Isolation and characterization of a salt-induced PsaG of photosystem I in Dunaliella salina.

Some cDNA sequences of subunit V (PsaG) of Photosystem I (PS I) reaction center in several species have been cloned, and PsaG has been characterized as a connection of light-harvesting complex I (LHC I) protein to photosystem reaction center. Here we present the isolation and characterization of its salt-induced homologue (DsPsaG) in Dunaliella salina. Sequence alignment shows that there is a significant similarity between the deduced amino acid sequence of DsPsaG and PsaG protein in Chlamydomonas reinhardtii, as well as between the deduced amino acid sequence of DsPsaG and other PsaG gene products. The differential expression of DsPsaG at different time points after salt stress reveals that DsPsaG mRNA was absent without salt stress and was indeed salt-induced. Its expression reached its maximum level 5 days after stress. Our study suggests that DsPsaG should be a compensation of PsaG in D. salina when the alga was in a hyperosmotic condition. It can also be useful to effectively transfer light energy from LHC I to PS I reaction center.