Chrysanthemum flower shape modification by suppression of chrysanthemum-AGAMOUS gene

Creation of new flower shapes is a major breeding target for ornamental plants. The ABC model on the flower structure is known to be applicable to a broad range of plants. Suppression of the C gene would produce a double flower phenotype with loss of floral determinacy. The flower shape of chrysanthemum (Chrysanthemum morifolium) was modified by suppressing the chrysanthemum-AGAMOUS (CAG) gene, which might be a C gene, with an antisense transgene. We obtained 103 transgenic plants; however, only a single line (951-2) showed modified flower shape. The pistil of each ray floret in line 951-2 was transformed to several corolla-like tissues (secondary corolla) and a pistil-like tissue. Southern blot analysis showed multiple-copy integration of the transgene into the 951-2 genome. The amount of CAG mRNA was reduced in line 951-2 compared to the wild-type. On the ray florets, the cell shapes of the adaxial surfaces of the corolla seemed to be almost the same between the proper corolla and the secondary corolla. The stigma was poorly developed and plain structured both on the ray and disk florets. We observed abnormally wide filaments in 951-2. The structure of the surface cells of the abnormal filaments transformed to corolla-like cells. In this study, we demonstrate that suppression of the CAG gene converted the stamen and pistil into corolla-like tissues.