Characterization of tocopherol cyclases from higher plants and cyanobacteria. Evolutionary implications for tocopherol synthesis and function

The light and hypoxia induced gene ZmPORB1 determines tocopherol content in the maize kernel

Tocopherol is an important lipid-soluble antioxidant beneficial for both human health and plant growth. Here, we fine mapped a major QTL-qVE1 affecting γ-tocopherol content in maize kernel, positionally cloned and confirmed the underlying gene ZmPORB1 (por1), as a protochlorophyllide oxidoreductase. A 13.7 kb insertion reduced the tocopherol and chlorophyll content, and the photosynthetic activity by repressing ZmPORB1 expression in embryos of NIL-K22, but did not affect the levels of the tocopherol precursors HGA (homogentisic acid) and PMP (phytyl monophosphate). Furthermore, ZmPORB1 is inducible by low oxygen and light, thereby involved in the hypoxia response in developing embryos. Concurrent with natural hypoxia in embryos, the redox state has been changed with NO increasing and H2O2 decreasing, which lowered γ-tocopherol content via scavenging reactive nitrogen species. In conclusion, we proposed that the lower light-harvesting chlorophyll content weakened embryo photosynthesis, leading to fewer oxygen supplies and consequently diverse hypoxic responses including an elevated γ-tocopherol consumption. Our findings shed light on the mechanism for fine-tuning endogenous oxygen concentration in the maize embryo through a novel feedback pathway involving the light and low oxygen regulation of ZmPORB1 expression and chlorophyll content.

Potential role of tocopherol in protecting crop plants against abiotic stresses

The changing global climate have given rise to abiotic stresses that adversely affect the metabolic activities of plants, limit their growth, and agricultural output posing a serious threat to food production. The abiotic stresses commonly lead to production of reactive oxygen species (ROS) that results in cellular oxidation. Over the course of evolution, plants have devised efficient enzymatic and non-enzymatic anti-oxidative strategies to counteract harmful effects of ROS. Among the emerging non-enzymatic anti-oxidative technologies, the chloroplast lipophilic antioxidant vitamin A (Tocopherol) shows great promise. Working in coordination with the other cellular antioxidant machinery, it scavenges ROS, prevents lipid peroxidation, regulates stable cellular redox conditions, simulates signal cascades, improves membrane stability, confers photoprotection and enhances resistance against abiotic stresses. The amount of tocopherol production varies based on the severity of stress and its proposed mechanism of action involves arresting lipid peroxidation while quenching singlet oxygen species and lipid peroxyl radicals. Additionally, studies have demonstrated its coordination with other cellular antioxidants and phytohormones. Despite its significance, the precise mechanism of tocopherol action and signaling coordination are not yet fully understood. To bridge this knowledge gap, the present review aims to explore and understand the biosynthesis and antioxidant functions of Vitamin E, along with its signal transduction and stress regulation capacities and responses. Furthermore, the review delves into the light harvesting and photoprotection capabilities of tocopherol. By providing insights into these domains, this review offers new opportunities and avenues for using tocopherol in the management of abiotic stresses in agriculture.

Vitamins as regulators of calcium-containing kidney stones - new perspectives on the role of the gut microbiome

Calcium-based kidney stone disease is a highly prevalent and morbid condition, with an often complicated and multifactorial aetiology. An abundance of research on the role of specific vitamins (B6, C and D) in stone formation exists, but no consensus has been reached on how these vitamins influence stone disease. As a consequence of emerging research on the role of the gut microbiota in urolithiasis, previous notions on the contribution of these vitamins to urolithiasis are being reconsidered in the field, and investigation into previously overlooked vitamins (A, E and K) was expanded. Understanding how the microbiota influences host vitamin regulation could help to determine the role of vitamins in stone disease.

The evolution of strictly monofunctional naphthoquinol C-methyltransferases is vital in cyanobacteria and plastids

Prenylated quinones are membrane-associated metabolites that serve as vital electron carriers for respiration and photosynthesis. The UbiE (EC 2.1.1.201)/MenG (EC 2.1.1.163) C-methyltransferases catalyze pivotal ring methylations in the biosynthetic pathways of many of these quinones. In a puzzling evolutionary pattern, prokaryotic and eukaryotic UbiE/MenG homologs segregate into 2 clades. Clade 1 members occur universally in prokaryotes and eukaryotes, excluding cyanobacteria, and include mitochondrial COQ5 enzymes required for ubiquinone biosynthesis; Clade 2 members are specific to cyanobacteria and plastids. Functional complementation of an Escherichia coli ubiE/menG mutant indicated that Clade 1 members display activity with both demethylbenzoquinols and demethylnaphthoquinols, independently of the quinone profile of their original taxa, while Clade 2 members have evolved strict substrate specificity for demethylnaphthoquinols. Expression of the gene-encoding bifunctional Arabidopsis (Arabidopsis thaliana) COQ5 in the cyanobacterium Synechocystis or its retargeting to Arabidopsis plastids resulted in synthesis of a methylated variant of plastoquinone-9 that does not occur in nature. Accumulation of methylplastoquinone-9 was acutely cytotoxic, leading to the emergence of suppressor mutations in Synechocystis and seedling lethality in Arabidopsis. These data demonstrate that in cyanobacteria and plastids, co-occurrence of phylloquinone and plastoquinone-9 has driven the evolution of monofunctional demethylnaphthoquinol methyltransferases and explains why plants cannot capture the intrinsic bifunctionality of UbiE/MenG to simultaneously synthesize their respiratory and photosynthetic quinones.

Phytol recycling: essential, yet not limiting for tomato fruit tocopherol accumulation under normal growing conditions

Tocopherols are potent membrane-bound antioxidant molecules that are paramount for plant physiology and also important for human health. In the past years, chlorophyll catabolism was identified as the primary source of phytyl diphosphate for tocopherol synthesis by the action of two enzymes, PHYTOL KINASE (VTE5) and PHYTHYL PHOSPHATE KINASE (VTE6) that are able to recycle the chlorophyll-derived phytol. While VTE5 and VTE6 were proven essential for tocopherol metabolism in tomato fruits, it remains unknown whether they are rate-limiting steps in this pathway. To address this question, transgenic tomato plants expressing AtVTE5 and AtVTE6 in a fruit-specific manner were generated. Although ripe transgenic fruits exhibited higher amounts of tocopherol, phytol recycling revealed a more intimate association with chlorophyll than with tocopherol content. Interestingly, protein-protein interactions assays showed that VTE5 and VTE6 are complexed, channeling free phytol and phytyl-P, thus mitigating their cytotoxic nature. Moreover, the analysis of tocopherol accumulation dynamics in roots, a chlorophyll-devoid organ, revealed VTE5-dependent tocopherol accumulation, hinting at the occurrence of shoot-to-root phytol trafficking. Collectively, these results demonstrate that phytol recycling is essential for tocopherol biosynthesis, even in chlorophyll-devoid organs, yet it is not the rate-limiting step for this pathway under normal growth conditions.

Structural diversity, biosynthesis, and health-promoting properties of brown algal meroditerpenoids

Marine algae that constitute hundreds of millions of tons of biomass are the oldest representatives of the plant kingdom. Recently, there has been growing interest in the utilization of algae as sustainable feedstocks for natural products with an economic value. Among these natural products are the meroditerpenoids, which are renowned for their protective effects against oxidative stress, inflammation, cancer, obesity, diabetes, and neurodegenerative disorders. Meroditerpenoids have a mixed biosynthetic origin and display a wide range of structural diversity. Their basic structure consists of a ring system bearing a diterpenoid side chain. Structural variations are observed in terms of the functional groups and saturation/cyclization of the diterpenoid side chain. This review classifies algal meroditerpenoids as plastoquinones, chromanols, chromenes, chromones, cyclic meroditerpenoids, nahocols, and isonahocols and examines their potential applications in functional foods and biopharmacology. Their lipid solubility, low molecular weight, and propensity to cross the blood-brain barrier places meroditerpenoids as potential drug candidates. There is growing interest in the study of algal meroterpenoids, and recent research has reported the structure of several new meroterpenoids and their biological activities. Further research is needed to extend the use of algal meroditerpenoids in preclinical trials. Understanding the mechanism of their biosynthesis will allow the development of de novo biosynthesis and biomimetic synthesis strategies for the industrial-scale production of meroditerpenoids and their synthetic derivatives to aid pharmaceutical research. This review is the first to summarize up-to-date information on all brown algae-derived meroditerpenoids.

