Abstract:

In order to clarify the expression regulation mechanism of the flowering signal integrator SOC1 gene，a 782 bp promoter of SOC1 gene was cloned from Brassica juncea‘QJ’via genome walking kit. Yeast promoter-reporter vector pAbAi was constructed with SOC1 promoter and transformed into Y1HGold strain. Then protein vectors，pGADT7-FLC and pGADT7-SVP，were transformed into Y1HGold（pAbAi-SOC1）strain，respectively，to test the interactions of SOC1 promoter with FLC and SVPvia yeast one hybrid system. The results showed that Brassica juncea FLC and SVP proteins could interact with SOC1 promoter，respectively. Further analysis indicated that SOC1 promoter had three CArG-box moitfs，which probably regulated the DNA-protein interactions. Thus，three fragments of SOC1 promoter were subcloned respectively and named SOC1-1，SOC1-2 and SOC1-3，each of which had a single CArG-box. The plasmids，pAbAi-SOC1-1，pAbAi-SOC1-2 and pAbAi-SOC1-3，were also constructed，and then transformed into Y1HGold strain and fused with pGADT7-FLC and pGADT7-SVP plasmids，respectively. All the zygote strains could grow on the SD/-Leu/AbA plates，suggesting that SOC1-1，SOC1-2 and SOC1-3 could be targeted by Brassica juncea FLC and SVP proteins，respectively. To verify the specificity of the interactions，we additionally constructed three mutants which deleted their whole CArG-box，as well as another three mutants that only exchanged A and T in CArG-box. However，the DNA–protein interactions vanished after CArG-box was deleted or mutated，which suggests that the three CArG-box motifs in SOC1-1，SOC1-2 and SOC1-3 could specifically interact with FLC and SVP proteins. The study provided valuable information for further studies on the transcriptional expression regulation of SOC1 gene in flowering-time control.

Key words: Brassica juncea, promoter of SOC1 gene, FLC, SVP, CArG-box, DNA–protein interaction