Regulation of Carotenoid Biosynthesis During Fruit Development

Differential expression of CCD4(4B) drives natural variation in fruit carotenoid content in strawberry (Fragaria spp.)

Carotenoids are a diverse group of pigments imparting red, orange, and yellow hues to many horticultural plants, also enhancing their nutritional properties and health benefits. In strawberry, the genetic and molecular mechanisms regulating the natural variation of fruit carotenoid composition remain largely unexplored. In this study, we use a population segregating in yellow/white flesh to detect a major quantitative trait locus (QTL), qYellow Flesh-4B, located on chromosome 4B and accounting for 82% of total phenotypic variation. In the QTL interval, specific polymorphisms on the promoter of the carotenoid cleavage dioxygenase CCD4(4B) were associated with yellow flesh, down-regulation of CCD4(4B) during ripening, and increased carotenoid content. The role of CCD4(4B) in carotenoid turnover was further confirmed through transient overexpression in strawberry fruits, which resulted in decreased concentrations of the xanthophylls violaxanthin, lutein, and zeaxanthin. Notably, a -35 C>T single-nucleotide polymorphism (SNP) in the CCD4(4B) promoter was predictive of both CCD4(4B) expression and carotenoid content across a diverse collection of octoploid Fragaria species. These findings provide valuable genetic insights into the natural variation of carotenoid composition and accumulation in strawberry. A high-resolution melting (HRM) DNA test developed in this study offers a rapid and reliable method for predicting high carotenoid content in strawberry fruits, representing a valuable tool for breeding projects aimed at enhancing the nutritional value of this crop.

Integrated metabolome and transcriptome analysis provides clues to fruit color formation of yellow, orange, and red bell pepper

Fruit color is a crucial trait for bell pepper. To investigate the mechanism of color formation, three bell pepper lines with different color (yellow, orange and red) were used as materials to conduct comprehensive targeted metabolomic and transcriptomic analyses. During the process of fruit development, 54 carotenoids metabolites were discovered, exhibiting unique accumulation patterns and notable variety specificity. The types and content of carotenoids in orange fruit (OM) were notably greater compared to the other two varieties. Red pigment (capsanthin and capsorubin) was specifically enriched in red fruit (RM), and yellow pigment (lutein and zeaxanthin) is the highest in yellow fruit (YM) and OM. Five modules positively correlated with carotenoid accumulation and one negative module was determined by weighted gene co-expression network analysis (WGCNA). Additionally, transcription factors (TFs) and hub genes related to carotenoid synthesis were predicted. By elucidating the regulation of 7 key carotenoid metabolites by 14 critical genes and 5 key TFs, we constructed a comprehensive carotenoid biosynthesis metabolic network that comprehensively explains the pigment changes observed in green and mature pepper fruit. Overall, the results not only provide important insights into carotenoid synthesis pathway, but also lay a solid base for revealing the mechanism of bell pepper color transformation.

EjWRKY6 Is Involved in the ABA-Induced Carotenoid Biosynthesis in Loquat Fruit during Ripening

The yellow-fleshed loquat is abundant in carotenoids, which determine the fruit's color, provide vitamin A, and offer anti-inflammatory and anti-cancer health benefits. In this research, the impact of abscisic acid (ABA), a plant hormone, on carotenoid metabolism and flesh pigmentation in ripening loquat fruits was determined. Results revealed that ABA treatment enhanced the overall content of carotenoids in loquat fruit, including major components like β-cryptoxanthin, lutein, and β-carotene, linked to the upregulation of most genes in the carotenoid biosynthesis pathway. Furthermore, a transcription factor, EjWRKY6, whose expression was induced by ABA, was identified and was thought to play a role in ABA-induced carotenoid acceleration. Transient overexpression of EjWRKY6 in Nicotiana benthamiana and stable genetic transformation in Nicotiana tabacum with EjWRKY6 indicated that both carotenoid production and genes related to carotenoid biosynthesis could be upregulated in transgenic plants. A dual-luciferase assay proposed a probable transcriptional control between EjWRKY6 and promoters of genes associated with carotenoid production. To sum up, pre-harvest ABA application could lead to carotenoid biosynthesis in loquat fruit through the EjWRKY6-induced carotenoid biosynthesis pathway.

