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Thalli of Porphyra yezoensis growing in the intertidal region periodically experience diverse abiotic stresses induced by tidal cycles. To investigate the contribution of 70-kDa heat shock proteins (HSP70s) to abiotic stress tolerance in P. yezoensis thalli, we isolated the cDNAs of two HSP70 genes (designated as PyHSP70-1 and PyHSP70-2) from P. yezoensis by in silico cloning and RT-PCR amplification, and examined their relative mRNA expression levels in P. yezoensis thalli responding to various abiotic stresses using real-time quantitative PCR. The deduced amino acid sequences of the two PyHSP70s lacked signal peptides, but contained signature motifs and conserved domains of the HSP70 family. The two PyHSP70s shared high amino acid sequence similarities with cytosolic HSP70s from other algae and higher plants, and clustered together with all cytosolic HSP70s in the phylogenetic tree, indicating they belong to the cytosolic HSP70 family. Expression of the two PyHSP70 genes was induced by cold shock at 0°C and heat shocks at 20°C and 25°C, and was significantly upregulated in a dose-dependent manner. The expression patterns under heat shock, along with the absence of introns in the coding regions, demonstrate that the two PyHSP70s are inducible HSP70s. Expression of the two PyHSP70 genes was repressed by desiccation stress, suggesting that they do not play a role in tolerance to desiccation stress. The expression patterns in response to salinity stress were different between PyHSP70-1 and PyHSP70-2 genes. The expression of PyHsp70-1 was induced by a salinity of 5; however, the expression of PyHsp70-2 was induced by salinities of 35 and 45. The different expression patterns suggest that they have distinct biological tasks.