Inhibition of Flavonoid Biosynthesis in Petunia Anthers by Antisense RNA: A Novel Way to Engineer Nuclear Male Sterility

Inhibition of flower pigmentation in transgenic petunia plants was previously accomplished by expressing an antisense chalcone synthase (chs) gene under control of the cauliflower (CaMV) 35S promoter. This chimeric gene was not effective in inhibiting pigmentation in anthers due to an inappropriate cell type-specificity of the 35S promoter within this organ. By inserting the anther box, a sequence homology found in other genes expressed in anthers, the expression pattern driven by this promoter was modified. Using this modified 35S promoter to drive antisense chs gene expression inhibition of anther pigmentation was realized. Transformants with white anthers are male sterile due to a defect in pollen development, indicating that flavonoids may have an essential function in microsporogenesis. Hence, blocking the synthesis of natural compounds during anther development provides a novel way to introduce nuclear male sterility.