A COTYLEDON REGULATORY REGION IS RESPONSIBLE FOR THE DIFFERENT SPATIAL EXPRESSION PATTERNS OF ARABIDOPSIS 2S ALBUMIN GENES

The 2S albumin genes of Arabidopsis thaliana are a model system to stu dy gene expression during late embryogenesis. The at2S1 gene has previ ously been shown to be expressed essentially in the embryo axis, unlik e at2S2, which is expressed throughout the embryo. Hybrid promoter con structs between at2S1 and at2S2 were introduced into Arabidopsis and u sed to identify a cotyledon regulatory region necessary for 2S albumin expression in palisade parenchyma and specific epidermal cells. Other promoter sequences flanking this tissue-specific promoter element wer e shown to control mRNA expression levels independently of the mRNA di stribution throughout the embryos. Certain hybrid promoters resulted i n the alteration of the time course of expression in cotyledons. Diffe rential expression of 2S albumin genes is discussed in terms of layere d cellular organization and mitotic activity throughout the embryo.