The Biotrophic Phase of Ustilago maydis: Novel Determinants for Compatibility

Abstract

The basidiomycete fungus Ustilago maydis establishes a biotrophic relationship with its host plant maize which is maintained throughout disease development. Recent insights from the genome sequence have revealed that this interaction is largely governed by a set of novel secreted proteins that are only found in U. maydis. Many of the respective genes are clustered and appear co-regulated during late stages of pathogenesis. Mutants in most of these gene clusters arrest development at distinct stages, suggesting that the secreted proteins fulfill discrete functions in the interaction with the host. One of the cluster mutants, however, displays increased virulence suggesting that it is not in the interest of U. maydis to use its full potential as a pathogen. In this chapter we will review these findings and place them in perspective for a comprehensive understanding of biotrophy.