Tocopherol Accumulation and Temporal Expression Analysis of VTE1 and VTE5 Gene Family in Fruit of Two Contrasting Avocado Genotypes

α-tocopherol is found in high concentrations in avocado fruit mesocarp, however, its accumulation and genetic control during maturation and ripening has not been elucidated. Based in the relevance of VTE1 and VTE5 genes in tocopherol biosynthesis and aiming to determine the association between tocopherol accumulation and expression of tocopherol biosynthetic genes, gene expression of VTE1 and VTE5 were evaluated through the time during three developmental stages: before harvest at 100, 160 and 220 days after flowering (DAF) and after harvest (220 DAF + 5) in two contrasting avocado genotypes (San Miguel and AVO40). San Miguel reached the highest levels at 220 DAF, whereas AVO40 increased α-tocopherol only after ripening (220 DAF + 5). A genome-wide search for VTE1 and VTE5 allowed to identify one and three genes, respectively. Both genotypes showed contrasting patterns of gene expression. Interestingly, AVO40 showed a highly positive correlation between α-tocopherol levels and gene expression of VTE1 and all VTE5 variants. On the other hand, San Miguel showed only a positive correlation between α-tocopherol level and VTE1gene expression.

Developing functional markers for vitamin E biosynthesis in oil palm

Vitamin E is essential for human health and plays positive roles in anti-oxidation. Previously, we detected large variation in vitamin E content among 161 oil palm accessions. In this study, twenty oil palm accessions with distinct variation in vitamin E contents (171.30 to 1 258.50 ppm) were selected for genetic variation analysis and developing functional markers associated with vitamin E contents. Thirty-seven homologous genes in oil palm belonging to vitamin E biosynthesis pathway were identified via BLASTP analysis, the lengths of which ranged from 426 to 25 717 bp (average 7 089 bp). Multiplex PCR sequencing for the 37 genes found 1 703 SNPs and 85 indels among the 20 oil palm accessions, with 226 SNPs locating in the coding regions. Clustering analysis for these polymorphic loci showed that the 20 oil palm accessions could be divided into five groups. Among these groups, group I included eight oil palm accessions whose vitamin E content (mean value: 893.50 ppm) was far higher than other groups (mean value 256.29 to 532.94 ppm). Correlation analysis between the markers and vitamin E traits showed that 134 SNP and 7 indel markers were significantly (p < 0.05) related with total vitamin E content. Among these functional markers, the indel EgTMT-1-24 was highly correlated with variation in vitamin E content, especially tocotrienol content. Our study identified a number of candidate function associated markers and provided clues for further research into molecular breeding for high vitamin E content oil palm.

Genetic engineering of potato (Solanum tuberosum L.) for enhanced α-tocopherols and abiotic stress tolerance

Vitamin E (α-tocopherol) is a lipid-soluble essential vitamin recognized for improvement in degenerative health conditions, abating cancer risk, and coronary heart diseases in humans. While in plants, it acts as a free radical scavenger that protects cells against oxidative and photooxidative damages. The daily consumption of potato makes it a key target for biofortification with vitamins for eliminating vitamin deficiency in large populations. Vitamin E biosynthetic pathway genes have been overexpressed in plants via genetic engineering to enhance the α-tocopherol content. Major genes involved in the vitamin E biosynthesis in plants viz. the homogentisate-phytyltransferase (At-HPT) and γ-tocopherol-methyltransferase (At-γ-TMT), isolated from Arabidopsis were constitutively overexpressed in potato (Solanum tuberosum L.). The molecular analyses of independent transgenic lines revealed a stable integration of both the genes in the plant genome. The transgenic potato exhibited significantly improved vitamin E contents up to 173-258% in comparison to the untransformed control plants. Transgenic tissues also exhibited increased cellular antioxidant enzymes, proline, osmolyte, and glutathione content that are directly correlated with the ability of the plant to withstand abiotic stresses imposed by salt (NaCl) and heavy metal (CdCl₂ ). Therefore, the current strategy of increasing the vitamin E content in potato with enhanced tolerance to abiotic stresses might greatly aid efforts to engineer crops for human health benefits and greater yield under adverse environmental conditions.

Assessing the Fatty Acid, Carotenoid, and Tocopherol Compositions of Seeds from Apple Cultivars (Malus domestica Borkh.) Grown in Norway

Apple production generates large amounts of apple pomace including seeds, leading to high transportation costs, public health hazards and undesirable odor. A new reuse strategy of this kind of waste could solve environmental issues and/or create unconventional sources of health beneficial products. In total, seeds from 75 apple cultivars grown in Norway (both domestic and international) have been analyzed for the first time for oil content and fatty acid profile together with tocopherols and carotenoids quantification in defatted seeds. Seeds from cultivar Håkonseple had the highest oil content (22.10%), with linoleic, oleic acid, and palmitic acid as the most abundant fatty acids. The levels of β-carotene and lycopene carotenoids and α-tocopherol were the highest in defatted seeds of the cultivar Sureple Grøn. Principal component analysis separated cultivars according to the total oil content. The Norwegian apple cultivars Håkonseple, Kviteple, Tolleivseple, Vinterrosenstrips, and Tokheimseple are recommended for obtaining vegetable oil due to their high oil contents, while cultivar Sureple Grøn can be separated due to its high levels of β-carotene, lycopene and total tocopherols.

Cysteine, glutathione and a new genetic code: biochemical adaptations of the primordial cells that spread into open water and survived biospheric oxygenation

Life most likely developed under hyperthermic and anaerobic conditions in close vicinity to a stable geochemical source of energy. Epitomizing this conception, the first cells may have arisen in submarine hydrothermal vents in the middle of a gradient established by the hot and alkaline hydrothermal fluid and the cooler and more acidic water of the ocean. To enable their escape from this energy-providing gradient layer, the early cells must have overcome a whole series of obstacles. Beyond the loss of their energy source, the early cells had to adapt to a loss of external iron-sulfur catalysis as well as to a formidable temperature drop. The developed solutions to these two problems seem to have followed the principle of maximum parsimony: Cysteine was introduced into the genetic code to anchor iron-sulfur clusters, and fatty acid unsaturation was installed to maintain lipid bilayer viscosity. Unfortunately, both solutions turned out to be detrimental when the biosphere became more oxidizing after the evolution of oxygenic photosynthesis. To render cysteine thiol groups and fatty acid unsaturation compatible with life under oxygen, numerous counter-adaptations were required including the advent of glutathione and the addition of the four latest amino acids (methionine, tyrosine, tryptophan, selenocysteine) to the genetic code. In view of the continued diversification of derived antioxidant mechanisms, it appears that modern life still struggles with the initially developed strategies to escape from its hydrothermal birthplace. Only archaea may have found a more durable solution by entirely exchanging their lipid bilayer components and rigorously restricting cysteine usage.

Metabolomics of Photosynthetically Active Tissues in White Grapes: Effects of Light Microclimate and Stress Mitigation Strategies

The effects of climate change are becoming a real concern for the viticulture sector, with impacts on both grapevine physiology and the quality of the fresh berries and wine. Short-term mitigation strategies, like foliar kaolin application and smart irrigation regimes, have been implemented to overcome these problems. We previously showed that these strategies also influence the photosynthetic activity of the berries themselves, specifically in the exocarp and seed. In the present work, we assessed the modulating effects of both canopy-light microclimate, kaolin and irrigation treatments on the metabolic profiles of the exocarp and seed, as well as the potential role of berry photosynthesis herein. Berries from the white variety Alvarinho were collected at two contrasting light microclimate positions within the vine canopy (HL—high light and LL—low light) from both irrigated and kaolin-treated plants, and their respective controls, at three fruit developmental stages (green, véraison and mature). Untargeted liquid chromatography mass spectrometry (LCMS) profiling of semi-polar extracts followed by multivariate statistical analysis indicate that both the light microclimate and irrigation influenced the level of a series of phenolic compounds, depending on the ripening stage of the berries. Moreover, untargeted gas chromatography mass spectrometry (GCMS) profiling of polar extracts show that amino acid and sugar levels were influenced mainly by the interaction of irrigation and kaolin treatments. The results reveal that both photosynthetically active berry tissues had a distinct metabolic profile in response to the local light microclimate, which suggests a specific role of photosynthesis in these tissues. A higher light intensity within the canopy mainly increased the supply of carbon precursors to the phenylpropanoid/flavonoid pathway, resulting in increased levels of phenolic compounds in the exocarp, while in seeds, light mostly influenced compounds related to carbon storage and seed development. In addition, our work provides new insights into the influence of abiotic stress mitigation strategies on the composition of exocarps and seeds, which are both important tissues for the quality of grape-derived products.

