The DNA-binding activity of an AP2 protein is involved in transcriptional regulation of a stress-responsive gene, SiWD40, in foxtail millet

A differentially expressed transcript, encoding a putative WD protein (Setaria italica WD40; SiWD40), was identified in foxtail millet. Tertiary structure modeling revealed that its C-terminus possesses eight blade β-propeller architecture. Its N-terminal has three α-helices and two 310-helices and was highly induced by different abiotic stresses. The SiWD40:GFP fusion protein was nuclear localized. Promoter analysis showed the presence of many cis-acting elements, including two dehydration responsive elements (DRE). A stress-responsive SiAP2 domain containing protein could specifically bind to these elements in the SiWD40 promoter. Thus, for the first time, we report that DREs probably regulate expression of SiWD40 during environmental stress. Molecular docking analysis revealed that the circumference of the β‐propeller structure was involved in an interaction with a SiCullin4 protein, supporting the adaptability of SiWD40 to act as a scaffold. Our study thus provides a vital clue for near future research on the stress-regulation of WD proteins.

► A stress-induced gene with 5 putative WD-repeats was isolated from Setaria italica. ► 3D model of this nuclear-localized protein showed 8 blade β-propeller architecture. ► Several stress responsive cis-acting elements were identified in SiWD40 promoter. ► DREs may probably regulate the expression of SiWD40 during stress conditions. ► SiWD40 interacted with SiCullin4 via the circumference of its β‐propeller structure.