Physiological Responses and Time-Course Transcriptomic Analysis of Morchella sextelata Strain Mel-21 During NaCl Exposure

Abstract

Salt stress limits fungal growth and distribution, but the mechanisms underlying salt tolerance in Morchella remain unclear. Here, we combined physiological measurements, transcriptomic analysis, weighted gene co-expression network analysis (WGCNA), and heterologous expression assays to characterize salt-stress responses in Morchella sextelata. Among 24 preselected isolates representing four Morchella species, M. sextelata Mel-21 obtained the highest composite screening score under 1 mol·L−1 NaCl and was selected for detailed analysis. A concentration of 300 mmol·L−1 NaCl was subsequently selected as the representative stress condition. Salt stress increased electrical conductivity, osmotic pressure, Na+ accumulation, antioxidant enzyme activities, and proline content, while decreasing the K+/Na+ and Ca2+/Na+ ratios. Intracellular and extracellular polysaccharides showed distinct time-dependent accumulation patterns, and the corresponding crude extracts exhibited increased radical-scavenging activities under NaCl stress. Relative to the common 0 h baseline, RNA-seq identified 3654, 3843, 4289, 3566, and 2494 differentially expressed genes after 3, 6, 12, 24, and 48 h of NaCl exposure, respectively. These genes were enriched in pathways related to ribosomes, oxidative phosphorylation, protein processing in the endoplasmic reticulum, carbohydrate metabolism, and ABC transporters. Gene05935, encoding a predicted multi-pass transmembrane protein, showed consistently higher transcript abundance during NaCl exposure than at the common 0 h baseline. Heterologous expression of Gene05935 in Saccharomyces cerevisiae was associated with higher mean endpoint OD600 values under the tested high-salinity conditions, while the Arabidopsis thaliana assay provided preliminary qualitative observations of seedling appearance during NaCl exposure. Because time-matched untreated controls were not included, the transcriptomic differences cannot be attributed specifically to NaCl. Together, the physiological measurements and temporal expression profiles identify Gene05935 as a candidate for further functional characterization and may inform future cultivation-oriented evaluation of Morchella under saline conditions.