1.10.20
IDENTIFICATION OF ERYSIPHE GRAMINIS F.SP. HORDEI GENES EXPRESSED DURING GERMINATION

RP OLIVER, SW RASMUSSEN, J ROUSTER, S THOMAS and LB JENSEN

Department of Physiology, Carlsberg Laboratory, DK-2500 Copenhagen Valby, Denmark

Background and objectives
Erysiphe graminis f.sp. hordei (EGH) is an economically important, biotrophic pathogen of barley. Pathogenesis involves a complex series of developmental changes whereby the conidia develop two distinct types of germ tube, one of which differentiates into the appressorium. The appressorium can penetrate the host epidermal cell and form the haustorium. Some days later, the superficial hyphae differentiate to form the conidiophore structures. Analysis of the genes involved in pathogenesis is hampered by the inability of the fungus to develop beyond the appressorium stage on artificial media. As a result of this, molecular genetic analysis is not as yet possible.

Results and conclusions
To overcome this hurdle, we have started a project to analyse systematically as many as possible of the fungal genes expressed during infection. As a first step, a cDNA library prepared from germinating conidia has been used [1]. 1000 clones representing about 5% of the total number of EGH genes have thus far been analysed by sequencing the terminal 500 bp of the inserts and database comparisons. Rather to our surprise, there is a low degree of redundancy in the library. Some 700 of the genes are represented on only one clone. Homology searches have suggested putative functions for more than 50% of the clones. Significant numbers of genes are likely to be involved in functions necessary for penetration, such as signal transduction and proteolysis. The identity of other genes reveals many unexpected functions which have suggested new avenues for research.

The analysis of these data has been made possible by a new, especially developed software package called DNA Tools. Initially we have concentrated on the analysis of genes likely to be involved in the transduction of signals leading to the formation of appressoria and haustoria. Analysis of these genes and of the library as a whole will be presented.

References
1. Justesen A, Somerville S, Giele H, 1996. Gene 170, 131-135.