Abstract:HSP70s are heat shock proteins that exist widely in prokaryotes and eukaryotes, and play important roles in biological resistance. The full cDNA sequence of a hsp70 gene in Saccharina japonica (Sjhsp70) of 3778 bp was obtained by RACE technology. Sjhsp70 consisted of an open reading frame (ORF) of 2892 bp, a 5ʹ untranslated region (UTR) of 101 bp, and a 3ʹ UTR of 785 bp. Analysis of amino acid content and physicochemical properties showed that SjHSP70 is a stable protein. Comparison between the amino acid sequences of SjHSP70 and the well-characterized orthologous HSP70 proteins from various species indicated that SjHSP70 shares the highest similarity with the orthologous protein from Ectocarpus siliculosus. The phylogenetic tree of the examined proteins indicated that SjHSP70 formed a group with a HSP70 from E. siliculosus. Secondary structure analysis of SjHSP70 showed that it is composed of 35 α-helices and 25 β-strands. Three-dimensional homology structure modeling of SjHSP70 was predicted by the I-TASSER server according to the 3C7N template. Overall, the folding and secondary structures of SjHSP70 were highly similar to those of 3C7N. To study the correlation between SjHSP70 and the resistance to high-temperature stress in S. japonica, real-time variation in the expression of Sjhsp70 under different temperatures and different stress times was determined. The results showed that high temperature had a significant effect on the expression of Sjhsp70. The expression of Sjhsp70 continued to increase with increase in temperature, with the maximum Sjhsp70 expression at 25℃ after 24 h of high-temperature stress. This result indicates that Sjhsp70 is probably related to high-temperature resistance in S. japonica. This study provides a foundation for the characterization of SjHSP70 and for the study of SjHSP70 function in the high-temperature stress response in S. japonica.
