The role of the plant cytoskeleton in the interaction between legumes and rhizobia

The study of the symbiotic interaction between rhizobia and legumes represents a major theme in plant biology. This interaction results in the formation of nodules, root organs in which the bacteria reduce atmospheric nitrogen into ammonia, which can subsequently be utilized by the plant. The execution of the different developmental stages observed during nodule ontogenesis involves many cellular processes with significant roles for the plant cytoskeleton. A challenging question in cell biology is how the cytoskeleton organizes itself into the dynamic arrays required for cell differentiation and functioning. Nodulation is, particularly, well qualified as an experimental system for cytoskeleton research because an early essential step of the plant/microbe interaction takes place in surface-exposed root hairs, well suited for cell biological in vivo experimentation. Moreover, the changes in the organization of the cytoskeleton can be elicited by a well-defined molecule, the Nod factor, or by bacterial inoculation, thus providing the researcher with the possibility of controlling the cytoskeletal changes in target cells. In addition, the well-known cytology of the symbiotic interaction facilitates the correlation between the changes in the organization of the plant cytoskeleton with both histological and cellular changes. In this review, the current knowledge on the role of the plant cytoskeleton during nodulation is summarized, with emphasis on the interaction between Medicago truncatula and Sinorhizobium meliloti.