A novel nodule-enhanced gene encoding a putative universal stress protein from Astragalus sinicus

A nodule-enhanced gene, AsD243, was identified from infected roots of Astragalus sinicus using suppressive subtractive hybridization (SSH). It encodes a 20-kD protein related to the bacterial universal stress protein family (Usp). Sequence analysis showed that AsD243 is highly similar to the bacterial MJ0577-type of ATP-binding Usp proteins, which have been proposed to function as a molecular switch. Expression analyses revealed that AsD243 was transcribed in all plant organs, and progressively during all stages of nodulation. Its transcripts increased significantly at 7 days after inoculation, which is 2 days later than the onset of leghemoglobin expression in A. sinicus nodules. AsD243 was expressed more strongly in mature roots than in young roots regardless of inoculation status. We suggest that the AsD243 may have other functions in plant processes besides nodulation.