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Abstract

The smut fungus Ustilago maydis is a ubiquitous pathogen of corn. Although of minor economical importance, U. maydis has become the most attractive model among the plant pathogenic basidiomycetes under study. This fungus undergoes a number of morphological transitions throughout its life-cycle, the most prominent being the dimorphic switch from budding to filamentous growth that is prerequisite for entry into the biotrophic phase. The morphological transition is controlled by the tetrapolar mating system. Understanding the mating system has allowed connections to signalling cascades operating during pathogenic development. Here, we will review the status and recent insights into understanding pathogenic development of U. maydis and emphasize areas and directions of future research. Contents Summary 31 I. Introduction 31 II. Important tools for exprimentation with Ustilago myadis 32 III. Cell fusion requres a complex signalling network 33 IV. Development of the dikaryon: the bE/bW complex at work 34 V. A connection between cell cycle, morphogenesis and virulence 36 VI. The early infection stages 38 VII. Proliferation and differentiaton in the plant host 38 VIII. The Ustilago maydis genome 39 IX. Conclusions 40 Acknowledgements 40 References 40.