Suppression of cell expansion by ectopic expression of the Arabidopsis SUPERMAN gene in transgenic petunia and tobacco

Molecular and genetic analyses have shown that the Arabidopsis thaliana gen e SUPERMAN (SUP) has at least two functions in Arabidopsis flower developme nt. SUP is necessary to control the correct distribution of cells with eith er a stamen or carpel fate, and is essential for proper outgrowth of the ov ule outer integument. Both these functions indicate a role for SUP in cell proliferation. To study the function of the Arabidopsis SUP gene in more de tail, we over-expressed the SUP gene in petunia and tobacco in a tissue-spe cific manner. The petunia FLORAL BINDING PROTEIN 1 (FBP1) gene promoter was used to restrict the expression of SUP to petals and stamens. The developm ent of petals and stamens was severely affected in both petunia and tobacco plants over-expressing SUP Petals remained small and did not unfold, resul ting in closed flowers. Stamen filaments were thin and very short. Detailed analysis of these floral organs from the petunia transformants showed that cell expansion was dramatically reduced without affecting cell division. T hese results reveal a novel activity for SUP as a regulator of cell expansi on.