Regulation of carotenoid metabolism and ABA biosynthesis during blueberry fruit ripening

Carotenoids and their derivates play critical physiologic roles in plants. However, these substrates and their metabolism have not been elucidated in fruit of blueberry (Vaccinium corymbosum). In this study, carotenoids and ABA were investigated by LC-MS and their biosynthesis were subject to proteomic analysis during fruit ripening. Activity of CCD1 and NCED1/3 were studied in vivo or in vitro. Also, effects of ethephon and 1-MCP on biosynthesis of carotenoid and ABA were investigated through the expression of corresponding genes using qPCR. As a result, carotenoid biosynthesis was prominently mitigated whereas its metabolism was enhanced during fruit ripening, which resulted in a decrease in the carotenoids. VcCCD1 could both cleave β-carotene, zeaxanthin and lutein at positions of 9, 10 (9', 10'), which was mainly responsible for the degradation of these carotenoids. Interestingly, in the situation of mitigation of carotenoid biosynthesis, ABA still rapidly accumulated, which was mainly attributed to the upregulated expression of VcNCED1/3. Notably, VcNCED1/3 also showed a cleavage activity of all-trans-zeaxanthin and a stereospecific cleavage activity of 9-cis-carotene to generate C15-carotenal. The C15-carotenal could be potentially converted to ABA through ZEP-independent ABA biosynthetic pathway during blueberry fruit ripening. Similar to a nature natural maturation, ethylene accelerated the carotenoid degradation and ABA biosynthesis trough downregulating the expression of genes in carotenoid biosynthesis and upregulating the expression of genes in ABA biosynthesis. These information help understand the regulation of carotenoids and ABA, and effects of ethylene on the regulation during blueberry fruit ripening.

Comparative Genomic Analysis of Sphingomonas morindae sp. NBD5 and Sphingopyxis sp. USTB-05 for Producing Macular Pigment

Sphingomonas morindae sp. NBD5, which we previously identified and tested, is a new bacterial strain for producing lutein. Here, based on the next-generation sequencing technology, we analyzed high throughput genomic sequences and compared related functional genes of Sphingomonas morindae sp. NBD5 and Sphingopyxis sp. USTB-05. The genome of Sphingomonas morindae sp. NBD5 has two sets of chromosomes, which is 4,239,716 bp and harbors 3882 protein coding genes. There are 59 protein-coding genes related to the macular pigment (MP) biosynthesis, of which four genes (ackA, pgm, gpmI and pckA) are unique. These genes, pckG, porB, meh, and fldA, are unique in Sphingopyxis sp. USTB-05. The analysis of Sphingomonas morindae sp. NBD5 and Sphingopyxis sp. USTB-05 genomes gives an insight into the new pathway for MP production. These genes for the transformation of glucose to MP were also found in Sphingomonas morindae sp. NBD5 and Sphingopyxis sp. USTB-05. This study expands the understanding of the pathway for complete biosynthesis of MP by Sphingomonas morindae sp. NBD5 and Sphingopyxis sp. USTB-05.

Metabolism of Carotenoids and β-Ionone Are Mediated by Carotenogenic Genes and PpCCD4 Under Ultraviolet B Irradiation and During Fruit Ripening

Carotenoids are essential pigments widely distributed in tissues and organs of higher plants, contributing to color, photosynthesis, photoprotection, nutrition, and flavor in plants. White- or yellow-fleshed colors in peach were determined by expression of carotenoids cleavage dioxygenase (PpCCD) genes, catalyzing the degradation of carotenoids. The cracked volatile apocarotenoids are the main contributors to peach aroma and flavor with low sensory threshold concentration. However, the detailed regulatory roles of carotenoids metabolism genes remained unclear under UV-B irradiation. In our study, metabolic balance between carotenoids and apocarotenoids was regulated by the expression of phytoene synthase (PSY), β-cyclase (LCY-B), ε-cyclase (LCY-E), and PpCCD4 under UV-B irradiation. The transcript levels of PpPSY, PpLCY-B, PpLCY-E, and PpCHY-B were elevated 2- to 10-fold compared with control, corresponding to a nearly 30% increase of carotenoids content after 6 h UV-B irradiation. Interestingly, the total carotenoids content decreased by nearly 60% after 48 h of storage, while UV-B delayed the decline of lutein and β-carotene. The transcript level of PpLCY-E increased 17.83-fold compared to control, partially slowing the decline rate of lutein under UV-B irradiation. In addition, the transcript level of PpCCD4 decreased to 30% of control after 48 h UV-B irradiation, in accordance with the dramatic reduction of apocarotenoid volatiles and the delayed decrease of β-carotene. Besides, β-ionone content was elevated by ethylene treatment, and accumulation dramatically accelerated at full ripeness. Taken together, UV-B radiation mediated the metabolic balance of carotenoid biosynthesis and catabolism by controlling the transcript levels of PpPSY, PpLCY-B, PpLCY-E, and PpCCD4 in peach, and the transcript level of PpCCD4 showed a positive relationship with the accumulation of β-ionone during the ripening process. However, the detailed catalytic activity of PpCCD4 with various carotenoid substrates needs to be studied further, and the key transcript factors involved in the regulation of metabolism between carotenoids and apocarotenoids need to be clarified.

