Abstract
During the processes of primary and secondary endosymbiosis, different microalgae evolved to synthesis different storage polysaccharides. In stramenopiles, the main storage polysaccharides are β-1,3-glucan, or laminarin, in vacuoles. Currently, laminarin is gaining considerable attention due to its application in the food, cosmetic and pharmaceuticals industries, and also its importance in global biogeochemical cycles (especially in the ocean carbon cycle). In this review, the structures, composition, contents, and bioactivity of laminarin were summarized in different algae. It was shown that the general features of laminarin are species-dependence. Furthermore, the proposed biosynthesis and catabolism pathways of laminarin, functions of key genes, and diel regulation of laminarin were also depicted and comprehensively discussed for the first time. However, the complete pathways, functions of genes, and diel regulatory mechanisms of laminarin require more biomolecular studies. This review provides more useful information and identifies the knowledge gap regarding the future studies of laminarin and its applications.
Highlights
Involving in the branching of chrysolaminarin chain and a putative β-1,3-glucan synthase (PtBGS (ID: 56808)) for the backbone β-1,3-glucan synthesis were apparently located in the vacuoles of P. tricornutum, indicating the synthesis of chrysolaminarin might happen in fusion enzyme that is used to synthesize activated glucose
While the enzymes related with the biosynthesis of chrysolaminarin from UDP-Glu are verified to vacuole localization, suggesting this process is carried out in vacuole
The genes involved in the biosynthesis of chrysolaminarin were high expressed during the light period, while genes involved in the metabolization were high during the night period
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Β-1,3-glucan in brown algae was termed laminarin, in diatom Phaeodactylum tricornutum, Chrysophyte Poterioochromonas malhamensis and Eustigmatophyceae class Nannochloropsis gaditana was named chrysolaminarin and, in oomycetes, mycolaminarin [9,10,11,12,13]. These β-1,3-glucans are the main carbohydrate molecules in the ocean carbon cycle and carbon pool [8]. The sequenced genomes and the development of genetic tools are important for the study of genes’ functions and their regulatory mechanisms during the biosynthesis of chrysolaminari They play fundamental roles in producing large amounts of bioactive chrysolaminarin. This review reports on recent findings regarding the species-specific features of laminarin, the proposed biosynthesis and catabolism pathway of laminarin, functions of some key genes and diel regulation of laminarin and summarizes the current knowledge of laminarin in stramenopiles
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