Jun Jiang

Frequent strain degeneration during subcultivation, characterized by impaired sporulation and fruiting body formation, represents a major constraint in fungal agricultural production. Our study systematically investigated two naturally degenerated Lentinula edodes strains classified as abortive (Abt: L808-13, L808-14) and malformed (Abn: L808-18) fruiting-body phenotypes, through comprehensive phenotypic characterization, enzymatic profiling, thermotolerance assessment, and transcriptomic analysis. While vegetative growth remained unaffected, degenerated strains exhibited premature hyphal knotting, significantly reduced thermotolerance, and Abn-specific suppression of carboxymethyl cellulase (CMCase) activity. Comparative transcriptomics revealed 1239 and 582 differentially expressed genes (DEGs) in Abt and Abn groups, respectively, accompanied by a global dysregulation in carbohydrate catabolism, phospholipid metabolism, and redox homeostasis. Furthermore, protein–protein interaction (PPI) networks and RT-qPCR data highlighted 12 core hub genes enriched in glycoside hydrolysis, cytochrome P450 signaling, and membrane lipid dynamics. These findings provide mechanistic insights into the molecular basis of fruiting body degeneration and establish a foundation for developing diagnostic indicators to screen for early-stage degeneration in industrial mushroom production.

Although the aroma profile of Lentinula edodes has been extensively studied in fruiting bodies, the mycelial stage provides a distinct context for elucidating the fundamental metabolic pathways, free from the complexities of organismal development. To elucidate the mechanism underlying aroma differences between L. edodes strain 808 (the control strain) and its mutant strain ww808 (with almost no shiitake aroma), this study employed GC-IMS combined with PCA and OPLS-DA to identify key aroma biomarkers during the mycelial stage. All analyses were performed with three biological replicates. Furthermore, fatty acids composition, key enzyme activities of the LOX pathway, and their gene expression levels were systematically compared. The results indicated significant differences in the content of volatile aroma compounds in the mycelia of the two strains, primarily stemming from fundamental restructuring of gene expression and enzyme activity in the LOX pathway. The LOX gene expression and LOX activity of 808 mycelium were relatively high, facilitating the accumulation of key aroma compounds such as phenylethanal, benzaldehyde, and ethyl acetate, which constitute its distinctive aromatic profile. However, although the mycelium of ww808 possessed richer fatty acid precursor (C18:2), its lower LOX gene expression restricted the flux of this pathway. The significantly increased expression of ADH2, ADH3, and ADH5 genes and higher ADH activity enhanced the conversion capacity of aldehydes to alcohols and ketones. Given the generally higher odor thresholds of alcohols and ketones compared to aldehydes, distinct aroma profiles emerged between the two strains. Pearson correlation analysis further confirmed the significant correlations between the aroma biomarkers, fatty acids, key genes, and enzyme activities. This study revealed the formation mechanism of aroma differences in the mycelia of the two strains from the perspective of metabolic pathways, providing a theoretical foundation and candidate targets for the directed genetic improvement of L. edodes aroma quality.

Delta-12 fatty acid desaturases (FAD2s) actively regulate stress responses and cell differentiation in living organisms. In this study, six homologous FAD2 genes were identified based on the genome sequence of Lentinula edodes. Then, the six FAD2 protein sequences were analyzed using bioinformatics tools, including ExPASy ProtParam, SignalP, TMHMM, and TargetP. These analyses were performed to predict the physical and chemical properties, signal peptides, and transmembrane and conserved domains of these proteins. The polypeptide sequences were aligned, and a maximum likelihood phylogenetic tree was constructed using MEGA 7.0 software to elucidate the phylogenetic relationships between homologous FAD2 sequences. The results demonstrated that the FAD2 proteins contained three conserved histidine-rich regions (HXXXH, HXXHH, and HXXHH), which included eight histidine residues. The linoleic acid content and FAD2 enzyme activity were further analyzed, and the levels in the mutagenic heat-tolerant strain 18N44 were lower than those in the wild-type strain 18. Interestingly, the expression levels of the FAD2-2 and FAD2-3 genes under heat stress in strain 18N44 were lower than those in strain 18. These findings indicated that FAD2-2 and FAD2-3 may play major roles in the synthesis of linoleic acid during heat stress.