Enhancing Extracellular Polysaccharide Production under Nitrate Condition through the Silencing of the Transcription Factor AreA in Ganoderma lucidum

Fungal polysaccharides are not only important components of cell walls but also important for their applications in food and medicine. Nitrogen is crucial for physiological functions of fungi. However, studies on how nitrogen affect polysaccharides biosynthesis are relatively scarce. In this study, transcriptomic profiles of strains cultured with ammonium or nitrate as the nitrogen source were examined, respevtively, and their comparative analysis resulted in the enrichment of polysaccharide synthesis pathway. Further studies revealed that ammonium nitrogen promotes the extracellular polysaccharides (EPS) synthesis, whereas nitrate enhances the intracellular polysaccharides (IPS) synthesis. Subsequently, the function of AreA, an important nitrogen metabolism transcription factor, on polysaccharides synthesis was studied. Under nitrate condition, compared to the wild-type (WT), the content of EPS increased by approximately 33%, while the content of IPS, chitin, and ?-1,3-glucan in the areA-silenced strain was significantly reduced by 24%, 20%, and 20%-25%, respectively. Changes in content of chitin and ?-1,3-glucan affect the structure and integrity of the cell wall. Compared to ammonium condition, under nitrate condition, the cell wall thinned by approximately 23% following areA silencing, and sensitivity to cell wall perturbing agents increased by approximately 20%-30%. In summary, this study elucidates the impact of nitrogen sources on the polysaccharides synthesis, offering valuable insights into strategies for enhancing polysaccharide content in G. lucidum Overall design: Analysis of differential genes in the transcriptome sequencing of Ganoderma lucidum wild-type treated with ammonium salts and nitrates.