Abstract
BackgroundAs a unique sulfated polysaccharide, fucoidan is an important component of cell wall in brown seaweeds. Its biochemical properties are determined by the positions and quantity of sulfate groups. Sulfotransferases (STs) catalyze the sulfation process, which transfer the sulfuryl groups to carbohydrate backbones and are crucial for fucoidan biosynthesis. Nevertheless, the structures and functions of STs in brown seaweeds are rarely investigated.ResultsThere are a total of 44 ST genes identified from our genome and transcriptome analysis of Saccharina japonica, which were located in the 17 scaffolds and 11 contigs. The S. japonica ST genes have abundant introns and alternative splicing sites, and five tandem duplicated gene clusters were identified. Generally, the ST genes could be classified into five groups (Group I ~ V) based on phylogenetic analysis. Accordingly, the ST proteins, which were encoded by genes within the same group, contained similar conserved motifs. Members of the S. japonica ST gene family show various expression patterns in different tissues and developmental stages. Transcriptional profiles indicate that the transcriptional levels of more than half of the ST genes are higher in kelp basal blades than in distal blades. Except for ST5 and ST28, most ST genes are down-regulated with the kelp development stages. The expression levels of nine ST genes were detected by real-time quantitative PCR, which demonstrates that they responded to low salinity and drought stresses.ConclusionsVarious characteristics of the STs allow the feasibilities of S. japonica to synthesize fucoidans with different sulfate groups. This enables the kelp the potential to adapt to the costal environments and meet the needs of S. japonica growth.
Highlights
As a unique sulfated polysaccharide, fucoidan is an important component of cell wall in brown seaweeds
He proposed two routes of GDPfucose production: 1) fructose-6-phosphate is catalyzed by mannose-6-phosphate isomerase (MPI), phosphomannomutase (PMM) and mannose-1-phosphate guanylyltransferase (MPG) to synthesize GDP-mannose, followed by the production of GDP-fucose, which is catalyzed by GDP-mannose 4, 6-dehydrogenase (GM46D) and the bifunctional enzyme GDP-L-fucoidase synthase (GFS); 2) alternatively, L-fucose is used as the substrate to synthesize GDP-fucose by fucose kinase (FK) and GDP-fucose pyrophosphorylase (GFPP)
Identification and expression profiles of fucoidan biosynthetic genes A total of 104 genes related to fucoidan biosynthesis were annotated based on our genome and transcriptome databases of S. japonica
Summary
As a unique sulfated polysaccharide, fucoidan is an important component of cell wall in brown seaweeds. Based on E. siliculosus genome sequencing and analogized with glycosaminoglycan (GAG) biosynthesis, Michel et al (2010) deduced that fucoidan may first be polymerized into neutral polysaccharides by fucosyltransferases, and sulfated by specific sulfotransferases [11]. He proposed two routes of GDPfucose production: 1) fructose-6-phosphate is catalyzed by mannose-6-phosphate isomerase (MPI), phosphomannomutase (PMM) and mannose-1-phosphate guanylyltransferase (MPG) to synthesize GDP-mannose, followed by the production of GDP-fucose, which is catalyzed by GDP-mannose 4, 6-dehydrogenase (GM46D) and the bifunctional enzyme GDP-L-fucoidase synthase (GFS); 2) alternatively, L-fucose is used as the substrate to synthesize GDP-fucose by fucose kinase (FK) and GDP-fucose pyrophosphorylase (GFPP). Zhang et al (2018) illustrated the expression and purification, enzymatic activity and response to light and temperature stress of PMM/PGM (phosphoglucomutase) in S. japonica [15]
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