Identification of a cAMP-dependent protein kinase catalytic subunit required for virulence and morphogenesis in Ustilago maydis

Abstract

Ustilago maydis, a fungal pathogen of maize, alternates between budding and filamentous growth in response to mating and other environmental signals. Defects in components of the cAMP signaling pathway affect this morphological transition and reveal an association of budding growth with elevated cAMP levels and filamentous growth with low cAMP levels. We have identified two genes, adr1 and uka1, encoding catalytic subunits of cAMP-dependent protein kinase (PKA). Disruption of adr1 resulted in a constitutively filamentous growth phenotype similar to that of mutants deficient in adenylyl cyclase. Importantly, adr1 is required for pathogenicity and is responsible for the majority of PKA activity in fungal cells. In contrast, uka1 has little inf luence on pathogenicity, and deletion of the uka1 gene does not affect cell morphology. These results provide compelling evidence that regulated PKA activity is crucial during infectious development of U. maydis.Pathogenesis, dimorphic growth, and sexual development are intricately interconnected in the corn smut fungus Ustilago maydis, and the perception of signals from the host plant is likely to play an important role in these processes (1, 2). Mating of haploid U. maydis cells, which are nonpathogenic and yeast-like, leads to the formation of infectious, dikaryotic hyphae. Dikaryons can be established in culture, but the resulting hyphae need the host environment to sustain mycelial proliferation. Infection of maize plants results in tumor induction and the eventual formation of masses of diploid teliospores.

Signaling via cAMP in fungi: interconnections with mitogen-activated protein kinase pathways

“…Disruption of adr1 results in mutants that display a filamentous phenotype quite similar to that of the uac1 mutant; these mutants are incapable of causing infection in plants (Dürrenberger et al 1998). In contrast, the uka1 gene has little effect on mating, morphogenesis, or virulence.…”

“…Two genes encoding catalytic subunits of PKA, adr1 and uka1, have been identified in U. maydis; adr1 appears to contribute the majority of PKA activity, while uka1 appears to make a minor contribution (Dürrenberger et al 1998). Disruption of adr1 results in mutants that display a filamentous phenotype quite similar to that of the uac1 mutant; these mutants are incapable of causing infection in plants (Dürrenberger et al 1998).…”

“…Microscopic observation of infected maize tissue showed that a dikaryon that is defective in both alleles of ubc1 is capable of growth in the plant, but is incapable of tumor formation (Gold et al 1997). Similarly, diploid strains lacking both copies of the ubc1 gene are also incapable of forming tumors on plants (Dürrenberger et al 1998).…”

Proteomic analysis of dimorphic transition in the phytopathogenic fungus Ustilago maydis

“…Among these genes were rep1, actin and a homologue of the YakC kinase [20]. Two genes encoding catalytic subunits of protein kinase A (adr1 and uka1) have also been identified as part of cAMP signalling [38,39]. In the U. maydis adr1 mutant strain the septin SEP3 has been identified as being up-regulated in these filamentously growing cells [21].…”

Ustilago maydis – a valuable model system for the study of fungal dimorphism and virulence

“…Two genes, uka1 and adr1, encoding potential catalytic subunits of PKA were identified by sequence homology. Whereas deletion of uka1 did not result in an obvious mating defect, adr1 mutants exhibit the same filamentous phenotype as uac1 mutants and are epistatic to ubc1 (Du$ rrenberger & Kronstad, 1999 ;Du$ rrenberger et al, 1998). This indicates that a functional cAMP signalling pathway is required for nutritional sensing, mating and pathogenic development.…”