The importance of thiamine (vitamin B1) in plant health: From crop yield to biofortification

Contrasting defence mechanisms against spider mite infestation in cyanogenic and non-cyanogenic legumes

Understanding the complex interactions between plants and herbivores is essential for improving crop resistance. Aiming to expand the role of cyanogenesis in plant defence, we investigated the response of the cyanogenic Phaseolus lunatus (lima bean) and the non-cyanogenic Phaseolus vulgaris (common bean) to Tetranychus urticae (spider mite) infestation. Despite mite infesting both legumes, leaf damage infringed by this feeder was reduced in lima bean. Comparative transcriptome analyses revealed that both species exhibited substantial metabolic and transcriptional changes upon infestation, although alterations in P. lunatus were significantly more pronounced. Specific differences in amino acid homeostasis and key genes associated with the cyanogenic pathway were observed in these species, as well as the upregulation of the mandelonitrile lyase gene (PlMNL1) following T. urticae feeding. Concomitantly, the PIMNL1 activity increased. Lima bean plants also displayed an induction of β-cyanoalanine synthase (PlCYSC1), a key enzyme for cyanide detoxification, suggesting an internal regulatory mechanism to manage the toxicity of their defence responses. These findings contribute to our understanding of the legume-herbivore interactions and underscore the potential role of cyanogenesis in the elaboration of specific defensive responses, even within the same genus, which may reflect distinctive evolutionary adaptations or varying metabolic capabilities between species.

'From metabolism to metabolism': holistic considerations on B-vitamin interactions, biofortification, and deficiencies

In the post-Green Revolution era, disparities in dietary access, rising obesity rates, demographic shifts, adoption of plant-based diets, and the impact of climate change collectively contribute to a progressive decline in dietary nutritional value, exacerbating B vitamin deficiencies across both low- and high-income countries. While the prevailing focus of biofortification has been on three micronutrients - provitamin A, iron, and zinc - utilizing conventional breeding, it is imperative to diversify biofortification strategies to combat micronutrient malnutrition. Metabolic engineering, facilitated by biotechnological tools, presents a promising avenue, contingent upon advances in fundamental knowledge, technological innovation, regulatory updates, and sustained public funding. Recognizing the intricate metabolic interplay of B vitamins in plants and humans, a comprehensive 'from metabolism to metabolism' approach is crucial for designing effective biofortification strategies that target multiple vitamins. This holistic perspective also extends beyond individual crops to encompass the entire food chain, a complex socioeconomic ecosystem that necessitates a paradigm shift, prioritizing quality over quantity.

Multiscale physiological responses to nitrogen supplementation of maize hybrids

Maize (Zea mays) production systems are heavily reliant on the provision of managed inputs such as fertilizers to maximize growth and yield. Hence, the effective use of nitrogen (N) fertilizer is crucial to minimize the associated financial and environmental costs, as well as maximize yield. However, how to effectively utilize N inputs for increased grain yields remains a substantial challenge for maize growers that requires a deeper understanding of the underlying physiological responses to N fertilizer application. We report a multiscale investigation of five field-grown maize hybrids under low or high N supplementation regimes that includes the quantification of phenolic and prenyl-lipid compounds, cellular ultrastructural features, and gene expression traits at three developmental stages of growth. Our results reveal that maize perceives the lack of supplemented N as a stress and, when provided with additional N, will prolong vegetative growth. However, the manifestation of the stress and responses to N supplementation are highly hybrid-specific. Eight genes were differentially expressed in leaves in response to N supplementation in all tested hybrids and at all developmental stages. These genes represent potential biomarkers of N status and include two isoforms of Thiamine Thiazole Synthase involved in vitamin B1 biosynthesis. Our results uncover a detailed view of the physiological responses of maize hybrids to N supplementation in field conditions that provides insight into the interactions between management practices and the genetic diversity within maize.

In silico biotechnological potential of Bacillus sp. strain MHSD_37 bacterial endophyte

BACKGROUND

Endophytic bacteria possess a range of unique characteristics that enable them to successfully interact with their host and survive in adverse environments. This study employed in silico analysis to identify genes, from Bacillus sp. strain MHSD_37, with potential biotechnological applications.

RESULTS

The strain presented several endophytic lifestyle genes which encode for motility, quorum sensing, stress response, desiccation tolerance and root colonisation. The presence of plant growth promoting genes such as those involved in nitrogen fixation, nitrate assimilation, siderophores synthesis, seed germination and promotion of root nodule symbionts, was detected. Strain MHSD_37 also possessed genes involved in insect virulence and evasion of defence system. The genome analysis also identified the presence of genes involved in heavy metal tolerance, xenobiotic resistance, and the synthesis of siderophores involved in heavy metal tolerance. Furthermore, LC-MS analysis of the excretome identified secondary metabolites with biological activities such as anti-cancer, antimicrobial and applications as surfactants.

CONCLUSIONS

Strain MHSD_37 thereby demonstrated potential biotechnological application in bioremediation, biofertilisation and biocontrol. Moreover, the strain presented genes encoding products with potential novel application in bio-nanotechnology and pharmaceuticals.

Plant Biostimulant as an Environmentally Friendly Alternative to Modern Agriculture

Ensuring the safety of crop production presents a significant challenge to humanity. Pesticides and fertilizers are commonly used to eliminate external interference and provide nutrients, enabling crops to sustain growth and defense. However, the addition of chemical substances does not meet the environmental standards required for agricultural production. Recently, natural sources such as biostimulants have been found to help plants with growth and defense. The development of biostimulants provides new solutions for agricultural product safety and has become a widely utilized tool in agricultural. The review summarizes the classification of biostimulants, including humic-based biostimulant, protein-based biostimulant, oligosaccharide-based biostimulant, metabolites-based biostimulants, inorganic substance, and microbial inoculant. This review attempts to summarize suitable alternative technology that can address the problems and analyze the current state of biostimulants, summarizes the research mechanisms, and anticipates future technological developments and market trends, which provides comprehensive information for researchers to develop biostimulants.

Ectopic expression of a bacterial thiamin monophosphate kinase enhances vitamin B1 biosynthesis in plants

Plants and bacteria have distinct pathways to synthesize the bioactive vitamin B1 thiamin diphosphate (TDP). In plants, thiamin monophosphate (TMP) synthesized in the TDP biosynthetic pathway is first converted to thiamin by a phosphatase, which is then pyrophosphorylated to TDP. In contrast, bacteria use a TMP kinase encoded by ThiL to phosphorylate TMP to TDP directly. The Arabidopsis THIAMIN REQUIRING2 (TH2)-encoded phosphatase is involved in TDP biosynthesis. The chlorotic th2 mutants have high TMP and low thiamin and TDP. Ectopic expression of Escherichia coli ThiL and ThiL-GFP rescued the th2-3 mutant, suggesting that the bacterial TMP kinase could directly convert TMP into TDP in Arabidopsis. These results provide direct evidence that the chlorotic phenotype of th2-3 is caused by TDP rather than thiamin deficiency. Transgenic Arabidopsis harboring engineered ThiL-GFP targeting to the cytosol, chloroplast, mitochondrion, or nucleus accumulated higher TDP than the wild type (WT). Ectopic expression of E. coli ThiL driven by the UBIQUITIN (UBI) promoter or an endosperm-specific GLUTELIN1 (GT1) promoter also enhanced TDP biosynthesis in rice. The pUBI:ThiL transgenic rice accumulated more TDP and total vitamin B1 in the leaves, and the pGT1:ThiL transgenic lines had higher TDP and total vitamin B1 in the seeds than the WT. Total vitamin B1 only increased by approximately 25-30% in the polished and unpolished seeds of the pGT1:ThiL transgenic rice compared to the WT. Nevertheless, these results suggest that genetic engineering of a bacterial vitamin B1 biosynthetic gene downstream of TMP can enhance vitamin B1 production in rice.

