Abstract
Legume plants can establish symbiosis with rhizobia by forming a nitrogen-fixing apparatus that is called nodules. In the nodule formation process, many membrane transport events are involved, but the understanding of those transport systems as well as transporter molecules involved is still very limited. As an approach to clarify the transport systems, especially necessary for the nodule formation process, we chose ATP-binding cassette (ABC) proteins to characterize in detail, which constitute one of the largest transporter families in plants and play divergent physiological roles by transporting broad range of substances across membranes.
We identified two ABC protein genes responsive to nodule formation in Lotus japonicus, LjABCB1 and LjABCB2. LjABCB1 is strongly up-regulated during nodulation, whereas LjABCB2 is down-regulated when nodulation has started. Expression analysis revealed LjABCB1 expression most clearly responded to NAA among various plant hormones.
