GENES AND ENZYMES OF CAROTENOID BIOSYNTHESIS IN PLANTS

Changes in the expression of genes encoding xanthophyl acyltransferases during the postharvest ripening of avocado (Persea americana) fruit

BACKGROUND

Avocado fruit is rich in xanthophylls, which have been related to positive effects on human health. Xanthophyl acetyltransferases (XATs) are enzymes catalyzing the esterification of carboxylic acids to the hydroxyl group of the xanthophyll molecule. This esterification is thought to increase the lipophilic nature of the xanthophyll and its stability in a lipophilic environment. Studies on XATs in fruits are very scarce, and no studies had been carried out in avocado fruit during postharvest. The objective of this work was to investigate the changes in the expression of genes encoding XAT, during avocado fruit ripening.

RESULTS

Avocado fruits were obtained from a local market and stored at 15 °C for 8 days. The fruit respiration rate, ethylene production, and fruit peel's color space parameters (L*, a*, b*) were measured during storage. Fruit mesocarp samples were taken after 1, 3, 5, and 7 days of storage and frozen with liquid nitrogen. Total RNA was extracted from fruit mesocarp, and the quantification of the two genes designated as COGE_ID: 936743791 and COGE_ID: 936800185 encoding XATs was performed with real-time quantitative reverse transcription polymerase chain reaction using actin as a reference gene. The presence of a climacteric peak and large changes in color were recorded during postharvest. The two genes studied showed a large expression after 3 days of fruit storage.

CONCLUSIONS

We conclude that during the last stages of ripening in avocado fruit there was an active esterification of xanthophylls with carboxylic acids, which suggests the presence of esterified xanthophylls in the fruit mesocarp. © 2024 Society of Chemical Industry.

Analysis of nutritional composition in opaque2- and crtRB1-based single- and double-biofortified super sweet corn

Sweet corn has emerged as a favorite food item worldwide owing to its kernel sweetness. However, traditional sweet corn cultivars are poor in provitamin-A (proA) and essential amino acids, viz., lysine and tryptophan. So far, no sweet corn hybrid with high nutritional qualities has been commercialized elsewhere. Here, we analyzed accumulation of provitamin-A (proA), lysine, and tryptophan in a set of mutant versions of (i) crtRB1-, (ii) o2-, and (iii) crtRB1 + o2-based sweet corn inbreds and hybrids with (iv) traditional sweet corn (wild-type: O2 + CrtRB1). The crtRB1- and crtRB1 + o2-based genotypes possessed significantly higher proA (17.31 ppm) over traditional sweet corn (2.83 ppm), while o2- and crtRB1 + o2-based genotypes possessed significantly higher lysine (0.345%) and tryptophan (0.080%) over traditional sweet corn (lysine 0.169%, tryptophan 0.036%). Late sowing favored high kernel lysine, proA, and green cob yield among hybrids. Sweetness (17.87%) among the improved inbreds and hybrids was comparable to the original sweetcorn genotypes (17.84%). Among the four genotypic classes, crtRB1 + o2-based improved genotypes showed stronger association among traits over genotypes with o2 and crtRB1 genes alone. Significant association was observed among (i) proA and BC (r = 0.99), (ii) proA and BCX (r = 0.93), (iii) lysine and tryptophan (r = 0.99), and (iv) green cob yield with fodder yield (r = 0.73) in sweet corn hybrids. The study demonstrated that combining crtRB1 and o2 genes did not pose any negative impact on nutritional, yield, and agronomic performance. Sweet corn with crtRB1 + o2 assumes significance for alleviating malnutrition through sustainable and cost-effective approach.

Tobacco rattle virus-based virus-induced gene silencing (VIGS) as an aid for functional genomics in Saffron (Crocus sativus L.)

Several limitations in genetic engineering interventions in saffron exist, hindering the development of genetically modified varieties and the widespread application of genetic engineering in this crop. Lack of genome sequence information, the complexity of genetic makeup, and lack of well-established genetic transformation protocols limit its in planta functional validation of genes that would eventually lead toward crop optimization. In this study, we demonstrate agro infiltration in leaves of adult plants and whole corm before sprouting are suitable for transient gene silencing in saffron using Tobacco Rattle Virus (TRV) based virus-induced gene silencing (VIGS) targeting phytoene desaturase (PDS). Silencing of PDS resulted in bleached phenotype in leaves in both methods. TRV-mediated VIGS could be attained in saffron leaves and corms, providing an opportunity for functional genomics studies in this expensive spice crop.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01459-0.

Tocopherol and phylloquinone biosynthesis in chloroplasts requires the phytol kinase VITAMIN E PATHWAY GENE5 (VTE5) and the farnesol kinase (FOLK)

Chlorophyll degradation causes the release of phytol, which is converted into phytyl diphosphate (phytyl-PP) by phytol kinase (VITAMIN E PATHWAY GENE5 [VTE5]) and phytyl phosphate (phytyl-P) kinase (VTE6). The kinase pathway is important for tocopherol synthesis, as the Arabidopsis (Arabidopsis thaliana) vte5 mutant contains reduced levels of tocopherol. Arabidopsis harbors one paralog of VTE5, farnesol kinase (FOLK) involved in farnesol phosphorylation. Here, we demonstrate that VTE5 and FOLK harbor kinase activities for phytol, geranylgeraniol, and farnesol with different specificities. While the tocopherol content of the folk mutant is unchanged, vte5-2 folk plants completely lack tocopherol. Tocopherol deficiency in vte5-2 plants can be complemented by overexpression of FOLK, indicating that FOLK is an authentic gene of tocopherol synthesis. The vte5-2 folk plants contain only ∼40% of wild-type amounts of phylloquinone, demonstrating that VTE5 and FOLK both contribute in part to phylloquinone synthesis. Tocotrienol and menaquinone-4 were produced in vte5-2 folk plants after supplementation with homogentisate or 1,4-dihydroxy-2-naphthoic acid, respectively, indicating that their synthesis is independent of the VTE5/FOLK pathway. These results show that phytyl moieties for tocopherol synthesis are completely but, for phylloquinone production, only partially derived from geranylgeranyl-chlorophyll and phytol phosphorylation by VTE5 and FOLK.

Reducing PHYTOENE SYNTHASE activity fine-tunes the abundance of a cis-carotene-derived signal that regulates the PIF3/HY5 module and plastid biogenesis

PHYTOENE SYNTHASE (PSY) is a rate-limiting enzyme catalysing the first committed step of carotenoid biosynthesis, and changes in PSY gene expression and/or protein activity alter carotenoid composition and plastid differentiation in plants. Four genetic variants of PSY (psy-4, psy-90, psy-130, and psy-145) were identified using a forward genetics approach that rescued leaf virescence phenotypes and plastid abnormalities displayed by the Arabidopsis CAROTENOID ISOMERASE (CRTISO) mutant ccr2 (carotenoid and chloroplast regulation 2) when grown under a shorter photoperiod. The four non-lethal mutations affected alternative splicing, enzyme-substrate interactions, and PSY:ORANGE multi-enzyme complex binding, constituting the dynamic post-transcriptional fine-tuning of PSY levels and activity without changing localization to the stroma and protothylakoid membranes. psy genetic variants did not alter total xanthophyll or β-carotene accumulation in ccr2, yet they reduced specific acyclic linear cis-carotenes linked to the biosynthesis of a currently unidentified apocarotenoid signal regulating plastid biogenesis, chlorophyll biosynthesis, and photomorphogenic regulation. ccr2 psy variants modulated the PHYTOCHROME-INTERACTING FACTOR 3/ELONGATED HYPOCOTYL 5 (PIF3/HY5) ratio, and displayed a normal prolamellar body formation in etioplasts and chlorophyll accumulation during seedling photomorphogenesis. Thus, suppressing PSY activity and impairing PSY:ORANGE protein interactions revealed how cis-carotene abundance can be fine-tuned through holoenzyme-metabolon interactions to control plastid development.

