Involved in the infection process during the plant-rhizobium interaction. Expressed during Rhizobium-induced nodule formation. In 4-day old nodules it is found in a small cluster of cells in the primordium, and in this cluster infection threads are present. At day 5, expression is seen in the complete central tissue. At day 20 expressed in the complete prefixation zone II where it is only active in the infected cells, and maximal accumulation occurs in the proximal part of this zone. Levels decrease to a lower level from one cell layer to another at the transition of prefixation zone into interzone II-III and remains at this reduced level in the fixation zone III.