Molecular cloning and characterization of a trehalose-6-phosphate synthase/phosphatase from Dunaliella viridis

Dunaliella is a group of green algae with exceptional stress tolerance capability, and is considered as an important model organism for stress tolerance study. Here we cloned a TPS (trehalose-6-phosphate synthase) gene from Dunaliella viridis and designated it as DvTPS (D. viridis trehalose-6-phosphate synthase/phosphatase).The DvTPS cDNA contained an ORF of 2793 bp encoding 930 aa. DvTPS had both TPS and TPP domain and belonged to the Group II TPS/TPP fusion gene family. Southern blots showed it has a single copy in the genome. Genome sequence analysis revealed that it has 18 exons and 17 introns. DvTPS had a constitutive high expression level under various NaCl culture conditions, however, could be induced by salt shock. Promoter analysis indicated there were ten STREs (stress response element) in its promoter region, giving a possible explanation of its inducible expression pattern upon salt shock. Yeast functional complementation analysis showed that DvTPS had neither TPS nor TPP activity. However, DvTPS could improve the salt tolerance of yeast salt sensitive mutant G19. Our results indicated that despite DvTPS showed significant similarity with TPS/TPP, its real biological function is still remained to be revealed.