FUSCA3 - A HETEROCHRONIC MUTATION AFFECTING LATE EMBRYO DEVELOPMENT IN ARABIDOPSIS

Molecular studies of late embryogenesis and seed development have emph asized differential gene expression as a means of identifying discrete stages of embryogenesis. Little has been done to identity factors tha t regulate the length of a given developmental stage or the degree of overlap between adjacent developmental programs. We designed a genetic screen to identify mutations that disrupt late embryo development in Arabidopsis without loss of hormonal responses. One such mutation, fus ca3 (fus3), alters late embryo functions, such as the establishment of dormancy and desiccation tolerance, and reduces storage protein level s. fus3 cotyledons bear trichomes, and their ultrastructure is similar to that of leaf primordia. Immature fus3 embryos enter germinative de velopment, and the shoot apical meristems develop leaf primordia befor e seed desiccation begins. The cotyledons resemble leaf primordia, yet retain some cotyledon characteristics; thus, cotyledon- and leaf-spec ific functions are expressed simultaneously. Together, these observati ons are consistent with a heterochronic interpretation of the fus3 mut ation.