Root nodule formation in legumes; a molecular chat-box

The formation of root nodules in legumes which is the result of the interaction of the plant with rhizobia forms an excellent opportunity to study signalling processes in plant development. Major advantages of this process are the specificity of the signals involved in the initiation of the process and to the fact that mutants affecting nodule organogenesis are non-lethal. Furthermore, the bacterial signalling molecule has a structure unique in nature. These advantages and the notion that many economical important crop plants are among the legumes, has led to the formation of networks aiming at unravelling processes that lead to nodule formation and nitrogen fixation. In this review, we highlight the progress made in dissecting root nodule formation.