Plant carotenoid cleavage oxygenases: structure-function relationships and role in development and metabolism

Regulation of apocarotenoids for quality improvement and biofortification of horticultural crops

BACKGROUND

Agro-food production and consumption impact climate change and human health. Bioactive secondary metabolites in horticulture crops make them an indispensable part of environmentally sustainable and healthy diet. Among them, apocarotenoids from carotenoid degradation are promising in promoting a preference for plant-based foods over other metabolites.

AIM OF REVIEW

In horticulture crops, carotenoids are vital for photosynthesis and antioxidant defense, but their enzymatic or oxidative metabolites, apocarotenoids, offer greater structural diversity and biological functions. They serve as pigments, scents, signaling molecules, and growth regulators in crop growth and development and provide antioxidant, nutraceutical, and pharmaceutical benefits to human health. The carotenoids as bioactive compounds are well understood. By contrast, much less is explored and reviewed about apocarotenoids.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Recently identified metabolic pathways and components of apocarotenoids are reviewed. Their significance for quality formation in horticulture crops, including the regulation of pigmentation, aroma, flavor, architecture, nutrition value, and broader ecological interactions is discussed. Additionally, this review specifically highlights two representative apocarotenoids, retinal and abscisic acid (ABA), that exhibit conserved yet distinct regulatory functions across plant and animal kingdoms. Comprehensive dissection of apocarotenoid metabolism and their regulatory mechanisms will enhance apocarotenoid biofortification and subsequent biotechnological exploitation in horticultural commodities. We put forward the perspective that apocarotenoids could enhance horticultural crop quality and then promote sensory- and health-driven dietary choices which will in turn increase consumption and production of horticultural plants and promote both human and ecosystem health.

Multidimensional analysis of the flavor characteristics of yellow peach at different ripening stages: Chemical composition profiling and sensory evaluation

The flavor evolution of yellow peaches during ripening was investigated using a gas chromatography-mass spectrometer (GC-MS), metabolomics, and electronic sensoristic techniques. Of the 41 volatiles quantified, 13 increased the intensity of the aroma based on the odor activity values (OAVs). Additionally, 142 non-volatile compounds were identified. Metabolic pathway analysis indicated that the formation of xanthophyll esters, due to substrate competition, resulted in a reduction of carotenoid-derived volatiles. Electronic nose (E-nose) analysis revealed that the key sensor W1C-associated volatiles had a green aroma, while W1S and W2S-associated volatiles showed a fruity aroma. Electronic tongue (E-tongue) analysis revealed that L-norleucine, L-isoleucine, isoleucine, L-tyrosine, L-valine, 4-Hydroxybenzaldehyde, cinnamic acid, and rutin positively correlated with umami and sweetness. Conversely, cis-aconitic acid and (-)-epigallocatechin positively correlated with sourness or astringency. Moreover, 20 volatiles, including γ-decalactone, linalool, and (Z)-3-hexenyl acetate, were positively correlated with umami or sweetness, while 7 volatiles were positively correlated with sourness or astringency.

Genome-wide identification and gene expression pattern analysis of the carotenoid cleavage oxygenase gene family in Fagopyrum tataricum

BACKGROUND

Carotenoid cleavage oxygenases (CCOs) convert carotenoids into volatile aromatic compounds implicated in plant growth and development. They affect the synthesis of hormones, including abscisic acid (ABA) and strigolactone (SL). However, the CCO family in Tartary buckwheat remains unelucidated.

