| The genetic control of desiccation tolerance was not fully characterized. I aimed to analyze ESTs from the resurrection moss Tortula ruralis to investigate genes that control vegetative desiccation-tolerance. The EST-derived cDNA TrDr3 (T ortula r uralis Desiccation-stress Related) was characterized. The deduced polypeptide TRDR3 has a predicted molecular mass of 25.5 kDa, predicted pI of 6.7, and 6 trans-membrane helical domains. Preliminary expression analysis demonstrated that the TrDr3 transcript ratio increased in response to slow desiccation relative to the hydrated control in both the total and polysomal mRNA (mRNP) fractions which classifies TrDr3 as a rehydrin. Bioinformatic searches of the gene databases showed that Tortula TRDR3 shares significant similarity to the hdeD gene product ( HNS-dependent expression) from Escherichia coli. The function of the HdeD protein in E. coli is unknown, but it is postulated to be involved in a mechanism of acid-stress defense. To establish the role of E. coli hdeD in abiotic stress-tolerance, I determined the log survival percentage from shaking cultures of wild-type bacteria and the isogenic hdeD deletion strain (DeltahdeD) in the presence of low temperature (28°C), elevated NaCl (5% (w/v)), or decreased pH (4.5), or all treatments simultaneously. The Delta hdeD deletion strain was less sensitive, as compared to wild-type E. coli, in response to decreased pH (P < 0.009), and the combination of all three stresses (P < 0.0001). |
