Regulation of root nodule formation in leguminous plants

Ito, Sayuri; Fujimaki, Shu; Kato, Taichi*; Otake, Norikuni*; Sueyoshi, Kuni*; Oyama, Takuji*

Leguminous plants can form root nodules as symbiotic organs with soil bacterium rhizobia. The rhizobia fix atmospheric nitrogen in nodules, and the host plants can use this fixed nitrogen in exchange for providing photosynthate as an energy source. The nodule formation is regulated systemically in the host plants to prevent excess nodulation. This process is referred to as autoregulation of nodulation (AON), which includes communication between shoot and root. Hypernodulation mutants, a part of the AON is impaired, can form large number of nodules than the wild type. Using the hypernodulation mutants is thought to be an effective approach to clarify the mechanism of the AON. Recently, we found that the AON is related to the control system of leaf cell proliferation by analysis of the growth of the mutants. In this report, the AON mechanism is reviewed especially in relations to physiological features of the hypernodulation mutants.