Constituents of the conserved Rho-family GTPases play many fundamental roles in cellular growth and differentiation. They play key roles in actin organization, membrane trafficking, polarized cell growth, and regulation of the cell cycle. In fungi, Rho GTPases also play more specialized roles in cell integrity pathways that include those for cell wall synthesis. They initiate and direct the cell wall biosynthetic machinery to the polar region via actin cytoskeletal reorganization. This consequently contributes to polarized cell growth, an essential feature in fungal morphogenesis. All fungi undergo morphological changes, a culmination of extracellular and intracellular stimuli, through polarized cell growth. For pathogenic fungi in particular, morphological transformation and polarized cell growth are key features that allow and sustain invasive development. Moreover, actin cytoskeletal reorganization in fungi due to Rho GTPases is a pivotal requirement for cytokinesis. Fungi are highly diverse and in many ways more tractable than multi-cellular organisms; consequently, we owe much to these microbes for research identifying the many crucial roles of Rho GTPases. Nonetheless, a complete understanding of how Rho GTPases are regulated in any particular process still remains elusive. Here we provide a comprehensive review of regulatory mechanisms employed by different species of fungi to influence how Rho GTPases conduct their myriad functions.
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