Abstract
Symbiotic nitrogen fixation in nodules that contain symbiotic rhizobia enables legumes to thrive in nitrogen-poor soils. However, it is so energy consuming that plants control nodulation at both local and systemic levels. Mutants deficient in such controls exhibit a range of hypernodulation phenotypes.
We isolated a novel hypernodulation mutant "plenty" from the M2 progeny of Lotus japonicus MG-20 mutagenized by ion beam irradiation. Grafting experiments demonstrated that the root of plenty was responsible for its hypernodulation phenotype. The plenty mutant suggested an unknown nodulation regulating pathway because of additive numbers of nodules in plenty;har1 double mutants, its partial tolerance to external nitrates and its normal triple response to ethylene.
The plenty mutant developed nodules of the same size as MG-20, though the number of nodules increased. This pattern is unlike other hypernodulation mutants such as har1, klv or tml. A biomass assay suggested that many normal-sized nodules in plenty were hindrances to plant growth, since they resulted in hyperactivity of nitrogen fixation per plant.
Map-based cloning of the PLENTY gene is being conducted.
