A novel heat shock protein from Gracilariopsis lemaneiformis: gene cloning and transcription analysis in response to heat stress

In previous work, two hsp70s (hsp70-1 and hsp70-2) were cloned from Gracilariopsis lemaneiformis and were found to be important in response to heat stress. In this paper, in order to gain insight into the comparative function of HSP70s under the heat stress in algae, a novel gene of hsp70-3 was cloned from G. lemaneiformis. The DNA sequence of hsp70-3 had only one exon and the obtained 5' flanking region was 416 nucleotides and the ORF was 1866 nucleotides encoding the protein of 621 amino acids, with a pI of 4.99. The hsp70-3s were identical in three strains of G. lemaneiformis, including the wild-type and the two heat-tolerant strains, cultivar 981and cultivar 2007. The unique signature sequences of the HSP70 family, VGIDLGTTNA, ILVFDLGGGTFV and VLVGGSTRIP, were found in HSP70-3. Protein BLAST in NCBI showed that the similarity between HSP70-1 and HSP70-3 was 48%, between HSP70-2 and HSP70-3 was 49%, and nucleotide BLAST of hsp70-3 shared more than 80% similarity with the hsp70s from Gracilaria tenuistipitata var. liui, Gracilaria salicornia and Chondrus crispus. These suggested that the HSP70-3 was a novel heat shock protein in G. lemaneiformis. The transcription levels of hsp70s under heat shock at 32 degrees C were tested by real-time quantitative PCR. Compared with hsp70-1 and hsp70-2, the transcription level of hsp70-3 was lower in the strain of the wild-type and 2007 under heat stress. In 981, hsp70-3 has a similar transcription profile with hsp70-1 and hsp70-2, and with the stress time extended, the gene transcription was increased and remained at a constantly high level. These results indicate that the novel heat shock protein probably plays a supportive role or may play a greater function in other stress resistance in G. lemaneiformis.