Deciphering the β-carotene hyperaccumulation in Dunaliella by the comprehensive analysis of Dunaliella salina and Dunaliella tertiolecta under high light conditions

The green microalga Dunaliella salina hyperaccumulates β-carotene in the chloroplast, which turns its cells orange. This does not occur in the sister species Dunaliella tertiolecta. However, the molecular mechanisms of β-carotene hyperaccumulation were still unclear. Here, we discovered the reasons for β-carotene hyperaccumulation by comparing the morphology, physiology, genome, and transcriptome between the carotenogenic D. salina and the noncarotenogenic D. tertiolecta after transfer to high light. The differences in photosynthetic capacity, cell growth, and the concentration of stored carbon suggest that these species regulate the supply and utilization of carbon differently. The number of β-carotene-containing plastid lipid globules increased in both species, but much faster and to a greater extent in D. salina than in D. tertiolecta. Consistent with the accumulation of plastid lipid globules, the expression of the methyl-erythritol-phosphate and carotenoid biosynthetic pathways increased only in D. salina, which explains the de novo synthesis of β-carotene. In D. salina, the concomitantly upregulated expression of the carotene globule proteins suggests that hyperaccumulation of β-carotene also requires a simultaneous increase in its sink capacity. Based on genomic analysis, we propose that D. salina has genetic advantages for routing carbon from growth to carotenoid metabolism.

The role of environmental stress in fruit pigmentation

For many fruit crops, the colour of the fruit outwardly defines its eating quality. Fruit pigments provide reproductive advantage for the plant as well as providing protection against unfavourable environmental conditions and pathogens. For consumers these colours are considered attractive and provide many of the dietary benefits derived from fruits. In the majority of species, the main pigments are either carotenoids and/or anthocyanins. They are produced in the fruit as part of the ripening process, orchestrated by phytohormones and an ensuing transcriptional cascade, culminating in pigment biosynthesis. Whilst this is a controlled developmental process, the production of pigments is also attuned to environmental conditions such as light quantity and quality, availability of water and ambient temperature. If these factors intensify to stress levels, fruit tissues respond by increasing (or ceasing) pigment production. In many cases, if the stress is not severe, this can have a positive outcome for fruit quality. Here, we focus on the principal environmental factors (light, temperature and water) that can influence fruit colour.

Outstanding women scientists who have broadened the knowledge on biological photoreceptors

Short biographical sketches are given of women born before 1955 who have contributed to our knowledge on the function, structure, and molecular basis of biological photoreceptors, both energy converters and photosensors.

Antioxidants of Non-Enzymatic Nature: Their Function in Higher Plant Cells and the Ways of Boosting Their Biosynthesis

Plants are exposed to a variety of abiotic and biotic stresses leading to increased formation of reactive oxygen species (ROS) in plant cells. ROS are capable of oxidizing proteins, pigments, lipids, nucleic acids, and other cell molecules, disrupting their functional activity. During the process of evolution, numerous antioxidant systems were formed in plants, including antioxidant enzymes and low molecular weight non-enzymatic antioxidants. Antioxidant systems perform neutralization of ROS and therefore prevent oxidative damage of cell components. In the present review, we focus on the biosynthesis of non-enzymatic antioxidants in higher plants cells such as ascorbic acid (vitamin C), glutathione, flavonoids, isoprenoids, carotenoids, tocopherol (vitamin E), ubiquinone, and plastoquinone. Their functioning and their reactivity with respect to individual ROS will be described. This review is also devoted to the modern genetic engineering methods, which are widely used to change the quantitative and qualitative content of the non-enzymatic antioxidants in cultivated plants. These methods allow various plant lines with given properties to be obtained in a rather short time. The most successful approaches for plant transgenesis and plant genome editing for the enhancement of biosynthesis and the content of these antioxidants are discussed.

Overexpression of a pseudo-etiolated-in-light-like protein in Taraxacum koksaghyz leads to a pale green phenotype and enables transcriptome-based network analysis of photomorphogenesis and isoprenoid biosynthesis

Introduction

Plant growth and greening in response to light require the synthesis of photosynthetic pigments such as chlorophylls and carotenoids, which are derived from isoprenoid precursors. In Arabidopsis, the pseudo-etiolated-in-light phenotype is caused by the overexpression of repressor of photosynthetic genes 2 (RPGE2), which regulates chlorophyll synthesis and photosynthetic genes.

Methods

We investigated a homologous protein in the Russian dandelion (Taraxacum koksaghyz) to determine its influence on the rich isoprenoid network in this species, using a combination of in silico analysis, gene overexpression, transcriptomics and metabolic profiling.

Results

Homology-based screening revealed a gene designated pseudo-etiolated-in-light-like (TkPEL-like), and in silico analysis identified a light-responsive G-box element in its promoter. TkPEL-like overexpression in dandelion plants and other systems reduced the levels of chlorophylls and carotenoids, but this was ameliorated by the mutation of one or both conserved cysteine residues. Comparative transcriptomics in dandelions overexpressing TkPEL-like showed that genes responsible for the synthesis of isoprenoid precursors and chlorophyll were downregulated, probably explaining the observed pale green leaf phenotype. In contrast, genes responsible for carotenoid synthesis were upregulated, possibly in response to feedback signaling. The evaluation of additional differentially expressed genes revealed interactions between pathways.

Discussion

We propose that TkPEL-like negatively regulates chlorophyll- and photosynthesis-related genes in a light-dependent manner, which appears to be conserved across species. Our data will inform future studies addressing the regulation of leaf isoprenoid biosynthesis and photomorphogenesis and could be used in future breeding strategies to optimize selected plant isoprenoid profiles and generate suitable plant-based production platforms.

Production of Astaxanthin by Animal Cells via Introduction of an Entire Astaxanthin Biosynthetic Pathway

Astaxanthin is a fascinating molecule with powerful antioxidant activity, synthesized exclusively by specific microorganisms and higher plants. To expand astaxanthin production, numerous studies have employed metabolic engineering to introduce and optimize astaxanthin biosynthetic pathways in microorganisms and plant hosts. Here, we report the metabolic engineering of animal cells in vitro to biosynthesize astaxanthin. This was accomplished through a two-step study to introduce the entire astaxanthin pathway into human embryonic kidney cells (HEK293T). First, we introduced the astaxanthin biosynthesis sub-pathway (Ast subp) using several genes encoding β-carotene ketolase and β-carotene hydroxylase enzymes to synthesize astaxanthin directly from β-carotene. Next, we introduced a β-carotene biosynthesis sub-pathway (β-Car subp) with selected genes involved in Ast subp to synthesize astaxanthin from geranylgeranyl diphosphate (GGPP). As a result, we unprecedentedly enabled HEK293T cells to biosynthesize free astaxanthin from GGPP with a concentration of 41.86 µg/g dry weight (DW), which represented 66.19% of the total ketocarotenoids (63.24 µg/g DW). Through optimization steps using critical factors in the astaxanthin biosynthetic process, a remarkable 4.14-fold increase in total ketocarotenoids (262.10 µg/g DW) was achieved, with astaxanthin constituting over 88.82%. This pioneering study holds significant implications for transgenic animals, potentially revolutionizing the global demand for astaxanthin, particularly within the aquaculture sector.

