Abstract
Bacteroid differentiation is one of the most important events in symbiotic nitrogen fixation between Rhizobium-legume symbiosis. However, there is little information available to understand bacteroid differentiation of Rhizobium. Here we show that differentiation of bacteroids in indeterminate nodules involves genome amplification and cell elongation. Mature bacteroids in indeterminate nodules are functional but non-viable cells. In contrast, bacteroids in determinate nodules are comparable to free-living bacteria in their DNA content, cell size and viability. By using recombinat Rhizobium strains that are able to nodulate both determinate and indeterminate legumes, it is revealed that bacteroid differentiation is controlled by the host plant not by the rhizobial genetic background. These results suggest that leguminous plants employ at least two different strategies to control bacteroid differentiation of their micro-symbionts.