Gene Replacement in Arabidopsis Reveals Manganese Transport as an Ancient Feature of Human, Plant and Cyanobacterial UPF0016 Proteins

The protein family 0016 (UPF0016) is conserved through evolution, and the few members characterized share a function in Mn²⁺ transport. So far, little is known about the history of these proteins in Eukaryotes. In Arabidopsis thaliana five such proteins, comprising four different subcellular localizations including chloroplasts, have been described, whereas non-photosynthetic Eukaryotes have only one. We used a phylogenetic approach to classify the eukaryotic proteins into two subgroups and performed gene-replacement studies to investigate UPF0016 genes of various origins. Replaceability can be scored readily in the Arabidopsis UPF0016 transporter mutant pam71, which exhibits a functional deficiency in photosystem II. The N-terminal region of the Arabidopsis PAM71 was used to direct selected proteins to chloroplast membranes. Transgenic pam71 lines overexpressing the closest plant homolog (CMT1), human TMEM165 or cyanobacterial MNX successfully restored photosystem II efficiency, manganese binding to photosystem II complexes and consequently plant growth rate and biomass production. Thus AtCMT1, HsTMEM165, and SynMNX can operate in the thylakoid membrane and substitute for PAM71 in a non-native environment, indicating that the manganese transport function of UPF0016 proteins is an ancient feature of the family. We propose that the two chloroplast-localized UPF0016 proteins, CMT1 and PAM71, in plants originated from the cyanobacterial endosymbiont that gave rise to the organelle.

Organelles-nucleus-plasmodesmata signaling (ONPS): an update on its roles in plant physiology, metabolism and stress responses

Plasmodesmata allow movement of metabolites and signaling molecules between plant cells and are, therefore, critical players in plant development and physiology, and in responding to environmental signals and stresses. There is emerging evidence that plasmodesmata are controlled by signaling originating from other organelles, primarily the chloroplasts and mitochondria. These signals act in the nucleus to alter expression of genetic pathways that control both trafficking via plasmodesmata and the plasmodesmatal pores themselves. This control circuit was dubbed organelle-nucleus-plasmodesmata signaling (ONPS). Here we discuss how ONPS arose during plant evolution and highlight the discovery of an ONPS-like module for regulating stomata. We also consider recent findings that illuminate details of the ONPS circuit and its roles in plant physiology, metabolism, and defense.

Engineering of a functional γ-tocopherol transfer protein

α-tocopherol transfer protein (TTP) was previously reported to self-aggregate into 24-meric spheres (α-TTP_S) and to possess transcytotic potency across mono-layers of human umbilical vein endothelial cells (HUVECs). In this work, we describe the characterisation of a functional TTP variant with its vitamer selectivity shifted towards γ-tocopherol. The shift was obtained by introducing an alanine to leucine substitution into the substrate-binding pocket at position 156 through site directed mutagenesis. We report here the X-ray crystal structure of the γ-tocopherol specific particle (γ-TTP_S) at 2.24 Å resolution. γ-TTP_S features full functionality compared to its α-tocopherol specific parent including self-aggregation potency and transcytotic activity in trans-well experiments using primary HUVEC cells. The impact of the A156L mutation on TTP function is quantified in vitro by measuring the affinity towards γ-tocopherol through micro-differential scanning calorimetry and by determining its ligand-transfer activity. Finally, cell culture experiments using adherently grown HUVEC cells indicate that the protomers of γ-TTP, in contrast to α-TTP, do not counteract cytokine-mediated inflammation at a transcriptional level. Our results suggest that the A156L substitution in TTP is fully functional and has the potential to pave the way for further experiments towards the understanding of α-tocopherol homeostasis in humans.

Genome-wide association analysis of natural variation in seed tocochromanols of barley

Tocochromanols (tocols for short), commonly called Vitamin E, are lipid-soluble plant antioxidants vital for regulating lipid peroxidation in chloroplasts and seeds. Barley (Hordeum vulgare L.) seeds contain all eight different isoforms of tocols; however, the extent of natural variation in their composition and their underlying genetic basis is not known. Tocol levels in barley seeds were quantified in diverse H. vulgare panels comprising 297 wild lines from a diversity panel and 160 cultivated spring-type accessions from the mini-core panel representing the genetic diversity of the USDA barley germplasm collection. Significant differences were observed in the concentration of tocols between the two panels. To identify the genes associated with tocols, genome-wide association analysis was conducted with single nucleotide polymorphisms (SNPs) from Illumina arrays for the mini-core panel and genotyping-by-sequencing for the wild barley panel. Forty unique SNPs in the wild barley and 27 SNPs in the mini-core panel were significantly associated with various tocols. Marker-trait associations (MTAs) were identified on chromosomes 1, 6, and 7 for key genes in the tocol biosynthesis pathway, which have also been reported in other studies. Several novel MTAs were identified on chromosomes 2, 3, 4 and 5 and were found to be in proximity to genes involved in the generation of precursor metabolites required for tocol biosynthesis. This study provides a valuable resource for barley breeding programs targeting specific isoforms of seed tocols and for investigating the physiological roles of these metabolites in seed longevity, dormancy, and germination.

α-Tocopherol Foliar Spray and Translocation Mediates Growth, Photosynthetic Pigments, Nutrient Uptake, and Oxidative Defense in Maize (Zea mays L.) under Drought Stress

A pot experiment was conducted to assess the induction of drought tolerance in maize by foliar-applied α-tocopherol at early growth stage. Experiment was comprised two maize cultivars (Agaiti-2002 and EV-1098), two water stress levels (70% and 100% field capacity), and two α-tocopherol levels (0 mmol and 50 mmol) as foliar spray. Experiment was arranged in a completely randomized design in factorial arrangement with three replications of each treatment. α-tocopherol was applied foliary at the early vegetative stage. Water stress reduced the growth of maize plants with an increase in lipid peroxidation in both maize cultivars. Contents of non-enzymatic antioxidants and activities of antioxidant enzymes increased in studied plant parts under drought, while the nutrient uptake was decreased. Foliary-applied α-tocopherol improved the growth of both maize cultivars, associated with improvements in photosynthetic pigment, water relations, antioxidative mechanism, and better nutrient acquisition in root and shoot along with tocopherol contents and a decrease in lipid peroxidation. Furthermore, the increase of tocopherol levels in roots after α-Toc foliar application confers its basipetal translocation. In conclusion, the findings confer the role of foliar-applied α-tocopherol in the induction of drought tolerance of maize associated with tissue specific improvements in antioxidative defense mechanism through its translocation.

Effect of soil temperature during seed filling period on oleic/linoleic ratio, tocopherols and sugar contents in peanut kernels

The relationship of chemical quality of peanut seed with the soil temperature (ST) has received little attention. The aim of this work was to determine the effects of ST in the seed growth environment, during the seed filling period, on the oleic/linoleic acid (O/L) ratio, alpha, beta, gamma, delta tocopherols and the sum of them (TT), fructose, glucose and sucrose and the sum of them (FGS), contents in peanut kernels. Field experiments included cultivars (Florman and ASEM), water regimes (irrigated and water stress), sowing dates and alteration of ST. The response of O/L ratio to ST fitted a linear model, where the O/L ratio increased while ST increased. Mean O/L ratios were 1.31 for ASEM and 1.20 for Florman. The TT mean concentration was similar for both genotypes (478 ppm). A positive association between α-tocopherol (the main source of vitamin E) and ST, and a negative association between δ and α tocopherols were detected. The responses of FGS and sucrose to ST fitted linear models, where increments in ST showed decreases in FGS and sucrose concentrations. However, the decrease rates of FGS and sucrose in ASEM were three times lower than in Florman. The results showed that ST affected the chemical composition of peanut kernels, which mainly determines the shelf life and flavor of both genotypes differentially.

