Objective The goal of this study is to analyze the protein structure of Medicago truncatula MtTOC1a, explore the biological function of MtTOC1a in the circadian clock system, and compare its similarities and differences in function with its ortholog AtTOC1 in Arabidopsis thaliana.

Method The orthologous genes of TOC1 in Medicago were identified through bioinformatics analysis, the expression vector of MtTOC1a gene was constructed and introduced into Arabidopsis wild-type Col and the corresponding loss-of-function mutant toc1-2 by Agrobacterium mediated method for genetic complementation analysis. Both MtTOC1a and MtTOC1b have conserved functional domains and protein structures. The genetic analysis indicated that during early photomorphogenesis, exogenously transformed MtTOC1a fully restored the hypocotyl elongation phenotype of toc1-2, but had no significant effect on the premature flowering phenotype of toc1-2. In the CAB::LUC reporter lines, MtTOC1a lengthened the period of the short period mutant toc1-2 under continuous light conditions, yet the mutant could not fully recover to the wild-type level.

Conclusion MtTOC1a and AtTOC1 have similar functions, but their roles in drownstream pathways are still different. The results provide a theoretical basis for further exploring the function of MtTOC1a gene and using MtTOC1a gene to modify the important traits in Medicago.