Analysis of theArabidopsis rsr4-1/pdx1-3Mutant Reveals the Critical Function of the PDX1 Protein Family in Metabolism, Development, and Vitamin B6 Biosynthesis

Abstract

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.

The Folylpolyglutamate Synthetase Plastidial Isoform Is Required for Postembryonic Root Development in Arabidopsis

“…For example, pyridoxine (vitamin B6) has been linked to the control of Arabidopsis root growth since a mutant in a gene that encodes a pyridoxine synthase 1 (pdx1) exhibited shorter primary roots compared with the wild type (Chen and Xiong, 2005;Wagner et al, 2006). In addition to their protective roles against oxidative stress, vitamins serve as cofactors for several enzymes that metabolize compounds required for normal cellular function.…”

“…Thus, the root growth defects reported in Arabidopsis pdx1 could be the result of alterations in metabolic pathways that are critical for the biosynthesis of compounds required for normal cell physiology. For example, the stunted root development in pdx1 was associated with impaired local auxin biosynthesis and a broad disruption in metabolism that led to altered levels of amino acids, sugars, and various organic acids (Wagner et al, 2006;Chen and Xiong, 2009).…”

The role of the pyridoxine (vitamin B6) biosynthesis enzyme PDX1 in ultraviolet-B radiation responses in plants

“…The two Arabidopsis proteins, PDX1.1 and PDX1.3, are too similar to be discriminated using our antibodies and we probably detect the functional PDX1.1 protein in the mutants. Recently, Wagner et al [20] concluded that both genes probably have overlapping functions, and both are required to act synergistically to establish pyridoxine homeostasis. Also, comparable basal levels of vitamin B 6 were detected in both the pdx1.3 mutant and in the Col-0 ecotype.…”

“…Tambasco-Studart et al [17] have shown that only the first and the third of these are functional homologues. Additionally, Wagner et al [20] have shown that both PDX1.1 and PDX1.3 can form a functional complex with the enzymatic partner PDX2. PDX1.2, on the other hand, could not.…”

Vitamin B6 Deficiency, Genome Instability and Cancer

“…Besides these roles, PLP also represents an important cofactor for the degradation of storage carbohydrates, such as glycogen. The PLP-dependent glycogen phosphorylase mediates the glycogen breakdown by the release of glucose from glycogen (Wagner, 2006). Furthermore, two PLP-dependent enzymes are involved in hemoglobin formation and chlorophyll biosynthesis.…”