Cloning, Function And Origin Of Dunaliella Salina Glycerol 3-phosphate Dehydrogenase Isoforms

Members of the genus Dunaliella are among the physiologically best studied unicellular green alga. Dunaliella contains some species that are recognized as the only eukaryotic and photosynthetic organisms able to grow in an extremely wide range of salt concentrations, from 0.3% to saturation (35%). Dunaliella lack a rigid cell wall and the cell is enclosed solely by a thin elastic plasma membrane. These factors make this alga a model organism to study salt and osmotic stress. Dunaliella cells can accumulate large amount glycerol quickly to balance the osmotic difference across plasma membrane. Two glycerol 3-phosphate dehydrogenase isoforms (the key enzyme in the glycerol synthesis pathway) are cloned by RACE methods. The cDNA are named GPDH1 and GPDH2. Expression study of GPDH1 and GPDH2 are performed using real-time PCR and Northern blot. The expression of GPDH1 is induced by salt stress, oxidative stress and anoxic stress. The expression of GPDH2 is induced by salt stress and anoxic stress, and inhibited by oxidative stress. Changes of the glycerol content are monitored under different conditions. We find that salt stress and oxidative stress can both induce glycerol synthesis in salina cells and the glycerol increases at almost the same rate despite the decrease of GPDH2 mRNA. Compare with Saccharomyces cerevisiae GPD1 and GPD2, we suggest that GPDH1 like GPD1 is induced by salt or osmotic stress,...