The Arabidopsis thiamin-deficient mutant pale green1 lacks thiamin monophosphate phosphatase of the vitamin B1 biosynthesis pathway

Physiological and Transcriptomic Analyses Reveal the Mechanisms Underlying Methyl Jasmonate-Induced Mannitol Stress Resistance in Banana

Exogenous methyl jasmonate (MeJA) application has shown promising effects on plant defense under diverse abiotic stresses. However, the mechanisms underlying MeJA-induced stress resistance in bananas are unclear. Therefore, in this study, we treated banana plants with 100 μM MeJA before inducing osmotic stress using mannitol. Plant phenotype and antioxidant enzyme activity results demonstrated that MeJA improved osmotic stress resistance in banana plants. Thereafter, to explore the molecular mechanisms underlying MeJA-induced osmotic stress resistance in banana seedlings, we conducted high-throughput RNA sequencing (RNA-seq) using leaf and root samples of "Brazilian" banana seedlings treated with MeJA for 0 h and 8 h. RNA-seq analysis showed that MeJA treatment upregulated 1506 (leaf) and 3341 (root) genes and downregulated 1768 (leaf) and 4625 (root) genes. Then, we performed gene ontology and Kyoto Encyclopedia of Genes and Genomes analyses on the differentially expressed genes. We noted that linoleic acid metabolism was enriched in both root and leaf samples, and the genes of this pathway exhibited different expression patterns; 9S-LOX genes were highly induced by MeJA in the leaves, whereas 13S-LOX genes were highly induced in the roots. We also identified the promoters of these genes, as the differences in response elements may contribute to tissue-specific gene expression in response to MeJA application in banana seedlings. Overall, the findings of this study provide insights into the mechanisms underlying abiotic stress resistance in banana that may aid in the improvement of banana varieties relying on molecular breeding.

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.

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.

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.

Vitamin B1 THIAMIN REQUIRING1 synthase mediates the maintenance of chloroplast function by regulating sugar and fatty acid metabolism in rice

Vitamin B₁ (VB1), including thiamin, thiamin monophosphate (TMP), and thiamin pyrophosphate (TPP), is an essential micronutrient for all living organisms. Nevertheless, the precise function of VB1 in rice remains unclear. Here, we described a VB1 auxotrophic mutant, chlorotic lethal seedling (cles) from the mutation of OsTH1, which displayed collapsed chloroplast membrane system and decreased pigment content. OsTH1 encoded a phosphomethylpyrimidine kinase/thiamin-phosphate pyrophosphorylase, and was expressed in various tissues, especially in seedlings, leaves, and young panicles. The VB1 content in cles was markedly reduced, despite an increase in the expression of VB1 synthesis genes. The decreased TPP content affected the tricarboxylic acid cycle, pentose phosphate pathway, and de novo fatty acid synthesis, leading to a reduction in fatty acids (C16:0 and C18:0) and sugars (sucrose and glucose) of cles. Additionally, irregular expression of chloroplast membrane synthesis genes led to membrane collapse. We also found that alternative splicing and translation allowed OsTH1 to be localized to both chloroplast and cytosol. Our study revealed that OsTH1 was an essential enzyme in VB1 biosynthesis and played crucial roles in seedling growth and development by participating in fatty acid and sugar metabolism, providing new perspectives on VB1 function in rice.

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.

Mapping of dwarfing QTL of Ari1327, a semi-dwarf mutant of upland cotton

BACKGROUND

Upland Cotton (Gossypium hirsutum L.) has few cotton varieties suitable for mechanical harvesting. The plant height of the cultivar is one of the key features that need to modify. Hence, this study was planned to locate the QTL for plant height in a 60Co γ treated upland cotton semi-dwarf mutant Ari1327.

RESULTS

Interestingly, bulk segregant analysis (BSA) and genotyping by sequencing (GBS) methods exhibited that candidate QTL was co-located in the region of 5.80-9.66 Mb at D01 chromosome in two F2 populations. Using three InDel markers to genotype a population of 1241 individuals confirmed that the offspring's phenotype is consistent with the genotype. Comparative analysis of RNA-seq between the mutant and wild variety exhibited that Gh_D01G0592 was identified as the source of dwarfness from 200 genes. In addition, it was also revealed that the appropriate use of partial separation markers in QTL mapping can escalate linkage information.

