[Expression of Brassica juncea BjuWRKY75 and its interactions with flowering integrator BjuFT]

Brassica juncea is a yearly or biennial vegetable in Brassica of Cruciferae. The yield and quality of its product organs are affected by flowering time. WRKY proteins family can respond to biological and abiotic stresses, developmental regulation and signal transduction. WRKY75 is an important member of WRKY family which can regulate flowering, but the flowering regulation mechanism in B. juncea has not been reported. In this study, a gene BjuWRKY75 in B. juncea was cloned, and the encoded-protein belonged to the group Ⅱ of WRKY protein with highly conserved domain. BjuWRKY75 had the highest homology with BriWRKY75 of Brassica nigra. The relative expression level of BjuWRKY75 in flowers was significantly higher than that in leaves and stems, and it was expressed stably in leaves. BjuWRKY75 protein was localized in the nucleus and interacted with the promoter of the flowering integrator BjuFT, which contained the W-box response element for the interaction between protein and DNA. Thus, it could transcriptionally activate the expression of the downstream genes. The overexpression of BjuWRKY75 in Arabidopsis led to earlier flowering significantly. In conclusion, BjuWRKY75 could directly target the promoter of BjuFT and accelerate flowering. These results may facilitate further study on the regulation of flowering molecules of BjuWRKY75.