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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Vitamer Levels, Stress Response, Enzyme Activity, and Gene Regulation of Arabidopsis Lines Mutant in the Pyridoxine/Pyridoxamine 5'-Phosphate Oxidase (PDX3) and the Pyridoxal Kinase (SOS4) Genes Involved in the Vitamin B₆ Salvage Pathway^1,[W],[OA]

Department of Plant Biology, North Carolina State University, Raleigh, North Carolina 27695–7612 (E.G., M.E.D.); and Department of Crop Science, North Carolina State University, Raleigh, North Carolina 27695–7620 (D.D.)

PDX3 and SALT OVERLY SENSITIVE4 (SOS4), encoding pyridoxine/pyridoxamine 5'-phosphate oxidase and pyridoxal kinase, respectively, are the only known genes involved in the salvage pathway of pyridoxal 5'-phosphate in plants. In this study, we determined the phenotype, stress responses, vitamer levels, and regulation of the vitamin B₆ pathway genes in Arabidopsis (Arabidopsis thaliana) plants mutant in PDX3 and SOS4. sos4 mutant plants showed a distinct phenotype characterized by chlorosis and reduced plant size, as well as hypersensitivity to sucrose in addition to the previously noted NaCl sensitivity. This mutant had higher levels of pyridoxine, pyridoxamine, and pyridoxal 5'-phosphate than the wild type, reflected in an increase in total vitamin B₆ observed through HPLC analysis and yeast bioassay. The sos4 mutant showed increased activity of PDX3 as well as of the B₆ de novo pathway enzyme PDX1, correlating with increased total B₆ levels. Two independent lines with T-DNA insertions in the promoter region of PDX3 (pdx3-1 and pdx3-2) had decreased PDX3 activity. Both also had decreased activity of PDX1, which correlated with lower levels of total vitamin B₆ observed using the yeast bioassay; however, no differences were noted in levels of individual vitamers by HPLC analysis. Both pdx3 mutants showed growth reduction in vitro and in vivo as well as an inability to increase growth under high light conditions. Increased expression of salvage and some of the de novo pathway genes was observed in both the pdx3 and sos4 mutants. In all mutants, increased expression was more dramatic for the salvage pathway genes.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Margaret E. Daub (margaret_daub{at}ncsu.edu).

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.107.105189

^* Corresponding author; e-mail margaret_daub{at}ncsu.edu.

Received July 6, 2007; accepted September 8, 2007; published September 14, 2007.