Proteomic Analysis Reveals Differential Expression of Extracellular and Intracellular Proteins in Epichloë sinensis Grown Under Selenium Conditions.

Epichloë sinensis, a symbiotic fungus of Festuca sinensis, can enhance its host’s resistance to both abiotic and biotic stresses. Some microorganisms can convert toxic selenite into various forms of selenium, however, few studies have investigated the mechanisms by which Epichloë endophytes respond to selenite exposure in vitro. In the present study, we conducted a proteomic analysis of E. sinensis mycelia and secretome following treatment with 0.1 mmol/L sodium selenite, using Nano UPLC-MS/MS. The results identified approximately 141 intracellular proteins and 63 extracellular proteins. Among these, only seven differentially expressed proteins were commonly altered under both conditions. Based on Cluster of Orthologous Groups of proteins (COG) annotation, a total of 68 proteins showed significant changes in the treated intracellular condition, including 15 upregulated and 53 downregulated proteins. These proteins were primarily involved in protein turnover and chaperones, energy production and conversion, and ribosomal structure and biogenesis, compared to the control condition. Among the extracellular proteins, 25 (10 upregulated and 15 downregulated) were differentially expressed and were associated with protein turnover and chaperones, as well as inorganic ion transport and metabolism. Proteins encoded by hsp78 and catA were markedly upregulated, whereas catB, stiA, cpn10, and hsp70A were significantly downregulated, enhancing the adaptation of E. sinensis to selenium stress. Our findings suggest that E. sinensis responds to selenium stress through differential changes in intracellular and extracellular proteomes, providing a theoretical foundation for understanding the mechanism of Se metabolism in this fungus.