Abstract: The flowering signal integrator SOC1 can interact with AGL24 in Brassica juncea，which plays an important role in regulating flowering time. Based on the binding sites in the K-domains of MIKC-type proteins predicted by ISIS system，we constructed five single-site mutants of SOC1（respectively named SOC1V77K，SOC1P81K，SOC1K108V，SOC1R109L and SOC1C137K）and three single-site mutants of AGL24（respectively named AGL24Q107L，AGL24R137L and AGL24E169L）to unravel themolecular mechanism of the protein interactions of SOC1 and AGL24. Yeast two-hybrid experiments and β-galactosidase activity assays showed that mutant of AGL24Q107L could no more interact with SOC1. However，AGL24R137L and AGL24E169L mutants as well as AGL24 retained similarly strong interacting with SOC1 protein. So it was suggested that the interactions of SOC1/AGL24 were probably not regulated by the amino acid sites of 137th or 169th but 107th in the K-domain of AGL24. Further research showed that mutants of SOC1V77K，SOC1P81K，SOC1K108V，SOC1R109L and SOC1C137K remained interacting with AGL24 protein. Mutants of SOC1V77K、SOC1P81K、SOC1K108V and SOC1R109L fused with AGL24 had significantly low interaction strength compared with SOC1/AGL24. On the contrary，the interaction strength of SOC1C137K and AGL24 was greatly higher than that of SOC1/AGL24. It was indicated that the interaction strength of SOC1/AGL24 could be controlled by negative regulation sites of 77th，81st，108th and 109th amino acids，as well as positive regulation site of 137th amino acid in the K-domain of SOC1 protein. The study provided valuable information for further studies on direct regulation of SOC1/AGL24 and molecular mechanisms of flowering time in Brassica juncea.

Key words: Brassica juncea Coss., flowering-time control, SOC1, AGL24, yeast two-hybrid system