The Arabidopsis SAC9 enzyme is enriched in a cortical population of early endosomes and restricts PI(4,5)P2 at the plasma membrane

Abstract

Membrane lipids, and especially phosphoinositides, are differentially enriched within the eukaryotic endomembrane system. This generates a landmark code by modulating the properties of each membrane. Phosphatidylinositol 4,5-bisphosphate [PI(4,5)P₂] specifically accumulates at the plasma membrane in yeast, animal, and plant cells, where it regulates a wide range of cellular processes including endocytic trafficking. However, the functional consequences of mispatterning PI(4,5)P₂ in plants are unknown. Here, we functionally characterized the putative phosphoinositide phosphatase <i>SUPPRESSOR OF ACTIN9</i> (SAC9) in <i>Arabidopsis thaliana</i> (<i>Arabidopsis</i>). We found that SAC9 depletion led to the ectopic localization of PI(4,5)P₂ on cortical intracellular compartments, which depends on PI4P and PI(4,5)P₂ production at the plasma membrane. SAC9 localizes to a subpopulation of <i>trans</i>-Golgi Network/early endosomes that are enriched in a region close to the cell cortex and that are coated with clathrin. Furthermore, it interacts and colocalizes with Src Homology 3 Domain Protein 2 (SH3P2), a protein involved in endocytic trafficking. In the absence of SAC9, SH3P2 localization is altered and the clathrin-mediated endocytosis rate is reduced. Together, our results highlight the importance of restricting PI(4,5)P₂ at the plasma membrane and illustrate that one of the consequences of PI(4,5)P₂ misspatterning in plants is to impact the endocytic trafficking.