Project description:In this study we have tried to utilize the unique aspects of the T. ruralis response to desiccation and rehydration to design a strategy to identify rehydrins that are of low abundance and perhaps completely novel to the desiccated or rehydration transcriptomes. We have constructed two Subtractive Suppression Hybridization (SSH) libraries (Diatchenko et al., 1996) that are designed to enrich for differentially expressed low-abundance transcripts contained within gametophytic cells either in the slow-dried state (mRNP sequestrated rehydrin transcripts) or cells that have been rapidly dried, rehydrated and sampled at 2h of hydration (rehydrin and recovery transcripts) when the translational change in gene expression is at its peak (Oliver 1991). To achieve this aim we constructed SSH libraries using PolyA RNA isolated from the polysomal (mRNP) fractions from the slow-dried and 2h rehydrated rapid dried gametophytes selected against PolyA RNA from hydrated control gametophytes as the source for driver cDNA. Collections of cDNA clones from each library were sequenced and used to generate a small T. ruralis SSH cDNA microarray for expression profiling of both total RNA extracts for transcript accumulation assessments and polysomal RNA extracts for transcript sequestration and recruitment assessments. To assess the expression characteristics of the transcripts represented by the SSH contigs we established a cDNA microarray containing the inserts (PCR derived fragment) from each of the 768 individual SSH ESTs, with the exception of thirteen that failed to generate a PCR fragment. Twelve of the missing thirteen SSH EST cDNAs were replaced with PCR fragments from previously isolated T. ruralis cDNAs four of which, representing the ribosomal proteins S14, S16, L23 and L15 (Wood et al., 2000, Zeng and Wood 2000), were previously reported to be constitutively expressed and were added to serve as normalization genes. The remaining eight clones, Tr155, Tr217, Tr403, Tr416, Tr421 (described by Scott and Oliver, 1994), and TrCDPK (U82087) were added as either positive â??up-regulatedâ?? (Tr155, Tr403, Tr421), negative â??down-regulated (Tr217, Tr416), or neutral (TrCDPK) controls based on previous northern analyses. The cDNAs were printed from two 384 well plates in 12 blocks (two columns of 6) of 24 x 8 spots such that each SSH EST and controls were represented in triplicate. Each of the triplicate cDNAs was separated within the blocks to eliminate possible spatial hybridization bias. All hybridizations were duplicated as dye swaps with two separate RNA preparations, from large populations of individual gametophytes (isolated from a minimum of three separate clumps), serving as the source for the sscDNA Cy3 and Cy5 labeled probes. The RNA preparations for the Total polyA RNA were by necessity separate samples from those used to isolate Polysomal poly A RNA.

Project description:Climate change is one of the main factors shaping the distribution and biodiversity of organisms, among others by greatly altering water availability, thus exposing species and ecosystems to harsh desiccation conditions. Insects are especially threatened by these challenging dry environments, because of their small size and thus large surface area to volume ratio. Drosophila melanogaster is a great model to study the response of populations to rapidly changing conditions, because of its southern-central African origin and recent worldwide colonization. Desiccation stress response is a complex and extensively studied trait, however the natural variation in tolerance, and the underlying transcriptomic and physiological mechanisms are still not clear. Here we subjected to desiccation stress 74 natural D. melanogaster European strains, belonging to five different climate zones. We found that the strains from cold semi-arid climates are more tolerant compared with the ones from hot summer mediterranean climate zones. Moreover, the variance in the tolerance of the strains correlates with the interaction of altitude and evaporation. We found that the tolerant strains had a lower level of initial water content and lose less water during desiccation stress. The reduction in the water loss is probably due to the decrease in the respiration rate in desiccation stress conditions, and to the cuticular hydrocarbon composition found in tolerant strains. Moreover, we found that the genes related to response to stimulus and environmental sensing are up-regulated only in the tolerant strains. Furthermore, we identified several desiccation candidate genes unique for the tolerant strains that can be targeted by tRNA derived fragments, known to be important in post-transcriptional gene regulation in several stress responses. We also looked for transposable element insertions possibly affecting the expression of genes relevant in desiccation tolerance, however, except for four insertions, there is no clear association between the presence of the TE insertions and the tolerance level of the strains. Overall, our study for the first time described the physiological and transcriptomic changes underlying the desiccation tolerance of natural European D. melanogaster strains and puts tRFs in the scope of desiccation related studies as possible regulators of desiccation tolerance.

Project description:Spingomonas wittichii strain RW1 can completely oxidize dibenzo-p-dioxins and dibenzofurans, which are persistent contaminants of soils and sediments. For successful application in soil bioremediation systems, strain RW1 must cope with fluctuations in water availability, or water potential. The objectives of this study were to characterize how strain RW1 responses to changes in different components of the total water potential (solute and matric potential) and to then connect these responses to more realistic scenarios of soil desiccation. To accomplish this task, transcriptome profiling was used to investigate the effects of decreasing the solute potential with sodium chloride (solute stress), decreasing the matric potential with high-molecular weight polyethylene glycol (matric stress), or inoculating cells directly into unsaturated sand (sand desiccation stress). Transcriptome profiling revealed a general response to solute, matric, and sand desiccation stress that involved synthesizing trehalose and modifying the composition of exopolysaccarides. Transcriptome profiling also revealed responses that were unique to each stress. Only solute and matric stress triggered the down-regulation of flagella genes. Only solute and sand desiccation stress triggered the up-regulation of two RNA polymerase ECF-type sigma factors along with several membrane proteins, mechanosensitive channels, and solute transporters. Finally, only matric stress triggered the up-regulation of the RNA polymerase sigma-32 factor along with several molecular chaperones. Together, this study revealed a general response to solute, matric and sand desiccation stress but also unique responses to only a subset of these stresses, suggesting that each stress affects strain RW1 in a fundamentally different way. Comparative transcriptome profiling was performed to assess the effects of acute (30 min) solute and matric stress (3 samples for acute solute stress, 3 samples for acute matric stress, 3 controls), the effects of chronic (24 hours) solute and matric stress (3 samples for chronic solute stress, 3 samples for chronic matric stress, 3 controls), and the effects of sand desiccation stress (4 samples for sand desiccation treatment, 3 controls).

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Syntrichia ruralis

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