RUI: Mechanisms of Early Embryogenesis in Arabidopsis: Characterization of the twn1 and emb88 Mutants

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Vernon 96-04344 In plants, embryogenesis is a crucial stage of development in which numerous cell types are defined, meristems are established, and the basic body plan is formed. Despite its importance, embryogenesis remains perhaps the least-understood period of plant development. One powerful strategy for investigating embryogenesis is the analysis of mutants impaired in various aspects of embryonic development. Many such embryo-defective (emb) mutants have been identified in the model plant system Arabidopsis thaliana. The proposed research will contribute to our understanding of plant embryogenesis via characterization of two intriguing Arabidopsis embryo-defective mutants, emb88 and twn 1. Emb88 is representative of a little-studied class of early embryo-defectives, the round embryo (rem) mutants. These mutants exhibit disorganized cell architecture and incomplete morphogenesis. Recent molecular analysis of EMB88 indicates that this gene encodes a novel plant protein similar to animal proteins involved in cell signal transduction. Thus, EMB88 may help define an essential cell signaling pathway not previously identified in plants. The proposed characterization of emb88 includes cloning and sequencing of the EMB88 CDNA, analysis of EMB88 gene expression, comparison of genomic structure of the mutant and wild-type alleles, and complementation of the mutant phenotype with the wild-type gene. This molecular characterization will elucidate the role of this gene in embryogenesis, and pave the way for future biochemical and genetic dissection of the pathway in which EMB88 may play a role. The second mutant, twn I, displays an unusual phenotype: two or more viable embryos often develop within a single seed. Secondary embryos arise when cells of the suspensor, a specialized structure that forms early in embryogenesis, lose their identity and undergo embryogenic transformation. Thus the twn I gene appears to suppress a default embryogenic pathway in suspensor cells, and this mutant offers an excellent system in which to investigate the relationship between cell differentiation and suppression of totipotency in the early plant embryo. The proposed experiments on twn I will address the physiological basis of the twn I phenotype and better define the role of this gene in embryo development.