Nitrogen is an element required for all living organisms and a constituent of amino acids, nucleic acids and signal molecules. Despite its importance and abundance, N is largely limiting because most of it is in a highly stable form, the gas dinitrogen (N2), which composes 78% of the Earth's atmosphere. This molecule has a triple covalent bond that requires 92.4 kJ/mol of energy to break. Diazotrophic bacteria evolved an enzymatic complex, nitrogenase, which reduces N2 into ammonia (NH3). Those bacteria can interact symbiotically with plants, making them nitrogen self-sufficient. This interaction, known as symbiotic nitrogen fixation (SNF), develops a �de novo� organ called a nodule. Within the nodule, rhizobia provide reduced nitrogen to the plant and the host plant feeds and provides an optimum environment for bacteria to thrive and fix nitrogen. Both organisms genetically control the nodulation, or nodule organogenesis, by an intricate genetic regulatory network, in which transcription factors (TFs) are essential. The gene Medtr7g086040.1 codes for a novel GRF zinc finger transcription factor (MtGRF) that is highly expressed and specific to root nodules of Medicago truncatula. Zinc Finger TFs have a binding domain that allows affinity to specific DNA regions and RNA polymerases to regulate gene expression. This gene is expressed from early stages of nodule development (4 days post inoculation) and its expression is sustained in mature nodules. Three insertional mutant lines have been identified in the Tnt1 mutant collection at Noble Foundation. Homozygous plants of an analyzed mutant developed nodules that are capable of growing, but remain non-functional. This suggests an important role of this transcription factor in controlling the regulatory gene network associated with SNF. Furthermore, mutants and genetically modified organisms are being used to understand SNF and the chemistry behind the regulation of gene expression through the affinity of TFs binding to DNA.

Functional analysis of a nodule-specific GRF zinc finger transcription factor in the model legume, Medicago truncatula

248th National Meeting (2014)

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