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 less than or equal to30% 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 52.9kDa, and a predicted pl 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.