Floridean Starch and Floridoside Metabolic Pathways of Neoporphyra haitanensis and Their Regulatory Mechanism under Continuous Darkness

Abstract

Floridean starch and floridoside are the main storage carbohydrates of red algae. However, their complete metabolic pathways and the origin, function, and regulatory mechanism of their pathway genes have not been fully elucidated. In this study, we identified their metabolic pathway genes and analyzed the changes in related gene expression and metabolite content in Neoporphyra haitanensis under continuous dark conditions. Our results showed that genes from different sources, including eukaryotic hosts, cyanobacteria, and bacteria, were combined to construct floridean starch and floridoside metabolic pathways in N. haitanensis. Moreover, compared with those in the control, under continuous dark conditions, floridean starch biosynthesis genes and some degradation genes were significantly upregulated with no significant change in floridean starch content, whereas floridoside degradation genes were significantly upregulated with a significant decrease in floridoside content. This implies that floridean starch content is maintained but floridoside is consumed in N. haitanensis under dark conditions. This study elucidates the “floridean starch–floridoside” metabolic network and its gene origins in N. haitanensis for the first time.

The Cell Wall Polysaccharides Biosynthesis in Seaweeds: A Molecular Perspective

“…The relationship between agar content and expression levels of UDP-glucose pyrophosphorylase (UGP) gene in G. lemaneiformis indicated that UGP was a potential molecular marker to reflect the agar yields ( Chang et al, 2014 ). Recently, Yu et al (2021) identified one GALT gene from Neoporphyra haitanensis , and proposed that it might be derived from primary endosymbiotic eukaryotic hosts. Unlike GALT, GME and UGP, which are shared by many organisms, the galactosyl transferases were unique in agarophytes and were difficult to be identified.…”

Single-cell transcriptome sequencing revealing the difference in photosynthesis and carbohydrate metabolism between epidermal cells and non-epidermal cells of Gracilariopsis lemaneiformis (Rhodophyta)

“…In the current study, FBP , PGK , GAPDH , and FAB/ALDO were up regulated in EC, which suggested that carbon fixed by photosynthesis in EC may largely flow into fructose 6-phosphate compared with NEC ( Figure 5B ). Fructose-6-P is a precursor substance of many LMWC, such as sucrose, raffinose, glucose, and floridoside ( Hofius and Börnke, 2007 ; Lemoine et al., 2013 ; Yu et al., 2021 ). In this study, the content of 13 LMWC which related to the DEGs-enriched carbohydrate metabolism pathways, such as “Starch and sucrose metabolism” and “Galactose metabolism”, were detected in EC and NEC.…”

“…In the present study, the encoding gene of TPS was up regulated in EC (Figure 5B). Moreover, the encoding gene of NAD-dependent glycerol-3-phosphate dehydrogenase (GPDH), an enzyme catalyzed dihydroxyacetone phosphate (DHAP) (a compound could be synthesized from early photosynthetic product) to be glycerol-3-phosphate (Yu et al, 2021), was also up regulated in ECs (Figure 5B). Furthermore, UDP-D-galactose could be converted from UDP-glucose and g a l a c t o s e -1 -p h o s p h a t e b y g a l a c t o s e -1 -p h o s p h a t e uridylyltransferase (GALT) and the gene expression result showed that GALT was up regulated in EC (Figure 5B).…”

Identification, Characteristics and Function of Phosphoglucomutase (PGM) in the Agar Biosynthesis and Carbon Flux in the Agarophyte Gracilariopsis lemaneiformis (Rhodophyta)

“…The Western blot analysis of GlPGM3 validated the same trend to agar variation, except for the changes in the different months. According to the biosynthesis pathways of agar, floridean starch and (iso)floridoside in red algae, they share the same upstream enzymes in the pathway, including glucose-6-phosphate isomerase (PGI), PGM and UGPase [ 26 ], (iso)floridoside can be decomposed to provide the precursor for floridean starch and agar synthesis. On the other hand, these three carbohydrates compete the same synthetic substrates, such as UDP-glucose and galactose-1-P [ 27 ].…”