Trehalose and (iso)floridoside production under desiccation stress in red algaPorphyra umbilicalisand the genes involved in their synthesis

The marine red algaPorphyra umbilicalishas high tolerance toward various abiotic stresses. In this study, the contents of floridoside, isofloridoside, and trehalose were measured using gas chromatography mass spectrometry (GC-MS) in response to desiccation and rehydration treatments; these conditions are similar to the tidal cycles thatP. umbilicalisexperiences in its natural habitats. The GC-MS analysis showed that the concentration of floridoside and isofloridoside did not change in response to desiccation as expected of compatible solutes. Genes involved in the synthesis of (iso)floridoside and trehalose were identified from the recently completedPorphyragenome, including four putative trehalose-6-phosphate synthase (TPS) genes, two putative trehalose-6-phosphate phosphatase (TPP) genes, and one putative trehalose synthase/amylase (TreS) gene. Based on the phylogenetic, conserved domain, and gene expression analyses, it is suggested that thePum4785andPum5014genes are related to floridoside and isofloridoside synthesis, respectively, and that thePum4637gene is probably involved in trehalose synthesis. Our study verifies the occurrences of nanomolar concentrations trehalose inP. umbilicalisfor the first time and identifies additional genes possibly encoding trehalose phosphate synthases.