Response of D. hansenii to osmotic stress

The euryhaline marine yeast Debaromyces hansenii is a model system for the study of genes related to osmotic stress. To study the transcriptional response of this organism to osmotic stress we have used the two color microarray based gene expression analysis of 6211 genes which constitutes the whole genome. Analysis was done at three time points after induction with salt (0.5h, 3h and 6h.) The mRNA level of 64 genes significantly increased at least 3-fold after induction with 2M NaCl whereas that of 45 genes was 3-fold diminished. The induced as well as the repressed genes were grouped into functional categories to identify biochemical processes possibly affected by osmotic shock. 53% of the induced genes encode for ribosomal proteins, 12.5% for mitochondrial and redox, 6% for aminoacid, cell wall and carbohydrate, and 1.5%for heat shock, protein transport and glycerol proteins. The function of 31% of repressed genes is currently unknown. 15% of the repressed genes are involved in carbohydrate metabolism and protective function, 6% are associated with cell wall, redox and signal transduction, and 4% in vacuolar and lipid functions. Surprisingly, the activity of NAD+ glycerol 3-phosphate dehydrogenase gene (GPD1) involved in the glycerol biosynthesis in response to osmotic stress did not show induction. Keywords: time course, stress response, mRNA expression The experimental design consisted of six microarray experiments. Cy-3 labeled cRNA control targets were combined with Cy-5 labeled cRNA experimental targets obtained from 0.5 hrs, 3 hrs and 6 hrs samples. The combined Cy-3 and Cy-5 cRNAs targets were used for probe hybridization onto the first, third, and fifth microarray, respectively. Dye swapping was done using different biological replicates for both Cy-5 labeled control targets and the Cy-3 experimental targets (as above) and used for hybridization on the second, fourth and the sixth microarray respectively, respectively. Dye swaps using different biological replicates were done to correct for any dye-bias.