Functional complementation between thePDX1vitamin B6biosynthetic gene ofCercospora nicotianaeandpdxJofEscherichia coli

Endophytic Fungi of Native Salvia abrotanoides Plants Reveal High Taxonomic Diversity and Unique Profiles of Secondary Metabolites

Endophytic fungi are often embedded in their host's metabolic networks, which can result in alterations of metabolite production and higher amounts of active compounds in medicinal plants. This study reports the occurrence, diversity, and secondary metabolite profiles of endophytic fungi isolated from Salvia abrotanoides plants obtained from three geographically distinct sites in Iran. A total of 56 endophytic fungi were isolated from roots and leaves of S. abrotanoides; site-specificity and root-dominated colonization was found to be a general characteristic of the endophytes. Based on molecular identification, the endophytic fungi were classified into 15 genera. Mycelial extracts of these isolates were subjected to high-resolution mass spectrometry analyses and revealed a broad spectrum of secondary metabolites. Our results demonstrated that Penicillium canescens, P. murcianum, Paraphoma radicina, and Coniolariella hispanica are producers of cryptotanshinone, which is a main bioactive compound of S. abrotanoides. Moreover, it was shown that it can be produced independent of the host plant. The effect of exogenous gibberellin on S. abrotanoides and endophytic fungi was shown to have a positive effect on increasing the cryptotanshinone production in the plant as well as in endophytic fungi cultivated under axenic conditions. Our findings provide further evidence that endophytic fungi play an important role in the production plant bioactive metabolites. Moreover, they provide an exploitable basis to increase cryptotanshinone production in S. abrotanoides.

Bacillus subtilis CBR05 induces Vitamin B6 biosynthesis in tomato through the de novo pathway in contributing disease resistance against Xanthomonas campestris pv. vesicatoria

Expression profiling for genes involved in Vitamin B6 (VitB6) biosynthesis was undertaken to delineate the involvement of de novo and salvage pathway induced by Bacillus subtilis CBR05 against, Xanthomonas campestris pv. vesicatoria in tomato. Pyridoxine biosynthesis (PDX) genes such as PDX1.2 and PDX1.3, were found to be overexpressed significantly at 72 hpi in B. subtilis and pyridoxine inoculated plants. Most significant upregulation was observed in the transcript profile of PDX1.3, which showed more than 12- fold increase in expression. Unfortunately, salt sensitive overlay4 (SOS4) profiling showed irregular expression which corroborates that SOS4 role in VitB6 biosynthesis needs further studies for deciphering a clear notion about their role in tomato. Antioxidant enzymes i.e., superoxide dismutase, catalase, polyphenol oxidase, and peroxidase activities clearly demonstrate escalation till 48 hpi and gets reduced in 72 hpi. Pot trials also confirm that B. subtilis compared to pyridoxine supplementation alone show plant disease resistance and elongated roots. The present study confirms that B. subtilis, as a versatile agent in eliciting induced systemic resistance regulated by de novo pathway as a model for plant defense against X. campestris pv. vesicatoria substantiated by VitB6 biosynthesis. Nevertheless, the study is preliminary and needs further evidence for affirming this phenomenon.

SNZ3 Encodes a PLP Synthase Involved in Thiamine Synthesis in Saccharomyces cerevisiae

