A combined subtractive suppression hybridization and expression profiling strategy to identify novel desiccation...

Vegetative desiccation tolerance of the bryophyte Tortula ruralis is characterized by two components: constitutive cellular protection and an inducible cellular recovery program activated upon rehydration. The inducible cellular recovery program is characterized by the increased translation of a number of proteins, termed rehydrins. Rehydins are postulated to be important in cellular repair and thus central to the mechanism of desiccation tolerance. However, as of yet, their identities are largely unknown. We used an EST/expression profiling strategy to identify rehydrins of low abundance and novel to the desiccated or rehydration transcriptomes. We constructed two subtractive suppression hybridization libraries; one to enrich for differentially expressed transcripts sequestered in slow-dried gametophytes and the other to enrich for transcripts differentially translated following rehydration. Collections of cDNAs from each library were sequenced and used to generate a small cDNA microarray. A total of 614 unique contigs were generated from a collection of 768 cDNAs. Half of the ESTs (298) are not represented within a much larger collection (Oliver et al. 2004) and are thus novel. Expression analysis supports the notion that transcripts sequestered during slow drying are a reflection of the need for a rapid recovery of metabolism and those recruited for translation upon rehydration following rapid drying reflect the more stressful nature of this treatment. Expression analysis revealed several new components to the desiccation tolerance mechanism: jasmonic acid signaling, proteosomal activation and alternative splicing. These are novel findings and have relevance to our understanding of the evolution of desiccation tolerance in the land plants.