Esr genes show different levels of expression in the same region of maize endosperm

Abstract

Esr genes share high homology among each other, code for small hydrophilic proteins, and are expressed in a restricted region of maize endosperm surrounding the embryo. We show here that not only Esr2 but also Esr1 and Esr3 are expressed in maize, and that the relative contribution of Esr1, Esr2 and Esr3 to total Esr mRNA is 17%, 55% and 28%, respectively. DNA sequence analysis of putative promoter fragments ranging from 0.53 kb to 3.54 kb revealed the presence of retrotransposons related to the Zeon and Cinful families in the distal parts of the promoters. The proximal parts show high homology that extended over 504bp between Esr2 and Esr3, and 265bp between Esr1 and the other two genes. The most conspicuous potential cis element is a fully conserved tandem repeat of the sequence CTACACCA close to the respective open reading frames (ORFs). By the analysis of transgenic maize plants carrying promoter-Gus fusions, it was shown that all three cloned upstream fragments contain functional promoters, that the spatial activity of all three Esr promoters is identical, and that the cis element(s) responsible for the expression in the embryo surrounding region reside in the 265 bp upstream of the respective ORFs.