Abstract
Previous work indicated that nuclear extracts isolated from embryogenic rice suspension cells treated with the phytohormone abscisic acid (ABA) have enhanced binding activity to an ABA response element (Em1a) in the promoter of the Em gene from wheat. We identified an activity in wheat and maize nuclear extracts that enhances binding of the recombinant transcription factor EmBP-1 to Em1a by 80-fold. Fractionation of nuclear extracts led us to identify histone H1 and HMGb (but not HMGc or -d) as two factors that can enhance the ability of EmBP-1 to bind to Em1a and account for at least a part of this activity of nuclear extracts. Our results, which indicate for the first time that histone H1 possesses this type of activity, lend further support to the model that positively charged proteins can drastically affect the DNA binding activity of specific transcription factors. Furthermore, our study points to these chromosomal proteins as potential targets of an ABA-mediated modification (e.g. acetylation) that could affect the regulation of Em gene expression.
Highlights
The Em protein from a number of plants accumulates to high levels exclusively in the embryo during the maturation stage of seed development
Nuclear extracts isolated from embryogenic rice suspension cells treated with abscisic acid (ABA) have enhanced Region I binding activity compared with nuclear extracts from untreated cells [6]
We found no differences between nuclear extracts prepared from maize wild type and vp1 mutant embryos in their ability to enhance the binding of EmBP-1 to Em1a
Summary
The Em protein from a number of plants accumulates to high levels exclusively in the embryo during the maturation stage of seed development. A transient assay utilizing embryogenic rice protoplasts has been used to identify cis elements in the promoter of Em that are responsive to both ABA and VP1. These studies showed that a 76-base pair sequence (Region I) from the Em promoter is required for ABA-inducible expression and is involved in VP1 transactivation [3,4,5]. Nuclear extracts isolated from embryogenic rice suspension cells treated with ABA have enhanced Region I binding activity compared with nuclear extracts from untreated cells [6]. Enhancement of EmBP-1 binding by histone H1 represents a novel activity for this protein
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