Legume Infection by Rhizobium: A Conceptual Approach

Infection of legume roots by Rhizobium appears to be the result of highly localized host plant cell wall degradation. The apparent root hair “invagination” forming the infection thread results ontogenically from direct penetration of the host wall and reorientation of active wall growth to the penetration site. Characteristic root hair deformation may be a manifestation of incomplete wall penetration. A unifying hypothesis is presented in which infection specificity is explained as a function of the degree of interaction of similar cell surface components and enzymes of rhizobia and legumes.