Background The heteroside floridoside is a primary photosynthetic product that is known to contribute to osmotic acclimation in almost all orders of Rhodophyta. However, the encoding genes and enzymes responsible for the synthesis of floridoside and its isomeric form, l - or d -isofloridoside, are poorly studied. Results Here, four putative trehalose-6-phosphate synthase (TPS) genes, designated as PhTPS1 , PhTPS2 , PhTPS3, and PhTPS4 , were cloned and characterized from the red alga Pyropia haitanensis (Bangiophyceae). The deduced amino acid sequence is similar to the annotated TPS proteins of other organisms, especially the UDP-galactose substrate binding sites of PhTPS1, 2, which are highly conserved. Of these, PhTPS1, 4 are involved in the biosynthesis of floridoside and isofloridoside, with isofloridoside being the main product. PhTPS3 is an isofloridoside phosphate synthase, while PhTPS2 exhibits no activity. When challenged by desiccation, high temperature, and salt stress, PhTPS members were expressed to different degrees, but the responses to thermal stress and desiccation were stronger. Conclusions Thus, in P. haitanensis , PhTPS s encode the enzymatical activity of floridoside and isofloridoside phosphate synthase and are crucial for the abiotic stress defense response. Electronic supplementary material The online version of this article (10.1186/s12870-019-1928-2) contains supplementary material, which is available to authorized users.

Background The heteroside floridoside is a primary photosynthetic product that is known to contribute to osmotic acclimation in almost all orders of Rhodophyta. However, the encoding genes and enzymes responsible for the synthesis of floridoside and its isomeric form, l- or d-isofloridoside, are poorly studied. Results Here, four putative trehalose-6-phosphate synthase (TPS) genes, designated as PhTPS1, PhTPS2, PhTPS3, and PhTPS4, were cloned and characterized from the red alga Pyropia haitanensis (Bangiophyceae). The deduced amino acid sequence is similar to the annotated TPS proteins of other organisms, especially the UDP-galactose substrate binding sites of PhTPS1, 2, which are highly conserved. Of these, PhTPS1, 4 are involved in the biosynthesis of floridoside and isofloridoside, with isofloridoside being the main product. PhTPS3 is an isofloridoside phosphate synthase, while PhTPS2 exhibits no activity. When challenged by desiccation, high temperature, and salt stress, PhTPS members were expressed to different degrees, but the responses to thermal stress and desiccation were stronger. Conclusions Thus, in P. haitanensis, PhTPSs encode the enzymatical activity of floridoside and isofloridoside phosphate synthase and are crucial for the abiotic stress defense response.