Abstract

Background: ESCRT mediates membrane remodeling in cellular processes such as endosomal sorting. The ATPase SKD1/VPS4 is essential for ESCRT function. Results: PROS is a plant-specific ESCRT component that increases SKD1/VPS4 ATPase activity and is required for cell expansion. Conclusion: Plants have evolved specific ESCRT components that are required for normal development. Significance: Diversification of ESCRT components in eukaryotes may provide additional regulatory mechanisms for ESCRT-dependent processes. ESCRT proteins mediate membrane remodeling and scission events and are essential for endosomal sorting of plasma membrane proteins for degradation. We have identified a novel, plant-specific ESCRT component called PROS (POSITIVE REGULATOR OF SKD1) in Arabidopsis thaliana. PROS has a strong positive effect on the in vitro ATPase activity of SKD1 (also known as Vacuolar Protein Sorting 4 or VPS4), a critical component required for ESCRT-III disassembly and endosomal vesiculation. PROS interacts with both SKD1 and the SKD1-positive regulator LIP5/VTA1. We have identified a putative MIM domain within PROS that mediate the interaction with the MIT domain of SKD1. Interestingly, whereas MIM domains are commonly found at the C terminus of ESCRT-III subunits, the PROS MIM domain is internal. The heterologous expression of PROS in yeast mutant cells lacking Vta1p partially rescues endosomal sorting defects. PROS is expressed in most tissues and cells types in Arabidopsis thaliana. Silencing of PROS leads to reduced cell expansion and abnormal organ growth.