Vitamin B6 biosynthesis in higher plants

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 102; no. 38; pp. 13687 - 13692
• Main Authors: Tambasco-Studart, M, Titiz, O, Raschle, T, Forster, G, Amrhein, N, Fitzpatrick, T.B
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 20.09.2005; National Acad Sciences
• Subjects: Amino Acid Sequence; amino acid sequences; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; biochemical pathways; Biological Sciences; Biosynthesis; Carbon-Nitrogen Lyases; Cytoplasm - enzymology; Dihydroxyacetone phosphate; Enzymes; Escherichia coli; Escherichia coli - enzymology; Escherichia coli - genetics; Escherichia coli Proteins - genetics; Escherichia coli Proteins - metabolism; Flowers & plants; Fungal Proteins - genetics; Fungal Proteins - metabolism; Fungi - enzymology; Fungi - genetics; genes; Glycolysis - physiology; Line spectra; Molecular Sequence Data; Nitrogenous Group Transferases - genetics; Nitrogenous Group Transferases - metabolism; nucleotide sequences; PDX1 gene; PDX2 gene; Pentose Phosphate Pathway - physiology; Pentosephosphates - genetics; Pentosephosphates - metabolism; Phenotypes; Proteins; Protoplasts; pyridoxine; Reaction products; Terpenoids; Vitamin B; Vitamin B 6 - biosynthesis; Vitamin B 6 - genetics; Yeasts
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0506228102

Vitamin B6 is an essential metabolite in all organisms. It can act as a coenzyme for numerous metabolic enzymes and has recently been shown to be a potent antioxidant. Plants and microorganisms have a de novo biosynthetic pathway for vitamin B6, but animals must obtain it from dietary sources. In Escherichia coli, it is known that the vitamin is derived from deoxyxylulose 5-phosphate (an intermediate in the nonmevalonate pathway of isoprenoid biosynthesis) and 4-phosphohydroxy-L-threonine. It has been assumed that vitamin B6 is synthesized in the same way in plants, but this hypothesis has never been experimentally proven. Here, we show that, in plants, synthesis of the vitamin takes an entirely different route, which does not involve deoxyxylulose 5-phosphate but instead utilizes intermediates from the pentose phosphate pathway, i.e., ribose 5-phosphate or ribulose 5-phosphate, and from glycolysis, i.e., dihydroxyacetone phosphate or glyceraldehyde 3-phosphate. The revelation is based on the recent discovery that, in bacteria and fungi, a novel pathway is in place that involves two genes (PDX1 and PDX2), neither of which is homologous to any of those involved in the previously doctrined E. coli pathway. We demonstrate that Arabidopsis thaliana has two functional homologs of PDX1 and a single homolog of PDX2. Furthermore, and contrary to what was inferred previously, we show that the pathway appears to be cytosolic and is not localized to the plastid. Last, we report that the single PDX2 homolog is essential for plant viability.