Isolation and characterization of a mitogen-activated protein kinase gene in the halotolerant alga Dunaliella salina

Mitogen-activated protein kinase (MAPK) is conserved gene family in all eukaryotic cells. MAPKs play an important role in abiotic stress responses. In green algae, few MAPK genes have been cloned, although MAPKs have been extensively studied in yeasts and humans. The microalga Dunaliella is a model for the study of a variety of abiotic stress tolerances. Dunaliella salina exhibits excellent adaptation to the hypersaline environment without a rigid cell wall. The cDNA of MAPK in D. salina was cloned using degenerate oligonucleotide primers in a polymerase chain reaction (PCR) amplification approach and rapid amplification of cDNA ends method. An open reading frame encoding a 53 kDa protein was identified. The deduced amino acid sequence showed high homology with other reported MAPKs. The conserved regions, including TEY activation loop and the common docking domain, were characterized in the deduced amino acid sequence. To our knowledge, we presented the initial full-length sequence of MAPK in D. salina. The quantitative real-time PCR demonstrated DsMPK expression level gradually decreases under the hyperosmotic and low temperature environments. The results provide valuable information about the response of DsMPK at the transcription level.