The metabolic profile of Asinara (albino) and Sardo donkeys (pigmented) (Equus asinus L., 1758) points to unequivocal breed assignment of individuals

This study pointed to explore if variations in circulating levels of metabolites in the blood stream of no. 25 feral donkeys occur in view of the different coat color between specimens of Asinara (albino, no. 8) vs. Sardo (dun-grey, no. 17) breed. All individuals involved in this investigation are living in the nature, at Mediterranean latitudes and roam in the same areas all over the National Park of Capo Caccia, where they feed on spontaneous vegetation sources. The study was conducted during the positive photoperiod of the boreal hemisphere (peak in the month of June, 2019) to maximize the effect of exposure to the natural sun radiation and thus elicit the coping ability of albino (Asinara) in comparison with pigmented donkeys (Sardo). The biochemical profile of all donkeys was used in a Discriminant Analysis (DA) to explore if circulating levels of metabolites could point to metabolic markers for breed assignment of individuals following a canonical discriminant analysis (CANDISC). The biochemical investigation included also the determination of the circulating Vitamin E (alpha tocopherol, α-TOH), as an essential biologically active compound involved in antioxidant mechanisms, and its respective status (circulating α-TOH to total triglycerides and total cholesterol ratio). In the CANDISC, the distance between the two breeds was not significant. However, it pointed to different metabolites (UREA, total protein, total triglycerides, Zn) capable of describing biochemical patterns on each respective breed (Asinara vs. Sardo). The multivariate analysis DA carried out using 22 metabolites correctly assigned individuals to the two breeds in the 100% of cases. In view of such metabolic background, circulating α-TOH found in the bloodstream of Asinara vs. Sardo donkeys under free grazing conditions turned out to reach similar values (2.114 vs. 1.872 µg/ml, respectively, p = 0.676). It is worth noting that significant differences were observed as to circulating lactate dehydrogenase (LDH, p = 0.022) levels, in association with increased creatine phosphokinase (CPK, p = 0.076), both above the upper limit of the physiological range reported in other donkey breeds, and found in the totality of Asinara (albino) donkeys solely, still apparently clinically healthy.

Interaction Between Induced and Natural Variation at oil yellow1 Delays Reproductive Maturity in Maize

We previously demonstrated that maize (Zea mays) locus very oil yellow1 (vey1) encodes a putative cis-regulatory expression polymorphism at the magnesium chelatase subunit I gene (aka oil yellow1) that strongly modifies the chlorophyll content of the semi-dominant Oy1-N1989 mutants. The vey1 allele of Mo17 inbred line reduces chlorophyll content in the mutants leading to reduced photosynthetic output. Oy1-N1989 mutants in B73 reached reproductive maturity four days later than wild-type siblings. Enhancement of Oy1-N1989 by the Mo17 allele at the vey1 QTL delayed maturity further, resulting in detection of a flowering time QTL in two bi-parental mapping populations crossed to Oy1-N1989. The near isogenic lines of B73 harboring the vey1 allele from Mo17 delayed flowering of Oy1-N1989 mutants by twelve days. Just as previously observed for chlorophyll content, vey1 had no effect on reproductive maturity in the absence of the Oy1-N1989 allele. Loss of chlorophyll biosynthesis in Oy1-N1989 mutants and enhancement by vey1 reduced CO₂ assimilation. We attempted to separate the effects of photosynthesis on the induction of flowering from a possible impact of chlorophyll metabolites and retrograde signaling by manually reducing leaf area. Removal of leaves, independent of the Oy1-N1989 mutant, delayed flowering but surprisingly reduced chlorophyll contents of emerging leaves. Thus, defoliation did not completely separate the identity of the signal(s) that regulates flowering time from changes in chlorophyll content in the foliage. These findings illustrate the necessity to explore the linkage between metabolism and the mechanisms that connect it to flowering time regulation.

Indigenous Tocopherol Improves Tolerance of Oilseed Rape to Cadmium Stress

Two oilseed rape genotypes (Jiu-Er-13XI and Zheyou-50), differing in seed oil content, were subjected to cadmium (Cd) stress in hydroponic experiment. Genotypic differences were observed in terms of tolerance to Cd exposure. Cd treatment negatively affected both genotypes, but the effects were more devastating in Jiu-Er-13XI (low seed oil content) than in Zheyou-50 (high seed oil content). Jiu-Er-13XI accumulated more reactive oxygen species (ROS), which destroyed chloroplast structure and decreased photosynthetic pigments, than Zheyou-50. Total fatty acids, especially 18:2 and 18:3, severely decreased as suggested by increase in MDA content. Roots and shoots of Jiu-Er-13XI plants accumulated more Cd content, while less amount of tocopherol (Toc) was observed under Cd stress, than Zheyou-50. Conversely, Zheyou-50 was less affected by Cd stress than its counterpart. It accumulated comparatively less amount of Cd in roots and shoots, along with reduced accumulation of malondialdehyde (MDA) and ROS under Cd stress, than Jiu-Er-13XI. Further, the level of Toc, especially α-Tocopherol, was much higher in Zheyou-50 than in Jiu-Er-13XI, which was also supported by high expression of Toc biosynthesis genes in Zheyou-50 during early hours. Toc not only restricted the absorption of Cd by roots and its translocation to shoot but also scavenged the ROS generated during oxidative stresses. The low level of MDA shows that polyunsaturated fatty acids in chloroplast membranes remained intact. In the present study the tolerance of Zheyou-50 to Cd stress, over Jiu-Er-13XI, is attributed to the activities of Toc. This study shows that plants with high seed oil content are tolerant to Cd stress due to high production of Toc.

Vitamin E Supplementation and Mitochondria in Experimental and Functional Hyperthyroidism: A Mini-Review

Mitochondria are both the main sites of production and the main target of reactive oxygen species (ROS). This can lead to mitochondrial dysfunction with harmful consequences for the cells and the whole organism, resulting in metabolic and neurodegenerative disorders such as type 2 diabetes, obesity, dementia, and aging. To protect themselves from ROS, mitochondria are equipped with an efficient antioxidant system, which includes low-molecular-mass molecules and enzymes able to scavenge ROS or repair the oxidative damage. In the mitochondrial membranes, a major role is played by the lipid-soluble antioxidant vitamin E, which reacts with the peroxyl radicals faster than the molecules of polyunsaturated fatty acids, and in doing so, protects membranes from excessive oxidative damage. In the present review, we summarize the available data concerning the capacity of vitamin E supplementation to protect mitochondria from oxidative damage in hyperthyroidism, a condition that leads to increased mitochondrial ROS production and oxidative damage. Vitamin E supplementation to hyperthyroid animals limits the thyroid hormone-induced increases in mitochondrial ROS and oxidative damage. Moreover, it prevents the reduction of the high functionality components of the mitochondrial population induced by hyperthyroidism, thus preserving cell function.

Comparative genomics of Sphingopyxis spp. unravelled functional attributes

Members of genus Sphingopyxis are known to thrive in diverse environments. Genomes of 21 Sphingopyxis strains were selected. Phylogenetic analysis was performed using GGDC, AAI and core-SNP showed agreement at sub-species level. Based on our results, we propose that both S. baekryungensis DSM16222 and Sphingopyxis sp. LPB0140 strains should not be included under genus Sphingopyxis. Core-analysis revealed, 1422 genes were shared which included essential pathways and genes for conferring adaptation against stress environment. Polyhydroxybutyrate degradation, anaerobic respiration, type IV secretion were notable abundant pathways and exopolysaccharide, hyaluronic acid production and toxin-antitoxin system were differentially present families. Interestingly, genome of S. witflariensis DSM14551, Sphingopyxis sp. MG and Sphingopyxis sp. FD7 provided a hint of probable pathogenic abilities. Protein-Protein Interactome depicted that membrane proteins and stress response has close integration with core-proteins while aromatic compounds degradation and virulence ability formed a separate network. Thus, these should be considered as strain specific attributes.

A Role for Tocopherol Biosynthesis in Arabidopsis Basal Immunity to Bacterial Infection

Tocopherols are lipid-soluble antioxidants synthesized in plastids of plants and other photosynthetic organisms. The four known tocopherols, α-, β-, γ-, and δ-tocopherol, differ in number and position of methyl groups on their chromanol head group. In unstressed Arabidopsis (Arabidopsis thaliana) leaves, α-tocopherol constitutes the main tocopherol form, whereas seeds predominantly contain γ-tocopherol. Here, we show that inoculation of Arabidopsis leaves with the bacterial pathogen Pseudomonas syringae induces the expression of genes involved in early steps of tocopherol biosynthesis and triggers strong accumulation of γ-tocopherol, moderate production of δ-tocopherol, and generation of the benzoquinol precursors of tocopherols. The pathogen-inducible biosynthesis of tocopherols is promoted by the immune regulators ENHANCED DISEASE SUSCEPTIBILITY1 and PHYTOALEXIN-DEFICIENT4. In addition, tocopherols accumulate in response to bacterial flagellin and reactive oxygen species. By quantifying tocopherol forms in inoculated wild-type plants and biosynthetic pathway mutants, we provide biochemical insights into the pathogen-inducible tocopherol pathway. Notably, vitamin E deficient2 (vte2) mutant plants, which are compromised in both tocopherol and benzoquinol precursor accumulation, exhibit increased susceptibility toward compatible P. syringae and possess heightened levels of markers of lipid peroxidation after bacterial infection. The deficiency of triunsaturated fatty acids in vte2-1 fatty acid desaturase3-2 (fad3-2) fad7-2 fad8 quadruple mutants prevents increased lipid peroxidation in the vte2 background and restores pathogen resistance to wild-type levels. Therefore, the tocopherol biosynthetic pathway positively influences salicylic acid accumulation and guarantees effective basal resistance of Arabidopsis against compatible P. syringae, possibly by protecting leaves from the pathogen-induced oxidation of trienoic fatty acid-containing lipids.

