Clathrin-coated vesicles are targeted for selective autophagy during osmotic stress

Plants experience hyperosmotic stress due to drought and salinity. This causes cellular water loss, decreases turgor pressure, and reduces cell volume. Osmotic stress affects plasma membrane tension, a property which must be maintained to enable cell signalling and growth. How plants maintain plasma membrane tension as the cell volume shrinks during hyperosmotic stress remains unclear. Here, we identified an autophagy pathway which degrades plasma membrane derived clathrin-coated vesicles (CCVs) during osmotic stress. Time-lapse imaging following osmotic shock shows a reduction in cell volume that correlates with an acute induction of autophagy. Using correlative-light and electron microscopy (CLEM) combined with electron tomography (ET), we visualised CCVs physically attached to autophagosome membranes. High resolution fluorescent microscopy showed that these CCVs are labelled with the endocytic TSET/TPLATE complex, which co-localize with autophagosomes specifically upon osmotic stress. The TPLATE complex subunits, AtEH1/Pan1 and AtEH2/Pan1 contain conserved ATG8 interaction motifs, which we demonstrate to directly interact with ATG8. We therefore propose that AtEH/Pan1 proteins act as selective autophagy receptors for plasma membrane-derived CCVs. We postulate that this pathway removes excess membrane during hyperosmotic stress to maintain plasma membrane tension and integrity. These findings contribute to our physiological understanding of how plants adapt to drought and salt stress.