Ectopic Expression of OsMADS3, a Rice Ortholog of AGAMOUS, Caused a Homeotic Transformation of Lodicules to Stamens in Transgenic Rice Plants

In order to clarify the evolutionary relationship of floral organs between grasses and dicots, we expressed OsMADS3, a rice (Oryza sativa L.) AGAMOUS(AG) ortholog, in rice plants under the control of an Actin1 promoter. As a consequence of the ectopic expression of the OsMADS3, lodicules were homeotically transformed into stamens. In total, the transformation of lodicules to staminoid organs was observed in 18 out of 26 independent transgenic lines. In contrast to the almost complete transformation occurring in lodicules, none of the transgenic plants exhibited any morphological alterations in the palea or the lemma. Our results confirmed the prediction that the lodicule is an equivalent of a dicot petal and that the ABC model can be applied to rice at least for organ specification in lodicules and stamens.