Uncovering the mechanisms of how corn steep liquor and microbial communities minimize cadmium translocation in Chinese cabbage

Corn steep liquor-assisted microbial remediation has been proposed as a promising strategy to remediate cadmium (Cd)-contaminated soil. In this study, we determined Bacillus subtilis (K2) with a high cadmium (Cd) accumulation ability and Cd resistance. However, studies on this strategy used in the Cd uptake of Chinese cabbage are lacking, and the effect of the combined incorporation of corn steep liquor and K2 on the functions and microbial interactions of soil microbiomes is unclear. Here, we study the Cd uptake and transportation in Chinese cabbage by the combination of K2 and corn steep liquor (K2 + C7) in a Cd-contaminated soil and corresponding microbial regulation mechanisms. Results showed that compared to inoculant K2 treatment alone, a reduction of Cd concentration in the shoots by 14.4% and the dry weight biomass of the shoots and the roots in Chinese cabbage increased by 21.6% and 30.8%, respectively, under K2 + C7 treatment. Meanwhile, hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels were decreased by enhancing POD and SOD activity, thereby reversing Cd-induced oxidative damage. Importantly, inoculation of K2 would decrease the diversity of the microbial community while enhancing the abundance of dominant species. These findings provide a promising strategy for reducing the Cd accumulation in Chinese cabbage and recovering soil ecological functions.

Join the green team: Inducers of plant immunity in the plant disease sustainable control toolbox

BACKGROUND

Crops are constantly attacked by various pathogens. These pathogenic microorganisms, such as fungi, oomycetes, bacteria, viruses, and nematodes, threaten global food security by causing detrimental crop diseases that generate tremendous quality and yield losses worldwide. Chemical pesticides have undoubtedly reduced crop damage; however, in addition to increasing the cost of agricultural production, the extensive use of chemical pesticides comes with environmental and social costs. Therefore, it is necessary to vigorously develop sustainable disease prevention and control strategies to promote the transition from traditional chemical control to modern green technologies. Plants possess sophisticated and efficient defense mechanisms against a wide range of pathogens naturally. Immune induction technology based on plant immunity inducers can prime plant defense mechanisms and greatly decrease the occurrence and severity of plant diseases. Reducing the use of agrochemicals is an effective way to minimize environmental pollution and promote agricultural safety.

AIM OF REVIEW

The purpose of this workis to offer valuable insights into the current understanding and future research perspectives of plant immunity inducers and their uses in plant disease control, ecological and environmental protection, and sustainable development of agriculture.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In this work, we have introduced the concepts of sustainable and environment-friendly concepts of green disease prevention and control technologies based on plant immunity inducers. This article comprehensively summarizes these recent advances, emphasizes the importance of sustainable disease prevention and control technologies for food security, and highlights the diverse functions of plant immunity inducers-mediated disease resistance. The challenges encountered in the potential applications of plant immunity inducers and future research orientation are also discussed.

Whole Genome Duplication Events Likely Contributed to the Aquatic Adaptive Evolution of Parkerioideae

As the only aquatic lineage of Pteridaceae, Parkerioideae is distinct from many xeric-adapted species of the family and consists of the freshwater Ceratopteris species and the only mangrove ferns from the genus Acrostichum. Previous studies have shown that whole genome duplication (WGD) has occurred in Parkerioideae at least once and may have played a role in their adaptive evolution; however, more in-depth research regarding this is still required. In this study, comparative and evolutionary transcriptomics analyses were carried out to identify WGDs and explore their roles in the environmental adaptation of Parkerioideae. Three putative WGD events were identified within Parkerioideae, two of which were specific to Ceratopteris and Acrostichum, respectively. The functional enrichment analysis indicated that the lineage-specific WGD events have played a role in the adaptation of Parkerioideae to the low oxygen concentrations of aquatic habitats, as well as different aquatic environments of Ceratopteris and Acrostichum, such as the adaptation of Ceratopteris to reduced light levels and the adaptation of Acrostichum to high salinity. Positive selection analysis further provided evidence that the putative WGD events may have facilitated the adaptation of Parkerioideae to changes in habitat. Moreover, the gene family analysis indicated that the plasma membrane H+-ATPase (AHA), vacuolar H+-ATPase (VHA), and suppressor of K+ transport growth defect 1 (SKD1) may have been involved in the high salinity adaptation of Acrostichum. Our study provides new insights into the evolution and adaptations of Parkerioideae in different aquatic environments.

The Main Functions of Plastids

Plastids are semi-autonomous organelles like mitochondria and derive from a cyanobacterial ancestor that was engulfed by a host cell. During evolution, they have recruited proteins originating from the nuclear genome, and only parts of their ancestral metabolic properties were conserved and optimized to limit functional redundancy with other cell compartments. Furthermore, large disparities in metabolic functions exist among various types of plastids, and the characterization of their various metabolic properties is far from being accomplished. In this review, we provide an overview of the main functions, known to be achieved by plastids or shared by plastids and other compartments of the cell. In short, plastids appear at the heart of all main plant functions.

Alleviation of drought stress through foliar application of thiamine in two varieties of pea (Pisum sativum L.)

Drought stress poorly impacts many morphological and physio-biochemical processes in plants. Pea (Pisum sativum L.) plants are highly nutritious crops destined for human consumption; however, their productivity is threatened under drought stress. Thiamine (vitamin B1) is well-known essential micronutrient, acting as a cofactor in key metabolic processes. Therefore, this study was designed to examine the protective effect of foliar application of thiamine (0, 250, and 500 ppm) on two varieties of pea plants under drought stress. Here, we conducted the pot experiment at the Government College Women University, Faisalabad, to investigate the physio-biochemical and morphological traits of two pea varieties (sarsabz and metior) grown under drought stress and thiamine treatment. Drought stress was applied to plants after germination period of 1 month. Results showed that root fresh and dry weight, shoot fresh and dry weight, number of pods, leaf area, total soluble sugars, total phenolics, total protein contents, catalase, peroxidase, and mineral ions were reduced against drought stress. However, the application of thiamine (both 250 and 500 ppm) overcome the stress and also enhances these parameters, and significantly increases the antioxidant activities (catalase and peroxidase). Moreover, the performance of sarsabz was better under control and drought stress conditions than metior variety. In conclusion, the exogenous application of thiamine enabled the plants to withstand drought stress conditions by regulating several physiological and biochemical mechanisms. In agriculture, it is a great latent to alleviate the antagonistic impact of drought stress on crops through the foliar application of thiamine.

