THE PLANT CELL, Vol 9, Issue 8 1469-1479, Copyright © 1997 by American Society of Plant Biologists
S2F, a Leaf-Specific trans-Acting Factor, Binds to a Novel cis-Acting Element and Differentially Activates the RPL21 Gene
T. Lagrange, S. Gauvin, H. J. Yeo and R. Mache
Laboratoire de Genetique Moleculaire des Plantes, Universite J. Fourier and Centre National de la Recherche Scientifique, BP 53, 38041 Grenoble Cedex 9, France
Tissue-specific factors control the differential expression of nuclear
genes encoding plastid proteins. To identify some of these factors, the
light-independent spinach RPL21 gene encoding the plastid ribosomal protein
L21 was chosen as a model. The RPL21 promoter organization was defined by
transient and stable transfections of RPL21 promoter deletion mutants fused
to a reporter gene. The following results were obtained. (1) We identified
a strong core promoter, spanning the transcription start site region,
sufficient to drive high levels of gene expression. (2) We identified two
non-overlapping positive and negative domains, located upstream from the
core promoter region, that modulate core promoter activity independently of
light. (3) We found that the positive domain contains a new cis-acting
element, the S2 site, related to but different from the light-responsive
GT-1 binding site. We show that the S2 site binds a leaf-specific nuclear
factor (named S2F). The S2 site is conserved in the promoter region of many
nuclear genes encoding plastid proteins. Experiments with transgenic
tobacco plants confirmed that the S2 site is critical for positive domain
activity in leaf tissues. The S2 site is thus identified as a new
tissue-specific, light-independent regulatory element.
