The cultivation of Auricularia heimuer, a species of edible mushroom, heavily relies on the availability of wood resources serving as substrate for the growth of the species. To ensure the sustainable development of the A. heimuer industry and optimize the utilization of corncob as a substrate, this study sought to investigate the potential use of corncob as a substrate for the cultivation of A. heimuer. The purpose of this study was to explore the utilization of corncob lignocellulose by A. heimuer at the mycelium, primordium, and fruiting stages, by specifically examining the expression profiles of both carbohydrate-active enzymes (CAZymes) and the transcriptome of differentially expressed genes (DEGs) relevant to corncob biomass degradation. The results revealed 10,979, 10,630, and 11,061 DEGs at the mycelium, primordium, and fruiting stages, respectively, while 639 DGEs were identified as carbohydrate-active enzymes. Of particular interest were 46 differentially expressed CAZymes genes that were associated directly with lignocellulose degradation. Furthermore, the study found that A. heimuer exhibited adaptive changes that enabled it to effectively utilize the cellulose present in the corncob. These changes were observed primarily at the primordium and fruiting stages. Key genes involved in lignocellulose degradation were also identified, including g6952, g8349, g12487, and g2976 at the mycelium stage, g5775, g2857, g3018, and g11016 at the primordium stage, and g10290, g2857, g12385, g7656, and g8953 at the fruiting stage. This study found that lytic polysaccharide monooxygenase (LPMO) played a crucial role in the degradation of corncob cellulose, further highlighting the complexity of the molecular mechanisms involved in the degradation of lignocellulose biomass by A. heimuer. The study sheds light on the molecular mechanisms underlying the ability of A. heimuer to degrade corncob biomass, with implications for the efficient utilization of lignocellulose resources. The findings from this study may facilitate the development of innovative biotechnologies for the transformation of corncob biomass into useful products.

Color is a crucial feature to consider when breeding and improving strains of Auricularia cornea. To uncover the mechanism of white strain formation in A. cornea, this study selected parental strains that were homozygous for the color trait and analyzed the genetic laws of A. cornea color through genetic population construction, such as test-cross, back-cross, and self-cross populations, and the statistical analysis of color trait segregation. Moreover, the study developed SSR molecular markers to construct a genetic linkage map, perform the fine mapping the color-controlling genetic locus, and verify candidate genes using yeast two-hybrid, transcriptome analysis, and different light treatments. The results of the study indicated that the color trait of A. cornea is controlled by two pairs of alleles. When both pairs of loci are dominant, the fruiting body is purple, while when both pairs of loci are recessive or one pair of loci is recessive, the fruiting body is white. Based on the linkage map, the study finely mapped the color locus within Contig9_29,619bp-53,463bp in the A. cornea genome and successfully predicted the color-controlling locus gene A18078 (AcveA), which belongs to the Velvet factor family protein and has a conserved structure domain of the VeA protein. It can form a dimer with the VelB protein to inhibit pigment synthesis in filamentous fungi. Lastly, the study validated the interaction between AcVeA and VelB (AcVelB) in A. cornea at the gene, protein, and phenotype levels, revealing the mechanism of inhibition of pigment synthesis in A. cornea. Under dark conditions, dimerization occurs, allowing it to enter the nucleus and inhibit pigment synthesis, leading to a lighter fruiting body color. However, under light conditions, the dimer content is low and cannot enter the nucleus to inhibit pigment synthesis. In summary, this study clarified the mechanism of white strain formation in A. cornea, which could aid in improving white strains of A. cornea and studying the genetic basis of color in other fungi.

Substrate type exerts a critical influence on the growth, development, and nutritional quality of Auricularia heimuer. In this study, agricultural waste-derived corncob was used as the treatment group (T1), with sawdust serving as the control (CK), to systematically investigate the variation in free amino acid (FAA) content and transcriptomic expression profiles in fruiting bodies of A. heimuer under the two substrate conditions. Principal component analysis (PCA) revealed a clear separation between CK and T1 samples in terms of FAA composition, indicating that substrate type significantly affects FAA profiles. The corncob substrate notably increased the total FAA content in A. heimuer (2624.57 mg/kg), representing an 11.4% elevation compared to the sawdust group (2355.86 mg/kg), and markedly enhanced the proportion of flavor-associated amino acids (49.2% vs. 42.6%). In particular, the umami amino acid content was 74% higher than in the CK group. Transcriptome analysis identified 20 differentially expressed genes associated with FAA biosynthesis and degradation, including key enzymes involved in umami amino acid metabolism, such as aspartate decarboxylase (ADC), glutamate decarboxylase (GAD), and glutamate N-acetyltransferase (GNA), which were downregulated in T1. This suggests that glutamate and aspartate may have accumulated due to suppressed catabolism. KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway enrichment analysis further indicated that the differentially expressed genes were significantly enriched in pathways related to branched-chain amino acid metabolism, carbon metabolism, and secondary metabolism. Collectively, these findings demonstrate that corncob substrate significantly alters the accumulation and metabolic profile of FAAs in A. heimuer by modulating the expression of key metabolic enzymes, providing a theoretical foundation for the efficient cultivation of A. heimuer using agricultural waste and for enhancing its flavor quality.

