IDENTIFICATION OF A CAMP-DEPENDENT PROTEIN-KINASE CATALYTIC SUBUNIT REQUIRED FOR VIRULENCE AND MORPHOGENESIS IN USTILAGO-MAYDIS

Ustilago maydis, a fungal pathogen of maize, alternates between buddin g and filamentous growth in response to mating and other environmental signals. Defects in components of the cAMP signaling pathway affect t his morphological transition and reveal an association of budding grow th with elevated cAMP levels and filamentous growth with low cAMP leve ls. We have identified two genes, adr1 rand uka1, encoding catalytic s ubunits of cAMP-dependent protein kinase (PKA), Disruption of adr1 res ulted in a constitutively filamentous growth phenotype similar to that of mutants deficient in adenylyl cyclase, Importantly, adr1 is requir ed for pathogenicity and is responsible for the majority of PKA activi ty in fungal cells. Hn contrast, uka1 has little influence on pathogen icity, and deletion of the uka1 gene does mot affect cell morphology. These results provide compelling evidence that regulated PKA activity is crucial during infectious development of U. maydis.