Endocytic and Secretory Traffic in <i>Arabidopsis</i> Merge in the Trans-Golgi Network/Early Endosome, an Independent and Highly Dynamic Organelle

TLDR

Plants constantly remodel plasma membrane proteins to mediate signaling and transport, yet the compartments and machinery governing secretory and endocytic trafficking remain incompletely understood. Using immunogold electron microscopy and confocal laser scanning microscopy, the authors traced the routes of the BRASSINOSTEROID INSENSITIVE1 receptor and the REQUIRES HIGH BORON1 boron exporter through the plant endomembrane system. The study shows that both secretory and endocytic cargo transit the trans‑Golgi network/early endosome, that late endosome/multivesicular body cargo is directed to vacuolar degradation, and that TGN/EE organelles move independently, associating only transiently with Golgi stacks.

Abstract

Abstract Plants constantly adjust their repertoire of plasma membrane proteins that mediates transduction of environmental and developmental signals as well as transport of ions, nutrients, and hormones. The importance of regulated secretory and endocytic trafficking is becoming increasingly clear; however, our knowledge of the compartments and molecular machinery involved is still fragmentary. We used immunogold electron microscopy and confocal laser scanning microscopy to trace the route of cargo molecules, including the BRASSINOSTEROID INSENSITIVE1 receptor and the REQUIRES HIGH BORON1 boron exporter, throughout the plant endomembrane system. Our results provide evidence that both endocytic and secretory cargo pass through the trans-Golgi network/early endosome (TGN/EE) and demonstrate that cargo in late endosomes/multivesicular bodies is destined for vacuolar degradation. Moreover, using spinning disc microscopy, we show that TGN/EEs move independently and are only transiently associated with an individual Golgi stack.