The small GTPase Rho5-Yet another player in yeast glucose signaling

The small GTPase Rho5 has been shown to be involved in regulating the Baker's yeast response to stress on the cell wall, high medium osmolarity, and reactive oxygen species. These stress conditions trigger a rapid translocation of Rho5 and its dimeric GDP/GTP exchange factor (GEF) to the mitochondrial surface, which was also observed upon glucose starvation. We here show that rho5 deletions affect carbohydrate metabolism both at the transcriptomic and the proteomic level, in addition to cell wall and mitochondrial composition. Epistasis analyses with deletion mutants in components of the three major yeast glucose signaling pathways indicate a primary role of Rho5 upstream of the Ras2 GTPase in cAMP-mediated protein kinase A signaling. Together with determinations of protein kinase A activities, glycogen and trehalose measurements they indicate a stimulation of Ras/cAMP signaling by Rho5.