In legumes, symbiotic nitrogen fixation (SNF) occurs through a cooperative relationship established with rhizobial diazotrophic bacteria. This association triggers the de novo development of a highly specialized organ from root, called nodule. In this dissertation, we explore the molecular functional genetics of nodulation in the model legume Medicago truncatula in the scope of knowledge. Followed by a linearization of the current knowledge about the roles of Transcription Factors in legume nodule symbiosis. In an attempt of understanding the orchestration dynamics of nodulation and processes that generate SNF. Legumes evolved novel genes related with nodule development, symbiosis establishment and nitrogen fixation, which are exclusively expressed at different stages of nodule development, and during nitrogen reduction per se. In the model legume Medicago truncatula, two genes encoding GRF-type zinc finger proteins present high and distinct expression pattern during symbiotic nitrogen fixation in root nodules. Both genes encode for very similar protein, part on a non-characterized protein family, GRF-type zinc finger, with putative function as transcriptional factor. The gene expression data present high and distinct transcription for both genes in specific zones of the indeterminate nodule: MtGRF1/MtN20 (Medtr7g086040.1) is highly expressed in an area below the nodule meristem (zone II, where endosymbiosis occurs), while MtGRF2 (Medtr1g064350.1) is expressed in the interzone, where bacteroid differentiation occurs. MtN20 is exclusively present in the distal-zone II of nodules, in tissue where the plant cells become colonized and bacteroids start to differentiate in SNF organelles . And a Tnt1-insertional line for MtN20 was genotyped and phenotype. Nodules of mtn20 present normal nodule formation but disruption in nitrogen fixation, showing early senescence, and loss of the rhizobial maturation, required in this process. MtGRF2 present expression pattern in the interzone of nodules, in a tissue where the and bacteroids pass through a singular differentiation stage to become a in SNF organelles . A genetic network for each gene of interest highlight high correlated genes that possible play essential roles on distinct stages of symbiotic nitrogen fixation and bacteroid differentiation, await to be functional characterized. This information contributes to understanding of symbiotic nitrogen fixation and emphasize important questions to be investigated and make possible to explore root nodulation in non-legumes
