Roles of salicylic acid-responsive cis-acting elements and W-boxes in salicylic acid induction of VCH3 promoter in transgenic tobaccos

A salicylic acid (SA)-inducible VCH3 promoter was recently identified from grapevine (Vitis amurensis) that contains two inverse SA-responsive cis-acting elements and four W-boxes. To further demonstrate the roles of these elements, four fragments with lengths from -1187, -892, -589, -276 to +7 bp were fused with the b-glucuronidase (GUS) reporter gene and transferred to Nicotiana tobacum, together with another four VCH3 promoter fragments with mutation in the two inverse SA-responsive elements. The functions of each promoter fragment were examined by analysis of GUS activity in the transgenic tobacco root treated with SA. Enhanced GUS activity was shown in the roots of transgenic tobaccos with the VCH3 (-1187)-GUS construct containing two SA-responsive cis-acting elements and four W-boxes. However, GUS activity directed by the VCH3 (-892)-GUS construct, containing one SA cis-acting element and four W-boxes, was reduced by up to 35% compared with that in tobaccos transformed with the VCH3 (-1187)-GUS construct, indicating that the SA cis-acting element plays an important role in SA induction of the VCH3 promoter. Neither the m2VCH3 (-1187)-GUS nor the mVCH3 (-892)-GUS construct, with mutation on the SA-responsive elements, abolished the expression of GUS activity, demonstrating that the W-boxes in the VCH3 promoter are also involved in SA induction. Histochemical analysis of GUS activity directed by each of the eight VCH3 promoter fragments showed that GUS was expressed specifically in vascular tissue. It was concluded that both the SA-responsive cis-acting elements and the W-boxes are important for the SA induction of the VCH3 promoter. This promoter might have a potential use in plant genetic engineering.