Fingerprinting cities: differentiating subway microbiome functionality

BACKGROUND

Accumulating evidence suggests that the human microbiome impacts individual and public health. City subway systems are human-dense environments, where passengers often exchange microbes. The MetaSUB project participants collected samples from subway surfaces in different cities and performed metagenomic sequencing. Previous studies focused on taxonomic composition of these microbiomes and no explicit functional analysis had been done till now.

RESULTS

As a part of the 2018 CAMDA challenge, we functionally profiled the available ~ 400 subway metagenomes and built predictor for city origin. In cross-validation, our model reached 81% accuracy when only the top-ranked city assignment was considered and 95% accuracy if the second city was taken into account as well. Notably, this performance was only achievable if the similarity of distribution of cities in the training and testing sets was similar. To assure that our methods are applicable without such biased assumptions we balanced our training data to account for all represented cities equally well. After balancing, the performance of our method was slightly lower (76/94%, respectively, for one or two top ranked cities), but still consistently high. Here we attained an added benefit of independence of training set city representation. In testing, our unbalanced model thus reached (an over-estimated) performance of 90/97%, while our balanced model was at a more reliable 63/90% accuracy. While, by definition of our model, we were not able to predict the microbiome origins previously unseen, our balanced model correctly judged them to be NOT-from-training-cities over 80% of the time. Our function-based outlook on microbiomes also allowed us to note similarities between both regionally close and far-away cities. Curiously, we identified the depletion in mycobacterial functions as a signature of cities in New Zealand, while photosynthesis related functions fingerprinted New York, Porto and Tokyo.

CONCLUSIONS

We demonstrated the power of our high-speed function annotation method, mi-faser, by analysing ~ 400 shotgun metagenomes in 2 days, with the results recapitulating functional signals of different city subway microbiomes. We also showed the importance of balanced data in avoiding over-estimated performance. Our results revealed similarities between both geographically close (Ofa and Ilorin) and distant (Boston and Porto, Lisbon and New York) city subway microbiomes. The photosynthesis related functional signatures of NYC were previously unseen in taxonomy studies, highlighting the strength of functional analysis.

Maize Carbohydrate Partitioning Defective33 Encodes an MCTP Protein and Functions in Sucrose Export from Leaves

To sustain plant growth, development, and crop yield, sucrose must be transported from leaves to distant parts of the plant, such as seeds and roots. To identify genes that regulate sucrose accumulation and transport in maize (Zea mays), we isolated carbohydrate partitioning defective33 (cpd33), a recessive mutant that accumulated excess starch and soluble sugars in mature leaves. The cpd33 mutants also exhibited chlorosis in the leaf blades, greatly diminished plant growth, and reduced fertility. Cpd33 encodes a protein containing multiple C2 domains and transmembrane regions. Subcellular localization experiments showed the CPD33 protein localized to plasmodesmata (PD), the plasma membrane, and the endoplasmic reticulum. We also found that a loss-of-function mutant of the CPD33 homolog in Arabidopsis, QUIRKY, had a similar carbohydrate hyperaccumulation phenotype. Radioactively labeled sucrose transport assays showed that sucrose export was significantly lower in cpd33 mutant leaves relative to wild-type leaves. However, PD transport in the adaxial-abaxial direction was unaffected in cpd33 mutant leaves. Intriguingly, transmission electron microscopy revealed fewer PD at the companion cell-sieve element interface in mutant phloem tissue, providing a possible explanation for the reduced sucrose export in mutant leaves. Collectively, our results suggest that CPD33 functions to promote symplastic transport into sieve elements.

Deciphering the genetic basis for vitamin E accumulation in leaves and grains of different barley accessions

Tocopherols and tocotrienols, commonly referred to as vitamin E, are essential compounds in food and feed. Due to their lipophilic nature they protect biomembranes by preventing the propagation of lipid-peroxidation especially during oxidative stress. Since their synthesis is restricted to photosynthetic organisms, plant-derived products are the major source of natural vitamin E. In the present study the genetic basis for high vitamin E accumulation in leaves and grains of different barley (Hordeum vulgare L.) accessions was uncovered. A genome wide association study (GWAS) allowed the identification of two genes located on chromosome 7H, homogentisate phytyltransferase (HPT-7H) and homogentisate geranylgeranyltransferase (HGGT) that code for key enzymes controlling the accumulation of tocopherols in leaves and tocotrienols in grains, respectively. Transcript profiling showed a correlation between HPT-7H expression and vitamin E content in leaves. Allele sequencing allowed to decipher the allelic variation of HPT-7H and HGGT genes corresponding to high and low vitamin E contents in the respective tissues. Using the obtained sequence information molecular markers have been developed which can be used to assist smart breeding of high vitamin E barley varieties. This will facilitate the selection of genotypes more tolerant to oxidative stress and producing high-quality grains.

Full-Length Transcriptome Analysis of the Genes Involved in Tocopherol Biosynthesis in Torreya grandis

The seeds of Torreya grandis (Cephalotaxaceae) are rich in tocopherols, which are essential components of the human diet as a result of their function in scavenging reactive oxygen and free radicals. Different T. grandis cultivars (10 cultivars selected in this study were researched, and their information is shown in Table S1 of the Supporting Information) vary enormously in their tocopherol contents (0.28-11.98 mg/100 g). However, little is known about the molecular basis and regulatory mechanisms of tocopherol biosynthesis in T. grandis kernels. Here, we applied single-molecule real-time (SMRT) sequencing to T. grandis (X08 cultivar) for the first time and obtained a total of 97 211 full-length transcripts. We proposed the biosynthetic pathway of tocopherol and identified eight full-length transcripts encoding enzymes potentially involved in tocopherol biosynthesis in T. grandis. The results of the correlation analysis between the tocopherol content and gene expression level in the 10 selected cultivars and different kernel developmental stages of the X08 cultivar suggested that homogentisate phytyltransferase coding gene ( TgVTE2b) and γ-tocopherol methyltransferase coding gene ( TgVTE4) may be key players in tocopherol accumulation in the kernels of T. grandis. Subcellular localization assays showed that both TgVTE2b and TgVTE4 were localized to the chloroplast. We also identified candidate regulatory genes similar to WRI1 and DGAT1 in Arabidopsis that may be involved in the regulation of tocopherol biosynthesis. Our findings provide valuable genetic information for T. grandis using full-length transcriptomic analysis, elucidating the candidate genes and key regulatory genes involved in tocopherol biosynthesis. This information will be critical for further molecular-assisted screening and breeding of T. grandis genotypes with high tocopherol contents.

Network-based microsynteny analysis identifies major differences and genomic outliers in mammalian and angiosperm genomes

Studying the organization of genes within genomes across broad evolutionary timescales can advance our understanding of the evolution of traits and clades. We have used a network approach to investigate genome dynamics of mammals and angiosperms. In general, genome organization and gene microcollinearity is much more conserved in mammals than in flowering plants. We then identified the genomic outliers or “rebel genes,” within each clade. Genes that have moved are unusual for mammals, whereas highly conserved single-copy genes are exceptional for plants. How conservation and changes in synteny or fundamental differences in genome organization have contributed to the evolution of lineages could be a new scientific frontier.

A comprehensive analysis of relative gene order, or microsynteny, can provide valuable information for understanding the evolutionary history of genes and genomes, and ultimately traits and species, across broad phylogenetic groups and divergence times. We have used our network-based phylogenomic synteny analysis pipeline to first analyze the overall patterns and major differences between 87 mammalian and 107 angiosperm genomes. These two important groups have both evolved and radiated over the last ∼170 MYR. Secondly, we identified the genomic outliers or “rebel genes” within each clade. We theorize that rebel genes potentially have influenced trait and lineage evolution. Microsynteny networks use genes as nodes and syntenic relationships between genes as edges. Networks were decomposed into clusters using the Infomap algorithm, followed by phylogenomic copy-number profiling of each cluster. The differences in syntenic properties of all annotated gene families, including BUSCO genes, between the two clades are striking: most genes are single copy and syntenic across mammalian genomes, whereas most genes are multicopy and/or have lineage-specific distributions for angiosperms. We propose microsynteny scores as an alternative and complementary metric to BUSCO for assessing genome assemblies. We further found that the rebel genes are different between the two groups: lineage-specific gene transpositions are unusual in mammals, whereas single-copy highly syntenic genes are rare for flowering plants. We illustrate several examples of mammalian transpositions, such as brain-development genes in primates, and syntenic conservation across angiosperms, such as single-copy genes related to photosynthesis. Future experimental work can test if these are indeed rebels with a cause.

