Molecular insights into salt tolerance in Dunaliella tertiolecta involving two betaine aldehyde dehydrogenases.

Understanding salt tolerance mechanisms is crucial for addressing the global challenge of soil salinization and advancing sustainable agricultural practices. Dunaliella tertiolecta, thriving in up to 4.5 M NaCl, is a model for studying salt tolerance mechanisms. Two betaine aldehyde dehydrogenase (BADH) genes were identified in D. tertiolecta, namely DtBADH1 and DtBADH2. The phylogenetic analysis revealed that DtBADH1 had similarity to Pseudomonas aeruginosa BADH, while DtBADH2 has high homology to aldehyde dehydrogenase from Chlorella sorokiniana. The 3D models of DtBADH1 and DtBADH2 docking with betaine aldehyde were performed to further validate their binding site, interactions binding the protein and its substrate as well as the conserved amino acids responsible for enzyme activity. We also conducted RNA interference of DtBADH1 and DtBADH2 in D. tertiolecta. Compared to the wild type D. tertiolecta, both BADH-RNAi D. tertiolecta had fewer cell numbers and relatively lower glycine betaine content under high salinity. The findings suggest that both DtBADH1 and DtBADH2 play a crucial role in betaine synthesis, indicating their potential involvement in salt tolerance mechanisms at the molecular level. Additionally, these results highlight D. tertiolecta as a promising candidate for identifying salt stress-responsive genes, which could be utilized for engineering algae or crops to enhance their ability to withstand salinity stress.