CONCLUSIONS

Overwhelmingly, the results will provide the basis to reveal the function of candidate genes and the utilization of excellent dwarf genetic resources in the future.

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.

Metabolic engineering of rice endosperm towards higher vitamin B1 accumulation

Rice is a major food crop to approximately half of the human population. Unfortunately, the starchy endosperm, which is the remaining portion of the seed after polishing, contains limited amounts of micronutrients. Here, it is shown that this is particularly the case for thiamin (vitamin B1). Therefore, a tissue-specific metabolic engineering approach was conducted, aimed at enhancing the level of thiamin specifically in the endosperm. To achieve this, three major thiamin biosynthesis genes, THIC, THI1 and TH1, controlled by strong endosperm-specific promoters, were employed to obtain engineered rice lines. The metabolic engineering approaches included ectopic expression of THIC alone, in combination with THI1 (bigenic) or combined with both THI1 and TH1 (trigenic). Determination of thiamin and thiamin biosynthesis intermediates reveals the impact of the engineering approaches on endosperm thiamin biosynthesis. The results show an increase of thiamin in polished rice up to threefold compared to WT, and stable upon cooking. These findings confirm the potential of metabolic engineering to enhance de novo thiamin biosynthesis in rice endosperm tissue and aid in steering future biofortification endeavours.

Antioxidants in Potatoes: A Functional View on One of the Major Food Crops Worldwide

With a growing world population, accelerating climate changes, and limited arable land, it is critical to focus on plant-based resources for sustainable food production. In addition, plants are a cornucopia for secondary metabolites, of which many have robust antioxidative capacities and are beneficial for human health. Potato is one of the major food crops worldwide, and is recognized by the United Nations as an excellent food source for an increasing world population. Potato tubers are rich in a plethora of antioxidants with an array of health-promoting effects. This review article provides a detailed overview about the biosynthesis, chemical and health-promoting properties of the most abundant antioxidants in potato tubers, including several vitamins, carotenoids and phenylpropanoids. The dietary contribution of diverse commercial and primitive cultivars are detailed and document that potato contributes much more than just complex carbohydrates to the diet. Finally, the review provides insights into the current and future potential of potato-based systems as tools and resources for healthy and sustainable food production.

Characterization and Fine Mapping of a Yellow-Virescent Gene Regulating Chlorophyll Biosynthesis and Early Stage Chloroplast Development in Brassica napus

Chlorophyll biosynthesis and chloroplast development are crucial to photosynthesis and plant growth, but their regulatory mechanism remains elusive in many crop species. We isolated a Brassica napus yellow-virescent leaf (yvl) mutant, which exhibited yellow-younger-leaf and virescent-older-leaf with decreased chlorophyll accumulation and delayed chloroplast development. We mapped yvl locus to a 70-kb interval between molecular markers yvl-O10 and InDel-O6 on chromosome A03 in BC₂F₂ population using whole genome re-sequencing and bulked segregant analysis. The mutant had a ‘C’ to ‘T’ substitution in the coding sequence of BnaA03.CHLH, which encodes putative H subunit of Mg-protoporphyrin IX chelatase (CHLH). The mutation resulted in an imperfect protein structure and reduced activity of CHLH. It also hampered the plastid encoded RNA polymerase which transcribes regulatory genes of photosystem II and I. Consequently, the chlorophyll a/b and carotenoid contents were reduced and the chloroplast ultrastructure was degraded in yvl mutant. These results explain that a single nucleotide mutation in BnaA03.CHLH impairs PEP activity to disrupt chloroplast development and chlorophyll biosynthesis in B. napus.

