An EST catalogue from the resurrection plant Selaginella lepidophylla reveals abiotic stress-adaptive genes

The resurrection plant Selaginella lepidophylla (Division Lycophyta) belongs to an ancient lineage of vascular plants that can withstand complete desiccation for years and be revived after only a few hours of rehydration. To better understand the molecular basis of dehydration tolerance, a complementary DNA library was constructed from S. lepidophylla microphyll fronds dehydrated for 2.5 h and used to generate an expressed sequence tag (EST) database. ESTs were obtained for 1046 clones representing 874 unique transcripts. Putative functions were assigned to 653 (62.4%) of these clones after comparison with protein databases, whereas 212 (20.2%) sequences having significant similarity to known sequences whose functions are unclear and 181 (17.3%) sequences having no similarity to known sequences. The S. lepidophylla ESTs were compared to the Selaginella moellendorffii EST database using the tBLASTX algorithm. Approximately 36-38% of the S. lepidophylla ESTs exhibited similarity to the S. moellendorffii ESTs, whereas 62-63% were unique to S. lepidophylla and S. moellendorffii, respectively. For those S. lepidophylla ESTs for which functional assignments could be made, the largest functional categories included photosynthesis (17%), followed by primary metabolism (14%) and disease/defense-related functions (11%). S. lepidophylla had a higher relative percentage of ESTs within the transporter, cell structure, secondary metabolism, molecular chaperones (i.e., heat shock proteins), and abiotic stress-related (i.e., late embryogenesis abundance proteins) functional categories than did S. moellendorffii. Thus, S. lepidophylla may serve as a rich genetic resource for the identification of novel genes associated with environmental stress and dehydration tolerance.