Trait stacking simultaneously enhances provitamin A carotenoid and mineral bioaccessibility in biofortified Sorghum bicolor

Vitamin A, iron, and zinc deficiencies are major nutritional inadequacies in sub-Saharan Africa and disproportionately affect women and children. Biotechnology strategies have been tested to individually improve provitamin A carotenoid or mineral content and/or bioaccessibility in staple crops including sorghum (Sorghum bicolor). However, concurrent carotenoid and mineral enhancement has not been thoroughly assessed and antagonism between these chemical classes has been reported. This work evaluated two genetically engineered constructs containing a suite of heterologous genes to increase carotenoid stability and pathway flux, as well as phytase to catabolize phytate and increase mineral bioaccessibility. Model porridges made from transgenic events were evaluated for carotenoid and mineral content as well as bioaccessibility. Transgenic events produced markedly higher amounts of carotenoids (26.4 μg g^-1 DW) compared to null segregants (4.2 μg g^-1 DW) and wild-type control (Tx430; 3.7 μg g^-1 DW). Phytase activation by pre-steeping flour resulted in significant phytate reduction (9.4 to 4.2 mg g^-1 DW), altered the profile of inositol phosphate catabolites, and reduced molar ratios of phytate to iron (16.0 to 4.1), and zinc (19.0 to 4.9) in engineered material, suggesting improved mineral bioaccessibility. Improved phytate : mineral ratios did not significantly affect micellarization and bioaccessible provitamin A carotenoids were over 23 times greater in transgenic events compared to corresponding null segregants and wild-type controls. A 200 g serving of porridge made with these transgenic events provide an estimated 53.7% of a 4-8-year-old child's vitamin A estimated average requirement. These data suggest that combinatorial approaches to enhance micronutrient content and bioaccessibility are feasible and warrant further assessment in human studies.

A Lycopene ε-Cyclase TILLING Allele Enhances Lycopene and Carotenoid Content in Fruit and Improves Drought Stress Tolerance in Tomato Plants

In the scenario of climate change, the availability of genetic resources for tomato cultivation that combine improved nutritional properties and more tolerance to water deficiency is highly desirable. Within this context, the molecular screenings of the Red Setter cultivar-based TILLING platform led to the isolation of a novel lycopene ε-cyclase gene (SlLCY-E) variant (G/3378/T) that produces modifications in the carotenoid content of tomato leaves and fruits. In leaf tissue, the novel G/3378/T SlLCY-E allele enhances β,β-xanthophyll content at the expense of lutein, which decreases, while in ripe tomato fruit the TILLING mutation induces a significant increase in lycopene and total carotenoid content. Under drought stress conditions, the G/3378/T SlLCY-E plants produce more abscisic acid (ABA) and still conserve their leaf carotenoid profile (reduction of lutein and increase in β,β-xanthophyll content). Furthermore, under said conditions, the mutant plants grow much better and are more tolerant to drought stress, as revealed by digital-based image analysis and in vivo monitoring of the OECT (Organic Electrochemical Transistor) sensor. Altogether, our data indicate that the novel TILLING SlLCY-E allelic variant is a valuable genetic resource that can be used for developing new tomato varieties, improved in drought stress tolerance and enriched in fruit lycopene and carotenoid content.

A gap-free and haplotype-resolved lemon genome provides insights into flavor synthesis and huanglongbing (HLB) tolerance

The lemon (Citrus limon; family Rutaceae) is one of the most important and popular fruits worldwide. Lemon also tolerates huanglongbing (HLB) disease, which is a devastating citrus disease. Here we produced a gap-free and haplotype-resolved chromosome-scale genome assembly of the lemon by combining Pacific Biosciences circular consensus sequencing, Oxford Nanopore 50-kb ultra-long, and high-throughput chromatin conformation capture technologies. The assembly contained nine-pair chromosomes with a contig N50 of 35.6 Mb and zero gaps, while a total of 633.0 Mb genomic sequences were generated. The origination analysis identified 338.5 Mb genomic sequences originating from citron (53.5%), 147.4 Mb from mandarin (23.3%), and 147.1 Mb from pummelo (23.2%). The genome included 30 528 protein-coding genes, and most of the assembled sequences were found to be repetitive sequences. Several significantly expanded gene families were associated with plant-pathogen interactions, plant hormone signal transduction, and the biosynthesis of major active components, such as terpenoids and flavor compounds. Most HLB-tolerant genes were expanded in the lemon genome, such as 2-oxoglutarate (2OG)/Fe(II)-dependent oxygenase and constitutive disease resistance 1, cell wall-related genes, and lignin synthesis genes. Comparative transcriptomic analysis showed that phloem regeneration and lower levels of phloem plugging are the elements that contribute to HLB tolerance in lemon. Our results provide insight into lemon genome evolution, active component biosynthesis, and genes associated with HLB tolerance.

Metabolic Engineering for Efficient Ketocarotenoid Accumulation in the Green Microalga Chlamydomonas reinhardtii

Astaxanthin is a valuable ketocarotenoid with various pharmaceutical and nutraceutical applications. Green microalgae harbor natural capacities for pigment accumulation due to their 2-C-methyl-d-erythritol 4-phosphate (MEP) pathway. Recently, a redesigned ß-carotene ketolase (BKT) was found to enable ketocarotenoid accumulation in the model microalga Chlamydomonas reinhardtii, and transformants exhibited reduced photoinhibition under high-light. Here, a systematic screening by synthetic transgene design of carotenoid pathway enzymes and overexpression from the nuclear genome identified phytoene synthase (PSY/crtB) as a bottleneck for carotenoid accumulation in C. reinhardtii. Increased ß-carotene hydroxylase (CHYB) activity was found to be essential for engineered astaxanthin accumulation. A combined BKT, crtB, and CHYB expression strategy resulted in a volumetric astaxanthin production of 9.5 ± 0.3 mg L^-1 (4.5 ± 0.1 mg g^-1 CDW) in mixotrophic and 23.5 mg L^-1 (1.09 mg L^-1 h^-1) in high cell density conditions, a 4-fold increase compared to previous reports in C. reinhardtii. This work presents a systematic investigation of bottlenecks in astaxanthin accumulation in C. reinhardtii and the phototrophic green cell factory design for competitive use in industrial biotechnology.

GmGSTU23 Encoding a Tau Class Glutathione S-Transferase Protein Enhances the Salt Tolerance of Soybean (Glycine max L.)

Salt stress has a detrimental impact on crop yield, quality, and profitability. The tau-like glutathione transferases (GSTs) represent a significant group of enzymes that play a crucial role in plant stress responses, including salt stress. In this study, we identified a tau-like glutathione transferase family gene from soybean named GmGSTU23. Expression pattern analysis revealed that GmGSTU23 was predominantly expressed in the roots and flowers and exhibited a concentration–time-specific pattern in response to salt stress. Transgenic lines were generated and subjected to phenotypic characterization under salt stress. The transgenic lines exhibited increased salt tolerance, root length, and fresh weight compared to the wild type. Antioxidant enzyme activity and malondialdehyde content were subsequently measured, and the data revealed no significant differences between the transgenic and wild-type plants in the absence of salt stress. However, under salt stress, the wild-type plants exhibited significantly lower activities of SOD, POD, and CAT than the three transgenic lines, whereas the activity of APX and the content of MDA showed the opposite trend. We identified changes in glutathione pools and associated enzyme activity to gain insights into the underlying mechanisms of the observed phenotypic differences. Notably, under salt stress, the transgenic Arabidopsis’s GST activity, GR activity, and GSH content were significantly higher than those of the wild type. In summary, our findings suggest that GmGSTU23 mediates the scavenging of reactive oxygen species and glutathione by enhancing the activity of glutathione transferase, thereby conferring enhanced tolerance to salt stress in plants.

