Evolutionarily unique mechanistic framework of clathrin-mediated endocytosis in plants

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.

High Temporal Resolution Reveals Simultaneous Plasma Membrane Recruitment of TPLATE Complex Subunits

“…Under normal conditions, there is a difference in recruitment between TPLATE and DRP1a or clathrin (Gadeyne et al, 2014;Narasimhan et al, 2020). Here, we describe that this difference increases upon lowering the temperature.…”

“…Although very fast endocytic events were observed in neurons (Balaji and Ryan, 2007), in yeast or cultured animal cells, the whole endocytic process takes up to minutes and the physiological role and precise temporal dynamics of endocytic proteins are well defined (Lu et al, 2016;Ma et al, 2016;Pascolutti et al, 2019;Picco and Kaksonen, 2018;Taylor et al, 2011;Wrobel et al, 2019). In plant cells, the endocytic process is much more dynamic, with larger clathrin cages being formed than those in yeast in shorter time periods (Narasimhan et al, 2020), which brings about more technical difficulties in monitoring the temporal recruitment of the diverse endocytic players (Zhang et al, 2015). To better understand the dynamics of endocytosis in plant cells, new approaches are required, which should provide us with enhanced temporal resolution.…”

“…TPC is an evolutionary ancient adaptor complex, which was not retained in yeast or animal cells (Hirst et al, 2014). It is proposed to function as an adaptor complex during CME and has been shown to be recruited to the PM earlier than Dynamin-related proteins while only slightly earlier than clathrin (Gadeyne et al, 2014;Narasimhan et al, 2020). Dictyostelium discoideum contains a similar complex, which however lacks the AtEH/Pan1 proteins and in contrast to TPC, TSET is not essential (Gadeyne et al, 2014;Hirst et al, 2014).…”

“…We performed a similar experiment comparing TPLATE and CLC2, which were previously shown only to have minor differences in their PM recruitment (Gadeyne et al, 2014;Narasimhan et al, 2020). Here, we also observed a temperature-enhancing effect of their differential recruitment with TPLATE being recruited before CLC2, yet less pronounced than the difference between TPLATE and DRP1a ( Taken together, these results show that lowering the temperature slows down dynamics of endocytosis as well as enhances the temporal resolution of recruitment of the endocytic proteins at the PM.…”

The Human-Covid Tango: Connecting the Dots

“…Unlike larger viruses (mimivirus-400nm) that require actin-dependent phagocytosis (Yaakov et al, 2019) Covid-19 (125 nm) enters the cell by clatherin mediated (CM) endocytosis . CM Endocytosis is a membrane process that needs a protein coat to induce curvature leading to the invagination of the memebrane (Lherbette et al,2019;Narasimhan et al,2020). It is a complex process requiring many cellular mediators.…”