Precision targeting by phosphoinositides: how PIs direct endomembrane trafficking in plants

- PIPs are biochemical and biophysical landmarks that specify membrane identity.
- PIPs and small GTPases couple membrane identity switches with trafficking.
- Two distinct PIP cascades exist in plants, centered around early and late endosomes.
- PI(3)P and PI(3,5)P2 regulate vacuolar biogenesis, endosomal sorting and autophagy.
- PIP patterning defines membrane domains for polarized exocytosis and endocytosis.

Each phosphoinositide (PI, also known as phosphatidylinositol phosphate, polyphosphoinositide, PtdInsP or PIP) species is partitioned in the endomembrane system and thereby contributes to the identity of membrane compartments. However, membranes are in constant flux within this system, which raises the questions of how the spatiotemporal pattern of phosphoinositides is established and maintained within the cell. Here, we review the general mechanisms by which phosphoinositides and membrane trafficking feedbacks on each other to regulate cellular patterning. We then use the specific examples of polarized trafficking, endosomal sorting and vacuolar biogenesis to illustrate these general concepts.

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