Molecular cloning and expression pattern analyses of heat shock protein 70 genes from Nicotiana tabacum

We have isolated three genomic clones that code tobacco HSP70s, using a tobacco hsp70 cDNA clone as a probe. NtHSP70-1, NtHSP70-2, and NtHSP70-3 contain full open reading frames of 653, 653, and 648 amino acid residues, respectively. All share three conserved regions, namely the C-terminal substrate binding domain, oligomerization domain, and N-terminal ATPase domain. in a comparison of their amino acid sequences, NtHSP70-1 and NtHSP70-2 were very similar to each other, while NtHSP70-3 showed significant differences, instead being highly homologous to the cytosolic HSP70 members of Arabidopsis thaliana and other plant species. Therefore, NtHSP70-1 and NtHSP70-3 were chosen for further analyses. RNA blot hybridizations showed typical heat shock-responsive expression patterns, although their signal intensities differed significantly. Transcription of NtHSP70-1 was also induced by dehydration stress and hormone treatments, such as RA, GA, and IAA, but that of NtHSP70-3 was not.