Some Structural Elements of Bacterial Protein MF3 That Influence Its Ability to Induce Plant Resistance to Fungi, Viruses, and Other Plant Pathogens

The ability of the MF3 protein from Pseudomonas fluorescens to protect plants by inducing their resistance to pathogenic fungi, bacteria, and viruses is well confirmed both in greenhouses and in the field; however, the molecular basis of this phenomenon remains unexplored. To find a relationship between the primary (and spatial) structure of the protein and its target activity, we analyzed the inducing activity of a set of mutants generated by alanine scanning and an alpha-helix deletion (ahD) in the part of the MF3 molecule previously identified by our group as a 29-amino-acid peptide working as the inducer on its own. Testing the mutants' inducing activity using the "tobacco-tobacco mosaic virus" pathosystem revealed that some of them showed an almost threefold (V60A and V62A) or twofold (G51A, L58A, ahD) reduction in inducing activity compared to the wild-type MF3 type. Interestingly, these mutations demonstrated close proximity in the homology model, probably contributing to MF3 reception in a host plant.

Transcriptomic Analysis Reveals the Response Mechanisms of Bell Pepper (Capsicum annuum) to Phosphorus Deficiency

Phosphorus (P) is an important nutritional element needed by plants. Roots obtain P as inorganic phosphate (Pi), mostly in H2PO-4 form. It is vital for plants to have a sufficient supply of Pi since it participates in important processes like photosynthesis, energy transfer, and protein activation, among others. The physicochemical properties and the organic material usually make Pi bioavailability in soil low, causing crops and undomesticated plants to experience variations in accessibility or even a persistent phosphate limitation. In this study, transcriptome data from pepper roots under low-Pi stress was analyzed in order to identify Pi starvation-responsive genes and their relationship with metabolic pathways and functions. Transcriptome data were obtained from pepper roots with Pi deficiency by RNASeq and analyzed with bioinformatic tools. A total of 97 differentially expressed genes (DEGs) were identified; Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment revealed that metabolic pathways, such as porphyrin and chlorophyll metabolism, were down-regulated, and galactose and fatty acid metabolism were up-regulated. The results indicate that bell pepper follows diverse processes related to low Pi tolerance regulation, such as the remobilization of internal Pi, alternative metabolic pathways to generate energy, and regulators of root development.

Thiamine deficiency: a commonly unrecognised but easily treatable condition

Thiamine is present in many foods and is well recognised as an essential nutrient critical for energy metabolism. While thiamine deficiency is commonly recognised in alcoholism, it can present in many other settings where it is often not considered and goes unrecognised. One challenging aspect to diagnosis is that it may have varied metabolic, neurological and cardiac presentations. Here we present an overview of the disorder, focusing on the multiple causes and clinical presentations. Interestingly, thiamine deficiency is likely increasing in frequency, especially among wildlife, where it is linked with changing environments and climate change. Thiamine deficiency should be considered whenever neurological or cardiological disease of unknown aetiology presents, especially in any patient presenting with lactic acidosis.

Thiamine-Mediated Microbial Interaction between Auxotrophic Rhodococcus ruber ZM07 and Prototrophic Cooperators in the Tetrahydrofuran-Degrading Microbial Community H-1

As a crucial growth factor, thiamine can regulate functional microbial communities; however, our current understanding of its effect on bioremediation is lacking. Using metatranscriptome and 16S rRNA gene sequencing, we explored the mechanism of response of an efficient tetrahydrofuran (THF)-degrading microbial culture, designated H-1, to exogenous thiamine. Rhodococcus ruber ZM07, a strain performing the THF degradation function in H-1, is a thiamine-auxotrophic bacterium. Furthermore, thiamine affected the microbial community structure of H-1 by altering resource and niche distributions. A microbial co-occurrence network was constructed to help us identify and isolate the cooperators of strain ZM07 in the microbial community. Based on the prediction of the network, two non-THF-degrading bacteria, Hydrogenophaga intermedia ZM11 and Pigmentiphaga daeguensis ZM12, were isolated. Our results suggest that strain ZM11 is a good cooperator of ZM07, and it might be more competitive than other cooperators (e.g., ZM12) in cocultured systems. Additionally, two dominant strains in our microbial culture displayed a "seesaw" pattern, and they showed completely different responses to exogenous thiamine. The growth of the THF degrader ZM07 was spurred by additional thiamine (with an increased relative abundance and significant upregulation of most metabolic pathways), while the growth of the cooperator ZM11 was obviously suppressed under the same circumstances. This relationship was the opposite without thiamine addition. Our study reveals that exogenous thiamine can affect the interaction patterns between THF- and non-THF-degrading microorganisms and provides new insight into the effects of micronutrients on the environmental microbial community. IMPORTANCE Auxotrophic microorganisms play important roles in the biodegradation of pollutants in nature. Exploring the interspecies relationship between auxotrophic THF-degrading bacteria and other microbes is helpful for the efficient utilization of auxotrophic functional microorganisms. Herein, the thiamine-auxotrophic THF-degrading bacterium ZM07 was isolated from the microbial culture H-1, and the effect of thiamine on the structure of H-1 during THF bioremediation was studied. Thiamine may help ZM07 occupy more niches and utilize more resources, thus improving THF degradation efficiency. This research provides a new strategy to improve the THF or other xenobiotic compound biodegradation performance of auxotrophic functional microorganisms/microbial communities by artificially adding special micronutrients. Additionally, the "seesaw" relationship between the thiamine-auxotrophic strain ZM07 and its prototrophic cooperator ZM11 during THF bioremediation could be changed by exogenous thiamine. This study reveals the effect of micronutrients on microbial interactions and provides an effective way to regulate the pollutant biodegradation efficiency of microbial communities.

Harnessing enzyme cofactors and plant metabolism: an essential partnership

Cofactors are fundamental to the catalytic activity of enzymes. Additionally, because plants are a critical source of several cofactors (i.e., including their vitamin precursors) within the context of human nutrition, there have been several studies aiming to understand the metabolism of coenzymes and vitamins in plants in detail. For example, compelling evidence has been brought forth regarding the role of cofactors in plants; specifically, it is becoming increasingly clear that an adequate supply of cofactors in plants directly affects their development, metabolism, and stress responses. Here, we review the state-of-the-art knowledge on the significance of coenzymes and their precursors with regard to general plant physiology and discuss the emerging functions attributed to them. Furthermore, we discuss how our understanding of the complex relationship between cofactors and plant metabolism can be used for crop improvement.

Effects of Date Palm Waste Compost Application on Root Proteome Changes of Barley (Hordeum vulgare L.)

Proteomic analysis was performed to investigate the differentially abundant proteins (DAPs) in barley roots during the tillering stage. Bioinformatic tools were used to interpret the biological function, the pathway analysis and the visualisation of the network amongst the identified proteins. A total of 72 DAPs (33 upregulated and 39 downregulated) among a total of 2580 proteins were identified in response to compost treatment, suggesting multiple pathways of primary and secondary metabolism, such as carbohydrates and energy metabolism, phenylpropanoid pathway, glycolysis pathway, protein synthesis and degradation, redox homeostasis, RNA processing, stress response, cytoskeleton organisation, and phytohormone metabolic pathways. The expression of DAPs was further validated by qRT-PCR. The effects on barley plant development, such as the promotion of root growth and biomass increase, were associated with a change in energy metabolism and protein synthesis. The activation of enzymes involved in redox homeostasis and the regulation of stress response proteins suggest a protective effect of compost, consequently improving barley growth and stress acclimation through the reduction of the environmental impact of productive agriculture. Overall, these results may facilitate a better understanding of the molecular mechanism of compost-promoted plant growth and provide valuable information for the identification of critical genes/proteins in barley as potential targets of compost.

