Characterization and expression patterns of nitrate reductase from Dunaliella bardawil under osmotic stress and...

A complementary DNA (cDNA) of nitrate reductase (NR) from Dunaliella bardawil was isolated using RT-PCR and RACEs techniques. The full-length D. bardawil NR (DbNR) cDNA is 3,107 bp containing a putative open reading frame of 2,670 bp in length which encodes 889 amino acids with a calculated molecular weight (MW) of 98.37 kDa, a 34-bp 5'-untranslated region, and a 3'-untranslated region of 403 bp with a poly (A) tail. BLAST search showed that the nucleotide and putative protein sequence exhibit sequence identities of 92 and 79% with the corresponding gene from Dunaliella tertiolecta, respectively. Protein structural analysis showed a typical NR structure of DbNR with five structural distinctive domains which form three common subparts of eukaryotic NR (Euk-NR). Phylogenetic analysis based on the holo-DbNR and sulfite oxidase (SO) and cytochrome b reductase (CbR) subparts manifested that (1) DbNR has a closer relationship with those counterparts from algae and higher plants than from other species and (2) DbNR might have evolved from ancient SO and CbR in a "domain shuffling" pattern. The glycerol contents and transcriptional expression patterns of DbNR under salt stress and dilution shock treatments were also traced. The results implied an indirect role of NaCl on the induction of DbNR through an osmoregulation pathway.