Epidermal cells of a symbiosis-defective mutant of Lotus japonicus show altered cytoskeleton organisation in the presence of a mycorrhizal fungus

Influence of the mycorrhizal fungus Gigaspora margarita on cytoskeleton organization in epidermal cells of Lotus japonicus roots was compared using plants of the wild type Gifu and the mutant LjSym4-2, in which the fungus is confined to the epidermal cells. Immunofluorescence labelling of plant microtubules (MTs) and microfilaments (MFs) showed only limited alterations in the peripheral cytoskeleton of epidermal cells during early stages of fungal interaction with the wild-type. Later, MTs and MFs enveloped the growing hypha, while the host cell nucleus moved close to the fungus. In contrast, epidermal cells of the mutant responded with disorganisation and disassembly of MTs and MFs before and during fungal penetration attempts. The fungus penetrated only as far as epidermal cells, whose cytoplasm became devoid of tubulin and actin, suggesting cell death. The close relationship between host cytoskeleton organization and compatibility with the fungus suggests that a functional Ljsym4 gene is necessary for correct reorganization of the epidermal cell cytoskeleton in presence of the fungus, and for avoiding hypersensitive-like reactions.