THE PLANT CELL, Vol 8, Issue 9 1477-1490, Copyright © 1996 by American Society of Plant Biologists
A Novel Extensin Gene Encoding a Hydroxyproline-Rich Glycoprotein Requires Sucrose for Its Wound-Inducible Expression in Transgenic Plants
J. H. Ahn, Y. Choi, Y. M. Kwon, S. G. Kim, Y. D. Choi and J. S. Lee
Department of Molecular Biology, Seoul National University, Seoul 151-742, Korea
A novel hydroxyproline-rich glycoprotein (SbHRGP3) that consists of two
different domains is encoded by an extensin gene from soybean. The first
domain (domain 1) located at the N terminus is composed of 11 repeats of
Ser-Pro4-Lys-His-Ser-Pro4-Tyr3-His, whereas the second domain (domain 2) at
the C terminus contains five repeats of
Ser-Pro4-Val-Tyr-Lys-Tyr-Lys-Ser-Pro4-Tyr-Lys-Tyr-Pro-Ser-Pro5-Tyr-Lys-Tyr-
Pro-Ser-Pro4-Val-Ty r-Lys-Tyr-Lys. These two repeat motifs are organized in
an extremely well-ordered pattern in each domain, which suggests that
SbHRGP3 belongs to a new group of proteins having the repeat motifs of two
distinct groups of dicot extensins. The expression of the SbHRGP3 gene
increased with seedling maturation, and its expression was relatively high
in the mature regions of the hypocotyl and in the root of soybean
seedlings. An SbHRGP3-[beta]-glucuronidase (SbHRGP3-GUS) chimeric gene was
constructed and expressed in transgenic tobacco plants. The expression of
the SbHRGP3-GUS gene was not induced by wounding alone in transgenic
tobacco plants; sucrose was also required. Expression was specific to
phloem tissues and cambium cells of leaves and stems. In transgenic tobacco
seedlings, SbHRGP3-GUS gene expression was activated by the maturation of
the primary root and then inactivated; however, reactivation was
specifically at the epidermis of the zone from which the lateral root was
to be initiated. Its reactivation occurred just before the lateral root
initiation. These results indicate that the SbHRGP3 gene in different
tissues responds to different signals.
