Comparative Transcriptome Profiles of the Response of Mycelia of the Genus Morchella to Temperature Stress: An Examination of Potential Resistance Mechanisms

Abstract

Temperature and moisture belong to the most important environmental factors affecting the growth and development of fungi. However, the effect of temperature on the mycelia of the edible Morchella mushrooms has not been determined. Here, a comprehensive analysis was performed to determine the influence of culture temperature on 13 strains of mycelia of three Morchella species (Morchella sextelata, Morchella septimelata, and Morchella importuna) at 5 °C, 10 °C, 15 °C, 20 °C, 25 °C, and 30 °C. The mycelial branching and growth rate data showed that 15–20 °C was a suitable temperature range for the mycelial growth of the 13 Morchella strains. RNA sequences revealed that a total of 2843, 2404, 1973, 1572, and 1866 differentially expressed genes (DEGs) were identified at 5 °C, 10 °C, 15 °C, 25 °C, and 30 °C compared with 20 °C. A Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis further indicated that the purine nucleotide and tyrosine metabolism pathways were crucial for mycelium development. Moreover, the enrichment of autophagy of mitochondria, regulation of cell morphogenesis, and piecemeal microautophagy of the nuclei at 25 °C (vs. 20 °C) indicated the damage caused by heat stress in Morchella mycelia. Notably, a total of four unique module eigengenes (MEs) were identified through a weighted gene coexpression network analysis (WGCNA). Among them, 2293 genes in the turquoise module were significantly positively correlated with temperature (r = 0.946, p < 0.001), whereas 739 genes in the blue module were significantly negatively correlated with temperature (r = −0.896, p < 0.001), suggesting that the effect of high temperatures on mycelial genes was significantly greater than that of low temperatures. Moreover, the coexpression network indicated that high culture temperatures accelerated the oxidative stress response and energy metabolism in mycelia, while upregulation of purine nucleotide catabolism and ribosomal protein-related genes were improved by low-temperature tolerance. In addition, the upregulated expression of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), and heat shock protein (HSP) genes in mycelia was associated with reactive oxygen species (ROS)-mediated damage at high temperatures. Overall, this study provides an important theoretical basis and application value for optimizing Morchella cultivation techniques.