THE PLANT CELL, Vol 5, Issue 8 877-886, Copyright © 1993 by American Society of Plant Biologists
A 22-bp Fragment of the Pea Lectin Promoter Containing Essential TGAC-like Motifs Confers Seed-Specific Gene Expression
S. de Pater, K. Pham, N. H. Chua, J. Memelink and J. Kijne
Center for Phytotechnology, Leiden University, Nonnensteeg 3, 2311 VJ Leiden, The Netherlands
To elucidate the molecular mechanisms responsible for seed-specific gene
expression in plants, the promoter of the pea lectin (psl) gene, encoding
an abundant seed protein, was used as a model. Leaf and seed nuclear
proteins bound to a region in the psl promoter containing three overlapping
TGAC-like motifs, which have been shown to be a binding site for
basic/leucine zipper proteins, including TGA1a. A trimer of a 22-bp region
of the psl promoter, containing the TGAC-like motifs, coupled to a
heterologous minimal promoter conferred low reporter gene expression in
root, stem, and leaf and high expression in seed of transgenic tobacco.
Expression increased during the midmaturation stage of seed development and
was observed in the endosperm as well as in the embryo, where it strongly
decreased within a few days after germination. This expression pattern is
qualitatively identical to the expression pattern conferred by a 2000-bp
fragment of the psl promoter. Nucleotides within the TGAC-like motifs
important for in vitro binding are also essential for in vivo transcription
activation in vegetative tissue as well as in seed. The electrophoretic
mobility of a DNA-protein complex containing seed nuclear protein was
different from that formed with leaf nuclear protein. Furthermore, the
TGA1a steady state mRNA level in immature seed was relatively low. These
results suggest that a seed-specific factor different from TGA1a, but with
similar binding specificity, is responsible for gene activation in seed. We
conclude that the 22-bp region contains all the information, including an
essential TGAGTCATCA sequence, necessary for seed-specific expression and
very likely plays an essential role in the seed-specific expression pattern
of the psl gene.