Isolation and characterization of differentially expressed genes in the mycelium and fruitbody of Tuber borchii.

The transition from vegetative mycelium to the fruit body in truffles requires differentiation processes which lead to edible ascomata consisting of different cell and tissue types. The identification of genes differentially expressed during these developmental processes can contribute greatly to a better understanding of truffle morphogenesis. A cDNA library was constructed from vegetative mycelium RNAs of the white truffle Tuber borchii and 214 cDNAs were sequenced. Up to 58% of the ESTs were coding for known genes. The majority of the identified sequences represented 'housekeeping' proteins, i.e., proteins involved in gene/protein expression, cell wall formation, primary and secondary metabolism and components of signaling pathways. We screened 171 arrayed cDNAs by using cDNA probes constructed from mRNAs of vegetative mycelium and ascomata to identify fruit body-regulated genes. Comparisons of signals from vegetative mycelium and fruit body, bearing 15% or 70% mature spores, revealed significant differences in the expression levels for up to 33% of the investigated genes. The expression level of six highly regulated genes was confirmed by RNA blot analysis. Expression of glutamine synthetase, 5-aminolevulinic acid synthetase, isocitrate lyase, thioredoxin, glucan 1,3-ß-glucosidase and UDP-glucurosyl transferase were highly up-regulated suggesting that amino acid biosynthesis, glyoxylate cycle pathway and cell wall synthesis are strikingly altered during morphogenesis.