The Membrane Nanodomain Flot1 Protein Participates in Formation of the Early Endosomes in the Root Cells of Arabidopsis thaliana

Abstract

Plants are subjected to various stress factors within their lifespan. In this respect, the plasma membraneis a principal cell compartment responsible for plant adaptations to stresses. It is capable of remodelingits protein composition by means of endocytosis. In the plants, the main mode of this process is a clathrinmediatedendocytosis. Several clathrin-independent pathways are also known; these alternative mechanismsinvolve Flot1 protein. In the present research, the role of Flot1 in the endocytosis process was examined inseedling roots of a wild type and an Atflot1ko knockout mutant of Arabidopsis thaliana (L.) Heynh. Lightmicroscopy with an FM4-64 lipophilic probe and transmission electron microscopy were used. It was foundthat endocytosis was arrested in the root cells of the wild type after a simultaneous treatment of the roots withan inhibitor of clathrin-mediated endocytosis (1-naphthylacetic acid) and the agent depleting the plasmamembrane of sterols (methyl-β-cyclodextrin). In this case, such morphological change as reduction in cytoplasmvesiculation (including the early endosomes, the small vesicles originated from the agranular ER, themicrovacuoles from its fragments, and the clathrin vesicles) was observed. The vesiculation was diminishedin both the control and the stressed plants (exposed to 100 mM NaCl). In the Atflot1ko mutant, the cisternsof the Golgi complex closed up to a ring, and the process of formation of the early endosomes was completelyabolished under these conditions. It is suggested that, in the roots of A. thaliana exposed to the inhibitors, themicrodomain-associated Flot1 protein of the plasma membrane conserves the structure of the Golgi complexand its capacity to build early endosomes on the trans-side. In addition, the protein appears to participate information of the early endosomes from the trans-Golgi network.