Pyropia tenera is an intertidal red alga of commercial significance owing to its popularity as a health-promoting seafood product. This alga grows in marine environments and is frequently exposed to high salinity and osmotic stress, which impact its growth. Therefore, the enhancement of stress tolerance in P. tenera is critical. In the present work, we aimed to elucidate the mechanisms underlying abiotic stress tolerance in this species; specifically, we identified the P. tenera S-adenosylmethionine synthetase-encoding gene (PtSAMS) and characterized its biological function. This gene, which is known to play a role in stress tolerance in other plants, was cloned and overexpressed in Escherichia coli under high-salinity conditions. The PtSAMS gene was found to encode a 385-amino-acid protein with a molecular weight of 41.8 kDa. In silico sequence alignment and phylogenetic analysis of the PtSAMS amino acid sequence showed that the encoded protein comprises three conserved domains and two motifs that are highly conserved in other plants. Growth assay results indicated that PtSAMS-overexpressing E. coli cells exhibit enhanced tolerance to salt stress. The results suggest that PtSAMS expression is induced by a combination of ion toxicity and osmotic stress resulting from exposure to high salinity in marine environments, and that this gene is expressed at housekeeping levels owing to growth in such conditions. The findings suggest that PtSAMS could be used as a potentially valuable bioresource with utility in the genetic engineering of salt stress-tolerant crop plants.

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