A nuclear fucosyltransferase-like protein, PtFUT, from marine red alga Pyropia tenera (Rhodophyta) confers osmotic stress tolerance

Pyropia tenera is a marine red alga that grows in the intertidal zone and may lose more than 90% of its water during twice-daily low tides. Based on the differentially expressed genes (DEGs) identified from the desiccation transcriptome of P. tenera gametophyte, a complementary DNA was isolated that upregulated strongly under desiccation stress and encoded a polypeptide of 591-amino acid residues showing a sequence homology with α-1,2-fucosyltransferase, named PtFUT. Fucosyltransferases transfer an l-fucose residue to various acceptor molecules, but information of their activity in the red algae is limited. PtFUT showed upregulation in transcription in gametophytes of P. tenera under desiccation and osmotic stress conditions induced by mannitol. Transcription of the PtFUT gene was also increased by abscisic acid as well as H2O2 treatment. The presence of a signal peptide for nucleus localization and fluorescence of the PtFUT-GFP fusion proteins in tobacco protoplasts indicated that PtFUT is located in the nucleus. When PtFUT was overexpressed in Chlamydomonas, the PtFUT improved the growth of transgenic cells under osmotic stress. These results suggest that PtFUT may play a role in tolerance to desiccation stress and provide insights into the molecular functions of the fucosyltransferases and understanding the desiccation tolerance mechanisms in marine red algae growing in intertidal zones.