LEAFY COTYLEDON1 IS AN ESSENTIAL REGULATOR OF LATE EMBRYOGENESIS AND COTYLEDON IDENTITY IN ARABIDOPSIS

LEAFY COTYLEDON1 (LEC1) is an embryo defective mutation that affects c otyledon identity in Arabidopsis. Mutant cotyledons possess trichomes that are normally a leaf trait in Arabidopsis, and the cellular organi zation of these organs is intermediate between that of cotyledons and leaves from wild-type plants. We present several lines of evidence tha t indicate that the control of late embryogenesis is compromised by th e mutation. First, mutant embryos are desiccation intolerant, yet embr yos can be rescued before they dry to yield homozygous recessive plant s that produce defective embryos exclusively, Second, although many ge nes normally expressed during embryonic development are active in the mutant, at least one maturation phase-specific gene is not activated. Third, the shoot apical meristem is activated precociously in mutant e mbryos. Fourth, in mutant embryos, several genes characteristic of pos tgerminative development are expressed at levels typical of wild-type seedlings rather than embryos. We conclude that postgerminative develo pment is initiated prematurely and that embryonic and postgerminative programs operate simultaneously in mutant embryos. The pleiotropic eff ects of the mutation indicate that the LEC1 gene plays a fundamental r ole in regulating late embryogenesis. The role of LEC1 and its relatio nship to other genes involved in controlling late embryonic developmen t are discussed.