A xanthophyll-derived apocarotenoid regulates carotenogenesis in tomato chromoplasts

Carotenoids possess important biological functions that make them essential components of the human diet. β-Carotene and some other carotenoids have vitamin A activity while lutein and zeaxanthin, typically referred to as the macular pigments, are involved in good vision and in delaying the onset of age-related eye diseases. In order to create a zeaxanthin-producing tomato fruit, two transgenic lines, one with a high β-carotene cyclase activity and the other with a high β-carotene hydroxylase activity, have been genetically crossed. Ripe fruits from the resulting progeny contained significant levels of violaxanthin, antheraxanthin, and xanthophyll esters. However, their zeaxanthin content was not as high as expected, and the total level of carotenoids was only 25% of the carotenoids found in ripe fruits of the comparator line. Targeted transcript analysis and apocarotenoids determinations indicated that transcriptional regulation of the pathway or degradation of synthesized carotenoids were not responsible for the low carotenoid content of hybrid fruits which instead appeared to result from a substantial reduction of carotenoid biosynthesis. Notably, the content of an unidentified hydroxylated cyclic (C13) apocarotenoid was 13 times higher in the hybrid fruits than in the control fruits. Furthermore, a GC-MS-based metabolite profiling demonstrated a perturbation of carotenogenesis in ripening hybrid fruits compatible with a block of the pathway. Moreover, carotenoid profiling on leaf, fruit, and petal samples from a set of experimental lines carrying the hp3 mutation, in combination with the two transgenes, indicated that the carotenoid biosynthesis in petal and fruit chromoplasts could be regulated. Altogether the data were consistent with the hypothesis of the regulation of the carotenoid pathway in tomato chromoplasts through a mechanism of feedback inhibition mediated by a xanthophyll-derived apocarotenoid. This chromoplast-specific post-transcriptional mechanism was disclosed in transgenic fruits of HU hybrid owing to the abnormal production of zeaxanthin and antheraxanthin, the more probable precursors of the apocarotenoid signal. A model describing the regulation of carotenoid pathway in tomato chromoplasts is presented.

Diversity and Distribution of Carotenogenic Algae in Europe: A Review

Microalgae are the richest source of natural carotenoids, which are valuable pigments with a high share of benefits. Often, carotenoid-producing algae inhabit specific biotopes with unfavorable or even extremal conditions. Such biotopes, including alpine snow fields and hypersaline ponds, are widely distributed in Europe. They can serve as a source of new strains for biotechnology. The number of algal species used for obtaining these compounds on an industrial scale is limited. The data on them are poor. Moreover, some of them have been reported in non-English local scientific articles and theses. This review aims to summarize existing data on microalgal species, which are known as potential carotenoid producers in biotechnology. These include Haematococcus and Dunaliella, both well-known to the scientific community, as well as less-elucidated representatives. Their distribution will be covered throughout Europe: from the Greek Mediterranean coast in the south to the snow valleys in Norway in the north, and from the ponds in Amieiro (Portugal) in the west to the saline lakes and mountains in Crimea (Ukraine) in the east. A wide spectrum of algal secondary carotenoids is reviewed: β-carotene, astaxanthin, canthaxanthin, echinenone, adonixanthin, and adonirubin. For convenience, the main concepts of biology of carotenoid-producing algae are briefly explained.

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.

Compartmentalization engineering of yeasts to overcome precursor limitations and cytotoxicity in terpenoid production

Metabolic engineering strategies for terpenoid production have mainly focused on bottlenecks in the supply of precursor molecules and cytotoxicity to terpenoids. In recent years, the strategies involving compartmentalization in eukaryotic cells has rapidly developed and have provided several advantages in the supply of precursors, cofactors and a suitable physiochemical environment for product storage. In this review, we provide a comprehensive analysis of organelle compartmentalization for terpenoid production, which can guide the rewiring of subcellular metabolism to make full use of precursors, reduce metabolite toxicity, as well as provide suitable storage capacity and environment. Additionally, the strategies that can enhance the efficiency of a relocated pathway by increasing the number and size of organelles, expanding the cell membrane and targeting metabolic pathways in several organelles are also discussed. Finally, the challenges and future perspectives of this approach for the terpenoid biosynthesis are also discussed.

Flashing lights affect the photophysiology and expression of carotenoid and lipid synthesis genes in Nannochloropsis gaditana

Nannochloropsis gaditana is a promising microalga for biotechnology. One of the strategies to stimulate its full potential in metabolite production is exposure to flashing lights. Here, we report how N. gaditana adapts to different flashing light regimes (5, 50, and 500 Hz) by changing its cellular physiology and the relative expression of genes related to critical cellular functions. We analyzed the differential mRNA abundance of genes related to photosynthesis, nitrogen assimilation and biosynthesis of chlorophyll, carotenoids, lipids, fatty acids and starch. Analysis of photosynthetic efficiency and high mRNA abundance of photoprotection genes supported the inference that excess excitation energy provided by light absorbance during photosynthesis was produced under low frequency flashing lights and was dissipated by photopigments via the xanthophyll-cycle. Increased relative expression levels of genes related to the synthesis of carotenoids and chlorophyll confirmed the accumulation of photopigments previously observed at low frequency flashing lights. Higher differential mRNA abundance of genes related to the triacylglycerol biosynthesis were observed at lower frequency flashing lights, possibly triggered by a poor nitrogen assimilation caused by low mRNA abundance of a nitrate reductase gene. This study advances a new understanding of algal physiology and metabolism leading to improved cellular performance and metabolite production.

Fortification and bioaccessibility of saffron apocarotenoids in potato tubers

Carotenoids are C40 isoprenoids with well-established roles in photosynthesis, pollination, photoprotection, and hormone biosynthesis. The enzymatic or ROS-induced cleavage of carotenoids generates a group of compounds named apocarotenoids, with an increasing interest by virtue of their metabolic, physiological, and ecological activities. Both classes are used industrially in a variety of fields as colorants, supplements, and bio-actives. Crocins and picrocrocin, two saffron apocarotenoids, are examples of high-value pigments utilized in the food, feed, and pharmaceutical industries. In this study, a unique construct was achieved, namely O6, which contains CsCCD2L, UGT74AD1, and UGT709G1 genes responsible for the biosynthesis of saffron apocarotenoids driven by a patatin promoter for the generation of potato tubers producing crocins and picrocrocin. Different tuber potatoes accumulated crocins and picrocrocin ranging from 19.41–360 to 105–800 μg/g DW, respectively, with crocetin, crocin 1 [(crocetin-(β-D-glucosyl)-ester)] and crocin 2 [(crocetin)-(β-D-glucosyl)-(β-D-glucosyl)-ester)] being the main compounds detected. The pattern of carotenoids and apocarotenoids were distinct between wild type and transgenic tubers and were related to changes in the expression of the pathway genes, especially from PSY2, CCD1, and CCD4. In addition, the engineered tubers showed higher antioxidant capacity, up to almost 4-fold more than the wild type, which is a promising sign for the potential health advantages of these lines. In order to better investigate these aspects, different cooking methods were applied, and each process displayed a significant impact on the retention of apocarotenoids. More in detail, the in vitro bioaccessibility of these metabolites was found to be higher in boiled potatoes (97.23%) compared to raw, baked, and fried ones (80.97, 78.96, and 76.18%, respectively). Overall, this work shows that potatoes can be engineered to accumulate saffron apocarotenoids that, when consumed, can potentially offer better health benefits. Moreover, the high bioaccessibility of these compounds revealed that potato is an excellent way to deliver crocins and picrocrocin, while also helping to improve its nutritional value.

Reactive Oxygen Species Enlightened Therapeutic Strategy for Oral and Maxillofacial Diseases-Art of Destruction and Reconstruction

Reactive oxygen species (ROS) are byproducts of cell metabolism produced by living cells and signal mediators in biological processes. As unstable and highly reactive oxygen-derived molecules, excessive ROS production and defective oxidant clearance, or both, are associated with the pathogenesis of several conditions. Among them, ROS are widely involved in oral and maxillofacial diseases, such as periodontitis, as well as other infectious diseases or chronic inflammation, temporomandibular joint disorders, oral mucosal lesions, trigeminal neuralgia, muscle fatigue, and oral cancer. The purpose of this paper is to outline how ROS contribute to the pathophysiology of oral and maxillofacial regions, with an emphasis on oral infectious diseases represented by periodontitis and mucosal diseases represented by oral ulcers and how to effectively utilize and eliminate ROS in these pathological processes, as well as to review recent research on the potential targets and interventions of cutting-edge antioxidant materials. The PubMed, Web of Science, and Embase databases were searched using the MesH terms "oral and maxillofacial diseases", "reactive oxygen species", and "antioxidant materials". Irrelevant, obsolete, imprecise, and repetitive articles were excluded through screening of titles, abstracts, and eventually full content. The full-text data of the selected articles are, therefore, summarized using selection criteria. While there are various emerging biomaterials used as drugs themselves or delivery systems, more attention was paid to antioxidant drugs with broad application prospects and rigorous prophase animal experimental results.

