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

Abstract

Agar is widely applied across the food, pharmaceutical and biotechnology industries, owing to its various bioactive functions. To better understand the agar biosynthesis in commercial seaweed Gracilariopsis lemaneiformis, the activities of four enzymes participating in the agar biosynthesis were detected, and phosphoglucomutase (PGM) was confirmed as highly correlated with agar accumulation. Three genes of PGM (GlPGM1, GlPGM2 and GlPGM3) were identified from the G. lemaneiformis genome. The subcellular localization analysis validated that GlPGM1 was located in the chloroplast and GlPGM3 was not significantly distributed in the organelles. Both the GlPGM1 and GlPGM3 protein levels showed a remarkable consistency with the agar variations, and GlPGM3 may participate in the carbon flux between (iso)floridoside, floridean starch and agar synthesis. After treatment with the PGM inhibitor, the agar and floridean starch contents and the activities of floridean starch synthase were significantly decreased; products identified in the Calvin cycle, pentose phosphate pathway, the Embden-Meyerhof-Parnas pathway and the tricarboxylic acid cycle were depressed; however, lipids, phenolic acids and the intermediate metabolites, fructose-1,6-phosphate were upregulated. These findings reveal the essential role of PGM in regulating the carbon flux between agar and other carbohydrates in G. lemaneiformis, providing a guide for the artificial regulation of agar accumulation.

Identification of Indicator Genes for Agar Accumulation in Gracilariopsis lemaneiformis (Rhodophyta)

“…According to researchers in the field, the transcription level of some agar biosynthesisrelated genes can indicate the agar content level. Chen verified that the enzyme activities of PGM and the agar content exhibited significant correlations (Pearson correlation coefficient: 0.896) after 7 days for G. lemaneiformis, under the nitrogen concentration treatment [33]. Most G. lemaneiformis strains in the high agar content group had higher transcription levels of galt than all strains in the low agar content group, which suggested that the galt gene played a crucial role in agar biosynthesis [34].…”

“…The normal distribution and the homogeneity of different datasets were confirmed by a Shapiro-Wilk test (p > 0.05) and Levene's test (p > 0.05), respectively. The one-way analysis of variance (ANOVA) was performed to determine the differences between the different datasets using Bonferroin's post hoc test and Tukey's post hoc test (Tukey HSD) [33]. If some datasets did not conform to the normal distribution, the Kruskal-Wallis test was used to analyse them [52].…”

“…In the laboratory, the algae were divided into several parts, which were almost identical in terms of length, branch number, and diameter. The algae were cultivated in the transparent tank at an irradiance of 40 ± 3 µmol photons m −2 •s −1 and 12 h:12 h light/dark cycle at 20 • C [33]. The density of cultivation was that every 5 g of algae was submerged in 1 L filtered natural seawater (salinity of 30‰).…”