RESULTS

We identified the FtCCO gene family based on Tartary buckwheat genomic data and analyzed the biological function of the FtCCO genes using bioinformatics methods and the expression pattern of the gene using fluorescence quantitative PCR. Three pairs of fragment duplication genes were found in FtCCOs, and the motifs were highly conserved within the same subfamily. FtCCO genes are closely related to the dicotyledonous Arabidopsis thaliana, which has the highest number of co-linear genes. The qRT-PCR showed that among the tissue-specific expression patterns of Tartary buckwheat CCO genes, the expression of the FtCCOs was higher in the leaves. In Tartary buckwheat grain development, the relative expression of most FtCCOs was higher at the later stage. The relative expression of many genes was higher in the stems under cold, dark, NaCl, and abiotic stress conditions. However, under the hormone and plant growth regulator treatments, the expression of the nine FtCCOs was relatively low in the stems. Notably, the relative expression of FtNCED4 was extremely high under abiotic stress and hormone induction, indicating that FtNCED4 may be involved in the growth and development of Tartary buckwheat. In this study, the FtCCO family genes of Tartary buckwheat were identified at the genome-wide level, and the gene expression pattern of the FtCCO gene family in different tissues or treatments was determined. This study provides a theoretical basis for further analysis of the functions of theFtCCO family, which is of great significance for the mining of resistance genes and trait improvement.

An intronic SNP in the Carotenoid Cleavage Dioxygenase 1 (CsCCD1) controls yellow flesh formation in cucumber fruit (Cucumis sativus L.)

Vitamin A is a crucial yet scarce vitamin essential for maintaining normal metabolism and bodily functions in humans and can only be obtained from food. Carotenoids represent a diverse group of functional pigments that act as precursors for vitamins, hormones, aroma volatiles and antioxidants. As a vital vegetable in the world, elevated carotenoid levels in cucumber fruit produce yellow flesh, enhancing both visual appeal and nutritional value. However, the genetic mechanisms and regulatory networks governing yellow flesh in cucumbers remain inadequately characterized. In this study, we employed map-based cloning to identify a Carotenoid Cleavage Dioxygenase 1 (CsCCD1) as a key genetic factor influencing yellow flesh in cucumbers. A causal single nucleotide polymorphism (SNP) in the eighth intron of CsCCD1 led to aberrant splicing, resulting in a truncated transcript. The truncated protein has significantly decreased enzyme activity and increased carotenoid accumulation in the fruit. CRISPR/Cas9-generated CsCCD1 knockout mutants exhibited yellow flesh and significantly higher carotenoid content compared to wild-type cucumbers. Metabolic profiling indicated a marked accumulation of β-cryptoxanthin in the flesh of these knockout mutants. The intronic SNP was shown to perfectly segregate with yellow flesh in 159 diverse cucumber germplasms, particularly within the semi-wild ecotype Xishuangbanna, known for its substantial carotenoid accumulation. Furthermore, transient overexpression of CsCCD1 in yellow-fleshed Xishuangbanna cucumbers restored a white flesh phenotype, underscoring the critical role of CsCCD1 in determining flesh colour in both cultivated and semi-wild cucumbers. These findings lay a theoretical foundation for breeding high-nutrient yellow-fleshed cucumber varieties.

Analysis of Volatile and Non-Volatile Components of Dried Chili Pepper (Capsicum annuum L.)

As an important crop in the world, dried pepper is widely used in various foods. However, the sensory quality, fruit shape index, edible index, nutrition index, and volatile components of dried pepper have not been comprehensively analyzed. This study elucidated the differences between different varieties of dried pepper and provided the basis for the selection of raw materials for different varieties of dried pepper products. The varieties with high scores in sensory evaluation were Henan new generation, Neihuang new generation, Chengdu Erjingtiao, India S17, and Honglong 12. The varieties with the highest fruit shape index, edible rate, and nutrition index were Chengdu Erjingtiao and Guizhou Erjingtiao. A total of 380 volatile organic compounds were identified by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry with headspace sampling (HS-GC-TOF MS), including 62 alcohols, 50 aldehydes, 68 ketones, 60 hydrocarbons, 99 esters, 18 acids, and 23 other substances such as pyrazoles and ethers.