Transcriptomic and Physiological Analyses Reveal Potential Genes Involved in Photoperiod-Regulated β-Carotene Accumulation Mechanisms in the Endocarp of Cucumber (Cucumis sativus L.) Fruit

The accumulation of carotenoids in plants is a key nutritional quality in many horticultural crops. Although the structural genes encoding the biosynthetic enzymes are well-characterized, little is known regarding photoperiod-mediated carotenoid accumulation in the fruits of some horticultural crops. Herein, we performed physiological and transcriptomic analyses using two cucumber genotypes, SWCC8 (XIS-orange-fleshed and photoperiod-sensitive) and CC3 (white-fleshed and photoperiod-non-sensitive), established under two photoperiod conditions (8L/16D vs. 12L/12D) at four fruit developmental stages. Day-neutral treatments significantly increased fruit β-carotene content by 42.1% compared to short day (SD) treatments in SWCC8 at 40 DAP with no significant changes in CC3. Day-neutral condition elevated sugar levels of fruits compared to short-day treatments. According to GO and KEGG analyses, the predominantly expressed genes were related to photosynthesis, carotenoid biosynthesis, plant hormone signaling, circadian rhythms, and carbohydrates. Consistent with β-carotene accumulation in SWCC8, the day-neutral condition elevated the expression of key carotenoid biosynthesis genes such as PSY1, PDS, ZDS1, LYCB, and CHYB1 during later stages between 30 to 40 days of fruit development. Compared to SWCC8, CC3 showed an expression of DEGs related to carotenoid cleavage and oxidative stresses, signifying reduced β-carotene levels in CC3 cucumber. Further, a WGCNA analysis revealed co-expression between carbohydrate-related genes (pentose-phosphatase synthase, β-glucosidase, and trehalose-6-phosphatase), photoperiod-signaling genes (LHY, APRR7/5, FKF1, PIF3, COP1, GIGANTEA, and CK2) and carotenoid-biosynthetic genes, thus suggesting that a cross-talk mechanism between carbohydrates and light-related genes induces β-carotene accumulation. The results highlighted herein provide a framework for future gene functional analyses and molecular breeding towards enhanced carotenoid accumulation in edible plant organs.

Genetic dissection of lutein content in common wheat via association and linkage mapping

Genetic architecture controlling grain lutein content of common wheat was investigated through an integration of genome-wide association study (GWAS) and linkage analysis. Putative candidate genes involved in carotenoid metabolism and regulation were identified, which provide a basis for gene cloning and development of nutrient-enriched wheat varieties through molecular breeding. Lutein, known as 'the eye vitamin', is an important component of wheat nutritional and end-use quality. However, the genetic manipulation of grain lutein content (LUC) in common wheat has not previously been well studied. Here, quantitative trait loci (QTL) associated with the LUC measured by high performance liquid chromatography (HPLC) were first identified by integrating a genome-wide association study (GWAS) and linkage mapping. A Chinese wheat mini-core collection (MCC) of 262 accessions and a doubled haploid (DH) population derived from Jinchun 7 and L1219 were genotyped using the 90K SNP array. A total of 124 significant marker-trait associations (MTAs) on all 21 wheat chromosomes except for 1A, 4D, and 5B that formed 58 QTL were detected. Among them, six stable QTL were identified on chromosomes 2AL, 2DS, 3BL, 3DL, 7AL, and 7BS. Meanwhile, three of the ten QTL identified in the DH population, QLuc.5A.1 and QLuc.5A.2 on chromosome 5AL and QLuc.6A.2 on 6AS, were stable and independently explained 5.58-10.86% of the phenotypic variation. The QLuc.6A.2 region colocalized with two MTAs identified by GWAS. Moreover, 71 carotenoid metabolism-related candidate genes were identified, and the allelic effects were analyzed in the MCC panel based on the 90K array. Results revealed that the genes CYP97A3 (Chr. 6B) and CCD1 (Chr. 5A) were significantly associated with LUC. Additionally, the gene PSY3 (QLuc.5A.1) and several candidate genes involved in the methylerythritol 4-phosphate (MEP) pathways colocalized with stable QTL regions. The present study provides potential targets for future functional gene exploration and molecular breeding in common wheat.

Multi-omics analyses of 398 foxtail millet accessions reveal genomic regions associated with domestication, metabolite traits, and anti-inflammatory effects

Foxtail millet (Setaria italica), which was domesticated from the wild species green foxtail (Setaria viridis), is a rich source of phytonutrients for humans. To evaluate how breeding changed the metabolome of foxtail millet grains, we generated and analyzed the datasets encompassing the genomes, transcriptomes, metabolomes, and anti-inflammatory indices from 398 foxtail millet accessions. We identified hundreds of common variants that influence numerous secondary metabolites. We observed tremendous differences in natural variations of the metabolites and their underlying genetic architectures between distinct sub-groups of foxtail millet. Furthermore, we found that the selection of the gene alleles associated with yellow grains led to altered profiles of metabolites such as carotenoids and endogenous phytohormones. Using CRISPR-mediated genome editing we validated the function of PHYTOENE SYNTHASE 1 (PSY1) gene in affecting millet grain color and quality. Interestingly, our in vitro cell inflammation assays showed that 83 metabolites in millet grains have anti-inflammatory effects. Taken together, our multi-omics study illustrates how the breeding history of foxtail millet has shaped its metabolite profile. The datasets we generated in this study also provide important resources for further understanding how millet grain quality is affected by different metabolites, laying the foundations for future millet genetic research and metabolome-assisted improvement.

NtDREB-1BL1 Enhances Carotenoid Biosynthesis by Regulating Phytoene Synthase in Nicotiana tabacum

As one of the most imperative antioxidants in higher plants, carotenoids serve as accessory pigments to harvest light for photosynthesis as well as photoprotectors for plants to adapt to high light stress. Phytoene synthase (PSY) is the entry enzyme and also the major rate-limiting enzyme in the carotenoid pathway. Here, we report a dehydration-responsive element-binding protein (DREB) transcription factor member in Nicotiana tabacum K326, NtDREB-1BL1, which regulates carotenoids biosynthesis by binding to the NtPSY promoter. The NtDREB-1BL1 transcript was widely distributed in leaves by Real-time PCR. Confocal image revealed that NtDREB-1BL1 was localized in the nucleus. The chromatin immunoprecipitation (ChIP) with the qPCR technique indicated that NtDREB-1BL1 could anchor the promoter region of NtPSY. Overexpression (NtDREB-1BL1 OE) and RNA interference (NtDREB-1BL1 RNAi) of NtDREB-1BL1 were performed to evaluate its biological function in N. tabacum. Both carotenoid and chlorophyll contents increased in transgenic plants of NtDREB-1BL1 OE compared with wild-type (WT) plants, with the augment of the genes involved in carotenoid biosynthesis. In contrast, the contents of carotenoid and chlorophyll significantly decreased in transgenic plants of NtDREB-1BL1 RNAi compared to WT, along with the decline in the expression of genes related to carotenoid biosynthesis. Moreover, transgenic plants of NtDREB-1BL1 OE exhibited enhanced tolerance under drought stress, with the weakened tolerance of drought stress in transgenic plants of NtDREB-1BL1 RNAi. In conclusion, our results illustrated the new role of transcription factor NtDREB-1BL1 in improving carotenoid biosynthesis through regulating NtPSY expression.

