Enhancing polysaccharide biosynthesis in Sanghuangporus baumii through phosphoglucose isomerase gene silencing.

Sanghuangporus baumii polysaccharides (SBP) are recognized for their valuable pharmacological activities, driving increasing interest in their medicinal potential. However, the biosynthetic pathway of SBP remains incompletely characterized. Phosphoglucose isomerase (PGI), a key enzyme in carbohydrate metabolism, catalyzes the reversible isomerization between glucose-6-phosphate (G-6-P) and fructose-6-phosphate (F-6-P) and is hypothesized to regulate polysaccharide biosynthesis in this fungus. In this study, the pgi gene from S. baumii (sbpgi) was cloned and created sbpgi-silenced mutants using RNA interference (RNAi) to investigate its function. Silencing sbpgi resulted in an approximately 20% reduction in mycelial biomass but concurrently enhanced the production of exopolysaccharide (EPS) and intracellular polysaccharide (IPS) by approximately 2.0-fold and 1.9-fold after 9 days, respectively. Furthermore, suppression of sbpgi expression markedly decreased the content of cell wall β-1,3-glucan (by ~23%) while increasing chitin deposition by about 1.7-fold, leading to alterations in cell wall architecture, including thickness, and changes in stress tolerance. Transcriptional analysis revealed that sbpgi silencing significantly upregulated the expression of key genes in the polysaccharide biosynthetic pathway, including ugpg and pmm, highlighting the critical regulatory role of sbpgi in polysaccharide production. Our findings provide a foundation for metabolic engineering strategies to develop high-yielding strains for the industrial production of SBP.