Protective effects of thiamine on Wickerhamomyces anomalus against ethanol stress

Wickerhamomyces anomalus (W. anomalus) is widely reported in the brewing industry and has positive effects on the aromatic profiles of wines because of its unique physiological characteristics and metabolic features. However, the accumulation of ethanol during fermentation inhibits the growth of W. anomalus. Thiamine is involved in the response against various abiotic stresses in microorganisms. Therefore, we used transcriptomic and metabolomic analyses to study the effect of thiamine on ethanol-stressed W. anomalus. The results indicate that thiamine could alleviate the inhibitory effect of ethanol stress on the survival of W. anomalus. Differentially expressed genes (DEGs) and differentially expressed metabolites (DEMs) caused by the thiamine intervention were identified as oxidative phosphorylation through integrated transcriptomic and metabolomic analyses. In addition, ethanol treatment decreased the content of intracellular adenosine triphosphate (ATP), while thiamine partially alleviated this phenomenon. The present comprehensive transcriptional overview and metabolomic analysis provide insights about the mechanisms of thiamine protection on W. anomalus under ethanol stress and promote the potential applications of W. anomalus in the fermentation industry.

Biological Functions of Hydrogen Sulfide in Plants

Hydrogen sulfide (H₂S), which is a gasotransmitter, can be biosynthesized and participates in various physiological and biochemical processes in plants. H₂S also positively affects plants' adaptation to abiotic stresses. Here, we summarize the specific ways in which H₂S is endogenously synthesized and metabolized in plants, along with the agents and methods used for H₂S research, and outline the progress of research on the regulation of H₂S on plant metabolism and morphogenesis, abiotic stress tolerance, and the series of different post-translational modifications (PTMs) in which H₂S is involved, to provide a reference for future research on the mechanism of H₂S action.

Variation of vitamin B contents in maize inbred lines: Potential genetic resources for biofortification

Vitamin B and its derivatives possess diverse physiological functions and are essential micronutrients for humans. Their variation in crops is important for the identification of genetic resources used to develop new varieties with enhanced vitamin B. In this research, remarkable variations were observed in kernels of 156 maize inbred lines, ranging from 107.61 to 2654.54 μg per 100 g for vitamin B1, 1.19–37.37 μg per 100 g for B2, 19.60–213.75 μg per 100 g for B3, 43.47–590.86 μg per 100 g for B5, and 138.59–1065.11 μg per 100 g for B6. Growing inbreeds in Hainan and Hebei provinces of China revealed environmental and genotype interactions among these vitamins and the correlations between them in maize grain. Several inbred lines were identified as good sources of vitamin B and promising germplasms for maize breeding, namely By855 and Si273 are overall rich in all the studied vitamins, and GY386B and CML118 are specially enriched with derivatives of vitamin B6. The present study can assist maize breeders with germplasm resources of vitamin B for biofortification to offer people nutritious foods.

Effects of copper accumulation on growth and development of Scopelophila cataractae grown in vitro

Scopelophila cataractae was cultured in vitro for 16 weeks to assess the contrasting effects of Cu on growth and reproduction, as well as gametophore stage. To induce buds and gametophores of S. cataractae, ten treatments (tr 1 to tr 10) of culture media were prepared using a combination of mineral salts, sugar, vitamin B complex, CuSO₄, and exogenous hormones. Highest numbers of gametophores and buds were formed in media containing 500 µM CuSO₄ in co-application with auxin and cytokinin, as shown in the modest Cu treatments (tr 6 and tr 7, 26 per cushion and 255 per 25 mm², respectively). A 5000 µM CuSO₄ concentration inhibited development of protonema, possibly due to Cu toxicity, resulting in chloronema forming contorted filaments or short cells containing lipid bodies, and brood body diaspores but no gametophore or bud formation. In this study, S. cataractae Cu accumulation in tissue was substantial (up to 2843.1 mg kg^-1; tr 6) with no or minimal adverse effects, reflecting its potential for phytoremediation of Cu in terrestrial and aquatic ecosystems. The highest atomic percentages of Cu and Zn were detected in the stem surfaces of gametophores treated with 500 µM CuSO₄ (11% atomic Cu and 7% atomic Zn), which served as a primary heavy metal storage site, ultimately protecting cells from metal toxicity. The success of this in vitro study on S. cataractae should also aid ex situ conservation efforts for a variety of rare moss taxa in the wild.

Combination of long-term 13CO2 labeling and isotopolog profiling allows turnover analysis of photosynthetic pigments in Arabidopsis leaves

BACKGROUND

Living cells maintain and adjust structural and functional integrity by continual synthesis and degradation of metabolites and macromolecules. The maintenance and adjustment of thylakoid membrane involve turnover of photosynthetic pigments along with subunits of protein complexes. Quantifying their turnover is essential to understand the mechanisms of homeostasis and long-term acclimation of photosynthetic apparatus. Here we report methods combining whole-plant long-term ¹³CO₂ labeling and liquid chromatography - mass spectrometry (LC-MS) analysis to determine the size of non-labeled population (NLP) of carotenoids and chlorophylls (Chl) in leaf pigment extracts of partially ¹³C-labeled plants.

RESULTS

The labeling chamber enabled parallel ¹³CO₂ labeling of up to 15 plants of Arabidopsis thaliana with real-time environmental monitoring ([CO₂], light intensity, temperature, relative air humidity and pressure) and recording. No significant difference in growth or photosynthetic pigment composition was found in leaves after 7-d exposure to normal CO₂ (~ 400 ppm) or ¹³CO₂ in the labeling chamber, or in ambient air outside the labeling chamber (control). Following chromatographic separation of the pigments and mass peak assignment by high-resolution Fourier-transform ion cyclotron resonance MS, mass spectra of photosynthetic pigments were analyzed by triple quadrupole MS to calculate NLP. The size of NLP remaining after the 7-d ¹³CO₂ labeling was ~ 10.3% and ~ 11.5% for all-trans- and 9-cis-β-carotene, ~ 21.9% for lutein, ~ 18.8% for Chl a and 33.6% for Chl b, highlighting non-uniform turnover of these pigments in thylakoids. Comparable results were obtained in all replicate plants of the ¹³CO₂ labeling experiment except for three that were showing anthocyanin accumulation and growth impairment due to insufficient water supply (leading to stomatal closure and less ¹³C incorporation).

CONCLUSIONS

Our methods allow ¹³CO₂ labeling and estimation of NLP for photosynthetic pigments with high reproducibility despite potential variations in [¹³CO₂] between the experiments. The results indicate distinct turnover rates of carotenoids and Chls in thylakoid membrane, which can be investigated in the future by time course experiments. Since ¹³C enrichment can be measured in a range of compounds, long-term ¹³CO₂ labeling chamber, in combination with appropriate MS methods, facilitates turnover analysis of various metabolites and macromolecules in plants on a time scale of hours to days.

