Signaling pathways mediating the roles of Rho1 in cell wall assembly and actin organization

Signaling pathways mediating the roles of Rho1 in cell wall assembly and actin organization. Cell wall stresses are sensed by the five type I membrane proteins Wsc1, Wsc2, Wsc3, Mid2, and Mtl1, with the major players indicated by the thick lines and boldface type. These sensors then activate the GEFs Rom1 and Rom2, which in turn activate Rho1. Activated Rho1 controls cell wall assembly in two distinct ways: as the regulatory subunit of the glucan synthases Fks1 and Fks2 and by activating the Pkc1-MAPK-mediated CWI pathway, which increases the expression of cell wall synthetic enzymes. Rho1-GTP also controls polarized exocytosis as indicated in Fig. . Rho1-GTP also regulates actin ring formation via Bni1 to effect cytokinesis. Mss4, the PI4P-5K, synthesizes the plasma membrane pool of PI4,5P2, which recruits the Rho1 GEFs to the plasma membrane, thus contributing to Rho1 activation. PI4,5P2 and Tor2 are involved in recruiting and/or maintaining the pair of PH domain-containing proteins, Slm1 and Slm2, at the plasma membrane. These Slm proteins are thought to function in actin organization via Pkc1 but not the MAPK pathway. In response to heat stress, Rho1-Pkc1 is thought to function in transient actin depolarization, whereas the MAPK pathway is thought to function in subsequent actin repolarization during the recovery phase (see the text for further details). SBF, Swi4/Swi6 cell cycle box binding factors.

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Central Roles of Small GTPases in the Development of Cell Polarity in Yeast and Beyond. (2007) Hay-Oak Park, et al. Microbiol Mol Biol Rev. 2007 Mar;71(1):48-96. Figure: F15. All organisms Homo sapiens Saccharomyces cerevisiae S288C

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