Cloning and expression study of a putative carotene biosynthesis related (cbr) gene from the halotolerant green alga Dunaliella salina.

Dunaliella salina, a unicelluar green alga that can tolerate an extreme variation of salt concentration is being studied as a model system to analyze the tolerance of abiotic stresses at the molecular level. Upon abnormal NaCl levels, new transcripts were abundantly expressed in cells of the alga. EST gene discovery efforts utilizing salt-shock cells had identified one cDNA designated Dscbr (GenBank accession no. DQ867041) with significant similarity to a carotene biosynthesis related gene (cbr) from Dunaliella bardawil and to early light inducible genes (elip) of higher plants. Dscbr was 976 bp in length, encoding a 190 amino acid deduced polypeptide (DsCBR) with a predicted molecular mass of 19.9 kDa and pI of 9.0. The three dimensional structure of DsCBR modeled by computer homology modeling techniques showed that the protein possessed three predicted transmembrane helices and six conserved pigment-binding residues. Real-Time Quantitative PCR clearly demonstrated that Dscbr mRNA can be rapidly induced by high light intensity and salt shocks. The results presented in this work are consistent with the earlier proposal (Jin et al. 2001 Biochim Biophys Acta 1506:244-259, 2003 Plant Physiol 132:352-364) that the DsCBR protein is an adaptive response to stress-induced photodamage within the alga chloroplast, and plays a key role in the protection and/or repair of the photosynthetic apparatus.