Agogbua J, R. Keyagha E, I. Nkanga I. Carotenoids in Cassava (Manihot esculenta Crantz)

Cassava is produced globally and consumed as an important staple in Africa for its calories, but the crop is deficient in micronutrients such as vitamin A. Pro-vitamin A carotenoids including β-carotene are precursors of vitamin A in the human body. Carotenoids are generally associated with colors of fruits and vegetables. Although most cassava varieties have white tuberous roots and generally accepted, naturally; some cassava roots are colored yellow and contain negligible amounts of vitamin A. Several genes have been identified in the carotenoids biosynthesis pathway of plants, but studies show that Phytoene synthase 2 (PSY2), lycopene epsilon cyclase, and β-carotene hydroxylase genes have higher expression levels in yellow cassava roots. So far, the PSY2 gene has been identified as the key gene associated with carotenoids in cassava. Some initiatives are implementing conventional breeding to increase pro-vitamin A carotenoids in cassava roots, and much success has been achieved in this regard. This chapter highlights various prediction tools employed for carotenoid content in fresh cassava roots, including molecular marker-assisted strategies developed to fast-track the conventional breeding for increased carotenoids in cassava.

Light Induces Carotenoid Biosynthesis-Related Gene Expression, Accumulation of Pigment Content, and Expression of the Small Heat Shock Protein in Apple Fruit

The coloration of the apple fruit (Malus × domestica Borkh.) depends on pigment content. Light stimulus activates a broad range of photosynthesis-related genes, including carotenoids. The effect of light on two red commercial apple cultivars, ‘Summer Prince’ and ‘Arisoo’ at the juvenile stage were examined. Apple fruits were either bagged to reduce light irradiation or were exposed to direct, enhanced sunlight (reflected). The pigment content and the expression of carotenoid metabolism genes in the peel and flesh of apple fruits were significantly different between the shaded and the reflected parts. These parameters were also different in the two cultivars, highlighting the contribution of the genetic background. Further, a combination of light and transient overexpression of carotenogenic genes increased fruit coloration and pigment content in the variety ‘RubyS’. Western blot analysis showed the expression of small heat shock proteins (smHSP) in lysates extracted from the reflected part of the fruits but not in the bagged fruits, indicating the activation of smHSP in response to heat generated by the reflected light. Therefore, the synergy between the genes and the environment dictates the color of apple fruits.

A cytochrome P450 superfamily gene, IbCYP82D47, increases carotenoid contents in transgenic sweet potato

The cytochrome P450 superfamily (CYP450) is one of the largest protein families in plants, and its members play diverse roles in primary and secondary metabolic biosynthesis. In this study, the CYP450 family gene IbCYP82D47 was cloned from the high carotenoid line HVB-3 of sweet potato (Ipomoea batatas). The IbCYP82D47 protein harbored two transmembrane domains and dynamically localized between plastid stroma and membrane. Overexpression of IbCYP82D47 not only increased total carotenoid, lutein, zeaxanthin and violaxanthin contents by 32.2-48.0%, 10.5-13.3%, 40.2-136% and 82.4-106%, respectively, but also increased the number of carotenoid globules in sweet potato storage roots. Furthermore, genes associated with the carotenoid biosynthesis (IbDXS, IbPSY, IbLCYE, IbBCH, IbZEP) were upregulated in transgenic sweet potato. In addition, IbCYP82D47 physically interacts with geranylgeranyl diphosphate synthase 12 (IbGGPPS12). Our findings suggest that IbCYP82D47 increases carotenoid contents by interacting with the carotenoid biosynthesis related protein IbGGPPS12, and influencing the expressions of carotenoid biosynthesis related genes in transgenic sweet potato.

Vitamin A fortification: Recent advances in encapsulation technologies

Vitamin A is an essential micronutrient whose deficiency is still a major health concern in many regions of the world. It plays an essential role in human growth and development, immunity, and vision, but may also help prevent several other chronic diseases. The total amount of vitamin A in the human diet often falls below the recommended dietary allowance of approximately 900-1000 μ $ \umu $ g/day for a healthy adult. Moreover, a significant proportion of vitamin A may be degraded during food processing, storage, and distribution, thereby reducing its bioactivity. Finally, the vitamin A in some foods has a relatively low bioavailability, which further reduces its efficacy. The World Health Organization has recommended fortification of foods and beverages as a safe and cost-effective means of addressing vitamin A deficiency. However, there are several factors that must be overcome before effective fortified foods can be developed, including the low solubility, chemical stability, and bioavailability of this oil-soluble vitamin. Consequently, strategies are required to evenly disperse the vitamin throughout food matrices, to inhibit its chemical degradation, to avoid any adverse interactions with any other food components, to ensure the food is palatable, and to increase its bioavailability. In this review article, we discuss the chemical, physical, and nutritional attributes of vitamin A, its main dietary sources, the factors contributing to its current deficiency, and various strategies to address these deficiencies, including diet diversification, biofortification, and food fortification.

Comparative effects of polystyrene nanoplastics with different surface charge on seedling establishment of Chinese cabbage (Brassica rapa L.)

Micro- and nano-plastics are common emerging pollutants of great interest. However, the impacts of them on terrestrial plants were still poorly understood. In this study, comparative effects of exposure of polystyrene nanoplastics (PS) and amino-modified polystyrene nanoplastics (PS-NH₂) on Chinese cabbage (Brassica rapa L.) plants at different growth stages were investigated. Hydroponically cultured seedlings were exposed to PS and PS-NH₂ at 0, 1, 10, and 100 mg/L at skotomorphogenesis stage for 48 h, photomorphogenesis stage for 18 h, and the whole stage, respectively. Results showed that both PS and PS-NH₂ had no discernible effect on radicle elongation at the skotomorphogenesis stage whereas significantly (P < 0.05) reduced photosynthetic pigment contents in varying degrees (18.06%-28.52%, 22.46%-36.86%) at the photomorphogenesis stage and the whole stage. Moreover, there was no significant difference between PS treatments and control except the 26.52% decline of chlorophyll a content at 1 mg/L at photomorphogenesis, while PS-NH₂ significantly (P < 0.05) decreased photosynthetic pigment contents except the chlorophyll b content at 10 mg/L at photomorphogenesis. The content of chlorophyll a decreased by 26.68% for the PS-NH₂-treated group and 22.46% for the PS-treated group at 1 mg/L during the whole stage. Results manifested that less negatively charged PS-NH₂ seemed to show more severe phytotoxicity both at the photomorphogenesis stage and the whole stage. Notably, the surface charge of nano-plastics and the integrity of seedling establishment could be the main factors impacting the above difference. These findings are expected to improve our understanding of the effects of PSNPs on crop plants.

RNAi of Sterol Δ24-Isomerase Implicated Its Involvement in Physalin Biosynthesis in Physalis angulata L

Physalis angulata is a renowned traditional Chinese medicine for the treatment of various conditions. Physalin is the major type of bioactive constituents conferring medicinal properties of P. angulata. Despite the medicinal importance, the pathways leading to physalin are largely unknown. In this study, we employed a transcriptomic approach to identify a Pa24ISO gene from P. angulata. Through heterologous expression in yeast, Pa24ISO was revealed to catalyze an isomerization reaction in converting 24-methylenecholesterol to 24-methyldesmosterol. Real-time PCR analysis showed that the abundance of Pa24ISO transcripts correlated with the accumulation pattern of physalin B in different tissues of P. angulata. A direct role of Pa24ISO in channeling of 24-methylenecholesterol for physalin B biosynthesis was illustrated by suppressing the gene in P. angulata via the VIGS approach. Down-regulation of Pa24ISO led to reduced levels of 24-methyldesmosterol and physalin B, accompanied with an increase of campesterol content in P. angulata. The results supported that 24ISO is involved in physalin biosynthesis in plants.