Sulfite-Catalyzed Nucleophilic Substitution Reactions with Thiamin and Analogous Pyrimidine Donors Proceed via an SNAE Mechanism

When treated with SO₃^2-, thiamin undergoes a substitution reaction to release a thiazole leaving group and the corresponding sulfonate. Although this reaction could proceed via a simple S_N2-like mechanism, a multistep addition-elimination (S_NAE) mechanism involving the addition of SO₃^2- to C6' of the 4-aminopyrimidine of thiamin has also been proposed. Although this reaction has potential utility in the synthesis of substituted pyrimidines and provides a direct analogue to reactions catalyzed by thiaminases, a detailed mechanistic picture of the SO₃^2--catalyzed cleavage of thiamin has remained elusive. Here, DFT calculations have been used to probe the relative energetics and the factors that shape the potential energy surfaces that define the possible mechanisms of substitution. These calculations provide clear support for the S_NAE mechanism over an S_N2-like process and illustrate that the unique ability of SO₃^2- to activate thiamin toward nucleophilic displacement is due to the combined nucleophilicity and relatively poor leaving group ability of SO₃^2-. Both of these factors favor the forward partitioning of the sulfite adduct toward the cleavage products whereas adducts formed with other nucleophiles overwhelmingly revert to reactants. Calculations performed with a range of substrates with various electrophilicities and nucleofugalities consistently suggest that the S_NAE pathway is significantly lower in energy than the direct substitution, illustrating that this SO₃^2--catalyzed multistep process is likely to be broadly applicable both in solution and in catalysis by thiaminases.

THIAMIN REQUIRING2 is involved in thiamin diphosphate biosynthesis and homeostasis

The THIAMIN REQUIRING2 (TH2) protein comprising a mitochondrial targeting peptide followed by a transcription enhancement A and a haloacid dehalogenase domain is a thiamin monophosphate (TMP) phosphatase in the vitamin B1 biosynthetic pathway. The Arabidopsis th2-3 T-DNA insertion mutant was chlorotic and deficient in thiamin diphosphate (TDP). Complementation assays confirmed that haloacid dehalogenase domain alone was sufficient to rescue the th2-3 mutant. In pTH2:TH2-GFP/th2-3 complemented plants, the TH2-GFP was localized to the cytosol, mitochondrion, and nucleus, indicating that the vitamin B1 biosynthetic pathway extended across multi-subcellular compartments. Engineered TH2-GFP localized to the cytosol, mitochondrion, nucleus, and chloroplast, could complement the th2 mutant. Together, these results highlight the importance of intracellular TMP and thiamin trafficking in vitamin B1 biosynthesis. In an attempt to enhance the production of thiamin, we created various constructs to overexpress TH2-GFP in the cytosol, mitochondrion, chloroplast, and nucleus. Unexpectedly, overexpressing TH2-GFP resulted in an increase rather than a decrease in TMP. While studies on th2 mutants support TH2 as a TMP phosphatase, analyses of TH2-GFP overexpression lines implicating TH2 may also function as a TDP phosphatase in planta. We propose a working model that the TMP/TDP phosphatase activity of TH2 connects TMP, thiamin, and TDP into a metabolic cycle. The TMP phosphatase activity of TH2 is required for TDP biosynthesis, and the TDP phosphatase activity of TH2 may modulate TDP homeostasis in Arabidopsis.

Coral holobiont cues prime Endozoicomonas for a symbiotic lifestyle

Endozoicomonas are prevalent, abundant bacterial associates of marine animals, including corals. Their role in holobiont health and functioning, however, remains poorly understood. To identify potential interactions within the coral holobiont, we characterized the novel isolate Endozoicomonas marisrubri sp. nov. 6c and assessed its transcriptomic and proteomic response to tissue extracts of its native host, the Red Sea coral Acropora humilis. We show that coral tissue extracts stimulated differential expression of genes putatively involved in symbiosis establishment via the modulation of the host immune response by E. marisrubri 6c, such as genes for flagellar assembly, ankyrins, ephrins, and serpins. Proteome analyses revealed that E. marisrubri 6c upregulated vitamin B1 and B6 biosynthesis and glycolytic processes in response to holobiont cues. Our results suggest that the priming of Endozoicomonas for a symbiotic lifestyle involves the modulation of host immunity and the exchange of essential metabolites with other holobiont members. Consequently, Endozoicomonas may play an important role in holobiont nutrient cycling and may therefore contribute to coral health, acclimatization, and adaptation.

B vitamin supply in plants and humans: the importance of vitamer homeostasis

B vitamins are a group of water-soluble micronutrients that are required in all life forms. With the lack of biosynthetic pathways, humans depend on dietary uptake of these compounds, either directly or indirectly, from plant sources. B vitamins are frequently given little consideration beyond their role as enzyme accessory factors and are assumed not to limit metabolism. However, it should be recognized that each individual B vitamin is a family of compounds (vitamers), the regulation of which has dedicated pathways. Moreover, it is becoming increasingly evident that individual family members have physiological relevance and should not be sidelined. Here, we elaborate on the known forms of vitamins B₁ , B₆ and B₉ , their distinct functions and importance to metabolism, in both human and plant health, and highlight the relevance of vitamer homeostasis. Research on B vitamin metabolism over the past several years indicates that not only the total level of vitamins but also the oft-neglected homeostasis of the various vitamers of each B vitamin is essential to human and plant health. We briefly discuss the potential of plant biology studies in supporting human health regarding these B vitamins as essential micronutrients. Based on the findings of the past few years we conclude that research should focus on the significance of vitamer homeostasis - at the organ, tissue and subcellular levels - which could improve the health of not only humans but also plants, benefiting from cross-disciplinary approaches and novel technologies.

Thiamine functions as a key activator for modulating plant health and broad-spectrum tolerance in cotton

Global climate changes cause an increase of abiotic and biotic stresses that tremendously threaten the world's crop security. However, studies on broad-spectrum response pathways involved in biotic and abiotic stresses are relatively rare. Here, by comparing the time-dependent transcriptional changes and co-expression analysis of cotton (Gossypium hirsutum) root tissues under abiotic and biotic stress conditions, we discovered the common stress-responsive genes and stress metabolism pathways under different stresses, which included the circadian rhythm, thiamine and galactose metabolism, carotenoid, phenylpropanoid, flavonoid, and zeatin biosynthesis, and the mitogen-activated protein kinase signaling pathway. We found that thiamine metabolism was an important intersection between abiotic and biotic stresses; the key thiamine synthesis genes, GhTHIC and GhTHI1, were highly induced at the early stage of stresses. We confirmed that thiamine was crucial and necessary for cotton growth and development, and its deficiency could be recovered by exogenous thiamine supplement. Furthermore, we revealed that exogenous thiamine enhanced stress tolerance in cotton via increasing calcium signal transduction and activating downstream stress-responsive genes. Overall, our studies demonstrated that thiamine played a crucial role in the tradeoff between plant health and stress resistance. The thiamine deficiency caused by stresses could transiently induce upregulation of thiamine biosynthetic genes in vivo, while it could be totally salvaged by exogenous thiamine application, which could significantly improve cotton broad-spectrum stress tolerance and enhance plant growth and development.

Mechanistic Studies on the Single-Turnover Yeast Thiamin Pyrimidine Synthase: Characterization of the Inactive Enzyme

The eukaryotic thiamin pyrimidine synthase, THI5p, has been identified as a suicidal/single-turnover enzyme that catalyzes the conversion of its active site histidine and lysine-bound pyridoxal phosphate (PLP) to the thiamin pyrimidine (HMP-P). Here we identify the histidine and PLP fragments using bottom-up proteomics and LC-MS analysis. We also identify the active form of the iron cofactor and quantitate the oxygen requirement of the THI5p reaction. This information is integrated into a mechanistic proposal for this remarkable reaction.