From in planta Function to Vitamin-Rich Food Crops: The ACE of Biofortification

Humans are highly dependent on plants to reach their dietary requirements, as plant products contribute both to energy and essential nutrients. For many decades, plant breeders have been able to gradually increase yields of several staple crops, thereby alleviating nutritional needs with varying degrees of success. However, many staple crops such as rice, wheat and corn, although delivering sufficient calories, fail to satisfy micronutrient demands, causing the so called 'hidden hunger.' Biofortification, the process of augmenting nutritional quality of food through the use of agricultural methodologies, is a pivotal asset in the fight against micronutrient malnutrition, mainly due to vitamin and mineral deficiencies. Several technical advances have led to recent breakthroughs. Nutritional genomics has come to fruition based on marker-assisted breeding enabling rapid identification of micronutrient related quantitative trait loci (QTL) in the germplasm of interest. As a complement to these breeding techniques, metabolic engineering approaches, relying on a continuously growing fundamental knowledge of plant metabolism, are able to overcome some of the inevitable pitfalls of breeding. Alteration of micronutrient levels does also require fundamental knowledge about their role and influence on plant growth and development. This review focuses on our knowledge about provitamin A (beta-carotene), vitamin C (ascorbate) and the vitamin E group (tocochromanols). We begin by providing an overview of the functions of these vitamins in planta, followed by highlighting some of the achievements in the nutritional enhancement of food crops via conventional breeding and genetic modification, concluding with an evaluation of the need for such biofortification interventions. The review further elaborates on the vast potential of creating nutritionally enhanced crops through multi-pathway engineering and the synergistic potential of conventional breeding in combination with genetic engineering, including the impact of novel genome editing technologies.

A role for β,β-xanthophylls in Arabidopsis UV-B photoprotection

Plastidial isoprenoids, such as carotenoids and tocopherols, are important anti-oxidant metabolites synthesized in plastids from precursors generated by the methylerythritol 4-phosphate (MEP) pathway. In this study, we found that irradiation of Arabidopsis thaliana plants with UV-B caused a strong increase in the accumulation of the photoprotective xanthophyll zeaxanthin but also resulted in slightly higher levels of γ-tocopherol. Plants deficient in the MEP enzymes 1-deoxy-D-xylulose 5-phosphate synthase and 1-hydroxy-2-methyl-2-butenyl 4-diphosphate synthase showed a general reduction in both carotenoids and tocopherols and this was associated with increased DNA damage and decreased photosynthesis after exposure to UV-B. Genetic blockage of tocopherol biosynthesis did not affect DNA damage accumulation. In contrast, lut2 mutants that accumulate β,β-xanthophylls showed decreased DNA damage when irradiated with UV-B. Analysis of aba2 mutants showed that UV-B protection was not mediated by ABA (a hormone derived from β,β-xanthophylls). Plants accumulating β,β-xanthophylls also showed decreased oxidative damage and increased expression of DNA-repair enzymes, suggesting that this may be a mechanism for these plants to decrease DNA damage. In addition, in vitro experiments also provided evidence that β,β-xanthophylls can directly protect against DNA damage by absorbing radiation. Together, our results suggest that xanthophyll-cycle carotenoids that protect against excess illumination may also contribute to protection against UV-B.

Effects of Foliar Redox Status on Leaf Vascular Organization Suggest Avenues for Cooptimization of Photosynthesis and Heat Tolerance

The interaction of heat stress with internal signaling networks was investigated through Arabidopsisthaliana mutants that were deficient in either tocopherols (vte1 mutant) or non-photochemical fluorescence quenching (NPQ; npq1, npq4, and npq1 npq4 mutants). Leaves of both vte1 and npq1 npq4 mutants that developed at a high temperature exhibited a significantly different leaf vascular organization compared to wild-type Col-0. Both mutants had significantly smaller water conduits (tracheary elements) of the xylem, but the total apparent foliar water-transport capacity and intrinsic photosynthetic capacity were similarly high in mutants and wild-type Col-0. This was accomplished through a combination of more numerous (albeit narrower) water conduits per vein, and a significantly greater vein density in both mutants relative to wild-type Col-0. The similarity of the phenotypes of tocopherol-deficient and NPQ-deficient mutants suggests that leaf vasculature organization is modulated by the foliar redox state. These results are evaluated in the context of interactions between redox-signaling pathways and other key regulators of plant acclimation to growth temperature, such as the C-repeat binding factor (CBF) transcription factors, several of which were upregulated in the antioxidant-deficient mutants. Possibilities for the future manipulation of the interaction between CBF and redox-signaling networks for the purpose of cooptimizing plant productivity and plant tolerance to extreme temperatures are discussed.

Maize Carbohydrate partitioning defective1 impacts carbohydrate distribution, callose accumulation, and phloem function

Plants synthesize carbohydrates in photosynthetic tissues, with the majority of plants transporting sucrose to non-photosynthetic tissues to sustain growth and development. While the anatomical, biochemical, and physiological processes regulating sucrose long-distance transport are well characterized, little is known concerning the genes controlling whole-plant carbohydrate partitioning. To identify loci influencing carbon export from leaves, we screened mutagenized maize plants for phenotypes associated with reduced carbohydrate transport, including chlorosis and excessive starch and soluble sugars in leaves. Carbohydrate partitioning defective1 (Cpd1) was identified as a semi-dominant mutant exhibiting these phenotypes. Phloem transport experiments suggested that the hyperaccumulation of starch and soluble sugars in the Cpd1/+ mutant leaves was due to inhibited sucrose export. Interestingly, ectopic callose deposits were observed in the phloem of mutant leaves, and probably underlie the decreased transport. In addition to the carbohydrate hyperaccumulation phenotype, Cpd1/+ mutants overaccumulate benzoxazinoid defense compounds and exhibit increased tolerance when attacked by aphids. However, double mutant studies between Cpd1/+ and benzoxazinoid-less plants indicate that the ectopic callose and carbon hyperaccumulation are independent of benzoxazinoid production. Based on the formation of callose occlusions in the developing phloem, we hypothesize that the cpd1 gene functions early in phloem development, thereby impacting whole-plant carbohydrate partitioning.

Rice tocopherol deficiency 1 encodes a homogentisate phytyltransferase essential for tocopherol biosynthesis and plant development in rice

RTD1 encodes a homogentisate phytyltransferase catalyzing a key step in rice tocopherol biosynthesis, confers cold tolerance and regulates rice development by affecting the accumulation of DELLA protein SLENDER RICE1. Tocopherols are one of the most important lipid-soluble antioxidants having indispensable roles in living organisms. The physiological functions of tocopherols have been comprehensively characterized in animals and artificial membranes. However, genetic and molecular functions of tocopherols in plants are less understood. This study aimed to isolate a tocopherol-deficient mutant rtd1 in rice. The rtd1 mutant showed overall growth retardation throughout the growth period. Most of the agronomic traits were impaired in rtd1. Map-based cloning revealed that the RTD1 gene encoded a homogentisate phytyltransferase, a key enzyme catalyzing the committed step in tocopherol biosynthesis. RTD1 was preferentially expressed in green leafy tissues, and the protein was located in chloroplasts. Cold tolerance was found to be reduced in rtd1. The cold-related C-repeat-binding factor (CBF)/dehydration-responsive element-binding protein 1 (DREB1) genes were significantly upregulated in rtd1 under natural growth conditions. Moreover, rtd1 exhibited a reduced response to gibberellin (GA).The transcript and protein levels of DELLA protein-coding gene SLENDER RICE 1 (SLR1) in rice was increased in rtd1. However, the GA content was not changed, suggesting a transcriptional, not posttranslational, regulation of SLR1. These findings implied that tocopherols play important roles in regulating rice growth and development.

