Actin versus tubulin configuration in arbuscule-containing cells from mycorrhizal tobacco roots

The involvement of the cytoskeleton in symbiotic interactions such as arbus cular mycorrhizas has received little attention. In this paper, we examine the organization of actin in tobacco mycorrhizal roots and compare actin an d tubulin patterns within arbuscule-containing cells. Our results show drastic reorganization of microfilaments and microtubules upon fungal infection and how those new cytoskeletal patterns relate to the host cytoplasm rearrangement and the intracellular fungal structures. Wher eas in uninfected cells a network of cortical and perinuclear actin filamen ts was observed, in infected cells actin filaments closely follow the funga l branches and envelop the whole arbuscule in a dense coating network. Micr otubules are less closely connected with the fungus surface. They run acros s the whole arbuscule mass, linking branches to each other and to the host cell cortex and nucleus. These major differences between the two cytoskeletal components are used to advance some suggestions concerning their contribution to structural funct ions in the plant-fungus interactions during the mycorrhizal symbiosis.