Like the two important crop legumes soybean and common bean, the model legume Lotus japonicus develops determinate root nodules. L. japonicus is normally infected through root hair infection threads in a process closely synchronised with the progressing primordial cell divisions and organ development. Recent studies of symbiotic mutants have however led to a remarkable and unexpected discovery of two alternative intercellular infection modes, crack entry and infection thread independent single

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... ell infection, in L. japonicus. These results provide genetic support for the origin of rhizobial infection of legumes through direct intercellular epidermal invasion and indicate that this ancient infection process in subsequent evolutionary steps was surpassed by the Nod-factor dependent crack entry and root hair infection thread invasions observed in most extant legumes.