Abstract
Plants rely on both actin and microtubule cytoskeletons to fine-tune sorting and spatial targeting of membranes during cell growth and stress adaptation. Considerable advances have been made in recent years in the comprehension of the relationship between the trans-Golgi network/early endosome (TGN/EE) and cytoskeletons, but studies have mainly focused on the transport to and from the plasma membrane. We address here the relationship of the cytoskeleton with different endoplasmic reticulum (ER) export mechanisms toward vacuoles. These emergent features of the plant endomembrane traffic are explored with an in vivo approach, providing clues on the traffic regulation at different levels beyond known proteins’ functions and interactions. We show how traffic of vacuolar markers, characterized by different vacuolar sorting determinants, diverges at the export from the ER, clearly involving different components of the cytoskeleton.
Highlights
Eukaryotic cells are characterized by a complex and dynamic endomembrane system, which further evolved with multicellularity to assure specialized functions
We observed that the intermediate compartments labeled by RFP-chitinase A signal (Chi) were more visible (Figure 1A–C) with respect to compartments highlighted by the GFP tagged form of the marker [15,16,27]
Golgi’s high motility, the same co-transformed protoplasts were treated with the actin depolymerizing agent cytochalasin D (Cyt D), which abolishes Golgi movement [30]
Summary
Eukaryotic cells are characterized by a complex and dynamic endomembrane system, which further evolved with multicellularity to assure specialized functions. It has been established that differently from metazoans, long-distance transport of endomembrane components in plants mainly relies on actin bundles and is mediated by myosin XI motor proteins [3]. Myosin XI motor proteins’ maximum speeds exceed those of microtubule-associated kinesin motors [4], and they are more effective at providing the driving force of cytoplasmic streaming, which assures the distribution of endomembrane compartments and cytosolic components in cells that are often much bigger than in other organisms. Membrane-bound Rab GTPases can recruit other proteins involved in compartment motility such as motor proteins, tethering factors and SNAREs (N-ethylmaleimide-sensitive factor adaptor protein receptors) [2], but the microtubule-based transport, for a long time unnoticed in plant cells, is an essential player in traffic too [5,6]. The necessary spatiotemporal control of traffic must depend on the trans-Golgi network/early endosome (TGN/EE), a morphologically complex post-Golgi compartment considered to be the hub for both secretory and endocytic pathways [7]
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