Abstract
Legumes establish symbiotic association with N2 fixing soil bacteria, termed rhizobia, resulting in the root nodule formation. In the nodule cells, rhizobia differentiate into endosymbiotic form, bacteroids and then start to fix N2. During the symbiosis, the bacteroids need to be supplied mineral nutrients from the host plant.
Nitrogenase, a key bacterial enzyme for N2 fixation, requires molybdenum (Mo) for its activity. Mo must be provided from the host plant to bacteroids. However, Mo transport mechanism(s) of the host plant to the bacteoids is still unclear.
Recently, we identified a Mo transporter from Arabidopsis thaliana (AtMOT1) (Tomatsu et al., 2007). To clarify the molecular base of Mo transport mechanism(s) required for the establishment of N2 fixing symbiosis, we identified Mo transporter in L. japonicus. We found four AtMOT1 homologue genes in L. japonicus genome (ST51-54). Expression of the ST54 was detected only in nodules and was increased during nodule development. In contrast, expression of remaining three genes was detected in all tested organs. It is expected that the ST54 is involved in Mo transport to bacteroids.