Site-Directed Mutagenesis of the Carotenoid Isomerase Gene BnaCRTISO Alters the Color of Petals and Leaves in Brassica napus L

The diversity of petal and leaf color can improve the ornamental value of rapeseed and promote the development of agriculture and tourism. The two copies of carotenoid isomerase gene (BnaCRTISO) in Brassica napus (BnaA09.CRTISO and BnaC08.CRTISO) was edited using the CRISPR/Cas9 system in the present study. The mutation phenotype of creamy white petals and yellowish leaves could be recovered only in targeted mutants of both BnaCRTISO functional copies, indicating that the redundant roles of BnaA09.CRTISO and BnaC08.CRTISO are vital for the regulation of petal and leaf color. The carotenoid content in the petals and leaves of the BnaCRTISO double mutant was significantly reduced. The chalcone content, a vital substance that makes up the yellow color, also decreased significantly in petals. Whereas, the contents of some carotenes (lycopene, α-carotene, γ-carotene) were increased significantly in petals. Further, transcriptome analysis showed that the targeted mutation of BnaCRTISO resulted in the significant down-regulation of important genes BnaPSY and BnaC4H in the carotenoid and flavonoid synthesis pathways, respectively; however, the expression of other genes related to carotenes and xanthophylls synthesis, such as BnaPDS3, BnaZEP, BnaBCH1 and BCH2, was up-regulated. This indicates that the molecular mechanism regulating petal color variation in B. napus is more complicated than those reported in Arabidopsis and other Brassica species. These results provide insight into the molecular mechanisms underlying flower color variation in rapeseed and provides valuable resources for rapeseed breeding.

Analysis of Biosynthetic Gene Clusters, Secretory, and Antimicrobial Peptides Reveals Environmental Suitability of Exiguobacterium profundum PHM11

Halotolerant bacteria produce a wide range of bioactive compounds with important applications in agriculture for abiotic stress amelioration and plant growth promotion. In the present study, 17 biosynthetic gene clusters (BGCs) were identified in Exiguobacterium profundum PHM11 belonging to saccharides, desmotamide, pseudaminic acid, dipeptide aldehydes, and terpene biosynthetic pathways representing approximately one-sixth of genomes. The terpene biosynthetic pathway was conserved in Exiguobacterium spp. while the E. profundum PHM11 genome confirms the presence of the 1-deoxy-d-xylulose 5-phosphate (DXP) pathway for the isopentenyl diphosphate (IPP) synthesis. Further, 2,877 signal peptides (SPs) were identified using the PrediSi server, out of which 592 proteins were prophesied for the secretion having a transmembrane helix (TMH). In addition, antimicrobial peptides (AMPs) were also identified using BAGEL4. The transcriptome analysis of PHM11 under salt stress reveals the differential expression of putative secretion and transporter genes having SPs and TMH. Priming of the rice, wheat and maize seeds with PHM11 under salt stress led to improvement in the root length, root diameters, surface area, number of links and forks, and shoot length. The study shows that the presence of BGCs, SPs, and secretion proteins constituting TMH and AMPs provides superior competitiveness in the environment and make E. profundum PHM11 a suitable candidate for plant growth promotion under salt stress.

Construction of Canthaxanthin-Producing Yeast by Combining Spatiotemporal Regulation and Pleiotropic Drug Resistance Engineering

The ketocarotenoid canthaxanthin has important applications in the feed industry. Its biosynthesis using microbial cell factories is an attractive alternative to the current chemical synthesis route. Canthaxanthin-producing Saccharomyces cerevisiae was constructed by introducing the β-carotene ketolase variant OBKTM29 into a β-carotene producer. Subcellular re-localization of OBKTM29 was explored, together with copy number adjustment both in the cytoplasm and on the periplasmic membrane, to accelerate the conversion of β-carotene to canthaxanthin. Moreover, pleiotropic drug resistance (PDR) regulators Pdr1 and Pdr3 were overexpressed to improve the stress tolerance of the yeast strain, leading to obviously enhanced canthaxanthin production. The synthetic pathway was then regulated by a temperature-responsive GAL system to separate product synthesis from cell growth. Finally, 1.44 g/L canthaxanthin was harvested in fed-batch fermentation. This work demonstrated the power of spatial and temporal regulation and the efficiency of PDR engineering in heterologous biosynthesis.

Horticultural innovation by viral-induced gene regulation of carotenogenesis

Multipartite viral vectors provide a simple, inexpensive and effective biotechnological tool to transiently manipulate (i.e. reduce or increase) gene expression in planta and characterise the function of genetic traits. The development of virus-induced gene regulation (VIGR) systems usually involve the targeted silencing or overexpression of genes involved in pigment biosynthesis or degradation in plastids, thereby providing rapid visual assessment of success in establishing RNA- or DNA-based VIGR systems in planta. Carotenoids pigments provide plant tissues with an array of yellow, orange, and pinkish-red colours. VIGR-induced transient manipulation of carotenoid-related gene expression has advanced our understanding of carotenoid biosynthesis, regulation, accumulation and degradation, as well as plastid signalling processes. In this review, we describe mechanisms of VIGR, the importance of carotenoids as visual markers of technology development, and knowledge gained through manipulating carotenogenesis in model plants as well as horticultural crops not always amenable to transgenic approaches. We outline how VIGR can be utilised in plants to fast-track the characterisation of gene function(s), accelerate fruit tree breeding programs, edit genomes, and biofortify plant products enriched in carotenoid micronutrients for horticultural innovation.

The Genetic Components of a Natural Color Palette: A Comprehensive List of Carotenoid Pathway Mutations in Plants

Carotenoids comprise the most widely distributed natural pigments. In plants, they play indispensable roles in photosynthesis, furnish colors to flowers and fruit and serve as precursor molecules for the synthesis of apocarotenoids, including aroma and scent, phytohormones and other signaling molecules. Dietary carotenoids are vital to human health as a source of provitamin A and antioxidants. Hence, the enormous interest in carotenoids of crop plants. Over the past three decades, the carotenoid biosynthesis pathway has been mainly deciphered due to the characterization of natural and induced mutations that impair this process. Over the year, numerous mutations have been studied in dozens of plant species. Their phenotypes have significantly expanded our understanding of the biochemical and molecular processes underlying carotenoid accumulation in crops. Several of them were employed in the breeding of crops with higher nutritional value. This compendium of all known random and targeted mutants available in the carotenoid metabolic pathway in plants provides a valuable resource for future research on carotenoid biosynthesis in plant species.

Multifaceted strategies for economic production of microalgae Haematococcus pluvialis-derived astaxanthin via direct conversion of CO2

Owing to its strong antioxidant properties, astaxanthin has a high market price in the nutraceutical and pharmaceutical fields, and its demand is increasing. Furthermore, with an increase in the demand for green technology, astaxanthin production through direct CO₂ conversion using the autotrophic green microalga Haematococcus pluvialis as a bio-platform has received much attention. Large-scale outdoor cultivation of H. pluvialis using waste CO₂ sources and sunlight can secure sustainability and improve economic efficiency. However, low strain performance, reduced light utilization because of increased cell density, and inefficient transfer of gaseous CO₂ into liquid culture broth hinder its large-scale commercialization of astaxanthin. Herein, we presented a multifaceted strategy, including the development of high-efficiency strains, a culture system for astaxanthin accumulation, and astaxanthin extraction from biomass, for economically producing astaxanthin from H. pluvialis through direct CO₂ conversion. Future perspectives were presented by comparing and analyzing various previous studies conducted using the latest technology.

