Arabidopsis VPS38 is required for vacuolar trafficking but dispensable for autophagy

Phosphatidylinositol 3-phosphate (PI3P) is a signaling molecule that controls a variety of processes in endosomal, autophagic and vacuolar/lysosomal trafficking in yeasts and mammals. Vacuolar protein sorting 34 (Vps34) is a conserved phosphatidylinositol 3-kinase (PI3K) present in multiple complexes with specific functions and regulation. In yeast, the PI3K complex II, consisting of Vps34p, Vps15p, Vps30p/Atg6p, and Vps38p, is essential for vacuolar protein sorting. Here, we describe the Arabidopsis thaliana homolog of yeast Vps38p and human UV radiation resistance-associated gene (UVRAG) protein. Arabidopsis VPS38 interacts with VPS30/ATG6 both in yeast and in planta. Although the level of PI3P in Arabidopsis vps38 mutants is similar to that in wild type, vps38 cells contain enlarged multivesicular endosomes and fewer organelles enriched in PI3P than the wild type. The vps38 mutants are defective in the trafficking of vacuolar cargo and its receptor VACUOLAR SORTING RECEPTOR 2;1 (VSR2;1). The mutants also exhibit abnormal cytoplasmic distributions of endocytic cargo such as auxin efflux carriers PINFORMED 1 (PIN1) and PIN2. Constitutive autophagy is normal in the mutants, but starvation-induced autophagy was slightly inhibited. We concluded that Arabidopsis VPS38 is dispensable for autophagy but essential for efficient targeting of biosynthetic and endocytic cargo to the vacuole.