The Heterotrimeric G-Protein GanB(α)-SfaD(β)-GpgA(γ) Is a Carbon Source Sensor Involved in Early cAMP-Dependent Germination inAspergillus nidulans

Abstract

The role of heterotrimeric G-proteins in cAMP-dependent germination of conidia was investigated in the filamentous ascomycete Aspergillus nidulans. We demonstrate that the Ga-subunit GanB mediates a rapid and transient activation of cAMP synthesis in response to glucose during the early period of germination. Moreover, deletion of individual G-protein subunits resulted in defective trehalose mobilization and altered germination kinetics, indicating that GanB(a)-SfaD(b)-GpgA(g) constitutes a functional heterotrimer and controls cAMP/PKA signaling in response to glucose as well as conidial germination. Further genetic analyses suggest that GanB plays a primary role in cAMP/PKA signaling, whereas the SfaDGpgA (Gbg) heterodimer is crucial for proper activation of GanB signaling sensitized by glucose. In addition, the RGS protein RgsA is also involved in regulation of the cAMP/PKA pathway and germination via attenuation of GanB signaling. Genetic epistatic analyses led us to conclude that all controls exerted by GanB(a)-SfaD(b)-GpgA(g) on conidial germination are mediated through the cAMP/PKA pathway. Furthermore, GanB may function in sensing various carbon sources and subsequent activation of downstream signaling for germination.

Dissecting the role of G-protein signalling in primary metabolism in the wheat pathogen Stagonospora nodorum

“…highlighted the significant effect on metabolism caused by the inactivation of Gna1, Gba1 and Gga1. Consistent with the deletion of the individual G-protein subunits of Aspergillus nidulans (Lafon et al, 2005) and other fungal systems (Kraakman et al, 1999) is an effect on the disaccharide trehalose. The decline in intracellular and extracellular glucose 10 days p.i.…”

“…It therefore appears that trehalose acts as a sink for excess glucose. Lafon et al (2005) also observed the (albeit less significant) reduced catabolism of trehalose in the sfaD and gpgA strains of Aspergillus nidulans. This implies a role for all three G-protein subunits in trehalose degradation, and supports a similar requirement for Gna1, Gba1 and Gga1 in S. nodorum.…”

Trehalose metabolism is important for heat stress tolerance and spore germination of Botrytis cinerea

“…Further support for this came from the observation that a B. cinerea Dbcg3 mutant, which is defective in cAMP signalling, does not show any degradation of trehalose during germination (Doehlemann et al, 2006; data not shown). Similarly, it has been demonstrated recently that G-protein-mediated cAMP signalling, activated by hexoses, is necessary for trehalase activity in A. nidulans (Lafon et al, 2005). This is supported by the fact that the predicted TRE1 protein contains the typical N-terminal RRXS motive, which has been described as a cAMP-dependent protein kinase phosphorylation site (Kopp et al, 1993;Rittenhouse et al, 1986).…”

Multiple Roles of a Heterotrimeric G-Protein γ-Subunit in Governing Growth and Development of Aspergillus nidulans

“…We propose that the heterotrimer composed of FadA and SfaDTGpgA functions in vegetative growth and fertilization signaling in A. nidulans (Yu et al 1996;Rosén et al 1999). Moreover, a recent study by Lafon et al (2005; see accompanying article in this issue) revealed that GanB and SfaDTGpgA constitute a functional heterotrimer that functions in conidial germination and sensing external carbon sources. In this model, it is speculated that during the vegetative growth phase FadA and SfaDTGpgA primarily mediate signaling for proliferation.…”