Abstract
Eukaryotic cells internalize cargo at the plasma membrane via endocytosis, a vital process that is accomplished through a complex network of endosomal organelles. In mammalian cells, the ER is in close association with endosomes and regulates their fission. Nonetheless, the physiological role of such interaction on endocytosis is yet unexplored. Here, we probed the existence of ER–endosome association in plant cells and assayed its physiological role in endocytosis. Through live-cell imaging and electron microscopy studies, we established that endosomes are extensively associated with the plant ER, supporting conservation of interaction between heterotypic organelles in evolutionarily distant kingdoms. Furthermore, by analyzing ER–endosome dynamics in genetic backgrounds with defects in ER structure and movement, we also established that the ER network integrity is necessary for homeostasis of the distribution and streaming of various endosome populations as well as for efficient endocytosis. These results support a novel model that endocytosis homeostasis depends on a spatiotemporal control of the endosome dynamics dictated by the ER membrane network.
Highlights
Endocytosis is an essential process in eukaryotes
An overall decrease in the fluorescence levels could be observed for the auxin transporters 35S::PIN5-GFP [50] or 35S::AUX1-YFP [51] (Supplementary Figure S8). These results indicate that loss of the endoplasmic reticulum (ER) shaping RHD3 leads to increased levels of auxin and disruption of the homeostasis of transport machinery, which perturbs the homeostatic distribution of these proteins at the plasma membrane
ER architecture defects lead to severe subcellular phenotypes, which in plants and mammals have been associated to severe growth and developmental phenotypes [14, 52,53,54], but the underlying mechanisms are unknown
Summary
Endocytosis is an essential process in eukaryotes. It mediates the recycling of membranes, cell surface receptors and ion channels, and is crucially important for the control of the lipid and protein composition of the plasma membrane. Through regulation of either recycling or degradation of plasma membrane receptors, this transport step contributes to the perception of external stimuli [1, 2]. Endocytosis of cargo is thought to be vesicle mediated and leads to a class of organelles loosely defined as endosomes. These are membranous compartments that function as critical sorting stations for membrane traffic, protein targeting and maturation.
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