Molecular and physiological characterization of the NAD-dependent glycerol 3-phosphate dehydrogenase in the filamentous fungus Aspergillus nidulans.
In filamentous fungi, glycerol biosynthesis has been proposed to play an important role during conidiospore germination and in response to a hyperosmotic shock, but little is known about the genes involved. Here, we report on the characterization of the major Aspergillus nidulans glycerol 3-phosphate dehydrogenase (G3PDH)-encoding gene, gfdA. G3PDH is responsible for the conversion of dihydroxyacetone phosphate (DHAP) into glycerol 3-phosphate (G3P), which is subsequently converted into glycerol by an as yet uncharacterized phosphatase. Inactivation of gfdA does not abolish glycerol biosynthesis, showing that the other pathway from DHAP, via dihydroxyacetone (DHA), to glycerol is also functional in A. nidulans. The gfdA null mutant displays reduced G3P levels and an osmoremediable growth defect on various carbon sources except glycerol. This growth defect is associated with an abnormal hyphal morphology that is reminiscent of a cell wall defect. Furthermore, the growth defect at low osmolarity is enhanced in the presence of the chitin-interacting agent calcofluor and the membrane-destabilizing agent sodium dodecyl sulphate (SDS). As inactivation of gfdA has no impact on phospholipid biosynthesis or glycolytic intermediates levels, as might be expected from reduced G3P levels, a previously unsuspected link between G3P and cell wall integrity is proposed to occur in filamentous fungi.
Fillinger
S
S
Unité de Physiologie Cellulaire, Institut Pasteur, 25-28, rue du Dr Roux, 75724 Paris cedex 15, France.
Ruijter
G
G
Tamás
M J
MJ
Visser
J
J
Thevelein
J M
JM
d'Enfert
C
C
D000595:Amino Acid Sequence; D001233:Aspergillus nidulans / Q000166:cytology / Q000201:enzymology* / Q000235:genetics*; D002454:Cell Differentiation; D002473:Cell Wall / Q000378:metabolism; D004098:Dihydroxyacetone / Q000378:metabolism; D004099:Dihydroxyacetone Phosphate / Q000378:metabolism; D017353:Gene Deletion; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D050536:Glycerol-3-Phosphate Dehydrogenase (NAD+); D005993:Glycerolphosphate Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D005994:Glycerophosphates / Q000378:metabolism; D006131:Growth Inhibitors / Q000494:pharmacology; D008969:Molecular Sequence Data; D009154:Mutation; D009243:NAD / Q000378:metabolism*; D009997:Osmotic Pressure; D010743:Phospholipids / Q000032:analysis; D017386:Sequence Homology, Amino Acid; D013172:Spores, Fungal / Q000166:cytology
D005994:Glycerophosphates; D006131:Growth Inhibitors; D010743:Phospholipids; D009243:NAD; D004099:Dihydroxyacetone Phosphate; C029620:alpha-glycerophosphoric acid; D005993:Glycerolphosphate Dehydrogenase; D050536:Glycerol-3-Phosphate Dehydrogenase (NAD+); D004098:Dihydroxyacetone