Pyridoxal 5′-phosphate (the active form of vitamin B₆) is a cofactor that is important for a broad number of biochemical reactions and is essential for all forms of life. Organisms that can synthesize pyridoxal 5′-phosphate use either the deoxyxylulose phosphate-dependent or -independent pathway, the latter is encoded by a two-component pyridoxal 5′-phosphate synthase. Saccharomyces cerevisiae contains three paralogs of the two-component SNZ/SNO pyridoxal 5′-phosphate synthase. Past work identified the biochemical activity of Snz1p, Sno1p and provided in vivo data that SNZ1 was involved in pyridoxal 5′-phosphate biosynthesis. Snz2p and Snz3p were considered redundant isozymes and no growth condition requiring their activity was reported. Genetic data herein showed that either SNZ2 or SNZ3 are required for efficient thiamine biosynthesis in Saccharomyces cerevisiae. Further, SNZ2 or SNZ3 alone could satisfy the cellular requirement for pyridoxal 5′-phosphate (and thiamine), while SNZ1 was sufficient for pyridoxal 5′-phosphate synthesis only if thiamine was provided. qRT-PCR analysis determined that SNZ2,3 are repressed ten-fold by the presence thiamine. In total, the data were consistent with a requirement for PLP in thiamine synthesis, perhaps in the Thi5p enzyme, that could only be satisfied by SNZ2 or SNZ3. Additional data showed that Snz3p is a pyridoxal 5′-phosphate synthase in vitro and is sufficient to satisfy the pyridoxal 5′-phosphate requirement in Salmonella enterica when the medium has excess ammonia.

Vitamin B6 biosynthetic genes expression and antioxidant enzyme properties in tomato against, Erwinia carotovora subsp. carotovora

Vitamin B6 (VitB6) is an essential cofactor for >140 biochemical reactions. Also, VitB6 is a potent antioxidant and helps plants cope with both biotic and abiotic stress conditions. However, the role of VitB6 in plant disease resistance has yet to be confirmed using molecular biology approaches. Here, we analyzed the expression patterns of VitB6 biosynthetic genes, including the de novo (PDX1 [PDX1.2 and 1.3] and PDX2) and the salvage (SOS4) pathways during the response to Erwinia carotovora subsp. carotovora. By quantitative PCR, we found that the most significant upregulation in the transcript profile of PDX2, which showed a 9.2-fold increase in expression at 12 h post inoculation (hpi) compared to 24-48 hpi. We also detected significant upregulation of PDX1.2 and PDX1.3, which were 6.6- and 4.3-fold upregulated at 24 hpi compared to 12 hpi, while SOS4 showed only low-level expression. Also, at 24 hpi, a significant increase in superoxide dismutase, catalase, peroxidase, and polyphenol oxidase activities was observed in plants. Our findings confirm that the expression of de novo and salvage pathway genes is induced by E. carotovora and that this plays an important role in the regulation of defense response by modulating cellular antioxidant capacity.

The de novo biosynthesis of vitamin B6 is required for disease resistance against Botrytis cinerea in tomato

Vitamin B6 (VB6), an essential cofactor for numerous metabolic enzymes, has recently been shown to act as a potent antioxidant and play important roles in developmental processes and stress responses. However, little is known about the possible function of VB6 in plant disease resistance response against pathogen infection. In the present study, we explored the possible involvement of VB6 in defense response against Botrytis cinerea through functional analysis of tomato VB6 biosynthetic genes. Three de novo VB6 biosynthetic genes (SlPDX1.2, SlPDX1.3, and SlPDX2) and one salvage pathway gene (SlSOS4) were identified and the SlPDX1.2, SlPDX1.3, and SlPDX2 genes were shown to encode functional enzymes involved in de novo biosynthesis of VB6, as revealed by complementation of the VB6 prototrophy in yeast snz1 and sno1 mutants. Expression of SlPDX1.2, SlPDX1.3, and SlSOS4 genes was induced by infection with B. cinerea. Virus-induced gene silencing-mediated knockdown of SlPDX1.2 or SlPDX1.3 but not SlPDX2 and SlSOS4 led to increased severity of disease caused by B. cinerea, indicating that the VB6 de novo biosynthetic pathway but not the salvage pathway is involved in tomato defense response against B. cinerea. Furthermore, the SlPDX1.2- and SlPDX1.3-silenced tomato plants exhibited reduced levels of VB6 contents and reactive oxygen species scavenging capability, increased levels of superoxide anion and H2O2 generation, and increased activity of superoxide dismutase after infection by B. cinerea. Our results suggest that VB6 and its de novo biosynthetic pathway play important roles in regulation of defense response against B. cinerea through modulating cellular antioxidant capacity.