Genome-Wide Identification and Expression Analysis of Carotenoid Cleavage Dioxygenase Genes in Salvia miltiorrhiza

In the process of catalyzing carotenoids into various apocarotenoids and other derivatives, carotenoid cleavage dioxygenases (CCDs) play key roles. However, little information on CCDs has been reported in regard to Salvia miltiorrhiza. In this study, a total of 21 CCD genes were identified in the whole genome of S. miltiorrhiza, mainly distributed between five chromosomes. Phylogenetic relationship analysis revealed that 21 SmCCD genes were classified into four subfamilies, including SmCCD4, 7, 8, and NCED; the members of the same subfamily show similar gene structures and tertiary structures. The interspecific collinearity with other plant species, such as Arabidopsis thaliana and Oryza sativa was analyzed. Cis-elements analysis demonstrated that the majority were stress response-, light response-, growth-, and development-related. The expression pattern of the SmCCD genes was expressed in the analyzed tissues. Furthermore, the majority of the SmCCD4 subfamily members varied in their expression levels under the treatment of MeJA, YE, and ABA, indicating the potential function of SmCCD4 in the metabolism process of S. miltiorrhiza. In general, this study provides a systematic analysis of SmCCD genes and lays the foundation for uncovering the regulation and function of SmCCD genes in S. miltiorrhiza.

Monitoring Fruit Growth and Development in Apricot (Prunus armeniaca L.) through Gene Expression Analysis

The main objective of this study was to monitor apricot development and ripening through gene expression analysis of key candidate genes using the RT-qPCR technique. Eight apricot cultivars were selected to analyze phenological and genetic patterns from pre-ripening stages through to postharvest. In addition, 19 selected genes were analyzed in the contrasting cultivars 'Cebas Red' and 'Rojo Pasión' in different stages (two preharvest stages S1 and S2, one harvest stage S3, and two postharvest stages S4 and S5). This pool of genes included genes related to fruit growth and ripening, genes associated with fruit color, and genes linked to the fruit's nutraceutical aspects. Among the studied genes, Polygalacturonase (PG), Pectin methylesterase (PME), Aminocyclopropane-1-carboxylate synthase (ACS), and Myo-inositol-1-phosphate synthase (INO1) were directly related to fruit maturation and quality. Significant differential expression was observed between the cultivars, which correlated with variations in firmness, shelf life, and sensory characteristics of the apricots. 'Rojo Pasión' displayed high levels of PG, associated with rapid maturation and shorter postharvest shelf life, whereas 'Cebas Red' exhibited lower levels of this gene, resulting in greater firmness and extended shelf life. Genes CCD4, CRTZ, and ZDS, related to carotenoids, showed varied expression patterns during growth and postharvest stages, with higher levels in 'Rojo Pasión'. On the other hand, Sucrose synthase (SUSY) and Lipoxygenase (LOX2) were prominent during the postharvest and growth stages, respectively. Additionally, GDP-L-galactose phosphorylase (VTC2_5) was linked to better postharvest performance. This research provides valuable insights for future breeding initiatives aimed at enhancing the quality and sustainability of apricot cultivation.

Genome-wide analysis and identification of Carotenoid Cleavage Oxygenase (CCO) gene family in coffee (coffee arabica) under abiotic stress

The coffee industry holds importance, providing livelihoods for millions of farmers globally and playing a vital role in the economies of coffee-producing countries. Environmental conditions such as drought and temperature fluctuations can adversely affect the quality and yield of coffee crops.Carotenoid cleavage oxygenases (CCO) enzymes are essential for coffee plants as they help break down carotenoids contributing to growth and stress resistance. However, knowledge about the CCO gene family in Coffee arabica was limited. In this study identified 21 CCO genes in Coffee arabica (C. arabica) revealing two subfamilies carotenoid cleavage dioxygenases (CCDs) and 9-cis-epoxy carotenoid dioxygenases (NCED) through phylogenic analysis. These subfamilies exhibited distribution patterns in terms of gene structure, domains, and motifs. The 21 CaCCO genes, comprising 5 NCED and 16 CCD genes were found across chromosomes. Promoter sequencing analysis revealed cis-elements that likely interact with plant stress-responsive, growth-related, and phytohormones, like auxin and abscisic acid. A comprehensive genome-wide comparison, between C. arabica and A. thaliana was conducted to understand the characteristics of CCO genes. RTqPCR data indicated that CaNCED5, CaNCED6, CaNCED12, and CaNCED20 are target genes involved in the growth of drought coffee plants leading to increased crop yield, in a conditions, with limited water availability. This reveals the role of coffee CCOs in responding to abiotic stress and identifies potential genes useful for breeding stress-resistant coffee varieties.

