DETERMINATION OF ARABIDOPSIS FLORAL MERISTEM IDENTITY BY AGAMOUS

Determinate growth of floral meristems in Arabidopsis requires the fun ction of the floral regulatory gene AGAMOUS (AG). Expression of AG mRN A in the central region of floral meristems relies on the partially ov erlapping functions of the LEAN(LFY) and APETALA1 (AP1) genes, which p romote initial floral meristem identity. Here, we provide evidence tha t AG function is required for the final definition of floral meristem identity and that constitutive AG function can promote, independent of LN and API functions, the determinate floral state in the center of r eproductive meristems. Loss-of-function analysis showed that the indet erminate central region of the ag mutant floral meristem undergoes con version to an inflorescence meristem when long-day-dependent flowering stimulus is removed. Furthermore, gain-of-function analysis demonstra ted that ectopic AG function results in precocious flowering and the f ormation of terminal flowers at apices of both the primary inflorescen ce and axillary branches of transgenic Arabidopsis plants in which AG expression is under the control of the 35S promoter from cauliflower m osaic virus. Similar phenotypes were also observed in Ify ap1 double m utants carrying a 35S-AG transgene. Together, these results indicate t hat AG is a principal developmental switch that controls the transitio n of meristem activity from indeterminate to determinate.