The vitamin B₆ biosynthesis pathway in Streptococcus pneumoniae is controlled by pyridoxal 5'-phosphate and the transcription factor PdxR and has an impact on ear infection

Vitamin B₆ is an essential cofactor for a large number of enzymes in both prokaryotes and eukaryotes. In this study, we characterized the pyridoxal 5'-phosphate (PLP) biosynthesis pathway in Streptococcus pneumoniae. Our results revealed that S. pneumoniae possesses a de novo vitamin B₆ biosynthesis pathway encoded by the pdxST genes. Purified PdxS functionally displayed as PLP synthase, whereas PdxT exhibited glutaminase activity in vitro. Deletion of pdxS, but not pdxT, resulted in a vitamin B₆ auxotrophic mutant. The defective growth of the ΔpdxS mutant in a vitamin B₆-depleted medium could be chemically restored in the presence of the B₆ vitamers at optimal concentrations. By analyzing PdxS expression levels, we demonstrated that the expression of pdxS was repressed by PLP and activated by a transcription factor, PdxR. A pneumococcal ΔpdxR mutant also exhibited as a vitamin B₆ auxotroph. In addition, we found that disruption of the vitamin B₆ biosynthesis pathway in S. pneumoniae caused a significant attenuation in a chinchilla middle ear infection model and a minor attenuation in a mouse pneumonia model, indicating that the impact of vitamin B₆ synthesis on virulence depends upon the bacterial infection niche.

Pyridoxal phosphate: biosynthesis and catabolism

Vitamin B(6) is an essential cofactor that participates in a large number of biochemical reactions. Pyridoxal phosphate is biosynthesized de novo by two different pathways (the DXP dependent pathway and the R5P pathway) and can also be salvaged from the environment. It is one of the few cofactors whose catabolic pathway has been comprehensively characterized. It is also known to function as a singlet oxygen scavenger and has protective effects against oxidative stress in fungi. Enzymes utilizing vitamin B(6) are important targets for therapeutic agents. This review provides a concise overview of the mechanistic enzymology of vitamin B(6) biosynthesis and catabolism. This article is part of a Special Issue entitled: Pyridoxal Phosphate Enzymology.

Complex assembly and metabolic profiling of Arabidopsis thaliana plants overexpressing vitamin B₆ biosynthesis proteins

In plants, vitamin B₆ biosynthesis requires the activity of PDX1 and PDX2 proteins. Arabidopsis thaliana encodes for three PDX1 proteins, named PDX1.1, 1.2, and 1.3, but only one PDX2. Here, we show in planta complex assembly of PDX proteins, based on split-YFP and FPLC assays, and can demonstrate their presence in higher complexes of around 750 kDa. Metabolic profiling of plants ectopically expressing the different PDX proteins indicates a negative influence of PDX1.2 on vitamin B₆ biosynthesis and a correlation between aberrant vitamin B6 content, PDX1 gene expression, and light sensitivity specifically for PDX1.3. These findings provide first insights into in planta vitamin B₆ synthase complex assembly and new information on how the different PDX proteins affect plant metabolism.

Vitamin B6: Killing two birds with one stone?

Vitamin B6 comprises a group of compounds that are involved in a surprisingly high diversity of biochemical reactions. Actually, most of these reactions are co-catalyzed by a single B6 vitamer, pyridoxal 5'-phosphate, making it a crucial and versatile co-factor in many metabolic processes in the cell. In addition, it has been demonstrated in recent years that vitamin B6 has a second important function by being an effective antioxidant. Because of these two characteristics the vitamin is an interesting compound to study in plants. This review provides a brief overview and update on such important aspects like vitamin B6-dependent enzymes and known biosynthetic pathways in plants, phenotypes of plant mutants affected in vitamin B6 biosynthesis, and the potential benefits of modifying vitamin B6 content in plants.

