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

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

Automated summary

Plants undergo various stress factors throughout their lifespan, and their plasma membrane is responsible for adapting to these stresses through protein remodeling via endocytosis. This study focused on the role of Flot1 protein in the endocytosis process. By inhibiting clathrin-mediated endocytosis and depleting the plasma membrane of sterols, morphological changes in the root cells were observed. In the mutant plants, the Golgi complex structure and early endosomes formation were affected under these conditions, suggesting that the microdomain-associated Flot1 protein plays a crucial role in maintaining Golgi complex structure and early endosome formation.