Red light-transmittance bagging promotes carotenoid accumulation of grapefruit during ripening

Light, a crucial environmental signal, is involved in the regulation of secondary metabolites. To understand the mechanism by which light influences carotenoid metabolism, grapefruits were bagged with four types of light-transmitting bags that altered the transmission of solar light. We show that light-transmitting bagging induced changes in carotenoid metabolism during fruit ripening. Compared with natural light, red light (RL)-transmittance treatment significantly increases the total carotenoid content by 62%. Based on weighted gene co-expression network analysis (WGCNA), ‘blue’ and ‘turquoise’ modules are remarkably associated with carotenoid metabolism under different light treatment (p < 0.05). Transcriptome analysis identifies transcription factors (TFs) bHLH128, NAC2-like/21/72, MYB-like, AGL11/AGL61, ERF023/062, WRKY20, SBPlike-7/13 as being involved in the regulation of carotenoid metabolism in response to RL. Under RL treatment, these TFs regulate the accumulation of carotenoids by directly modulating the expression of carotenogenic genes, including GGPPS2, PDS, Z-ISO, ZDS2/7, CRTISO3, CYP97A, CHYB, ZEP2, CCD1-2. Based on these results, a network of the regulation of carotenoid metabolism by light in citrus fruits is preliminarily proposed. These results show that RL treatments have great potential to improve coloration and nutritional quality of citrus fruits.

Grapefruits ripened in red light-transmitting bags have 62% more carotenoid content than those ripened in natural light, leading to better coloration and higher nutritional quality.

Perturbations in the Carotenoid Biosynthesis Pathway in Tomato Fruit Reactivate the Leaf-Specific Phytoene Synthase 2

The accumulation of the red carotenoid pigment lycopene in tomato (Solanum lycopersicum) fruit is achieved by increased carotenoid synthesis during ripening. The first committed step that determines the flux in the carotenoid pathway is the synthesis of phytoene catalyzed by phytoene synthase (PSY). Tomato has three PSY genes that are differentially expressed. PSY1 is exclusively expressed in fruits, while PSY2 mostly functions in green tissues. It has been established that PSY1 is mostly responsible for phytoene synthesis in fruits. Although PSY2 is found in the chromoplasts, it is inactive because loss-of-function mutations in PSY1 in the locus yellow flesh (r) eliminate carotenoid biosynthesis in the fruit. Here we demonstrate that specific perturbations of carotenoid biosynthesis downstream to phytoene prior and during the transition from chloroplast to chromoplast cause the recovery of phytoene synthesis in yellow flesh (r) fruits without significant transcriptional changes of PSY1 and PSY2. The recovery of carotenoid biosynthesis was abolished when the expression of PSY2 was silenced, indicating that the perturbations of carotenoid biosynthesis reactivated the chloroplast-specific PSY2 in fruit chromoplasts. Furthermore, it is demonstrated that PSY2 can function in fruit chromoplasts under certain conditions, possibly due to alterations in the plastidial sub-organelle organization that affect its association with the carotenoid biosynthesis metabolon. This finding provides a plausible molecular explanation to the epistasis of the mutation tangerine in the gene carotenoid isomerase over yellow flesh.

The transcription factor complex CmAP3-CmPI-CmUIF1 modulates carotenoid metabolism by directly regulating carotenogenic gene CmCCD4a-2 in chrysanthemum