Enhancement of vitamin B(6) levels in seeds through metabolic engineering

As a versatile cofactor for many enzymes catalyzing important biochemical reactions, vitamin B(6) is required for all cellular organisms. In contrast to bacteria, fungi and plants, which have the ability to synthesize vitamin B(6)de novo, animals have to take up the vitamin from their diet. Plants are the major source of vitamin B(6) for animals. The recent identification of vitamin B(6) biosynthetic enzymes PDX1 and PDX2 in plants makes it possible to regulate the biosynthesis of this important vitamin. In this study, we generated Arabidopsis plants overexpressing the PDX1 and/or PDX2 gene and used a liquid chromatography/mass spectrometry/mass spectrometry method to determine the levels of different forms of vitamin B(6) in these transgenic plants. It was found that expression of the PDX genes under control of the CaMV 35S promoter caused only a limited increase in pyridoxine contents in dry seeds but not in shoots or roots. When using the Arabidopsis seed-specific 12S promoter to drive the expression of the PDX genes, the levels of vitamin B(6) increased more than twofold in transgenic plants. Our work demonstrates that it is feasible to enhance vitamin B(6) content in seeds by metabolic engineering.

Gene-specific disruption in the filamentous fungus Cercospora nicotianae using a split-marker approach

To determine if DNA configuration, gene locus, and flanking sequences will affect homologous recombination in the phytopathogenic fungus Cercospora nicotianae, we evaluated and compared disruption efficiency targeting four cercosporin toxin biosynthetic genes encoding a polyketide synthase (CTB1), a monooxygenase/O-methyltransferase (CTB3), a NADPH-dependent oxidoreductase (CTB5), and a FAD/FMN-dependent oxidoreductase (CTB7). Transformation of C. nicotianae using a circular plasmid resulted in low disruption frequency. The use of endonucleases or a selectable marker DNA fragment flanked by homologous sequence either at one end or at both ends in the transformation procedures, increased disruption efficiency in some but not all CTB genes. A split-marker approach, using two DNA fragments overlapping within the selectable marker, increased the frequency of targeted gene disruption and homologous integration as high as 50%, depending on the target gene and on the length of homologous DNA sequence flanking the selectable marker. The results indicate that the split-marker approach favorably decreased ectopic integration and thus, greatly facilitated targeted gene disruption in this important fungal pathogen.

The Pdx1 family is structurally and functionally conserved between Arabidopsis thaliana and Ginkgo biloba

Vitamin B6 is one of the most important compounds in living organisms, and its biosynthesis has only recently been understood. Because it is required for more than 100 biochemical reactions, lack of the vitamin is fatal. This is of special importance to mammals and humans, which cannot biosynthesize the vitamin and thus depend on its external uptake. Here we describe the cloning of a vitamin B6 biosynthetic gene GbPDX1 from Ginkgo biloba. The gene is expressed in seeds, leaf and trunk tissue. Using yeast 2-hybrid and pull-down assays, we show that the protein can interact with itself and with members of Arabidopsis thaliana AtPDX1 and AtPDX2 families. Furthermore, we prove the function of GbPDX1 in vitamin B6 biosynthesis by complementation of an Arabidopsis AtPDX1.3 mutant rsr4-1, at the phenotypical level and increasing vitamin B6 levels caused by ectopic GbPDX1 expression in the mutant background. Overall, this study provides a first description of Ginkgo vitamin B6 metabolism, and demonstrates a high degree of conservation between Ginkgo and Arabidopsis.