Maize w3 disrupts homogentisate solanesyl transferase (ZmHst) and reveals a plastoquinone-9 independent path for phytoene desaturation and tocopherol accumulation in kernels

Maize white seedling 3 (w3) has been used to study carotenoid deficiency for almost 100 years, although the molecular basis of the mutation has remained unknown. Here we show that the w3 phenotype is caused by disruption of the maize gene for homogentisate solanesyl transferase (HST), which catalyzes the first and committed step in plastoquinone-9 (PQ-9) biosynthesis in the plastid. The resulting PQ-9 deficiency prohibits photosynthetic electron transfer and eliminates PQ-9 as an oxidant in the enzymatic desaturation of phytoene during carotenoid synthesis. As a result, light-grown w3 seedlings are albino, deficient in colored carotenoids and accumulate high levels of phytoene. However, despite the absence of PQ-9 for phytoene desaturation, dark-grown w3 seedlings can produce abscisic acid (ABA) and homozygous w3 kernels accumulate sufficient carotenoids to generate ABA needed for seed maturation. The presence of ABA and low levels of carotenoids in w3 nulls indicates that phytoene desaturase is able to use an alternate oxidant cofactor, albeit less efficiently than PQ-9. The observation that tocopherols and tocotrienols are modestly affected in w3 embryos and unaffected in w3 endosperm indicates that, unlike leaves, grain tissues deficient in PQ-9 are not subject to severe photo-oxidative stress. In addition to identifying the molecular basis for the maize w3 mutant, we: (1) show that low levels of phytoene desaturation can occur in w3 seedlings in the absence of PQ-9; and (2) demonstrate that PQ-9 and carotenoids are not required for vitamin E accumulation.

Identification of OsGGR2, a second geranylgeranyl reductase involved in α-tocopherol synthesis in rice

Tocopherol (Toc) and tocotrienol (T3) are abundant in rice bran. Geranylgeranyl reductase (GGR) is an essential enzyme for Toc production that catalyzes the reduction of geranylgeranyl pyrophosphate and geranylgeranyl-chlorophyll. However, we found that a rice mutant line with inactivated Os02g0744900 (OsGGR1/LYL1/OsChl P) gene produces Toc, suggesting that rice plants may carry another enzyme with GGR activity. Using an RNA-mediated interference technique, we demonstrated that the Os01g0265000 ("OsGGR2") gene product has GGR activity. This result supports the existence of two GGR genes (OsGGR1 and OsGGR2) in rice, in contrast to Arabidopsis thaliana (thale cress) and cyanobacterium Synechocystis that each have only one GGR gene. We also produced rice callus with inactivated OsGGR1 and OsGGR2 that produced T3 but not Toc. Such rice callus could be used as a resource for production of pure T3 for nutraceutical applications.

Molecular cloning, heterologous expression and functional characterization of gamma tocopherol methyl transferase (γ-TMT) from Glycine max

γ-Tocopherol methyltransferase (γ-TMT) (EC 2.1.1.95) is the last enzyme in the tocopherol biosynthetic pathway and it catalyzes the conversion of γ-tocopherol into α-tocopherol, the nutritionally significant and most bioactive form of vitamin E. Although the γ-TMT gene has been successfully overexpressed in many crops to enhance their α-tocopherol content but still only few attempts have been made to uncover its structural, functional and regulation aspects at protein level. In this study, we have cloned the complete 909bp coding sequence of Glycine max γ-TMT (Gm γ-TMT) gene that encodes the corresponding protein comprising of 302 amino acid residues. The deduced Gm γ-TMT protein showed 74-87% sequence identity with other characterized plant γ-TMTs. Gm γ-TMT belongs to Class I Methyl Transferases that have a Rossmann-like fold which consists of a seven-stranded β sheet joined by α helices. Heterologous expression of Gm γ-TMT in pET29a expression vector under the control of bacteriophage T7 promoter produced a 37.9 kDa recombinant Gm γ-TMT protein with histidine hexamer tag at its C-terminus. The expression of recombinant Gm γ-TMT protein was confirmed by western blotting using anti-His antibody. The recombinant protein was purified by Ni2+-NTA column chromatography. The purified protein showed SAM dependent methyltransferase activity. The α-tocopherol produced in the in-vitro reaction catalyzed by the purified enzyme was detected using reverse phase HPLC. This study has laid the foundation to unveil the biochemical understanding of Gm γ-TMT enzyme which can be further explored by studying its kinetic behaviour, substrate specificity and its interaction with other biomolecules.

Recent Advances in our Understanding of Tocopherol Biosynthesis in Plants: An Overview of Key Genes, Functions, and Breeding of Vitamin E Improved Crops

Tocopherols, together with tocotrienols and plastochromanols belong to a group of lipophilic compounds also called tocochromanols or vitamin E. Considered to be one of the most powerful antioxidants, tocochromanols are solely synthesized by photosynthetic organisms including plants, algae, and cyanobacteria and, therefore, are an essential component in the human diet. Tocochromanols potent antioxidative properties are due to their ability to interact with polyunsaturated acyl groups and scavenge lipid peroxyl radicals and quench reactive oxygen species (ROS), thus protecting fatty acids from lipid peroxidation. In the plant model species Arabidopsis thaliana, the required genes for tocopherol biosynthesis and functional roles of tocopherols were elucidated in mutant and transgenic plants. Recent research efforts have led to new outcomes for the vitamin E biosynthetic and related pathways, and new possible alternatives for the biofortification of important crops have been suggested. Here, we review 30 years of research on tocopherols in model and crop species, with emphasis on the improvement of vitamin E content using transgenic approaches and classical breeding. We will discuss future prospects to further improve the nutritional value of our food.

Environmental plasticity of Pinot noir grapevine leaves: A trans-European study of morphological and biochemical changes along a 1,500-km latitudinal climatic gradient

A 2-year study explored metabolic and phenotypic plasticity of sun-acclimated Vitis vinifera cv. Pinot noir leaves collected from 12 locations across a 36.69-49.98°N latitudinal gradient. Leaf morphological and biochemical parameters were analysed in the context of meteorological parameters and the latitudinal gradient. We found that leaf fresh weight and area were negatively correlated with both global and ultraviolet (UV) radiation, cumulated global radiation being a stronger correlator. Cumulative UV radiation (sumUVR) was the strongest correlator with most leaf metabolites and pigments. Leaf UV-absorbing pigments, total antioxidant capacities, and phenolic compounds increased with increasing sumUVR, whereas total carotenoids and xanthophylls decreased. Despite of this reallocation of metabolic resources from carotenoids to phenolics, an increase in xanthophyll-cycle pigments (the sum of the amounts of three xanthophylls: violaxanthin, antheraxanthin, and zeaxanthin) with increasing sumUVR indicates active, dynamic protection for the photosynthetic apparatus. In addition, increased amounts of flavonoids (quercetin glycosides) and constitutive β-carotene and α-tocopherol pools provide antioxidant protection against reactive oxygen species. However, rather than a continuum of plant acclimation responses, principal component analysis indicates clusters of metabolic states across the explored 1,500-km-long latitudinal gradient. This study emphasizes the physiological component of plant responses to latitudinal gradients and reveals the physiological plasticity that may act to complement genetic adaptations.

Conserved Function of Fibrillin5 in the Plastoquinone-9 Biosynthetic Pathway in Arabidopsis and Rice

Plastoquinone-9 (PQ-9) is essential for plant growth and development. Recently, we found that fibrillin5 (FBN5), a plastid lipid binding protein, is an essential structural component of the PQ-9 biosynthetic pathway in Arabidopsis. To investigate the functional conservation of FBN5 in monocots and eudicots, we identified OsFBN5, the Arabidopsis FBN5 (AtFBN5) ortholog in rice (Oryza sativa). Homozygous Osfbn5-1 and Osfbn5-2 Tos17 insertion null mutants were smaller than wild type (WT) plants when grown on Murashige and Skoog (MS) medium and died quickly when transplanted to soil in a greenhouse. They accumulated significantly less PQ-9 than WT plants, whereas chlorophyll and carotenoid contents were only mildly affected. The reduced PQ-9 content of the mutants was consistent with their lower maximum photosynthetic efficiency, especially under high light. Overexpression of OsFBN5 complemented the seedling lethal phenotype of the Arabidopsis fbn5-1 mutant and restored PQ-9 and PC-8 (plastochromanol-8) to levels comparable to those in WT Arabidopsis plants. Protein interaction experiments in yeast and mesophyll cells confirmed that OsFBN5 interacts with the rice solanesyl diphosphate synthase OsSPS2 and also with Arabidopsis AtSPS1 and AtSPS2. Our data thus indicate that OsFBN5 is the functional equivalent of AtFBN5 and also suggest that the SPSs-FBN5 complex for synthesis of the solanesyl diphosphate tail in PQ-9 is well conserved in Arabidopsis and rice.

