Summary The black morel (Morchella importuna Kuo, O'Donnell and Volk) was once an uncultivable wild mushroom, until the development of exogenous nutrient bag (ENB), making its agricultural production quite feasible and stable. To date, how the nutritional acquisition of the morel mycelium is fulfilled to trigger its fruiting remains unknown. To investigate the mechanisms involved in ENB decomposition, the genome of a cultivable morel strain (M. importuna SCYDJ1‐A1) was sequenced and the genes coding for the decay apparatus were identified. Expression of the encoded carbohydrate‐active enzymes (CAZymes) was then analyzed by metatranscriptomics and metaproteomics in combination with biochemical assays. The results show that a diverse set of hydrolytic and redox CAZymes secreted by the morel mycelium is the main force driving the substrate decomposition. Plant polysaccharides such as starch and cellulose present in ENB substrate (wheat grains plus rice husks) were rapidly degraded, whereas triglycerides were accumulated initially and consumed later. ENB decomposition led to a rapid increase in the organic carbon content in the surface soil of the mushroom bed, which was thereafter consumed during morel fruiting. In contrast to the high carbon consumption, no significant acquisition of nitrogen was observed. Our findings contribute to an increasingly detailed portrait of molecular features triggering morel fruiting.

Truffles are one group of the most famous ectomycorrhizal fungi in the world. There is little information on the ecological mechanisms of truffle ectomycorrhizal synthesis in vitro. In this study, we investigated the ecological effects of Tuber indicum – Quercus aliena ectomycorrhizal synthesis on microbial communities in the host plant roots and the surrounding soil using high-throughput sequencing and on the metabolic profiles of host plant roots using metabolomics approaches. We observed an increase in the diversity and richness of prokaryotic communities and a decrease in richness of fungal communities in the presence of T. indicum. The microbial community structures in the host roots and the surrounding soil were altered by ectomycorrhizal synthesis in the greenhouse. Bacterial genera Pedomicrobium, Variibacter, and Woodsholea and fungal genera Aspergillus, Phaeoacremonium, and Pochonia were significantly more abundant in ectomycorhizae and the ectomycorrhizosphere soil compared with the corresponding T. indicum-free controls (P < 0.05). Truffle-colonization reduced the abundance of some fungal genera surrounding the host tree, such as Acremonium, Aspergillus, and Penicillium. Putative prokaryotic metabolic functions and fungal functional groups (guilds) were also differentiated by ectomycorrhizal synthesis. The ectomycorrhizal synthesis had great impact on the measured soil physicochemical properties. Metabolic profiling analysis uncovered 55 named differentially abundant metabolites between the ectomycorhizae and the control roots, including 44 upregulated and 11 downregulated metabolites. Organic acids and carbohydrates were two major upregulated metabolites in ectomycorhizae, which were found formed dense interactions with other metabolites, suggesting their crucial roles in sustaining the metabolic functions in the truffle ectomycorrhization system. This study revealed the effects of truffle-colonization on the metabolites of ectomycorrhiza and illustrates an interactive network between truffles, the host plant, soil and associated microbial communities, shedding light on understanding the ecological effects of truffles.

Saprotrophic mushrooms cultivated in soils are subject to complex influences from soil microbial communities. Research on growing edible mushrooms has revealed connections between fungi and a few species of growth-promoting bacteria colonizing the mycosphere.