Two independent routes of de novo vitamin B6 biosynthesis: not that different after all

Vitamin B6 is well known in its biochemically active form as pyridoxal 5'-phosphate, an essential cofactor of numerous metabolic enzymes. The vitamin is also implicated in numerous human body functions ranging from modulation of hormone function to its recent discovery as a potent antioxidant. Its de novo biosynthesis occurs only in bacteria, fungi and plants, making it an essential nutrient in the human diet. Despite its paramount importance, its biosynthesis was predominantly investigated in Escherichia coli, where it is synthesized from the condensation of deoxyxylulose 5-phosphate and 4-phosphohydroxy-L-threonine catalysed by the concerted action of PdxA and PdxJ. However, it has now become clear that the majority of organisms capable of producing this vitamin do so via a different route, involving precursors from glycolysis and the pentose phosphate pathway. This alternative pathway is characterized by the presence of two genes, Pdx1 and Pdx2. Their discovery has sparked renewed interest in vitamin B6, and numerous studies have been conducted over the last few years to characterize the new biosynthesis pathway. Indeed, enormous progress has been made in defining the nature of the enzymes involved in both pathways, and important insights have been provided into their mechanisms of action. In the present review, we summarize the recent advances in our knowledge of the biosynthesis of this versatile molecule and compare the two independent routes to the biosynthesis of vitamin B6. Surprisingly, this comparison reveals that the key biosynthetic enzymes of both pathways are, in fact, very similar both structurally and mechanistically.

Elucidating biosynthetic pathways for vitamins and cofactors

The elucidation of the pathways to the water-soluble vitamins and cofactors has provided many biochemical and chemical challenges. This is a reflection both of their complex chemical nature, and the fact that they are often made in small amounts, making detection of the enzyme activities and intermediates difficult. Here we present an orthogonal review of how these challenges have been overcome using a combination of methods, which are often ingenious. We make particular reference to some recent developments in the study of biotin, pantothenate, folate, pyridoxol, cobalamin, thiamine, riboflavin and molybdopterin biosynthesis.

Infectivity of nanovirus DNAs: induction of disease by cloned genome components of Faba bean necrotic yellows virus

Circumstantial evidence suggests that the genome of Faba bean necrotic yellows virus (FBNYV), a nanovirus, consists of eight distinct, circular, single-stranded DNAs, each of about 1 kb and encoding only one protein. Here, the use of cloned full-length FBNYV DNAs for reproducing FBNYV-like symptoms in Vicia faba, the principal natural host of FBNYV, is reported. Characteristic symptoms of FBNYV infection were obtained in faba bean plants following biolistic DNA delivery or agroinoculation with all eight FBNYV DNAs. Although the eight different DNAs have been invariably detected in field samples infected with the various geographical FBNYV isolates, experimental infection with different combinations of fewer than eight DNAs also led to typical FBNYV symptoms. Even only five genome components, DNA-R, DNA-S, DNA-M, DNA-U1 and DNA-U2, were sufficient for inducing disease symptoms in V. faba upon agroinoculation. Symptomatic plants agroinoculated or bombarded with eight DNAs contained typical FBNYV virions; however, the virus was not transmitted by Aphis craccivora or Acyrthosiphon pisum, two efficient aphid vectors of FBNYV.

Analysis of the Arabidopsis rsr4-1/pdx1-3 mutant reveals the critical function of the PDX1 protein family in metabolism, development, and vitamin B6 biosynthesis

Vitamin B6 represents a highly important group of compounds ubiquitous in all living organisms. It has been demonstrated to alleviate oxidative stress and in its phosphorylated form participates as a cofactor in >100 biochemical reactions. By means of a genetic approach, we have identified a novel mutant, rsr4-1 (for reduced sugar response), with aberrant root and leaf growth that requires supplementation of vitamin B6 for normal development. Cloning of the mutated gene revealed that rsr4-1 carries a point mutation in a member of the PDX1/SOR1/SNZ (for Pyridoxine biosynthesis protein 1/Singlet oxygen resistant 1/Snooze) family that leads to reduced vitamin B6 content. Consequently, metabolism is broadly altered, mainly affecting amino acid, raffinose, and shikimate contents and trichloroacetic acid cycle constituents. Yeast two-hybrid and pull-down analyses showed that Arabidopsis thaliana PDX1 proteins can form oligomers. Interestingly, the mutant form of PDX1 has severely reduced capability to oligomerize, potentially suggesting that oligomerization is important for function. In summary, our results demonstrate the critical function of the PDX1 protein family for metabolism, whole-plant development, and vitamin B6 biosynthesis in higher plants.

