The stress-responsive Tortula ruralis gene ALDH21A1 describes a novel eukaryotic aldehyde dehydrogenase protein family

The desiccation-tolerant plant Tortula ruralis is an important experimental system for the study of gene control in response to severe water deficit-stress. EST gene discovery efforts have identified a cDNA ALDH21A1 encoding a member of the aldehyde dehydrogenase (ALDH) gene super family. The deduced polypeptide ALDH21A1 contains the ALDH active site signature sequence and 17 residues correlated with enzymatic activity, however ALDH21A1 is ≤30 % identical to known ALDH proteins. Based upon established nomenclature for ALDH proteins, ALDH21A1 describes a novel eukaryotic ALDH protein family designated ALDH21. ALDH21A1 has a predicted molecular mass of 52.9 kDa, and a predicted pI of 5.9. Genomic blot analysis indicated that ALDH21A1 is present in 1-to-2 copies within the haploid T. ruralis genome. RNA blot hybridizations were used to analyze expression of ALDH21A1 in response to desiccation, ABA, UV, and NaCl. ALDH21A1 steady-state transcript levels increased in response to all treatments and were more abundant within the polysomal mRNA fraction of salt-treated gametophytes. The data suggest that ALDH21A1 plays an important role in the detoxification of aldehydes generated in response to desiccation- and salinity-stress, and we postulate that ALDH21A1 expression represents a unique stress tolerance mechanism.