THE PLANT CELL, Vol 4, Issue 1 17-27, Copyright © 1992 by American Society of Plant Biologists
Subdomains of the Octopine Synthase Upstream Activating Element Direct Cell-Specific Expression in Transgenic Tobacco Plants
H. Kononowicz, Y. E. Wang, L. L. Habeck and S. B. Gelvin
Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907
Previous work has shown that the octopine synthase (ocs) gene encoded by
the Agrobacterium tumefaciens Ti-plasmid contains an upstream activating
sequence necessary for its expression in plant cells. This sequence is
composed of an essential 16-bp palindrome and flanking sequences that
modulate the level of expression of the ocs promoter in transgenic tobacco
calli. In this study, we have used RNA gel blot analysis of RNA extracted
from transgenic tobacco plants to show that the octopine synthase gene is
not constitutively expressed in all plant tissues and organs. This
tissue-specific pattern of expression is determined, to a large extent, by
the 16-bp palindrome. Histochemical analysis, using an ocs-lacZ fusion
gene, has indicated that the 16-bp palindrome directs the expression of the
ocs promoter in specific cell types in the leaves, stems, and roots of
transgenic tobacco plants. This expression is especially strong in the
vascular tissue of the leaves, leaf mesophyll cells, leaf and stem guard
cells, and the meristematic regions of the shoots and roots. Sequences
surrounding the palindrome in the upstream activating sequence restrict the
expression of the ocs promoter to fewer cell types, resulting in a reduced
level of expression of [beta]-galactosidase activity in the central
vascular tissue of leaves, certain types of leaf trichomes, and the leaf
primordia.