An acceleration of carotenoid production and growth of Haematococcus lacustris induced by host-microbiota network interaction

Haematococcus lacustris is a chlamydomonadalean with high biotechnological interest owing to its capacity to produce astaxanthin, a valuable secondary carotenoid with extraordinary antioxidation properties. However, its prolonged growth has limited its utility commercially. Thus, rapid growth to attain high densities of H. lacustris cells optimally producing astaxanthin is an essential biotechnological target to facilitate profitable commercialisation. Our study focused on characterising the bacterial communities associated with the alga's phycosphere by metagenomics. Subsequently, we altered the bacterial consortia in combined co-culture with key beneficial bacteria to optimise the growth of H. lacustris. The algal biomass increased by up to 2.1-fold in co-cultures, leading to a 1.6-fold increase in the astaxanthin yield. This study attempted to significantly improve the H. lacustris growth rate and biomass yield via Next-Generation Sequencing analysis and phycosphere bacterial augmentation, highlighting the possibility to overcome the hurdles associated with astaxanthin production by H. lacustris at a commercial scale.

The Vital Role of ShTHIC from the Endophyte OsiSh-2 in Thiamine Biosynthesis and Blast Resistance in the OsiSh-2-Rice Symbiont

Endophytes can benefit the growth and stress resistance of host plants by secreting bioactive components. Thiamine is an essential vitamin involved in many metabolic pathways and can only be synthesized by microbes and plants. In this study, we found that thiamine could inhibit the development of the phytopathogen Magnaporthe oryzae and decrease the rice blast index under field conditions. In the thiamine biosynthesis pathway, the key enzyme ShTHIC of an endophyte Streptomyces hygroscopicus OsiSh-2 and OsTHIC of rice (Oryza sativa) were highly homologous. Gene overexpression or knockout approaches revealed that both THIC contributed to thiamine synthesis and resistance to M. oryzae. Furthermore, S. hygroscopicus OsiSh-2 colonization led to a decrease in the thiamine synthesis level of rice but still maintained thiamine homeostasis in rice. However, inoculation with the ShTHIC knockout strain ΔTHIC reduced the thiamine content in rice, although the thiamine synthesis level of rice was increased. After infection with M. oryzae, blast resistance was dramatically improved in OsiSh-2-inoculated rice but decreased in ΔTHIC-inoculated rice compared with non-inoculated rice. This result demonstrated that ShTHIC could regulate thiamine biosynthesis and consequently assist blast resistance in the OsiSh-2-rice symbiont. Our results revealed a novel blast-resistance mechanism mediated by a key thiamine biosynthetic enzyme from an endophyte OsiSh-2.

Artificial Neural Networks Elucidated the Essential Role of Mineral Nutrients versus Vitamins and Plant Growth Regulators in Achieving Healthy Micropropagated Plants

The design of an adequate culture medium is an essential step in the micropropagation process of plant species. Adjustment and balance of medium components involve the interaction of several factors, such as mineral nutrients, vitamins, and plant growth regulators (PGRs). This work aimed to shed light on the role of these three components on the plant growth and quality of micropropagated woody plants, using Actinidia arguta as a plant model. Two experiments using a five-dimensional experimental design space were defined using the Design of Experiments (DoE) method, to study the effect of five mineral factors (NH₄NO₃, KNO₃, Mesos, Micros, and Iron) and five vitamins (Myo-inositol, thiamine, nicotinic acid, pyridoxine, and vitamin E). A third experiment, using 20 combinations of two PGRs: BAP (6-benzylaminopurine) and GA₃ (gibberellic acid) was performed. Artificial Neural Networks (ANNs) algorithms were used to build models with the whole database to determine the effect of those components on several growth and quality parameters. Neurofuzzy logic allowed us to decipher and generate new knowledge on the hierarchy of some minerals as essential components of the culture media over vitamins and PRGs, suggesting rules about how MS basal media formulation could be modified to assess the quality of micropropagated woody plants.

A novel panel of yeast assays for the assessment of thiamin and its biosynthetic intermediates in plant tissues

Thiamin (or thiamine), known as vitamin B1, represents an indispensable component of human diets, being pivotal in energy metabolism. Thiamin research depends on adequate vitamin quantification in plant tissues. A recently developed quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS) method is able to assess the level of thiamin, its phosphorylated entities and its biosynthetic intermediates in the model plant Arabidopsis thaliana, as well as in rice. However, their implementation requires expensive equipment and substantial technical expertise. Microbiological assays can be useful in deter-mining metabolite levels in plant material and provide an affordable alternative to MS-based analysis. Here, we evaluate, by comparison to the LC-MS/MS reference method, the potential of a carefully chosen panel of yeast assays to estimate levels of total vitamin B1, as well as its biosynthetic intermediates pyrimidine and thiazole in Arabidopsis samples. The examined panel of Saccharomyces cerevisiae mutants was, when implemented in microbiological assays, capable of correctly assigning a series of wild-type and thiamin biofortified Arabidopsis plant samples. The assays provide a readily applicable method allowing rapid screening of vitamin B1 (and its biosynthetic intermediates) content in plant material, which is particularly useful in metabolic engineering approaches and in germplasm screening across or within species.

Coenzymes and the primary and specialized metabolism interface

In plants, primary and specialized metabolism have classically been distinguished as either essential for growth or required for survival in a particular environment. Coenzymes (organic cofactors) are essential for growth but their importance to specialized metabolism is often not considered. In line with the recent proposal of viewing primary and specialized metabolism as an integrated whole rather than segregated lots with a defined interface, we highlight here the importance of collating information on the regulation of coenzyme supply with metabolic demands using examples of vitamin B derived coenzymes. We emphasize that coenzymes can have enormous influence on the outcome of metabolic as well as engineered pathways and should be taken into account in the era of synthetic biology.

Mitochondrial transport and metabolism of the vitamin B-derived cofactors thiamine pyrophosphate, coenzyme A, FAD and NAD+ , and related diseases: A review

Multiple mitochondrial matrix enzymes playing key roles in metabolism require cofactors for their action. Due to the high impermeability of the mitochondrial inner membrane, these cofactors need to be synthesized within the mitochondria or be imported, themselves or one of their precursors, into the organelles. Transporters belonging to the protein family of mitochondrial carriers have been identified to transport the coenzymes: thiamine pyrophosphate, coenzyme A, FAD and NAD⁺ , which are all structurally similar to nucleotides and derived from different B-vitamins. These mitochondrial cofactors bind more or less tightly to their enzymes and, after having been involved in a specific reaction step, are regenerated, spontaneously or by other enzymes, to return to their active form, ready for the next catalysis round. Disease-causing mutations in the mitochondrial cofactor carrier genes compromise not only the transport reaction but also the activity of all mitochondrial enzymes using that particular cofactor and the metabolic pathways in which the cofactor-dependent enzymes are involved. The mitochondrial transport, metabolism and diseases of the cofactors thiamine pyrophosphate, coenzyme A, FAD and NAD⁺ are the focus of this review.

