ISOLATION AND CHARACTERIZATION OF CDNA AND GENOMIC CLONES OF MSENOD40 - TRANSCRIPTS ARE DETECTED IN MERISTEMATIC CELLS OF ALFALFA

An alfalfa genomic clone and three cDNA clones for ENOD40 (MsENOD40) have been isolated and characterized. At the nucleotide level, the MsENOD40 clones exhibit ca. 79% identity to a soybean (GmENOD40) cDNA clone. The alfalfa cDNA clones lack an AUG translational start codon and potentially encode a polypeptide no longer than 46 amino acids. There is only 39% homology between the putative polypeptides of GmENOD40 and MsENOD40, suggesting that these two proteins may have different functions. However, MsENOD40 transcripts showed a pattern of localization similar to that of GmENOD40 transcripts in that mRNAs were detected by in situ hybridization in the pericycle of inoculated roots, in the nodule primordium, and in stem cells adjacent to the secondary phloem, i.e., the cells of the procambium. In addition, we detected MsENOD40 transcripts in other meristematic cells of the plant, including the nodule meristem, pre-emergent lateral root tips, and the margins of young leaf primordia. The location of MsENOD40 transcripts in dividing cells suggests that the ENOD40 gene product may play a role in mitosis or in associated processes, such as protein synthesis. However, because transcripts were associated with monosomes rather than polysomes, it is likely that MsENOD40 RNA is not translated into protein. Therefore, the RNA itself may have a function in developmental processes.