Leafy Controls Meristem Identity in Arabidopsis

Abstract

Flower development can be broken down into at least five steps: (1) Upon floral induction, the vegetative shoot meristem is converted into an inflorescence meristem. (2) The inflorescence meristem starts to generate floral meristems, or is itself transformed into a floral meristem. This step can be preceded by the generation of a limited number of secondary inflorescence meristems by the primary inflorescence meristem. (3) The floral meristems produce floral organ primordia. (4) The floral organ primordia adopt different fates according to their position within the developing flower. (5) The floral organ primordia differentiate into floral organs. Despite many efforts, very little is known about the molecules directing these processes. Since classical physiological approaches toward understanding flower development have met only with limited success, a genetic-molecular approach has recently been chosen by several groups (e.g., Komaki et al., 1988; Bowman et al., 1989, 1991, 1992; Hill and Lord, 1989; Kunst et al., 1989; Sommer et al., 1990; Yanofsky et al., 1990; Irish and Sussex, 1990; Carpenter and Coen, 1990; Coen et al., 1990; Martinez-Zapater and Somerville, 1990; Drews et al., 1991; Goto et al., 1991; Koornneef et al., 1991; Schultz and Haughn, 1991; Schultz et al. 1991; Shannon and Meeks-Wagner, 1991; Alvarez et al., 1992; Schwarz-Sommer et al., 1992; Jack et al., 1992; Huijser et al., 1992; Weigel et al., 1992; Huala and Sussex, 1992). The underlying rationale is to first identify mutations that specifically affect different steps of flower development, then to analyze these mutations at the genetic level, and finally to clone the corresponding genes to determine their function at the molecular level.