Abstract: Trehalose-6-phosphate synthase(TPS), the key enzyme involved in trehalose biosynthesis, plays particularly important roles in a variety of stress responses.In this study, based on unigene sequences which were obtained from whole transcriptome sequencing of Pyropia haitanensis, three full-length PhTPS genes were obtained by rapid amplification of cDNA ends(RACE), and named PhTPS1, PhTPS2-1 and PhTPS2-2.The full-length cDNA of the PhTPS gene comprised 3 557 nucleotides and contained an open reading frame of 3 462 bp(GenBank accession:KM580358), encoding a protein of 1 153 amino acid residues with the predicted molecular weight of 124.2 ku and theoretical isoelectric point of 6.73;the full-length cDNA of the PhTPS2-1 gene comprised 4 264 nucleotides and contained an open reading frame of 4 044 bp(GenBank accession:KM519457), encoding a protein of 1 374 amino acid residues with the predicted molecular weight of 145.2 ku and theoretical isoelectric point of 5.96;and the full-length cDNA of the PhTPS2-2 gene comprised 3 733 nucleotides and contained an open reading frame of 3 324 bp(GenBank accession:KM519458), encoding a protein of 1 107 amino acid residues with the predicted molecular weight of 120.2 ku and theoretical isoelectric point of 5.42.On the basis of conserved motifs and phylogenetic tree analysis, PhTPS1 belongs to the Ⅰ subfamily of TPS and PhTPS2-1 and PhTPS2-2 belong to the Ⅱ subfamily of TPS.The expressions of the three PhTPS genes, as measured by real-time quantitative PCR, were significantly induced by high-temperature stress and desiccation stress, but had different expression patterns.During high-temperature stress, the expression levels of the three PhTPS genes were all significantly upregulated firstly and then decreased, but as the high-temperature stress continues, the expression levels were upregulated again.However, during desiccation, the expression levels of PhTPS1 and PhTPS2-2 were significantly upregulateded only when the water loss was >60% or 75%, but the expression level of PhTPS2-1 was significantly upregulat when the water loss was >15%.These results suggested that the three PhTPS genes may play important roles in the response to higher desiccation stress.