ROPs

Rho-like GTPases from plants (ROPs) constitute a plant-specific subfamily of Rho-family small GTPases. The Rho family is conserved among all eukaryotic cells, and includes the Rho, Rac and Cdc42 subfamilies found in fungi and animals. Like other GTPases, ROPs act as molecular switches that cycle between the inactive GDP-bound and active GTP-bound states, and are typically involved in cell signaling. Functional studies have demonstrated that ROPs play key roles in regulating processes such as the establishment of cell polarity, polar growth of cells (e.g., pollen tubes and root hairs), cell shape formation, and cell wall patterning. These processes depend upon cytoskeletal dynamics and vesicular trafficking, which are commonly regulated by Rho-family GTPases in many organisms. However, in plants, the upstream input and downstream regulatory outputs are highly diverse, and ROPs have evolved distinct regulatory mechanisms and specialized functions adapted to plant-specific processes, such as hormone signaling, stress responses, meristem maintenance, and tropic growth. Evolutionary analysis shows that ROPs are highly conserved in land plants, and are encoded by a small gene family, whose members can be functionally redundant or distinct. Thus, distinct ROPs can serve as major players in different cellular systems, allowing a shared regulatory mechanism to diversify into cell type-specific functions. By comparing representative models of polarized cell growth, we highlight how multiple ROPs regulate both shared and cell type-specific signaling pathways and discuss how ROPs achieve functional diversity and serve as targets of genetic manipulation for potential applications in synthetic biology and agriculture.