Genome-wide identification of MtTCTPs and functional analysis of MtTCTP3 as a positive regulator of nodulation in Medicago truncatula.

The Translationally Controlled Tumor Protein (TCTP) is a conserved eukaryotic regulator of cell proliferation and stress responses, but its function in legume-rhizobium symbiosis remains unclear. Here, we identified five MtTCTP genes in the model legume Medicago truncatula and characterized the role of MtTCTP3 in symbiotic nodulation. MtTCTP3 is highly expressed in root nodules, particularly in the nodule apical meristem. Overexpression of MtTCTP3 significantly enhanced nodule formation, nitrogenase activity, and biomass accumulation, while silencing of MtTCTP3 caused reduced nodule number and nitrogenase activity, premature nodule senescence, and impaired plant growth. Furthermore, MtTCTP3 physically interacts with the ethylene receptors MtETR4 and MtETR5, with MtTCTP3-RNAi roots displaying marked upregulation of ethylene-responsive genes. Together, our findings identify MtTCTP3 as a positive regulator of symbiotic nodulation and nodule longevity, uncovering a functional link between MtTCTP3 and ethylene-related regulatory networks in M. truncatula.