Figure 10.

Model of CHMP1 Function in ESCRT-Mediated Sorting of Auxin Carriers.

AUX1, PIN1, and PIN2 cycle between endosomes and the plasma membrane by distinct mechanisms (Geldner et al., 2003; Kleine-Vehn et al., 2006; Robert et al., 2008). CHMP1 and ESCRT proteins mediate the degradation of PIN1, PIN2, and AUX1 in the vacuolar lumen in wild-type cells by sorting these proteins into MVB lumenal vesicles. In chmp1a chmp1b mutant cells, the sorting of PIN1, PIN2, and AUX1 and the formation of lumenal vesicles is compromised. As a result of MVB sorting defects, PIN1, PIN2, and AUX1 remain in the MVB limiting membrane and accumulate in the vacuolar membrane upon MVB vacuole fusion.