Ypt/Rab-type GTPases are key regulators of membrane trafficking and intracellular vesicular transport. They act as molecular switches that convert between GTP-bound and GDP-bound states, and regulate virtually all steps of membrane traffic from the formation of the transport vesicle at the donor membrane to its fusion at the target membrane. In the GDP-bound state, Ypt proteins are predominantly cytosolic, solubilized through the interaction with a GDP dissociation inhibitor (GDI). In the GTP-bound state, the proteins are membrane bound and interact with specific effector proteins that select cargo, promote vesicle movement, or verify the correct site of fusion (By similarity). Required for fungal morphogenesis, vacuole fusion, autophagy, stress resistance and pathogenicity (PubMed:25991510). Rab activation is generally mediated by a guanine exchange factor (GEF), while inactivation through hydrolysis of bound GTP is catalyzed by a GTPase activating protein (GAP). Interacts with the Rab GDP dissociation inhibitor GDI1. Exhibits defects in mycelial growth and production of conidia, and consequently fails to cause disease in rice and barley. Shows impairment in autophagy, breached cell wall integrity, and higher sensitivity to both calcium and heavy metal stress. Belongs to the small GTPase superfamily. Rab family.