THE PLANT CELL, Vol 6, Issue 6 827-834, Copyright © 1994 by American Society of Plant Biologists
Tissue-Specific Expression of as-1 in Transgenic Tobacco
G. Neuhaus, G. Neuhaus-Url, F. Katagiri, K. Seipel and N. H. Chua
Institute for Plant Sciences, Eidgenossische Technische Hochschule-Zurich, Zurich, Switzerland
When integrated as a transgene in one or a few copies, the -90 35S promoter
of cauliflower mosaic virus confers expression in roots with little or no
expression in cotyledons and leaves. The responsible cis element,
activation sequence-1 (as-1), can bind to the nuclear factor ASF-1 as well
as to the transcription factor TGA1a. Here, we show that microinjection of
104 molecules of TGA1a per cotyledon cell activated transgenes containing
as-1-linked promoters. Transgenes with promoters linked to the octopine
synthase (ocs) element, which also binds TGA1a, responded similarly. The
acidic, N-terminal segment of TGA1a is important for transcription
activation in vivo because a deletion mutant without the first 80 amino
acids was inactive. Finally, we show that the -90 35S-[beta]-glucuronidase
(GUS) fusion gene conferred GUS expression in cotyledon cells when injected
at 50,000 copies per cell. Collectively, these results provide support for
the hypothesis that the undetectable expression of the as-1-linked
transgene in cotyledon cells is most likely a result of its inability to
compete for a limiting amount of its cognate transcription factor(s),
presumably TGA1a or related proteins.