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

Ensuring that people have access to sufficient and nutritious food is necessary for a healthy life and the core tenet of food security. With the global population set to reach 9.8 billion by 2050, and the compounding effects of climate change, the planet is facing challenges that necessitate significant and rapid changes in agricultural practices. In the effort to provide food in terms of calories, the essential contribution of micronutrients (vitamins and minerals) to nutrition is often overlooked. Here, we focus on the importance of thiamine (vitamin B1) in plant health and discuss its impact on human health. Vitamin B1 is an essential dietary component, and deficiencies in this micronutrient underlie several diseases, notably nervous system disorders. The predominant source of dietary vitamin B1 is plant-based foods. Moreover, vitamin B1 is also vital for plants themselves, and its benefits in plant health have received less attention than in the human health sphere. In general, vitamin B1 is well-characterized for its role as a coenzyme in metabolic pathways, particularly those involved in energy production and central metabolism, including carbon assimilation and respiration. Vitamin B1 is also emerging as an important component of plant stress responses, and several noncoenzyme roles of this vitamin are being characterized. We summarize the importance of vitamin B1 in plants from the perspective of food security, including its roles in plant disease resistance, stress tolerance, and crop yield, and review the potential benefits of biofortification of crops with increased vitamin B1 content to improve human health.

On the nature of thiamine triphosphate in Arabidopsis

Vitamin B1 is a family of molecules, the most renowned member of which is diphosphorylated thiamine (TDP)-a coenzyme vital for the activity of key enzymes of energy metabolism. Triphosphorylated thiamine derivatives also exist within this family, specifically thiamine triphosphate (TTP) and adenosine thiamine triphosphate (ATTP). They have been investigated primarily in mammalian cells and are thought to act as metabolic messengers but have not received much attention in plants. In this study, we set out to examine for the presence of these triphosphorylated thiamine derivatives in Arabidopsis. We could find TTP in Arabidopsis under standard growth conditions, but we could not detect ATTP. Interestingly, TTP is found primarily in shoot tissue. Drivers of TTP synthesis are light intensity, the proton motive force, as well as TDP content. In plants, TTP accumulates in the organellar powerhouses, the plastids, and mitochondria. Furthermore, in contrast to other B1 vitamers, there are strong oscillations in tissue levels of TTP levels over diel periods peaking early during the light period. The elevation of TTP levels during the day appears to be coupled to a photosynthesis-driven process. We propose that TTP may signify TDP sufficiency, particularly in the organellar powerhouses, and discuss our findings in relation to its role.

Fine Mapping to Identify the Functional Genetic Locus for Red Coloration in Pyropia yezoensis Thallus

Pyropia yezoensis, commonly known as "Nori" or "Laver" is an economically important marine crop. In natural or selected populations of P. yezoensis, coloration mutants are frequently observed. Various coloration mutants are excellent materials for genetic research and study photosynthesis. However, the candidate gene controlling the Pyropia coloration phenotype remains unclear to date. QTL-seq, in combination with kompetitive allele-specific PCR (KASP) and RNA-seq, can be generally applied to population genomics studies to rapidly identify genes that are responsible for phenotypes showing extremely opposite traits. Through cross experiments between the wild line RZ and red-mutant HT, offsprings with 1-4 sectors chimeric blade were generated. Statistical analyses revealed that the red thallus coloration phenotype is conferred by a single nuclear allele. Two-pair populations, consisting of 24 and 56 wild-type/red-type single-genotype sectors from F1 progeny, were used in QTL-seq to detect a genomic region in P. yezoensis harboring the red coloration locus. Based on a high-quality genome, we first identified the candidate region within a 3.30-Mb region at the end of chromosome 1. Linkage map-based QTL analysis was used to confirm the candidate region identified by QTL-seq. Then, four KASP markers developed in this region were used to narrow down the candidate region to a 1.42-Mb region. Finally, we conducted RNA-seq to focus on 13 differentially expressed genes and further predicted rcl-1, which contains one non-synonymous SNP [A/C] in the coding region that could be regulating red thallus coloration in P. yezoensis. Our results provide novel insights into the underlying mechanism controlling blade coloration, which is a desirable trait in algae.

The coenzyme thiamine diphosphate displays a daily rhythm in the Arabidopsis nucleus

In plants, metabolic homeostasis—the driving force of growth and development—is achieved through the dynamic behavior of a network of enzymes, many of which depend on coenzymes for activity. The circadian clock is established to influence coordination of supply and demand of metabolites. Metabolic oscillations independent of the circadian clock, particularly at the subcellular level is unexplored. Here, we reveal a metabolic rhythm of the essential coenzyme thiamine diphosphate (TDP) in the Arabidopsis nucleus. We show there is temporal separation of the clock control of cellular biosynthesis and transport of TDP at the transcriptional level. Taking advantage of the sole reported riboswitch metabolite sensor in plants, we show that TDP oscillates in the nucleus. This oscillation is a function of a light-dark cycle and is independent of circadian clock control. The findings are important to understand plant fitness in terms of metabolite rhythms.

