Abstract
Components of the cAMP signaling pathway, such as the adenylate cyclase Bac and the protein kinase A (PKA) were shown to affect growth, morphogenesis and differentiation as well as virulence of the phytopathogenic fungus Botrytis cinerea. While loss of Bac caused drastically reduced intracellular cAMP levels, deletion of the PKA resulted in extremely increased cAMP concentrations. To regulate the intracellular level of the second messenger cAMP, a balance between its biosynthesis through adenylate cyclase activity and its hydrolysis by phosphodiesterases (PDEs) is crucial. Here, we report the functional characterization of the two PDEs in the ascomycete B. cinerea, BcPde1 and BcPde2. While deletion of bcpde2 resulted in severely affected vegetative growth, conidiation, germination and virulence, the bcpde1 deletion strain displayed a wild-type-like phenotype. However, the double bcpde1/2 deletion mutant exhibited an even stronger phenotype.Localization studies revealed that BcPde2 accumulates at the plasma membrane, but is also localized in the cytoplasm. BcPde1 was shown to be distributed in the cytoplasm as well, but also accumulates in so far unknown mobile vesicles. Overexpression of bcpde1 in the Δbcpde2 background rescued the deletion phenotype, and in addition an increased transcript level of bcpde1 in the Δbcpde2 strain was observed, indicating redundant functions of both PDEs and an interdependent gene expression.
Highlights
Botrytis cinerea is a phytopathogenic ascomycete causing gray mold disease in more than 200 plant species
In this study, we demonstrated that the high-affinity phosphodiesterase BcPde2 has great impact on growth, differentiation and virulence, whereas BcPde1 plays only a minor role in these processes
Bac is activated by the Ga subunits Bcg1 and Bcg3 resulting in increased cyclic adenosine monophosphate (cAMP) levels and subsequent elevation of protein kinase A (PKA) activity (1)
Summary
Botrytis cinerea is a phytopathogenic ascomycete causing gray mold disease in more than 200 plant species. In inappropriate conditions survival is ensured through formation of sclerotia, which can either germinate vegetatively or serve as female partner in sexual reproduction [1,2,3]. External signals, such as humidity, pH, osmotic stress or nutrient availability, have to be sensed and transduced via a diversity of signaling cascades, which can be activated via stimulation of a heterotrimeric G protein. Activation of adenylate cyclase (AC) activity leads to formation of the second messenger cAMP, which is subsequently bound by the regulatory subunits of the protein kinase A (PKA). Binding of cAMP induces the release of the catalytic subunits of the PKA which in turn may phosphorylate downstream targets such as transcription factors [7]
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