Abstract
Legumes strictly control their root nodule formation by a negative feedback mechanism, in which prior nodulation inhibit subsequent nodulation. This is because too many nodules deprive the plant of much energy and its growth retardation occurs. In fact, Lotus japonicus hypernodulating mutant har1 shows growth inhibition. Moreover, this negative regulation is through long-distance signaling from root to shoot and vice versa. Grafting experiments indicate that HAR1 functions in shoot, which suggests that the nodulation signal from root is converted through HAR1 to the suppression signal returning back to root. Another shoot-regulated klv and root-regulated tml have been isolated as hypernodulating mutants.
A hypernodulating mutant 3153 was isolated from MG-20 M2 seedlings from seeds irradiated with carbon ions. It was novel from allelism tests with har1, klv, or tml. Grafting experiments showed that its hypernodulating phenotype was regulated by the root genotype. It is monogenic recessive by segregation ratios observed in the F2 progeny from the cross of 3153 and its parent. Linkage analyses using SSR markers positioned its locus to the long arm of L. japonicus chromosome 2.