Noordally et al. show that the essential coenzyme thiamine diphosphate exhibits a daily rhythm in the Arabidopsis nucleus, which is driven by light-dark cycles and not by the circadian clock. This study provides insight into our understanding of the optimization of plant fitness.

Ascorbate and Thiamin: Metabolic Modulators in Plant Acclimation Responses

Cell compartmentalization allows incompatible chemical reactions and localised responses to occur simultaneously, however, it also requires a complex system of communication between compartments in order to maintain the functionality of vital processes. It is clear that multiple such signals must exist, yet little is known about the identity of the key players orchestrating these interactions or about the role in the coordination of other processes. Mitochondria and chloroplasts have a considerable number of metabolites in common and are interdependent at multiple levels. Therefore, metabolites represent strong candidates as communicators between these organelles. In this context, vitamins and similar small molecules emerge as possible linkers to mediate metabolic crosstalk between compartments. This review focuses on two vitamins as potential metabolic signals within the plant cell, vitamin C (L-ascorbate) and vitamin B₁ (thiamin). These two vitamins demonstrate the importance of metabolites in shaping cellular processes working as metabolic signals during acclimation processes. Inferences based on the combined studies of environment, genotype, and metabolite, in order to unravel signaling functions, are also highlighted.

Construction and applications of a B vitamin genetic resource for investigation of vitamin-dependent metabolism in maize

The B vitamins provide essential co-factors for central metabolism in all organisms. In plants, B vitamins have surprising emerging roles in development, stress tolerance and pathogen resistance. Hence, there is a paramount interest in understanding the regulation of vitamin biosynthesis as well as the consequences of vitamin deficiency in crop species. To facilitate genetic analysis of B vitamin biosynthesis and functions in maize, we have mined the UniformMu transposon resource to identify insertional mutations in vitamin pathway genes. A screen of 190 insertion lines for seed and seedling phenotypes identified mutations in biotin, pyridoxine and niacin biosynthetic pathways. Importantly, isolation of independent insertion alleles enabled genetic confirmation of genotype-to-phenotype associations. Because B vitamins are essential for survival, null mutations often have embryo lethal phenotypes that prevent elucidation of subtle, but physiologically important, metabolic consequences of sub-optimal (functional) vitamin status. To circumvent this barrier, we demonstrate a strategy for refined genetic manipulation of vitamin status based on construction of heterozygotes that combine strong and hypomorphic mutant alleles. Dosage analysis of pdx2 alleles in endosperm revealed that endosperm supplies pyridoxine to the developing embryo. Similarly, a hypomorphic bio1 allele enabled analysis of transcriptome and metabolome responses to incipient biotin deficiency in seedling leaves. We show that systemic pipecolic acid accumulation is an early metabolic response to sub-optimal biotin status highlighting an intriguing connection between biotin, lysine metabolism and systemic disease resistance signaling. Seed-stocks carrying insertions for vitamin pathway genes are available for free, public distribution via the Maize Genetics Cooperation Stock Center.

GmPGL1, a Thiamine Thiazole Synthase, Is Required for the Biosynthesis of Thiamine in Soybean

Thiamine is an essential cofactor in several enzymatic reactions for all living organisms. Animals cannot synthesize thiamine and depend on their diet. Enhancing the content of thiamine is one of the most important goals of plant breeding to solve the thiamine deficiency associated with the low-thiamin staple crops. In this study, a Glycine max pale green leaf 1 (Gmpgl1) mutant was isolated from the EMS mutagenized population of soybean cultivar, Williams 82. Map-based cloning of the GmPGL1 locus revealed a single nucleotide deletion at the 292th nucleotide residue of the first exon of Glyma.10g251500 gene in Gmpgl1 mutant plant, encoding a thiamine thiazole synthase. Total thiamine contents decreased in both seedlings and seeds of the Gmpgl1 mutant. Exogenous application of thiazole restored the pale green leaf phenotype of the mutant. The deficiency of thiamine in Gmpgl1 mutant led to reduced activities of the pyruvate dehydrogenase (PDH) and pyruvate decarboxylase (PDC), and decreased contents of six amino acids as compared to that in the wild type plants. These results revealed that GmPGL1 played an essential role in thiamine thiazole biosynthesis.