Carotenoid Biosynthetic Genes in Cabbage: Genome-Wide Identification, Evolution, and Expression Analysis

Carotenoids are natural functional pigments produced by plants and microorganisms and play essential roles in human health. Cabbage (Brassica oleracea L. var. capitata L.) is an economically important vegetable in terms of production and consumption. It is highly nutritious and contains β-carotene, lutein, and other antioxidant carotenoids. Here, we systematically analyzed carotenoid biosynthetic genes (CBGs) on the whole genome to understand the carotenoid biosynthetic pathway in cabbage. In total, 62 CBGs were identified in the cabbage genome, which are orthologs of 47 CBGs in Arabidopsis thaliana. Out of the 62 CBGs, 46 genes in cabbage were mapped to nine chromosomes. Evolutionary analysis of carotenoid biosynthetic orthologous gene pairs among B. oleracea, B. rapa, and A. thaliana revealed that orthologous genes of B. oleracea underwent a negative selection similar to that of B. rapa. Expression analysis of the CBGs showed functional differentiation of orthologous gene copies in B. oleracea and B. rapa. Exogenous phytohormone treatment suggested that ETH, ABA, and MeJA can promote some important CBGs expression in cabbage. Phylogenetic analysis showed that BoPSYs exhibit high conservatism. Subcellular localization analysis indicated that BoPSYs are located in the chloroplast. This study is the first to study carotenoid biosynthesis genes in cabbage and provides a basis for further research on carotenoid metabolic mechanisms in cabbage.

Sunscreen Effect Exerted by Secondary Carotenoids and Mycosporine-like Amino Acids in the Aeroterrestrial Chlorophyte Coelastrella rubescens under High Light and UV-A Irradiation

The microalga Coelastrella rubescens dwells in habitats with excessive solar irradiation; consequently, it must accumulate diverse compounds to protect itself. We characterized the array of photoprotective compounds in C. rubescens. Toward this goal, we exposed the cells to high fluxes of visible light and UV-A and analyzed the ability of hydrophilic and hydrophobic extracts from the cells to absorb radiation. Potential light-screening compounds were profiled by thin layer chromatography and UPLC-MS. Coelastrella accumulated diverse carotenoids that absorbed visible light in the blue-green part of the spectrum and mycosporine-like amino acids (MAA) that absorbed the UV-A. It is the first report on the occurrence of MAA in Coelastrella. Two new MAA, named coelastrin A and coelastrin B, were identified. Transmission electron microscopy revealed the development of hydrophobic subcompartments under the high light and UV-A exposition. We also evaluate and discuss sporopollenin-like compounds in the cell wall and autophagy-like processes as the possible reason for the decrease in sunlight absorption by cells, in addition to inducible sunscreen accumulation. The results suggested that C. rubescens NAMSU R1 accumulates a broad range of valuable photoprotective compounds in response to UV-A and visible light irradiation, which indicates this strain as a potential producer for biotechnology.

"Light modulates transcriptomic dynamics upregulating astaxanthin accumulation in Haematococcus: A review"

Haematococcus pluvialis is a green alga that can accumulate high astaxanthin content, a commercially demanding market keto food. Due to its high predicted market value of about 3.4 billion USD in 2027, it is essential to increase its production. Therefore, it is crucial to understand the genetic mechanism and gene expressions profile during astaxanthin synthesis. The effect of poly- and mono-chromatic light of different wavelengths and different intensities have shown to influence the gene expression towards astaxanthin production. This includes transcriptomic gene analysis in H. pluvialis underneath different levels of illumination stress. This review has placed the most recent data on the effects of light on bioastaxanthin production in the context of previous studies, which were more focused on the biochemical and physiological sides. Doing so, it contributes to delineate new ways along the biotechnological process with the aim to increase bioastaxanthin production while decreasing production costs.

Carotenoids and Apocarotenoids in Planta: Their Role in Plant Development, Contribution to the Flavour and Aroma of Fruits and Flowers, and Their Nutraceutical Benefits

Carotenoids and apocarotenoids are diverse classes of compounds found in nature and are important natural pigments, nutraceuticals and flavour/aroma molecules. Improving the quality of crops is important for providing micronutrients to remote communities where dietary variation is often limited. Carotenoids have also been shown to have a significant impact on a number of human diseases, improving the survival rates of some cancers and slowing the progression of neurological illnesses. Furthermore, carotenoid-derived compounds can impact the flavour and aroma of crops and vegetables and are the origin of important developmental, as well as plant resistance compounds required for defence. In this review, we discuss the current research being undertaken to increase carotenoid content in plants and research the benefits to human health and the role of carotenoid derived volatiles on flavour and aroma of fruits and vegetables.

Crosstalk between abscisic acid and nitric oxide under heat stress: exploring new vantage points

Heat stress adversely affects plants growth potential. Global warming is reported to increase in the intensity, frequency, and duration of heatwaves, eventually affecting ecology, agriculture and economy. With an expected increase in average temperature by 2-3 °C over the next 30-50 years, crop production is facing a severe threat to sub-optimum growth conditions. Abscisic acid (ABA) and nitric oxide (NO) are growth regulators that are involved in the adaptation to heat stress by affecting each other and changing the adaptation process. The interaction between these molecules has been discussed in various studies in general or under stress conditions; however, regarding high temperature, their interaction has little been worked out. In the present review, the focus is shifted on the role of these molecules under heat stress emphasizing the different possible interactions between ABA and NO as both regulate stomatal closure and other molecules including hydrogen peroxide (H₂O₂), hydrogen sulfide (H₂S), antioxidants, proline, glycine betaine, calcium (Ca²⁺) and heat shock protein (HSP). Exploring the crosstalk between ABA and NO with other molecules under heat stress will provide us with a comprehensive knowledge of plants mechanism of heat tolerance which could be useful to develop heat stress-resistant varieties.

Lycopene Accumulation in Cara Cara Red-flesh Navel Orange Is Correlated with Weak Abscisic Acid Catabolism

Lycopene is the main pigment in red-flesh citrus fruits, and its formation is a research hotspot. To explore the basis of lycopene accumulation in red-flesh mutants, we profiled the terpenoid metabolites. Compared with their respective wild types, Cara Cara (Cara) [and Red-Anliu (R-An)] oranges showed increased carotenoid and limonoid aglycone contents and decreased contents of abscisic acid (ABA) catabolites, monoterpenoid volatiles, and sesquiterpenoid volatiles. Cara contained less than half of the amount of ABA glucose ester (ABAGE), the main ABA derivative in oranges. Parallel lower transcript levels of NCED and ABA glucosyltransferase in Cara were detected at the mature green stage. These results document the changes in terpenoid profiles in Cara and show that the red flesh of citrus color mutants is related to weak ABA catabolism, especially ABAGE, and decreased transcript levels of two genes encoding uridine diphosphate (UDP)-glycosyltransferases that catalyze ABAGE biosynthesis.

Combined Production of Astaxanthin and β-Carotene in a New Strain of the Microalga Bracteacoccus aggregatus BM5/15 (IPPAS C-2045) Cultivated in Photobioreactor

Carotenoids astaxanthin and β-carotene are widely used natural antioxidants. They are key components of functional food, cosmetics, drugs and animal feeding. They hold leader positions on the world carotenoid market. In current work, we characterize the new strain of the green microalga Bracteacoccus aggregatus BM5/15 and propose the method of its culturing in a bubble-column photobioreactor for simultaneous production of astaxanthin and β-carotene. Culture was monitored by light microscopy and pigment kinetics. Fatty acid profile was evaluated by tandem gas-chromatography-mass spectrometry. Pigments were obtained by the classical two-stage scheme of autotrophic cultivation. At the first, vegetative, stage biomass accumulation occurred. Maximum specific growth rate and culture productivity at this stage were 100-200 mg∙L^-1∙day^-1, and 0.33 day^-1, respectively. At the second, inductive, stage carotenoid synthesis was promoted. Maximal carotenoid fraction in the biomass was 2.2-2.4%. Based on chromatography data, astaxanthin and β-carotene constituted 48 and 13% of total carotenoid mass, respectively. Possible pathways of astaxanthin synthesis are proposed based on carotenoid composition. Collectively, a new strain B. aggregatus BM5/15 is a potential biotechnological source of two natural antioxidants, astaxanthin and β-carotene. The results give the rise for further works on optimization of B. aggregatus cultivation on an industrial scale.