Carotenoids are one of the most important pigments for the coloring in many plants, fruits and flowers. Recently, significant progress has been made in carotenoid metabolism. However, the specific understanding on transcriptional regulation controlling the expression of carotenoid metabolic genes remains extremely limited. Anemone-type chrysanthemum, as a special group of chrysanthemum cultivars, contain elongated disc florets in capitulum, which usually appear in different colors compared with the ray florets since accumulating distinct content of carotenoids. In this study, the carotenoid composition and content of the ray and disc florets of an anemone-type chrysanthemum cultivar 'Dong Li Fen Gui' were analyzed by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) and the key structural gene CmCCD4a-2, of which differential expression resulted in the distinct content of carotenoids accumulated in these two types of florets, was identified. Then the promoter sequence of CmCCD4a-2 was used as bait to screen a chrysanthemum flower cDNA library and two transcription factors, CmAP3 and CmUIF1 were identified. Y2H, BiFC and Y3H experiments demonstrated that these two TFs were connected by CmPI to form CmAP3-CmPI-CmUIF1 TF complex. This TF complex regulated carotenoid metabolism through activating the expression of CmCCD4a-2 directly. Furthermore, a large number of target genes regulated directly by the CmAP3-CmPI-CmUIF1 TF complex, including carotenoid biosynthetic genes, flavonoid biosynthetic genes and flower development-related genes, were identified by DNA-affinity purification sequencing (DAP-seq), which indicated that the CmAP3-CmPI-CmUIF1 TF complex might participate in multiple processes. These findings expand our knowledge for the transcriptional regulation of carotenoid metabolism in plants and will be helpful to manipulating carotenoid accumulation in chrysanthemum.

Integrated Transcriptomics and Metabolomics Analyses Reveal the Molecular Mechanisms of Red-light on Carotenoids Biosynthesis in Tomato Fruit

Carotenoids are the main pigments responsible of the coloration and account for the major antioxidant activity of tomato (Solanum lycopersicum L.) fruit. Significant increments in total carotenoids and lycopene levels were observed in tomato fruit illuminated by red-light relative to white light in previous studies, but the mechanism of carotenoids biosynthesis regulated by red-light is still unclear. In the present study, the influence of red-light on carotenoids biosynthesis in postharvest tomato fruit was conducted using targeted metabolomics and transcriptomic methods. A total of 25 differentially accumulated carotenoids and 1939 differentially expressed genes were isolated and identified. The results illustrated that the content of phytoene and lycopene were considerably higher in fruit treated with red-light than those with white light at 12 h. These differentially expressed genes are mainly enriched in plant hormone signal transduction, photosynthesis, secondary metabolite biosynthesis, and plant circadian. Moreover, from the results of co-expression network analysis, 15 transcription factors from red-light treated fruit were screened, of these, transcription factors of SlERF4, SlbHLH93 and SlIAA29, which involves in signal transduction of light and hormones, respectively, that may also play important roles in carotenoids biosynthesis regulated by red-light in tomato fruit. It is concluded that red-light enhanced carotenoids biosynthesis in postharvest tomato fruit and the mechanisms of enhanced carotenoids biosynthesis were not only associated with the direct regulation by red-light signaling, but also with the indirect regulation by hormonal signaling.

Metabolomics of Chlorophylls and Carotenoids: Analytical Methods and Metabolome-Based Studies

Chlorophylls and carotenoids are two families of antioxidants present in daily ingested foods, whose recognition as added-value ingredients runs in parallel with the increasing number of demonstrated functional properties. Both groups include a complex and vast number of compounds, and extraction and analysis methods evolved recently to a modern protocol. New methodologies are more potent, precise, and accurate, but their application requires a better understanding of the technical and biological context. Therefore, the present review compiles the basic knowledge and recent advances of the metabolomics of chlorophylls and carotenoids, including the interrelation with the primary metabolism. The study includes material preparation and extraction protocols, the instrumental techniques for the acquisition of spectroscopic and spectrometric properties, the workflows and software tools for data pre-processing and analysis, and the application of mass spectrometry to pigment metabolomics. In addition, the review encompasses a critical description of studies where metabolomics analyses of chlorophylls and carotenoids were developed as an approach to analyzing the effects of biotic and abiotic stressors on living organisms.

HPLC-DAD-APCI-MS as a Tool for Carotenoid Assessment of Wild and Cultivated Cherry Tomatoes

Carotenoids are naturally occurring fat-soluble pigments found in many organisms. Because of their extensively conjugated carbon–carbon double bond system, carotenoids are potent antioxidants. Although the most abundant carotenoid and best singlet oxygen quencher found in red tomatoes is lycopene, carotenoid profiles may vary between genotypes. The objective of this work was to perform carotenoid profile indentification using HPLC-DAD-APCI-MS in ten wild cherry tomato accessions and one cultivated tomato. A mixture of hexane/acetone/ethanol (50:25:25) and 0.1% BHT was used for carotenoid extraction. For separation, a C30 column at 30 °C with a gradient consisting of methanol, methyl-tert-butyl ether, and water was used for their analysis. Ten major carotenoids were quantified within cherry tomato samples. All accessions present different profiles and quantities of carotenoids. Wild red tomatoes had more lycopene content that commercial tomato, whereas yellow tomatoes present no lycopene. From a functional viewpoint, higher concentrations of carotenoids that could play an antioxidant activity were measured from accessions IAC401, IAC426, LA1480, IAC391, and LA2692. This trait means that these germplasms may be targets for commercial activities. To the best of our knowledge, this is the first time that HPLC-DAD-APCI-MS has been used to analyze these accessions of wild cherry tomatoes that are both functionally promising and suitable for projects with social implementation at a local scale.

