Serine hydroxyl methyltransferase (SHMT) plays an important role in plant response to stress.Under adversity stress,the SHMT gene not only promotes the Calvin cycle to participate in the anti-stress reaction,but also participates in the synthesis of glycine,and then synthesis of glutathione,scavenging reactive oxygen species.Pyropia haitanensis,naturally grows in the coastal intertidal zone,is an important economic macroalgae in Fujian,Zhejiang and Guangdong provinces.Because of the special living environment,P.haitanensis has the unique ability to resist adversity.With global warming,the temperature of seawater increases,which causes damage to seedlings of P.haitanensis and leads to great economic losses in the aquaculture industry.As for the physiological and molecular response of P.haitanensis to high temperature and dehydration stress conditions,our previous studies found SHMT plays an important role in stress resistance.In this study,based on unigene sequences which were obtained from whole transcriptome sequencing of P.haitanensis,two full-length PhSHMT genes were obtained by ordinary PCR,and named PhSHMT-1 (GenBank accession No:MF687405) and PhSHMT-2 (GenBank accession No:MF687406).The full-length cDNA of the PhSHMT-1 gene comprised 1710 nucleotides and contained an open reading frame (ORF) of 1491 bp,encoding a protein of 497 amino acid residues,with the predicted molecular weight of 121.443 kDa and theoretical isoelectric point of 4.93;and the full-length cDNA of the PhSHMT-2 gene comprised 1957 nucleotides and contained an ORF of 1395 bp,encoding a protein of 465 amino acid residues with the predicted molecular weight of 113.969 kDa and theoretical isoelectric point of 4.95.Multiple sequence alignment and phylogenetic analysis indicated that the PhSHMT-1 and PhSHMT-2 belong to the plant SHMT enzyme family.The expressions of the two PhSHMT genes,as measured by real-time fluorescence quantitative PCR (qRT-PCR),were consistent under high temperature stress.During high-temperature stress,the expression levels of the two PhSHMT genes were significantly upregulated first and then decreased,but as the high-temperature stress continued,the expression levels were upregulated again.Results suggested that the gene of PhSHMT enzyme plays an important role in responses of P.haitanensis to high-temperature stress.