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

摘要

PDX3 and SALT OVERLY SENSITIVE4 (SOS4), encoding pyridoxine/pyridoxamine 5#-phosphate oxidase and pyridoxalnkinase, respectively, are the only known genes involved in the salvage pathway of pyridoxal 5#-phosphate in plants. In thisnstudy, we determined the phenotype, stress responses, vitamer levels, and regulation of the vitamin B6 pathway genes innArabidopsis (Arabidopsis thaliana) plants mutant in PDX3 and SOS4. sos4 mutant plants showed a distinct phenotypencharacterized by chlorosis and reduced plant size, as well as hypersensitivity to sucrose in addition to the previously notednNaCl sensitivity. This mutant had higher levels of pyridoxine, pyridoxamine, and pyridoxal 5#-phosphate than the wild type,nreflected in an increase in total vitamin B6 observed through HPLC analysis and yeast bioassay. The sos4 mutant showednincreased activity of PDX3 as well as of the B6 de novo pathway enzyme PDX1, correlating with increased total B6 levels. Twonindependent lines with T-DNA insertions in the promoter region of PDX3 (pdx3-1 and pdx3-2) had decreased PDX3 activity.nBoth also had decreased activity of PDX1, which correlated with lower levels of total vitamin B6 observed using the yeastnbioassay; however, no differences were noted in levels of individual vitamers by HPLC analysis. Both pdx3 mutants showedngrowth reduction in vitro and in vivo as well as an inability to increase growth under high light conditions. Increasednexpression of salvage and some of the de novo pathway genes was observed in both the pdx3 and sos4 mutants. In all mutants,nincreased expression was more dramatic for the salvage pathway genes.