Auricularia heimuer is a widely cultivated jelly mushroom. The fruiting bodies are categorized into cluster and chrysanthemum types. With changing consumer demands and the need to reduce bio-waste, the demand for clustered fruiting bodies is increasing. Therefore, gene mining for fruiting body types is a matter of urgency. We determined that the A. heimuer locus for fruiting body type was located at one end of the genetic linkage map. The locus was localized between the markers D23860 and D389 by increasing the density of the genetic linkage map. BlastN alignment showed that the marker SCL-18 was also located between D23860 and D389, and a total of 25 coding genes were annotated within this interval. Through parental transcriptome analysis and qRT-PCR verification, the locus g7219 was identified as the gene controlling the fruiting body type. A single-nucleotide substitution in the TATA box of g7219 was detected between the parents. By PCR amplification of the promoter region of g7219, the TATA-box sequences of the cluster- and chrysanthemum-type strains were found to be CATAAAA and TATAAAA, respectively. This study provides a foundation for the breeding of fruiting body types and strain improvement of A. heimuer.

Auricularia heimuer is drought tolerant, but the mechanism underlying its physiological response to drought has not been systematically studied. We selected 13 strains of A. heimuer and simulated drought stress using a complete yeast medium (CYM) containing 20% polyethylene glycol (PEG), while the medium used for the control treatments did not contain PEG. Strains were cultured on a shaker incubator at 25 °C at 120 rpm for 15 days under dark conditions. The contents of soluble sugars (SS) and soluble proteins (SP), the activities of superoxide dismutase (SOD) and catalase (CAT), the content of malondialdehyde (MDA), and the biomass were measured. Between the 20% PEG treatment and the control, as well as among different strains, there were significant differences in all of the physiological indices. The tested strains were classified into the following four categories according to their membership function values: the first category consisted of the highly drought-tolerant strain A; the second consisted of the drought-tolerant strains A127 and C; the third consisted of the moderately drought-tolerant strains A124, A14, A386, A462, A184, A496, A125, and B; and the fourth consisted of the drought-sensitive strains A356 and A508. Transcriptome analysis was performed on C before and after drought stress treatment, and 1762 differentially expressed genes (DEGs) were obtained, including 798 up- and 964 down-regulated genes. Through KEGG enrichment analysis, it was found for the first time that the synthesis pathway for trehalose in A. heimuer is trehalose phosphate synthase–trehalose phosphate phosphatase (TPS-TPP), which is involved in the response of A. heimuer to drought stress. In addition, two key enzyme genes involved in trehalose synthesis, namely trehalose-6-phosphate synthase (AhTPS) and trehalose-6-phosphate phosphatase (AhTPP), were significantly up-regulated after drought stress. The trehalose content significantly increased in 11 strains after drought stress treatment. This study discovered, for the first time, that the synthesis pathway of trehalose is involved in the response of edible fungi to drought stress, thus providing a reference for the genetic improvement of A. heimuer and the selection of drought-tolerant strains, laying a theoretical foundation for the resistance breeding of other edible fungi.

Auricularia heimuer is the second most widely cultivated edible fungus in China, with significant food and medicinal value, and is highly popular throughout Asia and globally. However, the differentiation of A. heimuer is simple, as its morphology is characterized by a small “black disc”, making it difficult to distinguish among germplasms with highly similar agronomic traits, thus posing challenges for germplasm identification. To address this issue, this study conducted whole-genome resequencing analysis on 150 A. heimuer germplasms. Through filtering 9,589,911 SNPs obtained from 280 G resequencing data, a total of 1,202,947 high-quality SNP sites were identified. Based on these high-quality SNPs, population structure analysis, principal component analysis (PCA), and phylogenetic tree analysis revealed that the 150 A. heimuer germplasms could be divided into five groups, with wild strains from the same geographical origin exhibiting significant geographical clustering patterns. This finding underscores the relationship between the genetic diversity of wild A. heimuer and its geographical distribution in China. A further selection of 71 SNP sites was made, and 61 KASP markers were successfully developed using kompetitive allele-specific PCR (KASP) technology, with 54 of them demonstrating good polymorphism. The average values for the polymorphism information content (PIC), minor allele frequency (MAF), gene diversity, and heterozygosity of these core KASP markers were 0.34, 0.35, 0.34, and 0.43, respectively. Based on the 54 core KASP markers, a DNA fingerprinting map of the 150 A. heimuer germplasms was constructed in this study. The findings provide important molecular marker resources and theoretical support for the identification of A. heimuer germplasm, molecular marker-assisted breeding, and the selection of superior varieties.