摘要As a carbon-storage compound and osmoprotectant in brown algae, mannitol is synthe-sized and then accumulated at high levels in Saccharina japonica (Sja);however, the underlying con-trol mechanisms have not been studied. Our analysis of genomic and transcriptomic data from Sja shows that mannitol metabolism is a cyclic pathway composed of four distinct steps. A mannitol-1-phosphate dehydrogenase (M1PDH2) and two mannitol-1-phosphatases (M1Pase1 and MIPase2) work together or in combination to exhibit full enzymatic properties. Based on comprehensive tran-scriptomic data from different tissues, generations, and sexes as well as under different stress con-ditions, coupled with droplet digital PCR (ddPCR) and proteomic confirmation, we suggest that SjaM1Pase1 plays a major role in mannitol biosynthesis and that the basic mannitol anabolism and the carbohydrate pool dynamics are responsible for carbon storage and anti-stress mechanism. Our proteomic data indicate that mannitol metabolism remains constant during diurnal cycle in Sja. In addition, we discover that mannitol-metabolism-associated (MMA) genes show differential expression between the multicellular filamentous (gametophyte) and large parenchymal thallus (sporophyte) generations and respond differentially to environmental stresses, such as hyposalineand hyperthermia conditions. Our results indicate that the ecophysiological significance of such dif-ferentially expressed genes may be attributable to the evolution of heteromorphic generations (fil-amentous and thallus) and environmental adaptation of Laminariales.