Morphological and molecular modifications induced by different carbohydrate sources in Tuber borchii

During the mycorrhizal fungi life cycle, several morphological, genetic and metabolic modifications are induced in both symbiotic partners. These changes are influenced by multiple environmental factors: light, gravity, oxygen, temperature, soil typology, nutrients, root exudates and the presence of particular bacterial populations in the mycorrhizosphere. In order to verify if nutritional sources leads to cell signaling events and morpho-functional changes in Tuber borchii mycelium, the expression level of genes involved in the morphological modifications was investigated using the array technique and real time RT-PCR, on mycelia grown on culture media containing different carbohydrates. The results obtained by morphological analyses highlighted an increased growth of Tuber borchii mycelia in the presence of glucose, while the hyphae are thinner and less branched in the presence of sucrose and maltose. These data corroborates with gene expression analyses, that evidenced an upregulation of the genes involved in apical growth and general metabolism. Since glucose is also present in root plant exudates, it can act as a signal for the fungus to indicate the presence of the plant, and to trigger the complex symbiotic process. These mechanisms can lead to morphological modifications, among which an increase branching, necessary for the fungus to establish the symbiosis.