Exogenous CaCl2 reduces the oxidative cleavage of carotenoids in shredded carrots by targeting CAMTA4-mediated transcriptional repression of carotenoid degradation pathway

Carotenoid oxidative cleavage is a significant factor contributing to the color changes of shredded carrots and treatment with calcium chloride (CaCl2, 1% w/v) has been observed to alleviate the whitening symptom and color loss. However, the specific mechanism by which CaCl2 treatment suppresses carotenoid degradation remains unclear. In this study, the effect of CaCl2 and EGTA (calcium ion chelating agent) treatment on carotenoid biosynthesis and degradation in shredded carrots and the mechanism involved was investigated. CaCl2 treatment promoted the expression and activity of carotenoid biosynthetic enzyme (phytoene synthase, PSY), but inhibited the increases of the degradative enzyme activity of carotenoid cleavage dioxygenase (CCD) and down-regulated the corresponding transcripts, thus delayed the degradation of total carotenoid and maintaining higher levels of major carotenoid compounds including β-carotene, α-carotene, lycopene, and lutein in shredded carrots during storage. However, EGTA treatment promoted the gene expression and enzyme activity of CCD and increased the degradation of carotenoid compounds in shredded carrots during storage. Furthermore, the CaCl2 treatment induced DcCAMTA4, identified as a calcium decoder in shredded carrots, which, in turn, suppressed the expressions of DcCCD1 and DcCCD4 by interacting with their promoters. The transient overexpression of DcCAMTA4 in tobacco leaves led to reduced expression of NtCCD1 and NtCCD4, maintaining a higher content of carotenoids. Thus, CaCl2 alleviated the oxidative cleavage of carotenoids in shredded carrots through the DcCAMTA4-mediated carotenoid degradation pathway.

Genome-wide identification and in-silico expression analysis of CCO gene family in sunflower (Helianthus annnus) against abiotic stress

Carotenoid cleavage oxygenases (CCOs) enzymes play an important role in plant growth and development by producing a wide array of apocarotenoids and their derivatives. These compounds are vital for colouring flowers and fruits and synthesizing plant hormones such as abscisic acid and strigolactones. Despite their importance, the gene family responsible for CCO enzymes in sunflowers has not been identified. In this study, we identify the CCO genes of the sunflower plant to fill this knowledge gap. Phylogenetic and synteny analysis indicated that the Helianthus annnus CCO (HaCCO) genes were conserved in different plant species and they could be divided into three subgroups based on their conserved domains. Analysis using MEME tool and multiple sequence alignment identified conserved motifs in the HaCCO gene sequence. Cis-regulatory elements (CREs) analysis of the HaCCO genes indicated the presence of various responsive elements related to plant hormones, development, and responses to both biotic and abiotic stresses. This implies that these genes may respond to plant hormones, developmental cues, and drought stress, offering potential applications in the development of more resistant crops. Genes belonging to the 9-cis-epoxy carotenoid dioxygenases (NCED) subgroups predominantly exhibited chloroplast localization, whereas the genes found in other groups are primarily localized in the cytoplasm. These 21 identified HaCCOs were regulated by 60 miRNAs, indicating the crucial role of microRNAs in gene regulation in sunflowers. Gene expression analysis under drought stress revealed significant up-regulation of HaNCED16 and HaNCED19, genes that are pivotal in ABA hormone biosynthesis. During organ-specific gene expression analysis, HaCCD12 and HaCCD20 genes exhibit higher activity in leaves, indicating a potential role in leaf pigmentation. This study provides a foundation for future research on the regulation and functions of the CCO gene family in sunflower and beyond. There is potential for developing molecular markers that could be employed in breeding programs to create new sunflower lines resistant to biotic and abiotic stresses.