Evaluation of Carotenoids Accumulation and Biosynthesis in Two Genotypes of Pomelo (Citrus maxima) during Early Fruit Development

Pomelo is rich in bioactive compounds (carotenoids, phenolics and essential oil) in the early stage of fruit development, but it is often wasted in the cultivation and management process. To gain an insight into the carotenoid metabolism pathway in pomelo, the carotenoid profiles and the expression patterns of carotenogenic genes were investigated in two genotypes of pomelo during early fruit development. The results showed that a higher carotenoid content was observed in honey pomelo as compared with golden pomelo, which may be related to different gene regulation mechanisms. Lutein, α-carotene, and β-carotene were the main carotenoids in pomelo young fruit, and lutein was the highest one. The accumulation of carotenoids during fruit early development in honey pomelo is related to the transcriptional regulation of ZISO and LUT5. In golden pomelo, the rate-limiting gene for carotenoids is PDS and ZDS. In addition, the expression of seven genes except CRTISO in honey pomelo was higher than that in golden pomelo. The results are helpful to further clarify the regulatory mechanism of carotenoid accumulation during early fruit development and provide a direction for the high-value utilization of young fruits in pomelo.

Synthetic conversion of leaf chloroplasts into carotenoid-rich plastids reveals mechanistic basis of natural chromoplast development

Plastids, the defining organelles of plant cells, undergo physiological and morphological changes to fulfill distinct biological functions. In particular, the differentiation of chloroplasts into chromoplasts results in an enhanced storage capacity for carotenoids with industrial and nutritional value such as beta-carotene (provitamin A). Here, we show that synthetically inducing a burst in the production of phytoene, the first committed intermediate of the carotenoid pathway, elicits an artificial chloroplast-to-chromoplast differentiation in leaves. Phytoene overproduction initially interferes with photosynthesis, acting as a metabolic threshold switch mechanism that weakens chloroplast identity. In a second stage, phytoene conversion into downstream carotenoids is required for the differentiation of chromoplasts, a process that involves a concurrent reprogramming of nuclear gene expression and plastid morphology for improved carotenoid storage. We hence demonstrate that loss of photosynthetic competence and enhanced production of carotenoids are not just consequences but requirements for chloroplasts to differentiate into chromoplasts.

A de novo transcriptome analysis revealed that photomorphogenic genes are required for carotenoid synthesis in the dark-grown carrot taproot

Carotenoids are terpenoid pigments synthesized by all photosynthetic and some non-photosynthetic organisms. In plants, these lipophilic compounds are involved in photosynthesis, photoprotection, and phytohormone synthesis. In plants, carotenoid biosynthesis is induced by several environmental factors such as light including photoreceptors, such as phytochromes (PHYs) and negatively regulated by phytochrome interacting factors (PIFs). Daucus carota (carrot) is one of the few plant species that synthesize and accumulate carotenoids in the storage root that grows in darkness. Contrary to other plants, light inhibits secondary root growth and carotenoid accumulation suggesting the existence of new mechanisms repressed by light that regulate both processes. To identify genes induced by dark and repressed by light that regulate carotenoid synthesis and carrot root development, in this work an RNA-Seq analysis was performed from dark- and light-grown carrot roots. Using this high-throughput sequencing methodology, a de novo transcriptome model with 63,164 contigs was obtained, from which 18,488 were differentially expressed (DEG) between the two experimental conditions. Interestingly, light-regulated genes are preferably expressed in dark-grown roots. Enrichment analysis of GO terms with DEGs genes, validation of the transcriptome model and DEG analysis through qPCR allow us to hypothesize that genes involved in photomorphogenesis and light perception such as PHYA, PHYB, PIF3, PAR1, CRY2, FYH3, FAR1 and COP1 participate in the synthesis of carotenoids and carrot storage root development.

