A COMMON MECHANISM CONTROLS THE LIFE-CYCLE AND ARCHITECTURE OF PLANTS

The overall aerial architecture of flowering plants depends on a group of meristematic cells in the shoot apex. We demonstrate that the Arab idopsis TERMINAL FLOWER 1 gene has a unified effect on the rate of pro gression of the shoot apex through different developmental phases. In transgenic Arabidopsis plants which ectopically express TERMINAL FLOWE R 1, both the vegetative and reproductive phases are greatly extended. As a consequence, these plants exhibit dramatic changes in their over all morphology, producing an enlarged vegetative rosette of leaves, fo llowed by a highly branched inflorescence which eventually forms norma l flowers. Activity of the floral meristem identity genes LEAFY and AP ETALA 1 is not directly inhibited by TERMINAL FLOWER 1, but their upre gulation is markedly delayed compared to wild-type controls. These phe notypic and molecular effects complement those observed in the tfl1 mu tant, where all phases are shortened. The results suggest that TERMINA L FLOWER I participates in a common mechanism underlying major shoot a pical phase transitions, rather than there being unrelated mechanisms which regulate each specific transition during the life cycle.