Biological Properties of Vitamins of the B-Complex, Part 1: Vitamins B1, B2, B3, and B5

This review summarizes the current knowledge on essential vitamins B₁, B₂, B₃, and B₅. These B-complex vitamins must be taken from diet, with the exception of vitamin B₃, that can also be synthetized from amino acid tryptophan. All of these vitamins are water soluble, which determines their main properties, namely: they are partly lost when food is washed or boiled since they migrate to the water; the requirement of membrane transporters for their permeation into the cells; and their safety since any excess is rapidly eliminated via the kidney. The therapeutic use of B-complex vitamins is mostly limited to hypovitaminoses or similar conditions, but, as they are generally very safe, they have also been examined in other pathological conditions. Nicotinic acid, a form of vitamin B₃, is the only exception because it is a known hypolipidemic agent in gram doses. The article also sums up: (i) the current methods for detection of the vitamins of the B-complex in biological fluids; (ii) the food and other sources of these vitamins including the effect of common processing and storage methods on their content; and (iii) their physiological function.

Vitamin B1, eye and brain

Vitamin B1 (aneurin, thiamine) is a water-soluble vitamin necessary for the normal function of the nervous system, visual system and heart and is part of important enzymes in the body. Thiamine enables the normal use of glucose, other carbohydrates and proteins, and enables the supply of energy to the organism. The main sources of thiamine are exogenous and small amounts are synthesized by microorganisms of the human intestinal microbiome. Vitamin B1 cannot accumulate in the body, so signs of deficiency are quickly manifested. Hypovitaminosis B1 is seen in chronic ethyl abuse, persistent vomiting (as in some pregnant women) or after bariatric surgical procedures, but in a mild form it is present in the general population. Normal daily needs for vitamin B1 depend on calorie intake, and 0.4 mg should be ingested for every 1000 kcal.

Natural Variation in Vitamin B1 and Vitamin B6 Contents in Rice Germplasm

Insufficient dietary intake of micronutrients contributes to the onset of deficiencies termed hidden hunger-a global health problem affecting approximately 2 billion people. Vitamin B₁ (thiamine) and vitamin B₆ (pyridoxine) are essential micronutrients because of their roles as enzymatic cofactors in all organisms. Metabolic engineering attempts to biofortify rice endosperm-a poor source of several micronutrients leading to deficiencies when consumed monotonously-have led to only minimal improvements in vitamin B₁ and B₆ contents. To determine if rice germplasm could be exploited for biofortification of rice endosperm, we screened 59 genetically diverse accessions under greenhouse conditions for variation in vitamin B₁ and vitamin B₆ contents across three tissue types (leaves, unpolished and polished grain). Accessions from low, intermediate and high vitamin categories that had similar vitamin levels in two greenhouse experiments were chosen for in-depth vitamer profiling and selected biosynthesis gene expression analyses. Vitamin B₁ and B₆ contents in polished seeds varied almost 4-fold. Genes encoding select vitamin B₁ and B₆ biosynthesis de novo enzymes (THIC for vitamin B₁, PDX1.3a-c and PDX2 for vitamin B₆) were differentially expressed in leaves across accessions contrasting in their respective vitamin contents. These expression levels did not correlate with leaf and unpolished seed vitamin contents, except for THIC expression in leaves that was positively correlated with total vitamin B₁ contents in polished seeds. This study expands our knowledge of diversity in micronutrient traits in rice germplasm and provides insights into the expression of genes for vitamin B₁ and B₆ biosynthesis in rice.

Chitosan thiamine nanoparticles intervene innate immunomodulation during Chickpea-Fusarium interaction

The present study evaluated the effect of chitosan thiamine nanoparticles (TCNP) on the activation of defence responses in chickpea against stress caused by wilt pathogen, Fusarium oxysporum f. sp. ciceri (FOC), under greenhouse condition. A significant increase in enzymatic and non-enzymatic antioxidants was observed in the TCNP treated chickpea plants challenged with FOC compared to the untreated control. Histochemical staining showed high deposition of lignin in the vascular bundles of chickpea stem tissues in TCNP treated plants challenged with FOC. More than 90% protection against wilt pathogen was observed in TCNP treated chickpea plants challenged with FOC, under greenhouse condition. Higher accumulation of antioxidants and phenylpropanoids in TCNP treated challenged chickpea plants well correlates with resistance against wilt pathogen. These results suggest that the elicitation of stress response in TCNP treated chickpea during FOC interaction play a vital role in suppressing the wilt disease in chickpea.

A Core Metabolome Response of Maize Leaves Subjected to Long-Duration Abiotic Stresses

Abiotic stresses reduce crop growth and yield in part by disrupting metabolic homeostasis and triggering responses that change the metabolome. Experiments designed to understand the mechanisms underlying these metabolomic responses have usually not used agriculturally relevant stress regimes. We therefore subjected maize plants to drought, salt, or heat stresses that mimic field conditions and analyzed leaf responses at metabolome and transcriptome levels. Shared features of stress metabolomes included synthesis of raffinose, a compatible solute implicated in tolerance to dehydration. In addition, a marked accumulation of amino acids including proline, arginine, and γ-aminobutyrate combined with depletion of key glycolysis and tricarboxylic acid cycle intermediates indicated a shift in balance of carbon and nitrogen metabolism in stressed leaves. Involvement of the γ-aminobutyrate shunt in this process is consistent with its previously proposed role as a workaround for stress-induced thiamin-deficiency. Although convergent metabolome shifts were correlated with gene expression changes in affected pathways, patterns of differential gene regulation induced by the three stresses indicated distinct signaling mechanisms highlighting the plasticity of plant metabolic responses to abiotic stress.

Update on Thiamine Triphosphorylated Derivatives and Metabolizing Enzymatic Complexes

While the cellular functions of the coenzyme thiamine (vitamin B1) diphosphate (ThDP) are well characterized, the triphosphorylated thiamine derivatives, thiamine triphosphate (ThTP) and adenosine thiamine triphosphate (AThTP), still represent an intriguing mystery. They are present, generally in small amounts, in nearly all organisms, bacteria, fungi, plants, and animals. The synthesis of ThTP seems to require ATP synthase by a mechanism similar to ATP synthesis. In E. coli, ThTP is synthesized during amino acid starvation, while in plants, its synthesis is dependent on photosynthetic processes. In E. coli, ThTP synthesis probably requires oxidation of pyruvate and may play a role at the interface between energy and amino acid metabolism. In animal cells, no mechanism of regulation is known. Cytosolic ThTP levels are controlled by a highly specific cytosolic thiamine triphosphatase (ThTPase), coded by thtpa, and belonging to the ubiquitous family of the triphosphate tunnel metalloenzymes (TTMs). While members of this protein family are found in nearly all living organisms, where they bind organic and inorganic triphosphates, ThTPase activity seems to be restricted to animals. In mammals, THTPA is ubiquitously expressed with probable post-transcriptional regulation. Much less is known about the recently discovered AThTP. In E. coli, AThTP is synthesized by a high molecular weight protein complex from ThDP and ATP or ADP in response to energy stress. A better understanding of these two thiamine derivatives will require the use of transgenic models.

