The characteristic morphological change especially perceived in mushrooms, namely, fruiting body development, is an essentially biological process for subsequent sexual reproduction such as spore formation, which is produced at the specific tissue in fruiting body. In response to gravity change, morphogenetic changes in mushrooms are clearly observed as “gravitropism”. Similar response to this phenomenon is commonly observed in plants.
Although gravitropism in higher fungi has been investigated since the beginning of the previous century, there still is no criterial evidence on cellular mechanism for gravity perception. To understand this issue in mushrooms, we carried out the gravitational assay to identify differentially expressed genes in Pleurotus ostreatus (oyster mushroom) fruiting bodies that were developed artificially under simulated microgravity by using three-dimensional (3D) clinostat, a special apparatus reducing the effect of terrestrial gravitation. The gene subtraction method, cDNA representational difference analysis (cDNA-RDA), resulted in an isolation of individually upregulated- and downregulated-genes, which were differentially expressed under the condition of simulated microgravity generated by clinorotation. These gravity-responsive genes are likely to be involved in potential cellular mechanisms during fruiting body formation in the basidiomycetous mushroom P. ostreatus. The obtained phenotype of P. ostreatus fruit bodies that were developed under simulated microgravity vividly depicted the gravitropism commonly observed in mushrooms.
Most of reported studies on the response of microorganisms to gravity have been carried out on unicellular organisms such as bacteria, yeasts, etc. Unlike the cells of higher animals and plants, almost every cell of the mushroom can function as a “stem cell”; therefore, the mushroom would be a multicellular model organism for physiological experiments on changes in environmental factors such as the gravity and other stresses. Experiments using mushrooms, including P. ostreatus, will provide more information to clarify the cellular response involved in gravitropism, especially in the morphological development of fruiting bodies.