Molecular cloning and characterization of an Hsp70 gene from the bloom green alga Chaetomorpha valida (Cladophorales, Chlorophyta)

The full-length complimentary DNA (cDNA) of an Hsp70 gene from the bloom forming green alga Chaetomorpha valida (designated as CvHsp70) was isolated based on homologous cloning and the rapid amplification of cDNA ends (RACE) (Accession: KF812520). It was 2,225 bp, with an open reading frame of 1,995 bp. The deduced 664 amino acids possessed an ATPase domain of 429 amino acids, a substrate peptide-binding domain of 124 amino acids and a C-terminus domain of 111 amino acids. About 46-71 % similarities were detected between CvHsp70 and other 39 known Hsp70s of algae and higher plants; highly conserved motifs were also indentified in CvHsp70, which suggest the conservation of Hsp70 function. Although CvHsp70 presented the endoplasmic reticulum (ER) consensus sequence HDEL in the C-terminal, the subcellular prediction programs presumed that it was targeted to cytoplasm or ER; In the phylogenetic trees, the CvHsp70 formed a basal clade in the cytosolic group with high node support, which implies that it is possibly a chimera of ER and cytosolic Hsp70. Real-time PCR detection revealed the CvHsp70 expression was dramatically upregulated by temperature, desiccation, and salinities induction, which suggests that CvHsp70 might act as a stress responsive gene involved with protecting C. valida from abiotic stresses, thus indirectly facilitating growth and accumulation in unfavorable natural environments. In vitro expression showed one distinct band existed at 72 kDa, and western blot detection showed that it was positive to the anti-His antibody with high specificity. This is the first study to characterize Hsp70 gene from Cladophoraceae species. Our results facilitate deeper analysis Hsp70 detailed functions in abiotic stress tolerance of C. valida and shed more light on the intrinsic mechanisms underlying the seasonal abundance.