Functional characterisation and in silico modelling of MdPSY2 variants and MdPSY5 phytoene synthases from Malus domestica

Carotenoids are plastid isoprenoid pigments that play critical roles in light harvesting, photoprotection, and phytohormone biosynthesis. They are also vitamin-A precursors and antioxidant molecules important for human nutrition. Apples (e.g. Malus x domestica Borkh), one of the most widely consumed fruits with high nutrient levels, have a very low carotenoid concentration in flesh, compared with other fruits and vegetables. This could be explained by a deficiency in carotenoid synthesis/accumulation and/or accelerated degradation. We analysed the contribution of M. domestica cv. 'Fuji' phytoene synthase (PSY) in the biosynthesis of carotenoids and determined that among four MdPSY genes present in the organism, MdPSY2 and MdPSY5 are highly expressed in leaves and during fruit ripening in line with an increment in carotenoid content in fruits. Furthermore, two representative polymorphic MdPSY2 variants were found, one with a Tyr358Phe substitution (MdPSY2_F) and the other that additionally has a six-amino-acid deletion in the signal peptide (MdPSY2_CG). MdPSY2, MdPSY5, MdPSY2_F and MdPSY2_CG are all localised in plastids. Interestingly, the polymorphic MdPSY2_F and MdPSY2_CG variants show lower enzymatic activity than the wild-type form in a heterologous complementation assay, which could be attributed to the Tyr358Phe substitution close to the active-site pocket, as was suggested by 3-D modelling analysis. The presence of polymorphic MdPSY2 variants with lower enzymatic activity could be partially responsible for the low carotenoid content in Fuji apple fruits.

Boosting carotenoid content in Malus domestica var. Fuji by expressing AtDXR through an Agrobacterium-mediated transformation method

Apple (Malus domestica) fruits accumulate negligible levels of carotenoids, antioxidant pigments that are precursors for vitamin A in humans. As vitamin A deficiency is an important public health issue, we aimed at increasing carotenoids in apple by constitutively expressing the Arabidopsis thaliana DXR gene, one of the key regulatory steps in the plastidial isoprenoid pathway. For this purpose, we optimized an Agrobacterium-mediated transformation method in the commercial Fuji Raku Raku variety. This resulted in a shoot establishment efficiency of 0.75% at 20 weeks after infection. Molecular and microscopical analyses revealed that 80% of the hygromycin resistant shoots contained and expressed AtDXR:eGFP and that the AtDXR:eGFP fusion protein located in plastids. Transgenic seedlings displayed up to 3-fold increase in total carotenoids and in individual carotenoids compared to the WT, correlating with an increased transcript abundance of endogenous carotenogenic genes such as MdDXS, MdPSY1, MdPSY2, MdPSY3, MdLCYB1, and MdLCYB2. In addition, buds of 2-year-old transgenic dormant trees showed an increment up to 3-fold in lutein, and transient transformation of fruits revealed that AtDXR induced a 2-fold increment in total carotenoids. Thus, these results suggest that DXR may be a good candidate for increasing carotenoid levels in apple fruits through metabolic engineering.

Histochemical Analysis of Anthocyanins, Carotenoids, and Flavan-3-ols/Proanthocyanidins in Prunus domestica L. Fruits during Ripening

As a result of the high variability of fruit properties in the European plum Prunus domestica, a histochemical analysis of fruits at different stages of development was performed to understand the ripening process in cv. 'Colora' (yellow-red skinned) and cv. 'Topfive' (purple skinned). Histological analysis showed that carotenoids in the fruit had two different origins. In the fruit flesh, they derived from chloroplasts that turned into chromoplasts, whereas carotenoids in the fruit skin derived probably from proplastids. Flavan-3-ols and proanthocyanidins showed differential localization during ripening. They were visible in the vacuole in different fruit tissues or organized in tannosomes in the fruit flesh. Tanninoplasts were observed only in hypodermal cells of 'Colora'. Toward maturity, anthocyanins were detected in the epidermis and later in the hypodermis of both cultivars. The study forms a basis for the analysis of the biosynthesis of secondary metabolites in European plums and their biological effects.

Fractionation of Tomato Fruit Chromoplasts

Chromoplast differentiation involves an active synthesis of carotenoids associated with the remodeling of the preexisting plastid membrane systems to form specialized structures involved in the sequestration and storage of the synthesized carotenoids. These subplastidial structures show remarkable morphological differences and seem to be adapted to the accumulation of particular carotenoids in some plant species and organs. At present, very little is known about chromoplast biogenesis and the role of the different suborganellar structures in the synthesis and storage of carotenoids. The combination of classical fractionation methods with the use of biochemical and -omics techniques represents an attractive approach to unravel novel aspects related with the biochemical and cellular mechanisms underlying the biogenesis of the structures involved in the biosynthesis and storage of carotenoids during chromoplast differentiation. Here we describe a combined protocol for the isolation, lysis and fractionation of tomato fruit chromoplast. The fractions obtained are suitable for metabolomics and proteomics analysis.

