Search for Nodulation Gene Inducer for Mesorhizobium loti Secreted from Roots of Lotus corniculatus

It has been established that an inducer secreted from roots of host leguminous plants is needed for the expression of the nod genes. Several types of compounds, e.g., flavonoids, betains and aldonic acids, have been identified as inducers. In the particular case of nod-gene expression in Mesorhizobium loti, which makes root nodules on the Lotus plants, tetronic acid was reported to act as an effective inducer at a high (mM) concentration. However, there is no evidence that tetronic acid is secreted from Lotus plant roots. This suggests the existence of another inducer. Therefore, we searched to identify which compound was secreted from seeds and was in intact roots exudates of Lotus corniculatus.