LEAFY EXPRESSION AND FLOWER INITIATION IN ARABIDOPSIS

During the initial vegetative phase, the Arabidopsis shoot meristem pr oduces leaves with associated lateral shoots at its hanks, while the l ater reproductive phase is characterized by the formation of flowers, The LEAFY gene is an important element of the transition from the vege tative to the reproductive phase, as LEAFY is both necessary and suffi cient for the initiation of individual flowers, We have analyzed in de tail the expression of LEAFY during the plant life cycle, and found th at LEAFY is extensively expressed during the vegetative phase, In long days, Arabidopsis plants flower soon after germination, and this is p aralleled by rapid upregulation of LEAFY. In short days, Arabidopsis p lants flower several weeks later than in long days, but LEAFY expressi on increases gradually before flowering commences, Application of the plant hormone gibberellin, which hastens flowering in short days, enha nces the gradual change in LEAFY expression observed in short days, Ch anges in LEAFY expression before the transition to flowering suggest t hat the time point of this transition is at least partly controlled by the levels of LEAFY activity that are prevalent at a given time of th e life cycle, This assumption is horne out by the finding that increas ing the copy number of endogenous LEAFY reduces the number of leaves p roduced before the first flower is formed, Thus, LEAFY combines proper ties of flowering-time and flower-meristem-identity genes, indicating that LEAFY is a direct link between the global process of floral induc tion and the regional events associated with the initiation of individ ual flowers.