A mutant allele of ζ-carotene isomerase (Z-ISO) is associated with the yellow pigmentation of the "Pinalate" sweet orange mutant and reveals new insights into its role in fruit carotenogenesis

BACKGROUND

Fruit coloration is one of the main quality parameters of Citrus fruit primarily determined by genetic factors. The fruit of ordinary sweet orange (Citrus sinensis) displays a pleasant orange tint due to accumulation of carotenoids, representing β,β-xanthophylls more than 80% of the total content. 'Pinalate' is a spontaneous bud mutant, or somatic mutation, derived from sweet orange 'Navelate', characterized by yellow fruits due to elevated proportions of upstream carotenes and reduced β,β-xanthophylls, which suggests a biosynthetic blockage at early steps of the carotenoid pathway.

RESULTS

To identify the molecular basis of 'Pinalate' yellow fruit, a complete characterization of carotenoids profile together with transcriptional changes in carotenoid biosynthetic genes were performed in mutant and parental fruits during development and ripening. 'Pinalate' fruit showed a distinctive carotenoid profile at all ripening stages, accumulating phytoene, phytofluene and unusual proportions of 9,15,9'-tri-cis- and 9,9'-di-cis-ζ-carotene, while content of downstream carotenoids was significantly decreased. Transcript levels for most of the carotenoid biosynthetic genes showed no alterations in 'Pinalate'; however, the steady-state level mRNA of ζ-carotene isomerase (Z-ISO), which catalyses the conversion of 9,15,9'-tri-cis- to 9,9'-di-cis-ζ-carotene, was significantly reduced both in 'Pinalate' fruit and leaf tissues. Isolation of the 'Pinalate' Z-ISO genomic sequence identified a new allele with a single nucleotide insertion at the second exon, which generates an alternative splicing site that alters Z-ISO transcripts encoding non-functional enzyme. Moreover, functional assays of citrus Z-ISO in E.coli showed that light is able to enhance a non-enzymatic isomerization of tri-cis to di-cis-ζ-carotene, which is in agreement with the partial rescue of mutant phenotype when 'Pinalate' fruits are highly exposed to light during ripening.

CONCLUSION

A single nucleotide insertion has been identified in 'Pinalate' Z-ISO gene that results in truncated proteins. This causes a bottleneck in the carotenoid pathway with an unbalanced content of carotenes upstream to β,β-xanthophylls in fruit tissues. In chloroplastic tissues, the effects of Z-ISO alteration are mainly manifested as a reduction in total carotenoid content. Taken together, our results indicate that the spontaneous single nucleotide insertion in Z-ISO is the molecular basis of the yellow pigmentation in 'Pinalate' sweet orange and points this isomerase as an essential activity for carotenogenesis in citrus fruits.

Network analysis of noncoding RNAs in pepper provides insights into fruit ripening control

Pepper is an important vegetable worldwide and is a model plant for nonclimacteric fleshy fruit ripening. Drastic visual changes and internal biochemical alterations are involved in fruit coloration, flavor, texture, aroma, and palatability to animals during the pepper fruit ripening process. To explore the regulation of bell pepper fruit ripening by noncoding RNAs (ncRNAs), we examined their expression profiles; 43 microRNAs (miRNAs), 125 circular RNAs (circRNAs), 366 long noncoding RNAs (lncRNAs), and 3266 messenger RNAs (mRNAs) were differentially expressed (DE) in mature green and red ripe fruit. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed that the targets of the DE ncRNAs and DE mRNAs included several kinds of transcription factors (TFs) (ERF, bHLH, WRKY, MYB, NAC, bZIP, and ARF), enzymes involved in cell wall metabolism (beta-galactosidase, beta-glucosidase, beta-amylase, chitinase, pectate lyase (PL), pectinesterase (PE) and polygalacturonase (PG)), enzymes involved in fruit color accumulation (bifunctional 15-cis-phytoene synthase, 9-cis-epoxycarotenoid dioxygenase, beta-carotene hydroxylase and carotene epsilon-monooxygenase), enzymes associated with fruit flavor and aroma (glutamate-1-semialdehyde 2,1-aminomutase, anthocyanin 5-aromatic acyltransferase, and eugenol synthase 1) and enzymes involved in the production of ethylene (ET) (ACO1/ACO4) as well as other plant hormones such as abscisic acid (ABA), auxin (IAA), and gibberellic acid (GA). Based on accumulation profiles, a network of ncRNAs and mRNAs associated with bell pepper fruit ripening was developed that provides a foundation for further developing a more refined understanding of the molecular biology of fruit ripening.