The Thiamin-Requiring 3 Mutation of Arabidopsis 5-Deoxyxylulose-Phosphate Synthase 1 Highlights How the Thiamin Economy Impacts the Methylerythritol 4-Phosphate Pathway

The thiamin-requiring mutants of Arabidopsis have a storied history as a foundational model for biochemical genetics in plants and have illuminated the central role of thiamin in metabolism. Recent integrative genetic and biochemical analyses of thiamin biosynthesis and utilization imply that leaf metabolism normally operates close to thiamin-limiting conditions. Thus, the mechanisms that allocate thiamin-diphosphate (ThDP) cofactor among the diverse thiamin-dependent enzymes localized in plastids, mitochondria, peroxisomes, and the cytosol comprise an intricate thiamin economy. Here, we show that the classical thiamin-requiring 3 (th3) mutant is a point mutation in plastid localized 5-deoxyxylulose synthase 1 (DXS1), a key regulated enzyme in the methylerythritol 4-phosphate (MEP) isoprene biosynthesis pathway. Substitution of a lysine for a highly conserved glutamate residue (E323) located at the subunit interface of the homodimeric enzyme conditions a hypomorphic phenotype that can be rescued by supplying low concentrations of thiamin in the medium. Analysis of leaf thiamin vitamers showed that supplementing the medium with thiamin increased total ThDP content in both wild type and th3 mutant plants, supporting a hypothesis that the mutant DXS1 enzyme has a reduced affinity for the ThDP cofactor. An unexpected upregulation of a suite of biotic-stress-response genes associated with accumulation of downstream MEP intermediate MEcPP suggests that th3 causes mis-regulation of DXS1 activity in thiamin-supplemented plants. Overall, these results highlight that the central role of ThDP availability in regulation of DXS1 activity and flux through the MEP pathway.

Metabolic engineering provides insight into the regulation of thiamin biosynthesis in plants

Thiamin (or thiamine) is a water-soluble B-vitamin (B1), which is required, in the form of thiamin pyrophosphate, as an essential cofactor in crucial carbon metabolism reactions in all forms of life. To ensure adequate metabolic functioning, humans rely on a sufficient dietary supply of thiamin. Increasing thiamin levels in plants via metabolic engineering is a powerful strategy to alleviate vitamin B1 malnutrition and thus improve global human health. These engineering strategies rely on comprehensive knowledge of plant thiamin metabolism and its regulation. Here, multiple metabolic engineering strategies were examined in the model plant Arabidopsis thaliana. This was achieved by constitutive overexpression of the three biosynthesis genes responsible for B1 synthesis, HMP-P synthase (THIC), HET-P synthase (THI1), and HMP-P kinase/TMP pyrophosphorylase (TH1), either separate or in combination. By monitoring the levels of thiamin, its phosphorylated entities, and its biosynthetic intermediates, we gained insight into the effect of either strategy on thiamin biosynthesis. Moreover, expression analysis of thiamin biosynthesis genes showed the plant's intriguing ability to respond to alterations in the pathway. Overall, we revealed the necessity to balance the pyrimidine and thiazole branches of thiamin biosynthesis and assessed its biosynthetic intermediates. Furthermore, the accumulation of nonphosphorylated intermediates demonstrated the inefficiency of endogenous thiamin salvage mechanisms. These results serve as guidelines in the development of novel thiamin metabolic engineering strategies.

Nutritional and Functional Evaluation of Inula crithmoides and Mesembryanthemum nodiflorum Grown in Different Salinities for Human Consumption

The nutritional composition and productivity of halophytes is strongly related to the biotic/abiotic stress to which these extremophile salt tolerant plants are subjected during their cultivation cycle. In this study, two commercial halophyte species (Inula crithmoides and Mesembryanthemum nodiflorum) were cultivated at six levels of salinity using a soilless cultivation system. In this way, it was possible to understand the response mechanisms of these halophytes to salt stress. The relative productivity decreased from the salinities of 110 and 200 mmol L⁻¹ upwards for I. crithmoides and M. nodiflorum, respectively. Nonetheless, the nutritional profile for human consumption remained balanced. In general, I. crithmoides vitamin (B1 and B6) contents were significantly higher than those of M. nodiflorum. For both species, β-carotene and lutein were induced by salinity, possibly as a response to oxidative stress. Phenolic compounds were more abundant in plants cultivated at lower salinities, while the antioxidant activity increased as a response to salt stress. Sensory characteristics were evaluated by a panel of culinary chefs showing a preference for plants grown at the salt concentration of 350 mmol L⁻¹. In summary, salinity stress was effective in boosting important nutritional components in these species, and the soilless system promotes the sustainable and safe production of halophyte plants for human consumption.

Wastewater from Washed Rice Water as Plant Nutrient Source: Current Understanding and Knowledge Gaps

A significant wastewater source in every household is washed rice water (WRW) because it contains leached nutrients (from washing the rice prior to cooking) that could be used as fertilizer. The paper reviewed the current understanding of the potential use of WRW as a plant nutrient source. WRW was shown to increase vegetables growth, such as water spinach, pak choy, lettuce, mustard, tomato, and eggplant. Different researchers have used various amounts of WRW, and their results followed a similar trend: the higher the amount of WRW, the higher the plant growth. WRW has also been used for other purposes, such as a source of carbon for microbial growth. WRW from brown rice and white rice had nutrients ranging from 40-150, 43-16306, 51-200, 8-3574, 36-1425, 27-212, and 32-560 mg L-1 of N, P, K, Ca, Mg, S, and vitamin B1 (thiamine), respectively. Proper utilization of WRW could reduce chemical fertilizer use and prevent both surface and groundwater contamination and environmental pollution. However, only a few of the studies have compared the use of WRW with the use of conventional NPK fertilizer. The major drawback of WRW studies is that they lack depth and scope, such as determining the initial and (or) final soil physico-chemical properties or plant nutrient contents. Considering the rich nutrient content in WRW, it will impact plant growth and soil fertility when used as both irrigation water and plant nutrient source. Therefore, it is recommended that studies on WRW effect on soil microbial population, plant, and soil nutrient contents to be carried out to ascertain the sustainability of WRW use as a plant nutrient source.

Conferring thermotolerant phenotype to wild-type Yarrowia lipolytica improves cell growth and erythritol production

In microbial engineering, heat stress is an important environmental factor modulating cell growth, metabolic flux distribution and the synthesis of target products. Yarrowia lipolytica, as a GARS (generally recognized as safe) nonconventional yeast, has been widely used in the food industry, especially as the host of erythritol production. Biomanufacturing economics is limited by the high operational cost of cooling energy in large-scale fermentation. It is of great significance to select thermotolerant Y. lipolytica to reduce the cooling cost and elucidate the heat-resistant mechanism at molecular level. For this purpose, we performed adaptive evolution and obtained a thermotolerant strain named Y. lipolytica BBE-18. Transcriptome analysis allows us to identify four genes in thiamine metabolism pathway that are responsible for the complicated thermotolerant phenotype. The heat-resistant phenotype was validated with the model strain Y. lipolytica Po1f by overexpression of single and combined genes. Then, conferring the thermotolerant phenotype to the wild-type Y. lipolytica BBE-17 enable the strain to produce three-times more erythritol of the control strain with 3°C higher than optimal cultivation temperature. To our knowledge, this is the first report on engineering heat-resistant phenotype to improve the erythritol production in Y. lipolytica. However, due to the increase of culture temperature, a large amount of adenosine triphosphate is consumed to ensure the life activities of Y. lipolytica which limits the potential of cell synthetic products to a certain extent. Even so, this study provides a reference for Y. lipolytica to produce other products under high temperature.