Identification of Ampelomyces quisqualis genes involved in the early stage of mycoparasitism (host recognition) of powdery mildew

Ampelomyces quisqualis is a naturally occurring mycoparasite of several powdery mildew species. The anatomy of the mycoparasitic relationship between A. quisqualis and its hosts has been widely investigated, but the interaction at molecular level is poorly understood. An extensive catalogue of unique transcripts was obtained by 454 pyrosequencing of 3’ cDNA fragments from a normalized library constructed from pooled RNAs extracted at different A. quisqualis mycoparasitization stages (recognition, early and late parasitisation) and was used to develop a microarray for large scale analysis of genes involved in A. quisqualis mycoparasitism. We focused our study in the early stage of mycoparasitism when an unidentified substance produced by powdery mildews induces germination in A. quisqualis conidia (host recognition). The expression profiling of A. quisqualis during host recognition was studied in a dialysis system (A. quisqualis conidia were in contact with the substance released in water by Podosphaera xanthii grown on Cucurbita pepo leaves). Overall, 5229 genes were identified as being differentially expressed during host recognition. To explore the cellular processes that are active during conidia germination (early and late germination stages) the differentially expressed genes in the treated conidia were hierarchically clustered with respect to their expression profiles and biological functions were assigned using Gene Ontology terms. Results will be discussed. Our data provide the most comprehensive sequence resource currently available for A. quisqualis, and include an extensive collection of potential genetic markers involved in the early stage of mycoparasitism