Multi-species transcriptome analyses for the regulation of crocins biosynthesis in Crocus

BACKGROUND

Crocins are soluble apocarotenoids that mainly accumulate in the stigma tissue of Crocus sativus and provide the characteristic red color to saffron spice, in addition to being responsible for many of the medicinal properties of saffron. Crocin biosynthesis and accumulation in saffron is developmentally controlled, and the concentration of crocins increases as the stigma develops. Until now, little has been known about the molecular mechanisms governing crocin biosynthesis and accumulation. This study aimed to identify the first set of gene regulatory processes implicated in apocarotenoid biosynthesis and accumulation.

RESULTS

A large-scale crocin-mediated RNA-seq analysis was performed on saffron and two other Crocus species at two early developmental stages coincident with the initiation of crocin biosynthesis and accumulation. Pairwise comparison of unigene abundance among the samples identified potential regulatory transcription factors (TFs) involved in crocin biosynthesis and accumulation. We found a total of 131 (up- and downregulated) TFs representing a broad range of TF families in the analyzed transcriptomes; by comparison with the transcriptomes from the same developmental stages from other Crocus species, a total of 11 TF were selected as candidate regulators controlling crocin biosynthesis and accumulation.

CONCLUSIONS

Our study generated gene expression profiles of stigmas at two key developmental stages for apocarotenoid accumulation in three different Crocus species. Differential gene expression analyses allowed the identification of transcription factors that provide evidence of environmental and developmental control of the apocarotenoid biosynthetic pathway at the molecular level.

Nitro-oxidative metabolism during fruit ripening

Pepper (Capsicum annuum L.) and tomato (Solanum lycopersicum L.), which belong to the Solanaceae family, are among the most cultivated and consumed fleshy fruits worldwide and constitute excellent sources of many essential nutrients, such as vitamins A, C, and E, calcium, and carotenoids. While fruit ripening is a highly regulated and complex process, tomato and pepper have been classified as climacteric and non-climacteric fruits, respectively. These fruits differ greatly in shape, color composition, flavor, and several other features which undergo drastic changes during the ripening process. Such ripening-related metabolic and developmental changes require extensive alterations in many cellular and biochemical processes, which ultimately leads to fully ripe fruits with nutritional and organoleptic features that are attractive to both natural dispersers and human consumers. Recent data show that reactive oxygen and nitrogen species (ROS/RNS) are involved in fruit ripening, during which molecules, such as hydrogen peroxide (H2O2), NADPH, nitric oxide (NO), peroxynitrite (ONOO-), and S-nitrosothiols (SNOs), interact to regulate protein functions through post-translational modifications. In light of these recent discoveries, this review provides an update on the nitro-oxidative metabolism during the ripening of two of the most economically important fruits, discusses the signaling roles played by ROS/RNS in controlling this complex physiological process, and highlights the potential biotechnological applications of these substances to promote further improvements in fruit ripening regulation and nutritional quality. In addition, we suggest that the term 'nitro-oxidative eustress' with regard to fruit ripening would be more appropriate than nitro-oxidative stress, which ultimately favors the consolidation of the plant species.

A New Feature Ensemble with a Multistage Classification Scheme for Breast Cancer Diagnosis

A new and effective feature ensemble with a multistage classification is proposed to be implemented in a computer-aided diagnosis (CAD) system for breast cancer diagnosis. A publicly available mammogram image dataset collected during the Image Retrieval in Medical Applications (IRMA) project is utilized to verify the suggested feature ensemble and multistage classification. In achieving the CAD system, feature extraction is performed on the mammogram region of interest (ROI) images which are preprocessed by applying a histogram equalization followed by a nonlocal means filtering. The proposed feature ensemble is formed by concatenating the local configuration pattern-based, statistical, and frequency domain features. The classification process of these features is implemented in three cases: a one-stage study, a two-stage study, and a three-stage study. Eight well-known classifiers are used in all cases of this multistage classification scheme. Additionally, the results of the classifiers that provide the top three performances are combined via a majority voting technique to improve the recognition accuracy on both two- and three-stage studies. A maximum of 85.47%, 88.79%, and 93.52% classification accuracies are attained by the one-, two-, and three-stage studies, respectively. The proposed multistage classification scheme is more effective than the single-stage classification for breast cancer diagnosis.