Analysis of the vitamin B6 biosynthesis pathway in the human malaria parasite Plasmodium falciparum

Vitamin B6 is an essential cofactor for more than 100 enzymatic reactions. Mammalian cells are unable to synthesize vitamin B6 de novo, whereas bacteria, plants, fungi, and as shown here Plasmodium falciparum possess a functional vitamin B6 synthesis pathway. P. falciparum expresses the proteins Pdx1 and Pdx2, corresponding to the yeast enzymes Snz1-p and Sno1-p, which are essential for the vitamin B6 biosynthesis. An involvement of PfPdx1 and PfPdx2 in the de novo synthesis of vitamin B6 was shown by complementation of pyridoxine auxotroph yeast cells. Both plasmodial proteins act together in the glutaminase activity with a specific activity of 209 nmol min(-1) mg(-1) and a K(m) value for glutamine of 1.3 mm. Incubation of the parasites with methylene blue revealed by Northern blot analysis an elevated transcriptional level of pdx1 and pdx2, suggesting a participation of these proteins in the defenses against singlet oxygen. To be an active cofactor, vitamin B6 has to be phosphorylated by the pyridoxine kinase (PdxK). The recombinant plasmodial PdxK revealed K(m) values for the B6 vitamers pyridoxine and pyridoxal and for ATP of 212, 70, and 82 microM, respectively. All three enzymes expose a stage-specific transcription pattern within the trophozoite stage that guarantees the concurrent expression of Pdx1, Pdx2, and PdxK for the indispensable provision of vitamin B6. The occurrence of the vitamin B6 de novo synthesis pathway displays a potential new drug target, which can be exploited for the development of new chemotherapeutics against the human malaria parasite P. falciparum.

The Methylerythritol Phosphate Pathway Is Functionally Active in All Intraerythrocytic Stages of Plasmodium falciparum

Two genes encoding the enzymes 1-deoxy-D-xylulose-5-phosphate synthase and 1-deoxy-D-xylulose-5-phosphate reductoisomerase have been recently identified, suggesting that isoprenoid biosynthesis in Plasmodium falciparum depends on the methylerythritol phosphate (MEP) pathway, and that fosmidomycin could inhibit the activity of 1-deoxy-D-xylulose-5-phosphate reductoisomerase. The metabolite 1-deoxy-D-xylulose-5-phosphate is not only an intermediate of the MEP pathway for the biosynthesis of isopentenyl diphosphate but is also involved in the biosynthesis of thiamin (vitamin B1) and pyridoxal (vitamin B6) in plants and many microorganisms. Herein we report the first isolation and characterization of most downstream intermediates of the MEP pathway in the three intraerythrocytic stages of P. falciparum. These include, 1-deoxy-D-xylulose-5-phosphate, 2-C-methyl-D-erythritol-4-phosphate, 4-(cytidine-5-diphospho)-2-C-methyl-D-erythritol, 4-(cytidine-5-diphospho)-2-C-methyl-D-erythritol-2-phosphate, and 2-C-methyl-D-erythritol-2,4-cyclodiphosphate. These intermediates were purified by HPLC and structurally characterized via biochemical and electrospray mass spectrometric analyses. We have also investigated the effect of fosmidomycin on the biosynthesis of each intermediate of this pathway and isoprenoid biosynthesis (dolichols and ubiquinones). For the first time, therefore, it is demonstrated that the MEP pathway is functionally active in all intraerythrocytic forms of P. falciparum, and de novo biosynthesis of pyridoxal in a protozoan is reported. Its absence in the human host makes both pathways very attractive as potential new targets for antimalarial drug development.