ORIGINAL ARTICLE
Gene regulation patterns in triterpene biosynthetic pathway
driven by overexpression of squalene synthase and methyl
jasmonate elicitation in Bupleurum falcatum
Young Soon Kim
•
Jung Hyun Cho
•
Sangkyu Park
•
Jung-Yeon Han
•
Kyoungwhan Back
•
Yong-Eui Choi
Received: 5 August 2010 / Accepted: 4 October 2010 / Published online: 30 October 2010
Ó Springer-Verlag 2010
Abstract The root of Bupleurum falcatum L. (Apiaceae)
has long been one of the most important traditional herbal
medicines in Asian countries. A group of triterpene sapo-
nins (saikosaponins) are the major constituents of this
plant. Squalene synthase (SS) may play a regulatory role in
directing triterpene intermediates and sterol pathways.
Here, we investigated the regulatory role of the squalene
synthase (BfSS1) gene in the biosynthesis of phytosterol
and triterpene in B. falcatum. BfSS1 mRNA accumulated
ubiquitously in plant organs and markedly increased in
roots after treatment with methyl jasmonate (MeJA), ABA
and ethephon. Transgenic B. falcatum constructs over-
expressing BfSS1 in the sense and antisense orientations
were assembled using the Agrobacterium-mediated
method. Transgenic roots overexpressing BfSS1 in the
sense orientation resulted in enhanced production of both
phytosterol and saikosaponins. Overexpression of the
BfSS1 gene in the sense orientation increased the mRNA
accumulation of downstream genes such as squalene
epoxidase and cycloartenol synthase but unexpectedly
decreased the mRNA levels of b-amyrin synthase (b-AS), a
triterpene synthase mRNA. MeJA treatment of wild-type
roots strongly stimulated b-AS mRNA accumulation and
saikosaponin production but suppressed phytosterol pro-
duction. MeJA treatment of transgenic roots overexpress-
ing BfSS1 in the sense orientation failed to stimulate b-AS
mRNA accumulation but still enhanced saikosaponin and
phytosterol production. These results indicate that over-
expression of BfSS1 in B. falcatum regulates more power-
fully the downstream genes than elicitor (MeJA) treatment
in triterpene and phytosterol biosynthesis.
Keywords Bupleurum Á Methyl jasmonate Á Phytosterol Á
Squalene synthase Á Triterpene saponin
Abbreviations
b-AS b-Amyrin synthase
FPP Farnesyl pyrophosphate
MeJA Methyl jasmonate
OSC Oxidosqualene cyclase
SS Squalene synthase
BfSS1 Bupleurum falcatum squalene synthase
SE Squalene epoxidase
CAS Cycloartenol synthase
Introduction
Plant sterols and triterpenes are synthesized via the mev-
alonate-dependent isoprenoid pathway (Abe et al. 1993).
Sterols are involved in various cellular functions in
eukaryotes, such as maintaining membrane integrity and
providing the biosynthetic precursors of steroid hormones.
In plants, the vast majority of sterols are present in
The nucleotide sequence data reported in this paper are available in
the DDBJ/EMBL/GenBank nucleotide sequence database with the
accession number AY964186.
Y. S. Kim Á J. H. Cho Á S. Park Á K. Back
Bioenergy Research Institute, Interdisciplinary Program for
Bioenergy and Biomaterials of Graduate School, Chonnam
National University, 300 Yongbong-dong, Gwangju 500-757,
Korea
J.-Y. Han Á Y.-E. Choi (&)
Division of Forest Resources, College of Forest and
Environmental Sciences, Kangwon National University,
Chunchon 200-701, Kangwon-do, Republic of Korea
e-mail: yechoi@kangwon.ac.kr
123
Planta (2011) 233:343–355
DOI 10.1007/s00425-010-1292-9