Crocus genome reveals the evolutionary origin of crocin biosynthesis

Crocus sativus (saffron) is a globally autumn-flowering plant, and its stigmas are the most expensive spice and valuable herb medicine. Crocus specialized metabolites, crocins, are biosynthesized in distant species, Gardenia (eudicot) and Crocus (monocot), and the evolution of crocin biosynthesis remains poorly understood. With the chromosome-level Crocus genome assembly, we revealed that two rounds of lineage-specific whole genome triplication occurred, contributing important roles in the production of carotenoids and apocarotenoids. According to the kingdom-wide identification, phylogenetic analysis, and functional assays of carotenoid cleavage dioxygenases (CCDs), we deduced that the duplication, site positive selection, and neofunctionalization of Crocus-specific CCD2 from CCD1 members are responsible for the crocin biosynthesis. In addition, site mutation of CsCCD2 revealed the key amino acids, including I143, L146, R161, E181, T259, and S292 related to the catalytic activity of zeaxanthin cleavage. Our study provides important insights into the origin and evolution of plant specialized metabolites, which are derived by duplication events of biosynthetic genes.

Desiccation tolerance in the resurrection plant Barbacenia graminifolia involves changes in redox metabolism and carotenoid oxidation

Desiccation tolerance in vegetative tissues enables resurrection plants to remain quiescent under severe drought and rapidly recover full metabolism once water becomes available. Barbacenia graminifolia is a resurrection plant that occurs at high altitudes, typically growing on rock slits, exposed to high irradiance and limited water availability. We analyzed the levels of reactive oxygen species (ROS) and antioxidants, carotenoids and its cleavage products, and stress-related phytohormones in fully hydrated, dehydrated, and rehydrated leaves of B. graminifolia. This species exhibited a precise adjustment of its antioxidant metabolism to desiccation. Our results indicate that this adjustment is associated with enhanced carotenoid and apocarotenoids, α-tocopherol and compounds of ascorbate-glutathione cycle. While α-carotene and lutein increased in dried-leaves suggesting effective protection of the light-harvesting complexes, the decrease in β-carotene was accompanied of 10.2-fold increase in the content of β-cyclocitral, an apocarotenoid implicated in the regulation of abiotic stresses, compared to hydrated plants. The principal component analysis showed that dehydrated plants at 30 days formed a separate cluster from both hydrated and dehydrated plants for up to 15 days. This regulation might be part of the protective metabolic strategies employed by this resurrection plant to survive water scarcity in its inhospitable habitat.

5'-UTR allelic variants and expression of the lycopene-ɛ-cyclase LCYE gene in maize (Zea mays L.) inbred lines of Russian selection

In breeding, biofortification is aimed at enriching the edible parts of the plant with micronutrients. Within the framework of this strategy, molecular screening of collections of various crops makes it possible to determine allelic variants of genes, new alleles, and the linkage of allelic variants with morphophysiological traits. The maize (Zea mays L.) is an important cereal and silage crop, as well as a source of the main precursor of vitamin A - β-carotene, a derivative of the β,β-branch of the carotenoid biosynthesis pathway. The parallel β,ε-branch is triggered by lycopene-ε-cyclase LCYE, a low expression of which leads to an increase in provitamin A content and is associated with the variability of the 5'-UTR gene regulatory sequence. In this study, we screened a collection of 165 maize inbred lines of Russian selection for 5'- UTR LCYE allelic variants, as well as searched for the dependence of LCYE expression levels on the 5'-UTR allelic variant in the leaves of 14 collection lines. 165 lines analyzed were divided into three groups carrying alleles A2 (64 lines), A5 (31) and A6 (70), respectively. Compared to A2, allele A5 contained two deletions (at positions -267- 260 and -296-290 from the ATG codon) and a G251→T substitution, while allele A6 contained one deletion (-290-296) and two SNPs (G251→T, G265→T). Analysis of LCYE expression in the leaf tissue of seedlings from accessions of 14 lines differing in allelic variants showed no associations of the 5'-UTR LCYE allele type with the level of gene expression. Four lines carrying alleles A2 (6178-1, 6709-2, 2289-3) and A5 (5677) had a significantly higher level of LCYE gene expression (~0.018-0.037) than the other 10 analyzed lines (~0.0001-0.004), among which all three allelic variants were present.

