The transcription factor GCN4 contributes to maintaining intracellular amino acid contents under nitrogen-limiting conditions in the mushroom Ganoderma lucidum

Abstract

Background Edible mushrooms are delicious in flavour and rich in high-quality protein and amino acids required by humans. A transcription factor, general control nonderepressible 4 (GCN4), can regulate the expression of genes involved in amino acid metabolism in yeast and mammals. A previous study revealed that GCN4 plays a pivotal role in nitrogen utilization and growth in Ganoderma lucidum. However, its regulation is nearly unknown in mushrooms. Results In this study, we found that the amino acid contents reached 120.51 mg per gram of mycelia in the WT strain under 60 mM asparagine (Asn) conditions, but decreased by 62.96% under 3 mM Asn conditions. Second, silencing of gcn4 resulted in a 54.2% decrease in amino acid contents under 60 mM Asn, especially for the essential and monosodium glutamate-like flavour amino acids. However, these effects were more pronounced under 3 mM Asn. Third, silencing of gcn4 markedly inhibited the expression of amino acid biosynthesis and transport genes. In addition, GCN4 enhanced the tricarboxylic acid cycle (TCA) and glycolytic pathway and inhibited the activity of target of rapamycin complex 1 (TORC1), thus being beneficial for maintaining amino acid homeostasis. Conclusion This study confirmed that GCN4 contributes to maintaining the amino acid contents in mushrooms under low concentrations of nitrogen. In conclusion, our study provides a research basis for GCN4 to regulate amino acid synthesis and improve the nutrient contents of edible mushrooms.

Current Advances in the Functional Genes of Edible and Medicinal Fungi: Research Techniques, Functional Analysis, and Prospects

“…Edible and medicinal fungi are rich in the high-quality proteins and amino acids required by humans, and their content and composition are important indicators for evaluating the nutrition and flavor of edible and medicinal fungi. Lian et al [177] silenced the alkaline leucine-transcription-factor-coding gene Gcn4 in G. lucidum and reported that the amino acid content of the mutant strain was reduced by 54.2-88.3% compared with the wild type. They hypothesized that GCN4 could modulate the expression of amino-acid-related synthesis genes and transporter genes, providing precursors for amino acid biosynthesis by enhancing the TCA cycle and glycolytic pathway.…”