ENOD40 expression in the pericycle precedes cortical cell division in Rhizobium-legume interaction and the highly conserved internal region of the gene does not encode a peptide

In situ expression studies show that MsENOD40 is expressed in pericycle cel ls of alfalfa roots within 3 hr after addition of Sinorhizobium meliloti 10 21. This is about 15 hr before cortical cell divisions become apparent. All ENOD40 clones isolated so far share two conserved regions, box 1 and box 2 . Translational fusions of GEP to potential open reading frames within the conserved regions of NtENOD40 have been expressed in cowpea protoplasts to study which open reading frames are translated. In this way it was shown th at only the first AUG of the transcript, present in box 1, is used as a tra nslational start in cowpea protoplasts. The open reading frame in this cons erved region in ENOD40 transcripts encodes a peptide of 10-13 amino acids. In legumes, we suggest a role for the ENOD40 peptide as a signal molecule i n the formation of the nodule primordium.