Figure 2.

Autoregulation of nodulation in legumes. A nodulation factor is received by a complex closely associated with nodulation receptor kinase (NORK), which induces cell divisions. (a) The cell divisions signal the leaf-associated nodulation autoregulation receptor kinase (NARK) to produce a shoot-derived inhibitor (SDI) of further primordial progression. Root NARK activity, however cannot 'cross-feed' to contribute to autoregulation, leading to leaf control of nodulation. (b) SDI is absent in plants with a super- or hypernodulating mutation. Root systems of soybean with nodules induced by the soil bacterium Bradyrhizobium japonicum show either (c) an autoregulated phenotype or (d) a supernodulation phenotype; shown is a supernodulation mutant nts1007. Photo courtesy of Qunyi Jiang.