Plant Physiol, April 2001, Vol. 125, pp. 1831-1841
A Novel Dark-Inducible Protein, LeDI-2, and Its Involvement in
Root-Specific Secondary Metabolism in Lithospermum
erythrorhizon1
Kazufumi
Yazaki,*
Hideaki
Matsuoka,
Koichiro
Shimomura,
Andreas
Bechthold, and
Fumihiko
Sato
Molecular and Cellular Biology of Totipotency, Division of
Integrated Life Sciences, Graduate School of Biostudies, Kyoto
University, Kitashirakawa, Kyoto 606-8502, Japan (K.Y., H.M., F.S.);
Tsukuba Medicinal Plant Research Station, National
Institute of Health Sciences, 1 Hachimandai, Tsukuba, Ibaraki,
305-0843, Japan (K.S.); and Institut fuer Pharmazeutische
Biologie, Universitaet Tuebingen, Auf der Morgenstelle 8, Tuebingen,
Federal Republic of Germany (A.B.)
Lithospermum erythrorhizon produces red
naphthoquinone pigments that are shikonin derivatives. They are
accumulated exclusively in the roots of this plant. The
biosynthesis of shikonin is strongly inhibited by light, even though
other environmental conditions are optimized. Thus, L.
erythrorhizon dark-inducible genes (LeDIs) were isolated to
investigate the regulatory mechanism of shikonin biosynthesis. LeDI-2,
showing the strict dark-specific expression, was further characterized
by use of cell suspension cultures and hairy root cultures as model
systems. Its mRNA accumulation showed a similar pattern with that of
shikonin. In the intact plants LeDI-2 expression was observed solely in
the root, and the longitudinal distribution of its mRNA was also in
accordance to that of shikonin. LeDI-2 encoded a very hydrophobic
polypeptide of 114 amino acids that shared significant similarities
with some root-specific polypeptides such as ZRP3 (maize) and RcC3
(rice). Reduction of LeDI-2 expression by its antisense DNA in hairy
roots of L. erythrorhizon decreased the shikonin
accumulation, whereas other biosynthetic enzymes, e.g.
p-hydroxybenzoic acid:geranyltransferase, which
catalyzed a critical biosynthetic step, showed similar activity as the
wild-type clone. This is the first report of the gene that is involved
in production of secondary metabolites without affecting biosynthetic enzyme activities.
1
This work was supported in part by the Japanese
Society for Promotion of Science (grant to A.B.) and by a Grant-in-Aid
for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan (to K.Y.).
*
Corresponding author; e-mail yazaki{at}kais.kyoto-u.ac.jp; fax
81-75-753-6398.
© 2001 American Society of Plant Physiologists
