Budding yeast Rho1 guanosine triphosphatase (GTPase) plays an essential role in polarized cell growth by regulating cell wall glucan synthesis and actin organization. Upon cell wall damage, Rho1 blocks polarized cell growth and repairs the wounds by activating the cell wall integrity (CWI) Pkc1-mitogen-activated protein kinase (MAPK) pathway. A fundamental question is how active Rho1 promotes distinct signaling outputs under different conditions. Here we identified the Zds1/Zds2-protein phosphatase 2ACdc55 (PP2ACdc55) complex as a novel Rho1 effector that regulates Rho1 signaling specificity. Zds1/Zds2-PP2ACdc55 promotes polarized growth and cell wall synthesis by inhibiting Rho1 GTPaseactivating protein (GAP) Lrg1 but inhibits CWI pathway by stabilizing another Rho1 GAP, Sac7, suggesting that active Rho1 is biased toward cell growth over stress response. Conversely, upon cell wall damage, Pkc1-Mpk1 activity inhibits cortical PP2ACdc55, ensuring that Rho1 preferentially activates the CWI pathway for cell wall repair. We propose that PP2ACdc55 specifies Rho1 signaling output and that reciprocal antagonism between Rho1-PP2ACdc55 and Rho1-Pkc1 explains how only one signaling pathway is robustly activated at a time.
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