ACR11 modulates levels of reactive oxygen species and salicylic acid-associated defense response in Arabidopsis

The ACT domain (aspartate kinase, chorismate mutase and TyrA), an allosteric effector binding domain, is commonly found in amino acid metabolic enzymes. In addition to ACT domain-containing enzymes, plants have a novel family of ACT domain repeat (ACR) proteins, which do not contain any recognizable catalytic domain. Arabidopsis has 12 ACR proteins, whose functions are largely unknown. To study the functions of Arabidopsis ACR11, we have characterized two independent T-DNA insertion mutants, acr11-2 and acr11-3. RNA gel-blot analysis revealed that the expression of wild-type ACR11 transcripts was not detectable in the acr11 mutants. Interestingly, a lesion-mimic phenotype occurs in some rosette leaves of the acr11 mutants. In addition, high levels of reactive oxygen species (ROS), salicylic acid (SA), and callose accumulate in the mutant leaves when grown under normal conditions. The expression of several SA marker genes and the key SA biosynthetic gene ISOCHORISMATE SYNTHASE1 is up-regulated in the acr11 mutants. Furthermore, the acr11 mutants are more resistant to the infection of bacterial pathogen Pseudomonas syringae pathovar tomato DC3000. These results suggest that ACR11 may be directly or indirectly involved in the regulation of ROS and SA accumulation, which in turn modulates SA-associated defense responses and disease resistance in Arabidopsis.

Redesigning thiamin synthesis: Prospects and potential payoffs

Thiamin is essential for plant growth but is short-lived in vivo and energetically very costly to produce - a combination that makes thiamin biosynthesis a prime target for improvement by redesign. Thiamin consists of thiazole and pyrimidine moieties. Its high biosynthetic cost stems from use of the suicide enzyme THI4 to form the thiazole and the near-suicide enzyme THIC to form the pyrimidine. These energetic costs lower biomass yield potential and are likely compounded by environmental stresses that destroy thiamin and hence increase the rate at which it must be made. The energy costs could be slashed by refactoring the thiamin biosynthesis pathway to eliminate the suicidal THI4 and THIC reactions. To substantiate this design concept, we first document the energetic costs of the THI4 and THIC steps in the pathway and explain how cutting these costs could substantially increase crop biomass and grain yields. We then show that a refactored pathway must produce thiamin itself rather than a stripped-down analog because the thiamin molecule cannot be simplified without losing biological activity. Lastly, we consider possible energy-efficient alternatives to the inefficient natural THI4- and THIC-mediated steps.

Toward Eradication of B-Vitamin Deficiencies: Considerations for Crop Biofortification

'Hidden hunger' involves insufficient intake of micronutrients and is estimated to affect over two billion people on a global scale. Malnutrition of vitamins and minerals is known to cause an alarming number of casualties, even in the developed world. Many staple crops, although serving as the main dietary component for large population groups, deliver inadequate amounts of micronutrients. Biofortification, the augmentation of natural micronutrient levels in crop products through breeding or genetic engineering, is a pivotal tool in the fight against micronutrient malnutrition (MNM). Although these approaches have shown to be successful in several species, a more extensive knowledge of plant metabolism and function of these micronutrients is required to refine and improve biofortification strategies. This review focuses on the relevant B-vitamins (B1, B6, and B9). First, the role of these vitamins in plant physiology is elaborated, as well their biosynthesis. Second, the rationale behind vitamin biofortification is illustrated in view of pathophysiology and epidemiology of the deficiency. Furthermore, advances in biofortification, via metabolic engineering or breeding, are presented. Finally, considerations on B-vitamin multi-biofortified crops are raised, comprising the possible interplay of these vitamins in planta.