A systematic in silico report on iron and zinc proteome of Zea mays

Zea mays is an essential staple food crop across the globe. Maize contains macro and micronutrients but is limited in essential mineral micronutrients such as Fe and Zn. Worldwide, serious health concerns have risen due to the deficiencies of essential nutrients in human diets, which rigorously jeopardizes economic development. In the present study, the systematic in silico approach has been used to predict Fe and Zn binding proteins from the whole proteome of maize. A total of 356 and 546 putative proteins have been predicted, which contain sequence and structural motifs for Fe and Zn ions, respectively. Furthermore, the functional annotation of these predicted proteins, based on their domains, subcellular localization, gene ontology, and literature support, showed their roles in distinct cellular and biological processes, such as metabolism, gene expression and regulation, transport, stress response, protein folding, and proteolysis. The versatile roles of these shortlisted putative Fe and Zn binding proteins of maize could be used to manipulate many facets of maize physiology. Moreover, in the future, the predicted Fe and Zn binding proteins may act as relevant, novel, and economical markers for various crop improvement programs.

More Than Pigments: The Potential of Astaxanthin and Bacterioruberin-Based Nanomedicines

Carotenoids are natural products regulated by the food sector, currently used as feed dyes and as antioxidants in dietary supplements and composing functional foods for human consumption. Of the nearly one thousand carotenoids described to date, only retinoids, derived from beta carotene, have the status of a drug and are regulated by the pharmaceutical sector. In this review, we address a novel field: the transformation of xanthophylls, particularly the highly marketed astaxanthin and the practically unknown bacterioruberin, in therapeutic agents by altering their pharmacokinetics, biodistribution, and pharmacodynamics through their formulation as nanomedicines. The antioxidant activity of xanthophylls is mediated by routes different from those of the classical oral anti-inflammatory drugs such as corticosteroids and non-steroidal anti-inflammatory drugs (NSAIDs): remarkably, xanthophylls lack therapeutic activity but also lack toxicity. Formulated as nanomedicines, xanthophylls gain therapeutic activity by mechanisms other than increased bioavailability. Loaded into ad hoc tailored nanoparticles to protect their structure throughout storage and during gastrointestinal transit or skin penetration, xanthophylls can be targeted and delivered to selected inflamed cell groups, achieving a massive intracellular concentration after endocytosis of small doses of formulation. Most first reports showing the activities of oral and topical anti-inflammatory xanthophyll-based nanomedicines against chronic diseases such as inflammatory bowel disease, psoriasis, atopic dermatitis, and dry eye disease emerged between 2020 and 2023. Here we discuss in detail their preclinical performance, mostly targeted vesicular and polymeric nanoparticles, on cellular models and in vivo. The results, although preliminary, are auspicious enough to speculate upon their potential use for oral or topical administration in the treatment of chronic inflammatory diseases.

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

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

ZAXINONE SYNTHASE 2 regulates growth and arbuscular mycorrhizal symbiosis in rice

Carotenoid cleavage, catalyzed by CAROTENOID CLEAVAGE DIOXYGENASEs (CCDs), provides signaling molecules and precursors of plant hormones. Recently, we showed that zaxinone, a apocarotenoid metabolite formed by the CCD ZAXINONE SYNTHASE (ZAS), is a growth regulator required for normal rice (Oryza sativa) growth and development. The rice genome encodes three OsZAS homologs, called here OsZAS1b, OsZAS1c, and OsZAS2, with unknown functions. Here, we investigated the enzymatic activity, expression pattern, and subcellular localization of OsZAS2 and generated and characterized loss-of-function CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats and associated protein 9)-Oszas2 mutants. We show that OsZAS2 formed zaxinone in vitro. OsZAS2 was predominantly localized in plastids and mainly expressed under phosphate starvation. Moreover, OsZAS2 expression increased during mycorrhization, specifically in arbuscule-containing cells. Oszas2 mutants contained lower zaxinone content in roots and exhibited reduced root and shoot biomass, fewer tillers, and higher strigolactone (SL) levels. Exogenous zaxinone application repressed SL biosynthesis and partially rescued the growth retardation of the Oszas2 mutant. Consistent with the OsZAS2 expression pattern, Oszas2 mutants displayed a lower frequency of arbuscular mycorrhizal colonization. In conclusion, OsZAS2 is a zaxinone-forming enzyme that, similar to the previously reported OsZAS, determines rice growth, architecture, and SL content, and is required for optimal mycorrhization.

