Cytosolic hydroxymethyldihydropterin pyrophosphokinase/dihydropteroate synthase from Arabidopsis thaliana: a specific role in early development and stress response.
In plants, 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase/7,8-dihydropteroate synthase (mitHPPK/DHPS) is a bifunctional mitochondrial enzyme, which catalyzes the first two consecutive steps of tetrahydrofolate biosynthesis. Mining the Arabidopsis genome data base has revealed a second gene encoding a protein that lacks a potential transit peptide, suggesting a cytosolic localization of the isoenzyme (cytHPPK/DHPS). When the N-terminal part of the cytHPPK/DHPS was fused to green fluorescent protein, the fusion protein appeared only in the cytosol, confirming the above prediction. Functionality of cytHPPK/DHPS was addressed by two parallel approaches: first, the cytHPPK/DHPS was able to rescue yeast mutants lacking corresponding activities; second, recombinant cytHPPK/DHPS expressed and purified from Escherichia coli displayed both HPPK and DHPS activities in vitro. In contrast to mitHPPK/DHPS, which was ubiquitously expressed, the cytHPPK/DHPS gene was exclusively expressed in reproductive tissue, more precisely in developing seeds as revealed by histochemical analysis of a transgenic cytHPPK/DHPS promoter-GUS line. In addition, it was observed that expression of cytHPPK/DHPS mRNA was induced by salt stress, suggesting a potential role of the enzyme in stress response. This was supported by the phenotype of a T-DNA insertion mutant in the cytHPPK/DHPS gene, resulting in lower germination rates as compared with the wild-type upon application of oxidative and osmotic stress.
Storozhenko
Sergei
S
Unit of Plant Hormone Signaling and Bio-imaging, Department of Molecular Genetics, Ghent University, K. L. Ledeganckstraat 35, B-9000 Gent, Belgium.
Navarrete
Oscar
O
Ravanel
Stéphane
S
De Brouwer
Veerle
V
Chaerle
Peter
P
Zhang
Guo-Fang
GF
Bastien
Olivier
O
Lambert
Willy
W
Rébeillé
Fabrice
F
Van Der Straeten
Dominique
D
D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D001483:Base Sequence; D003593:Cytoplasm / Q000201:enzymology* / Q000235:genetics; D004094:Dihydropteroate Synthase / Q000235:genetics / Q000378:metabolism*; D017854:Diphosphotransferases / Q000235:genetics / Q000378:metabolism*; D018745:Genome, Plant; D018525:Germination / Q000235:genetics; D008928:Mitochondria / Q000201:enzymology* / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D009997:Osmotic Pressure; D018384:Oxidative Stress / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D013763:Tetrahydrofolates / Q000096:biosynthesis
D010940:Plant Proteins; D013763:Tetrahydrofolates; C030371:5,6,7,8-tetrahydrofolic acid; D004094:Dihydropteroate Synthase; D017854:Diphosphotransferases; C019684:2-amino-4-hydroxy-6-hydroxymethyldihydropteridine pyrophosphokinase