Abstract
In plants, clathrin mediated endocytosis (CME) represents the major route for cargo internalisation from the cell surface. It has been assumed to operate in an evolutionary conserved manner as in yeast and animals. Here we report characterisation of ultrastructure, dynamics and mechanisms of plant CME as allowed by our advancement in electron microscopy and quantitative live imaging techniques. Arabidopsis CME appears to follow the constant curvature model and the bona fide CME population generates vesicles of a predominantly hexagonal-basket type; larger and with faster kinetics than in other models. Contrary to the existing paradigm, actin is dispensable for CME events at the plasma membrane but plays a unique role in collecting endocytic vesicles, sorting of internalised cargos and directional endosome movement that itself actively promote CME events. Internalized vesicles display a strongly delayed and sequential uncoating. These unique features highlight the independent evolution of the plant CME mechanism during the autonomous rise of multicellularity in eukaryotes.
Highlights
Clathrin mediated endocytosis (CME) is the key cellular progress of internalising a cargo, either on the plasma membrane (PM) or outside the cell, into the cell
We established a method for using Scanning Electron Microscopy (SEM) on metal replicas of unroofed Arabidopsis root protoplast cells, which allowed the direct examination of clathrin coated structures (CCSs)
Metal replicas of Arabidopsis root protoplast cells provided a detailed view of well-preserved clathrincoated pits (CCP) at various stages of invagination at the PM and fully formed clathrin coated vesicles (CCVs) deeper inside the cell, which are often attached to cytoskeletal and intracellular membrane structures (Figure 1A and Figure 1— figure supplement 1A,B)
Summary
Clathrin mediated endocytosis (CME) is the key cellular progress of internalising a cargo, either on the plasma membrane (PM) or outside the cell, into the cell. CME represents a major endocytic route in eukaryotes (Goh et al, 2010). In plants, it is even more significant as most, if not all, endocytosis occurs via CME, and many important PM proteins implicated in key physiological processes, such as growth and development, nutrient uptake or pathogen defence, are established cargos for the CME pathway (Barberon et al, 2011; Dhonukshe et al, 2007; Di Rubbo et al, 2013; Mbengue et al, 2016; Yoshinari et al, 2016). Functional characterisation of these, and other plant EAPs, is greatly lacking
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