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

Barcelona, authors Abstract Membrane lipids, and especially phosphoinositides, are differentially enriched within the eukaryotic endomembrane system. This generates a landmark code by modulating the proper-ties of each membrane. Phosphatidylinositol 4,5-bisphosphate [PI(4,5)P-2] 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)P-2 in plants are unknown. Here, we functionally characterized the putative phosphoinositide phosphatase SUPPRESSOR OF ACTIN9 (SAC9) in Arabidopsis thaliana (Arabidopsis). We found that SAC9 depletion led to the ectopic localization of PI(4,5)P-2 on cortical intracellular compart-ments, which depends on PI4P and PI(4,5)P-2 production at the plasma membrane. SAC9 localizes to a subpopulation of trans- 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, SH3P(2) 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)P(2 )misspatterning in plants is to impact the endocytic trafficking.

Automated summary

Membrane lipids, especially phosphoinositides, are differentially enriched within the eukaryotic endomembrane system. In this study, the authors characterized the functional role of a phosphoinositide phosphatase, SAC9, in Arabidopsis. They found that the depletion of SAC9 led to misplaced accumulation of PI(4,5)P-2 on cortical intracellular compartments, impacting endocytic trafficking.