THE PLANT CELL, Vol 2, Issue 12 1171-1180, Copyright © 1990 by American Society of Plant Biologists
Identification of an Enhancer Element for the Endosperm-Specific Expression of High Molecular Weight Glutenin
M. S. Thomas and R. B. Flavell
Department of Molecular Genetics, AFRC Institute of Plant Science Research, Cambridge Laboratory, Maris Lane, Trumpington, Cambridge CB2 2JB, United Kingdom
Genes encoding high molecular weight (HMW) glutenin, a wheat seed storage
protein, are expressed only in the developing endosperm. It was previously
demonstrated that sequences essential for endosperm-specific transcription
reside within 436 base pairs upstream of the initiation codon for HMW
glutenin translation. We have further analyzed this region by testing the
ability of a series of truncated HMW glutenin promoter fragments to enhance
transcription from an adjacent heterologous promoter. The activity of these
hybrid promoters was determined by measuring the expression of a linked
[beta]-glucuronidase (GUS) reporter gene in transgenic tobacco plants. An
HMW glutenin promoter fragment spanning nucleotides -375 to -45 relative to
the transcription start site was found to stimulate GUS expression in
tobacco seeds when inserted in either orientation upstream of the
heterologous promoter. Furthermore, this fragment could also potentiate
transcription when located 3[prime] to the GUS reporter gene. Stimulation
of GUS gene expression in transgenic tobacco seeds did not occur until 9
days to 12 days after anthesis, coincident with the onset of storage
protein synthesis in the developing tobacco and wheat seed, and was
confined to the endosperm tissue. By testing progressively shorter promoter
fragments, the enhancer element responsible for this pattern of expression
was localized to a 40-base pair region some 170 base pairs upstream of the
start site for HMW glutenin transcription.
