Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK

Background and objectives
Hydrophobins are small molecular-weight proteins which have been found in a number of fungi [1]. They are known to assemble on the outer surface of the hyphal and conidial cell walls to which they confer hydrophobic properties. The distribution of hydrophobins on the surface of hyphae suggests a function in the interaction between fungi and the environment. In the case of some plant pathogenic fungi they are necessary for successful infection, e.g. in Magnaporthe grisea the main hydrophobin MPG1 is involved in surface recognition and in the cascade of events which lead to formation of appressoria. In addition to adhesion, it has been proposed that hyphal hydrophobins may act in some fungi as 'stealth determinants' by screening the fungus from detection by the plant [2]; this may be particularly true in those biotrophic and hemibiotrophic pathogens, such as Cladosporium fulvum, which penetrate the plant tissues without being recognized by the host. In this work I assess the role of two hydrophobins from C. fulvum in protecting the fungus from detection by the host plant.

Results and conclusions
Two hydrophobins, named HCf-1 and HCf-2, respectively, are secreted in the medium when C. fulvum is grown in liquid culture. These proteins were partially purified and the N-terminus was sequenced. The corresponding cDNAs were cloned by RT-PCR and used to obtain genomic clones. Mutants defective in either HCf-1, HCf-2, or both were obtained by gene deletion based on homologous recombination. The hydrophobicity of the mutant fungi is reduced. The strains in which both HCf-1 and HCf-2 are missing are the most hydrophilic. The pathogenicity of the mutants is being analysed by assaying fungal biomass (see Karpovich-Tate et al., this meeting) to determine whether these hydrophobins are necessary to infect tomato.

1. Wessels JGH, 1996. Trends in Plant Science 1, 9-15. 2. Templeton MD, Rikkerink EHA, Beever RE, 1994. Molecular Plant-Microbe Interactions 7, 320-325.