained, which proved that carotenoid synthesis of algae is similar to that of plants. In bacteria, CRT can directly catalyze 4-step continuous dehydrogenation to produce all trans-lycopene. In plants, four enzymes (PDS, ZISO, ZDS, and CRTISO) are involved in this process. Although a carotenoid synthetase similar to that of bacteria has been found in algae, it does not play a major role. This research reveals the evolutionary relationship of carotenoid metabolism in bacteria, algae, and plants and is of methodologically innovative significance for molecular evolution research.

Carotenoid metabolism: New insights and synthetic approaches.

Carotenoids are well-known isoprenoid pigments naturally produced by plants, algae, photosynthetic bacteria as well as by several heterotrophic microorganisms. In plants, they are synthesized in plastids where they play essential roles in light-harvesting and in protecting the photosynthetic apparatus from reactive oxygen species (ROS). Carotenoids are also precursors of bioactive metabolites called apocarotenoids, including vitamin A and the phytohormones abscisic acid (ABA) and strigolactones (SLs). Genetic engineering of carotenogenesis made possible the enhancement of the nutritional value of many crops. New metabolic engineering approaches have recently been developed to modulate carotenoid content, including the employment of CRISPR technologies for single-base editing and the integration of exogenous genes into specific "safe harbors" in the genome. In addition, recent studies revealed the option of synthetic conversion of leaf chloroplasts into chromoplasts, thus increasing carotenoid storage capacity and boosting the nutritional value of green plant tissues. Moreover, transient gene expression through viral vectors allowed the accumulation of carotenoids outside the plastid. Furthermore, the utilization of engineered microorganisms allowed efficient mass production of carotenoids, making it convenient for industrial practices. Interestingly, manipulation of carotenoid biosynthesis can also influence plant architecture, and positively impact growth and yield, making it an important target for crop improvements beyond biofortification. Here, we briefly describe carotenoid biosynthesis and highlight the latest advances and discoveries related to synthetic carotenoid metabolism in plants and microorganisms.

Biology of Two-Spotted Spider Mite (Tetranychus urticae): Ultrastructure, Photosynthesis, Guanine Transcriptomics, Carotenoids and Chlorophylls Metabolism, and Decoyinine as a Potential Acaricide.

Two-Spotted Spider Mites (TSSMs, Tetranychus urticae Koch 1836 (Acari: Tetranychidae)) is one of the most important pests in many crop plants, and their feeding activity is based on sucking leaf cell contents. The purpose of this study was to evaluate the interaction between TSSMs and their host Lima bean (Phaseolus lunatus) by analyzing the metabolomics of leaf pigments and the transcriptomics of TSSM guanine production. We also used epifluorescence, confocal laser scanning, and transmission electron microscopies to study the morphology and structure of TSSMs and their excreta. Finally, we evaluated the potential photosynthetic ability of TSSMs and the activity and content of Ribulose-1,5-bisphosphate Carboxylase/Oxigenase (RubisCO). We found that TSSMs express several genes involved in guanine production, including Guanosine Monophosphate Synthetase (GMPS) and decoyinine (DCY), a potential inhibitor of GMPS, was found to reduce TSSMs proliferation in infested Lima bean leaves. Despite the presence of intact chloroplasts and chlorophyll in TSSMs, we demonstrate that TSSMs do not retain any photosynthetic activity. Our results show for the first time the transcriptomics of guanine production in TSSMs and provide new insight into the catabolic activity of TSSMs on leaf chlorophyll and carotenoids. Finally, we preliminary demonstrate that DCY has an acaricidal potential against TSSMs.

Genetic dissection of the roles of β-hydroxylases in carotenoid metabolism, photosynthesis, and plant growth in tetraploid wheat (Triticum turgidum L.)

Key messageFunctional redundancy and subfunctionalization of β-hydroxylases in tetraploid wheat tissues open up opportunities for manipulation of carotenoid metabolism for trait improvement.The genetic diversity provided by subgenome homoeologs in allopolyploid wheat can be leveraged for developing improved wheat varieties with modified chemical traits, including profiles of carotenoids, which play critical roles in photosynthesis, photoprotection, and growth regulation. Carotenoid profiles are greatly influenced by hydroxylation catalyzed by β-hydroxylases (HYDs). To genetically dissect the contribution of HYDs to carotenoid metabolism and wheat growth and yield, we isolated loss-of-function mutants of the two homoeologs of HYD1 (HYD-A1 and HYD-B1) and HYD2 (HYD-A2 and HYD-B2) from the sequenced ethyl methanesulfonate mutant population of the tetraploid wheat cultivar Kronos, and generated various mutant combinations. Although functional redundancy between HYD1 and HYD2 paralogs was observed in leaves, HYD1 homoeologs contributed more than HYD2 homoeologs to carotenoid β-ring hydroxylation in this tissue. By contrast, the HYD2 homoeologs functioned toward production of lutein, the major carotenoid in mature grains, whereas HYD1 homoeologs had a limited role. These results collectively suggested subfunctionalization of HYD genes and homoeologs in different tissues of tetraploid wheat. Despite reduced photoprotective responses observed in the triple hyd-A1 hyd-B1 hyd-A2 and the quadruple hyd-A1 hyd-B1 hyd-A2 hyd-B2 combinatorial mutants, comprehensive plant phenotyping analysis revealed that all mutants analyzed were comparable to the control for growth, yield, and fertility, except for a slight delay in anthesis and senescence as well as accelerated germination in the quadruple mutant. Overall, this research takes steps toward untangling the functions of HYDs in wheat and has implications for improving performance and consumer traits of this economically important global crop.

Effects of Postharvest Treatment with 1-Naphthaleneacetic Acid on Chlorophyll and Carotenoid Metabolism in Citrus Fruit

Effects of Postharvest Treatment with 1-Naphthaleneacetic Acid on Chlorophyll and Carotenoid Metabolism in Citrus Fruit

Regulation of Chlorophyll and Carotenoid Metabolism in Citrus Fruit During Maturation and Regreening

Regulation of Chlorophyll and Carotenoid Metabolism in Citrus Fruit During Maturation and Regreening