An expression cDNA library for suppression cloning in yeast mutants, complementation of a yeast his4 mutant, and EST analysis from the symbiotic basidiomycete Hebeloma cylindrosporum.

An oriented expression library was constructed from the mycelia of the symbiotic model fungus Hebeloma cylindrosporum in the high-level yeast expression vector pDR196. DNA sequencing of approximately 500 expressed sequence tags (ESTs) showed that 15% correspond to known genes, two thirds contain sequences with unknown function, andthe remaining 20% showed no significant similarity to any known genes. The ESTs had a GC content between 44 and 56%, with most of them having a GC content of 52-54%, which could be correlated with GC contents of fungal genes. The library was successfully used to identify the Hebeloma HIS4 gene by functional complementation of a yeast his4 mutant. Thus, the library may serve as a powerful tool for identification and characterization of mycorrhizal genes by EST analysis and for the identification of ectomycorrhizal genes by means of suppression cloning.