A Tortula ruralis cDNA encoding small-subunit ribosomal protein S3a: Polysomal retention of transcript in response to desiccation and rehydration

A Tortula ruralis cDNA Rps3a, encoding a predicted polypeptide with significant similarity to the small-subunit ribosomal protein S3a, was isolated from a desiccated gametophyte cDNA library. The deduced 248 amino acid polypeptide is approximately 28 kDa, with a predicted pi of 10.09, and shares extensive identity (> 75%) with S3a ribosomal proteins from Arabidopsis thaliana and Helianthus annuus. The deduced polypeptide (RPS3a) contains three nuclear targeting signals, one of which is unique to the bryophyte S3a homologue, and is strongly predicted by PSORT to be nuclear localized (> 97% certainty). Northern blot hybridization using total and polysomal RNA demonstrated Rsp3a is constitutively expressed in moss gametophytes during a wet/dry/wet cycle. Phylogenetic analysis of the deduced amino acid sequence demonstrates T. ruralis RPS3a is most similar to S3a ribosomal proteins front Tracheophytes.