Identifying the role of the CLE34 peptide as a nitrogen sensor in the autoregulation of nodulation in Medicago truncatula

Legumes and rhizobial bacteria are capable of forming a symbiotic relationship. Dinitrogen (N2) from the atmosphere is converted by the rhizobia into a form of nitrogen usable by the plant within plant-derived root nodules, and in return, the rhizobia gains carbon compounds for growth. The Autoregulation of Nodulation (AON) mechanism regulates nodule numbers and activity in the legume Medicago truncatula, as nodule formation and upkeep can be costly in energy for the plant. CLAVATA3/ESR (CLE) peptides have previously been implicated to have a role as a signal in this mechanism. The aim of the project is to characterise the overlooked CLE34 peptide in Medicago truncatula, as our evidence links it to the AON pathway. CLE35 will be studied alongside this, as has yet to be characterised extensively, and is closely related to CLE34, thus may have an overlapping role.
Synthesised CLE34 and CLE35 peptides are being applied to confirm the function of the peptides and a split root method has been adapted for Medicago truncatula, where the impact of different nitrogen concentrations and presence of rhizobia on root development in the same plant can be analysed via phenotype and measured by gene expression with qPCR. Preliminary data has led to the hypothesis that CLE34 and CLE35 act within a mechanism relaying nitrogen levels. Therefore, targeting these genes for future crop improvement studies may lead to generating plants with altered AON, capable of producing nodules to increase plant yield even in high-nitrogen soils, with broad impact.