Phylogenetic analysis and cloning of psaB gene of Dunaliella salina

One pair of degenerate primers was designed according to conserved motifs of the psaB(A2 subunit of photosystem I) of Chlamydomonas reinhardtii,Chlamydomonas moewusii,Chlorella vulgaris,and a total RNA of Dunaliella salina was extracted with TRIzol reagent.A cDNA fragment,about 1.8 kb in length,from green algal D.salina was obtained through RT-PCR method.The resulting PCR product was cloned into T-vector and screened to determine its sequence.Homologous analysis of the deduced amino acid sequence was performed by BLAST and subsequently compared to GenBank data.The obtained cDNA sequence was 1815 bp long,which encoded 605 amino acids(GenBank accession number:AY820754).The sequence shared high homologue with the following psaB:92%for Chlamydomonas reinhardtii,91% for Chlamydomonas moewusii,86% for Chlorella vulgaris,85% for Mesostigma viride,85% for Physcomitrella patens subsp.Patens and 84% for Nephroselmis olivacea.It can be concluded that the cloned sequence is psaB cDNA fragment from D.salina.In addition,codon bias analysis shows that the content of A and T(35.7% and 39.17%,respectively)is used significantly more frequently in the third position composition than that of G and C(7.27% and 17.85%,respectively),that is to say,the codons of psaB of D.salina are mainly composed of NNA and NNT.At the same time,through phylogenetic analysis of the Chlorophyta with psaB gene,it is shown that D.salina is the nearest to the most species of Haematococcaceae in the phylogenetic relationship,which is contrary to previous opinion that D.salina is the nearest to the most species of Chlamydomonadaceae in the phylogenetic relationship.These studies will help clarify the genetic background of D.salina.