MTENOD16 AND MTENOD20 ARE MEMBERS OF A FAMILY OF PHYTOCYANIN-RELATED EARLY NODULINS

We have identified two single-copy genes from the model legume Medicag o truncatula (MtENOD16 and 20) whose expression can be correlated with early stages of root nodulation and whose predicted coding sequences are partially homologous to both pea/vetch ENOD5 and soybean N315/ENOD 55. Database searching and sequence alignment have defined the encoded early nodulins as a distinct sub-family of phytocyanin-related protei ns, although the absence of key ligands implies that they are unlikely to bind copper. Molecular modelling based on known phytocyanin struct ure has been used to predict the 3-dimensional conformation of the pri nciple globular domain of MtENOD 16/20. Additional structural features common to both early nodulin and phytocyanin precursors include an N- terminal transit peptide, a highly variable (hydroxy)proline-rich sequ ence which probably undergoes extensive post-translational modificatio n, and a hydrophobic C-terminal tail.