1Institut für Genetik und Mikrobiologie der Universität München, Maria-Ward-Str.1a, D-80638 Munich, Germany; 2Institut für Botanik der Universität München, Menzinger Str. 61-65, D-80638 Munich, Germany
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Accepted 1 July 2000.
In the corn smut fungus Ustilago maydis, mating of two haploid sporidia is a prerequisite for subsequent colonization of the host. Cyclic AMP (cAMP) and pheromone signals have been implicated in this developmental program. The cAMP pathway is also needed for subsequent fungal development in planta, as null mutants in any component of the pathway fail to form tumors. Here we show that moderate activation of the pathway conferred either by mutation in the Gα subunit or by mutation in the regulatory subunit of the protein kinase A influences tumor morphology. In the resulting tumors, the amount of fungal material is drastically reduced and fungal development is arrested at the stage of sporogenic hyphae. We conclude that tight regulation of the cAMP pathway is crucial for fungal development within the plant but does not interfere with the tumor induction process.
© 2000 The American Phytopathological Society