1Tokyo University of Agriculture and Technology, Tokyo, Japan, 2IRD, Symbioses Tropicales et M_diterran_ennes, CIRAD, France
Legume-rhizobium symbiosis involves molecular dialogue between the two partners. For a long, rhizobial Nod factors (NFs) and their leguminous receptors (NFRs) were assumed to be necessary for all legume-rhizobium symbiosis. In 2007, however, it was reported that some photosynthetic Bradyrhizobia able to induce nodules on some Aeschynomene species in the absence of NFs (Giraud E. 2007). To clarify the NF-independent symbiosis, we examined the ability of a large collection of rhizobia to interact with A. indica.
We found that a number of non-photosynthetic bradyrhizobia are able to nodulate on A. indica but that the bacterial infection and nitrogen fixation differed between species. By mutagenesis, we revealed that the type 3 secretion system (T3SS) has an essential role in nodule organogenesis. These data indicate that photosynthetic and non-photosynthetic Bradyrhizobia can nodulate Aeschynomene plants via two NF-independent processes that differ in the requirement of a T3SS.
keywords:symbiosis,plant-bacteria interaction,type 3 secretion system