Nitrogen-dependent regulation of extracellular and intracellular polysaccharide content in Ganoderma lucidum via the transcription factor AreA

Fungal polysaccharides serve as vital components and hold significant value in food and medicinal applications. Nitrogen plays a crucial role in the biosynthesis of fungal polysaccharides, yet our comprehension of its specific influence on fungal polysaccharides biosynthesis remains limited. In this study, we analyzed the transcriptomic profiles of Ganoderma lucidum cultured under ammonium or nitrate sources, revealing an enrichment of the polysaccharide synthesis pathway. Further studies revealed that ammonium nitrogen promotes the synthesis of extracellular polysaccharides (EPS), while nitrate enhances that of intracellular polysaccharides (IPS). Subsequently, the role of AreA, a key transcription factor in nitrogen metabolism, in polysaccharide synthesis was investigated. Under nitrate conditions, compared to the wild-type (WT), EPS content increased by approximately 33 %, whereas IPS, chitin, and β-1,3-glucan content in the areA-silenced strains were significantly reduced by 24 %, 20 %, and 20 %-25 %, respectively. Changes in the content of chitin and β-1,3-glucan affect the cell wall's structure and integrity. Compared to ammonium conditions, under nitrate conditions, 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 polysaccharide synthesis, providing valuable insights into strategies for enhancing polysaccharide content in G.lucidum.