As a carbon-storage compound and osmoprotectant in brown algae, mannitol is synthesized and then accumulated at high levels in Saccharina japonica (Sja); however, the underlying control 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 transcriptomic data from different tissues, generations, and sexes as well as under different stress conditions, 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 hyposaline and hyperthermia conditions. Our results indicate that the ecophysiological significance of such differentially expressed genes may be attributable to the evolution of heteromorphic generations (filamentous and thallus) and environmental adaptation of Laminariales.

作为褐藻中的碳储存化合物和渗透保护剂，甘露醇在糖精( Sja ) 中合成并大量积累；然而，潜在的控制机制尚未被研究。我们对Sja的基因组和转录组数据的分析表明，甘露醇代谢是由四个不同步骤组成的循环途径。 1-甘露醇-1-磷酸脱氢酶 (M1PDH2) 和两种 1-甘露醇-1-磷酸酶（M1Pase1 和 MIPase2）一起或组合发挥作用，以展现完整的酶特性。基于不同组织、世代、性别以及不同应激条件下的综合转录组数据，结合液滴数字PCR（ddPCR）和蛋白质组学确认，我们认为SjaM1Pase1在甘露醇生物合成中发挥着重要作用，并且甘露醇的基本合成代谢碳水化合物库动态负责碳储存和抗应激机制。我们的蛋白质组数据表明，甘露醇代谢在Sja的昼夜周期中保持恒定。此外，我们发现甘露醇代谢相关（MMA）基因在多细胞丝状（配子体）和大型实质叶状体（孢子体）世代之间表现出差异表达，并对环境应激（例如低盐和高温条件）做出不同的反应。我们的结果表明，这种差异表达基因的生态生理学意义可能归因于海带目异形世代（丝状和叶状体）的进化和环境适应。