Plant carotenoids: recent advances and future perspectives

Carotenoids are isoprenoid metabolites synthesized de novo in all photosynthetic organisms. Carotenoids are essential for plants with diverse functions in photosynthesis, photoprotection, pigmentation, phytohormone synthesis, and signaling. They are also critically important for humans as precursors of vitamin A synthesis and as dietary antioxidants. The vital roles of carotenoids to plants and humans have prompted significant progress toward our understanding of carotenoid metabolism and regulation. New regulators and novel roles of carotenoid metabolites are continuously revealed. This review focuses on current status of carotenoid metabolism and highlights recent advances in comprehension of the intrinsic and multi-dimensional regulation of carotenoid accumulation. We also discuss the functional evolution of carotenoids, the agricultural and horticultural application, and some key areas for future research.

Making extra room for carotenoids in plant cells: New opportunities for biofortification

Plant carotenoids are essential for photosynthesis and photoprotection and provide colors in the yellow to red range to non-photosynthetic organs such as petals and ripe fruits. They are also the precursors of biologically active molecules not only in plants (including hormones and retrograde signals) but also in animals (including retinoids such as vitamin A). A carotenoid-rich diet has been associated with improved health and cognitive capacity in humans, whereas the use of carotenoids as natural pigments is widespread in the agrofood and cosmetic industries. The nutritional and economic relevance of carotenoids has spurred a large number of biotechnological strategies to enrich plant tissues with carotenoids. Most of such approaches to alter carotenoid contents in plants have been focused on manipulating their biosynthesis or degradation, whereas improving carotenoid sink capacity in plant tissues has received much less attention. Our knowledge on the molecular mechanisms influencing carotenoid storage in plants has substantially grown in the last years, opening new opportunities for carotenoid biofortification. Here we will review these advances with a particular focus on those creating extra room for carotenoids in plant cells either by promoting the differentiation of carotenoid-sequestering structures within plastids or by transferring carotenoid production to the cytosol.

Establishment of strigolactone-producing bacterium-yeast consortium

Strigolactones (SLs) are a class of phytohormones playing diverse roles in plant growth and development, yet the limited access to SLs is largely impeding SL-based foundational investigations and applications. Here, we developed Escherichia coli–Saccharomyces cerevisiae consortia to establish a microbial biosynthetic platform for the synthesis of various SLs, including carlactone, carlactonoic acid, 5-deoxystrigol (5DS; 6.65 ± 1.71 μg/liter), 4-deoxyorobanchol (3.46 ± 0.28 μg/liter), and orobanchol (OB; 19.36 ± 5.20 μg/liter). The SL-producing platform enabled us to conduct functional identification of CYP722Cs from various plants as either OB or 5DS synthase. It also allowed us to quantitatively compare known variants of plant SL biosynthetic enzymes in the microbial system. The titer of 5DS was further enhanced through pathway engineering to 47.3 μg/liter. This work provides a unique platform for investigating SL biosynthesis and evolution and lays the foundation for developing SL microbial production process.

Carotenoids: Potent to Prevent Diseases Review

Carotenoids are the phytochemicals known for their biological activities. They are found in nature in the form of plants, algae, fungi and in microorganisms. This is the major group having two different structure one with oxygen and without oxygen. The Present article aims to present these molecules as a new therapeutic agent, as it has unrealized efficiency to prevent and reduce the symptoms of many diseases like cancer, neurodegenerative diseases such as Alzheimer, cerebral ischemia, diabetes associated with obesity and hypertension, ophthalmic diseases and many more. It can be utilized in the form of dietary supplement as nutraceutical and pharmaceutical compounds. Yet more research and developing test knowledge is needed to make it available to the humans. In this article its sources, biosynthesis, properties, applicability and commercialization of pigments from naturally produced sources are discussed.