Overexpression of HvHGGT Enhances Tocotrienol Levels and Antioxidant Activity in Barley

Vitamin E is a potent lipid-soluble antioxidant and essential nutrient for human health. Tocotrienols are the major form of vitamin E in seeds of most monocots. It has been known that homogentisate geranylgeranyl transferase (HGGT) catalyzes the committed step of tocotrienol biosynthesis. In the present study, we generated transgenic barley overexpressing HvHGGT under endogenous D-Hordein promoter (proHor). Overexpression of HvHGGT increased seed size and seed weight in transgenic barley. Notably, total tocotrienol content increased by 10-15% in seeds of transgenic lines, due to the increased levels of δ-, β-, and γ-tocotrienol, but not α-tocotrienol. Total tocopherol content decreased by 14-18% in transgenic lines, compared to wild type. The antioxidant activity of seeds was determined by using 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), and lipid peroxidation assays. Compared to wild type, radical scavenging activity of seed extracts was enhanced by 17-18% in transgenic lines. Meanwhile, the lipid peroxidation level was decreased by about 20% in transgenic barley seeds. Taken together, overexpression of HvHGGT enhanced the tocotrienol levels and antioxidant capacity in barley seeds.

The Combined Use of Proteomics and Transcriptomics Reveals a Complex Secondary Metabolite Network in Peperomia obtusifolia

Peperomia obtusifolia, an ornamental plant from the Piperaceae family, accumulates a series of secondary metabolites with interesting biological properties. From a biosynthesis standpoint, this species produces several benzopyrans derived from orsellinic acid, which is a polyketide typically found in fungi. Additionally, the chiral benzopyrans were reported as racemic and/or as diastereomeric mixtures, which raises questions about the level of enzymatic control in the cyclization step for the formation of the 3,4-dihydro-2H-pyran moiety. Therefore, this article describes the use of shotgun proteomic and transcriptome studies as well as phytochemical profiling for the characterization of the main biosynthesis pathways active in P. obtusifolia. This combined approach resulted in the identification of a series of proteins involved in its secondary metabolism, including tocopherol cyclase and prenyltransferases. The activity of these enzymes was supported by the phytochemical profiling performed in different organs of P. obtusifolia. However, the polyketide synthases possibly involved in the production of orsellinic acid could not be identified, suggesting that orsellinic acid may be produced by endophytes intimately associated with the plant.

Light, temperature and tocopherol status influence foliar vascular anatomy and leaf function in Arabidopsis thaliana

This study addressed whether the winter annual Arabidopsis thaliana can adjust foliar phloem and xylem anatomy both differentially and in parallel. In plants acclimated to hot vs cool temperature, foliar minor vein xylem-to-phloem ratio was greater, whereas xylem and phloem responded concomitantly to growth light intensity. Across all growth conditions, xylem anatomy correlated with transpiration rate, while phloem anatomy correlated with photosynthetic capacity for two plant lines (wild-type Col-0 and tocopherol-deficient vte1 mutant) irrespective of tocopherol status. A high foliar vein density (VD) was associated with greater numbers and cross-sectional areas of both xylem and phloem cells per vein as well as higher rates of both photosynthesis and transpiration under high vs low light intensities. Under hot vs cool temperature, high foliar VD was associated with a higher xylem-to-phloem ratio and greater relative rates of transpiration to photosynthesis. Tocopherol status affected development of foliar vasculature as dependent on growth environment. The most notable impact of tocopherol deficiency was seen under hot growth temperature, where the vte1 mutant exhibited greater numbers of tracheary elements (TEs) per vein, a greater ratio of TEs to sieve elements, with smaller individual sizes of TEs, and resulting similar total areas of TEs per vein and transpiration rates compared with Col-0 wild-type. These findings illustrate the plasticity of foliar vascular anatomy acclimation to growth environment resulting from independent adjustments of the vasculature's components.

Sporobolus stapfianus: Insights into desiccation tolerance in the resurrection grasses from linking transcriptomics to metabolomics

BACKGROUND

Understanding the response of resurrection angiosperms to dehydration and rehydration is critical for deciphering the mechanisms of how plants cope with the rigors of water loss from their vegetative tissues. We have focused our studies on the C4 resurrection grass, Sporobolus stapfianus Gandoger, as a member of a group of important forage grasses.

METHODS

We have combined non-targeted metabolomics with transcriptomics, via a NimbleGen array platform, to develop an understanding of how gene expression and metabolite profiles can be linked to generate a more detailed mechanistic appreciation of the cellular response to both desiccation and rehydration.

RESULTS

The rehydration transcriptome and metabolome are primarily geared towards the rapid return of photosynthesis, energy metabolism, protein turnover, and protein synthesis during the rehydration phase. However, there are some metabolites associated with ROS protection that remain elevated during rehydration, most notably the tocopherols. The analysis of the dehydration transcriptome reveals a strong concordance between transcript abundance and the associated metabolite abundance reported earlier, but only in responses that are directly related to cellular protection during dehydration: carbohydrate metabolism and redox homeostasis. The transcriptome response also provides strong support for the involvement of cellular protection processes as exemplified by the increases in the abundance of transcripts encoding late embryogenesis abundant (LEA) proteins, anti-oxidant enzymes, early light-induced proteins (ELIP) proteins, and cell-wall modification enzymes. There is little concordance between transcript and metabolite abundance for processes such as amino acid metabolism that do not appear to contribute directly to cellular protection, but are nonetheless important for the desiccation tolerant phenotype of S. stapfianus.

CONCLUSIONS

The transcriptomes of both dehydration and rehydration offer insight into the complexity of the regulation of responses to these processes that involve complex signaling pathways and associated transcription factors. ABA appears to be important in the control of gene expression in both the latter stages of the dehydration and the early stages of rehydration. These findings add to the growing body of information detailing how plants tolerate and survive the severe cellular perturbations of dehydration, desiccation, and rehydration.

Enhanced plastochromanol-8 accumulation during reiterated drought in maize (Zea mays L.)

Plastochromanol-8 (PC-8) belongs to the group of tocochromanols, and together with tocopherols and carotenoids, might help protect photosystem II from photoinhibition during environmental stresses. Here, we aimed to unravel the time course evolution of PC-8 together with that of vitamin E compounds, in maize (Zea mays L.) plants exposed to reiterated drought. Measurements were performed in plants grown in a greenhouse subjected to two consecutive cycles of drought-recovery. PC-8 contents, which accounted for more than 25% of tocochromanols in maize leaves, increased progressively in response to reiterated drought stress. PC-8 contents paralleled with those of vitamin E, particularly α-tocopherol. Profiling of the stress-related phytohormones (ABA, jasmonic acid and salicylic acid) was consistent with a role of ABA in the regulation of PC-8 and vitamin E biosynthesis during drought stress. Results also suggest that PC-8 may help tocopherols prevent damage to the photosynthetic apparatus. A better knowledge of the ABA-dependent regulation of PC-8 may help us manipulate the contents of this important antioxidant in crops.

P-HYDROXYPHENYLPYRUVATE DIOXYGENASE from Medicago sativa is involved in vitamin E biosynthesis and abscisic acid-mediated seed germination

P-HYDROXYPHENYLPYRUVATE DIOXYGENASE (HPPD) is the first committed enzyme involved in the biosynthesis of vitamin E, and is characterized by catalyzing the conversion of p-hydroxyphenyl pyruvate (HPP) to homogentisic acid (HGA). Here, an HPPD gene was cloned from Medicago sativa L. and designated MsHPPD, which was expressed at high levels in alfalfa leaves. PEG 6000 (polyethylene glycol), NaCl, abscisic acid and salicylic acid were shown to significantly induce MsHPPD expression, especially in the cotyledons and root tissues. Overexpression of MsHPPD was found to significantly increase the level of β-tocotrienol and the total vitamin E content in Arabidopsis seeds. Furthermore, these transgenic Arabidopsis seeds exhibited an accelerated germination time, compared with wild-type seeds under normal conditions, as well as under NaCl and ABA treatments. Meanwhile, the expression level of several genes associated with ABA biosynthesis (NCED3, NCED5 and NCED9) and the ABA signaling pathway (RAB18, ABI3 and ABI5) were significantly down-regulated in MsHPPD-overexpressing transgenic lines, as well as the total free ABA content. Taken together, these results demonstrate that MsHPPD functions not only in the vitamin E biosynthetic pathway, but also plays a critical role in seed germination via affecting ABA biosynthesis and signaling.

Profiling of BABA-induced differentially expressed genes of Zea mays using suppression subtractive hybridization

This study aims to identify differentially expressed transcripts in BABA-primed maize leaves using suppression subtractive hybridization (SSH) strategy. Findings shed new light on the BABA potentiated defense mechanisms in plants.