15th International Conference on Arabidopsis Research - TAIR

T07-093
Regulation of the Anthocyanin Pathway by bHLH,
Myb, and TTG1 proteins in Arabidopsis
Tony Gonzalez(1), Alan Lloyd(1)
1-University of Texas at Austin
The bHLH proteins GL3, EGL3, and TT8 are regulators of anthocyanin
production in Arabidopsis. egl3 and tt8 single mutant seedlings show a
reduction in anthocyanins while multiple mutant combinations such as
gl3/egl3 and gl3/egl3/tt8 seedlings show no anthocyanin accumulation at all.
The WD40 protein TTG1 is also an anthocyanin synthesis regulator with ttg1
mutants showing a complete lack of pigment. The PAP1 and PAP2 genes of
Arabidopsis that both encode R2R3 Myb transcription factors are candidate
anthocyanin regulators because overexpression of either one results in overproduction
of anthocyanins. We have previously shown that, like ttg1 mutant,
bHLH mutants show decreased expression levels of the structural anthocyanin
gene TT3 (DFR) but not TT4 (CHS). In this study we used a Q-PCR
approach to analyze the expression levels of structural anthocyanin genes
TT18 (LDOX), TT19 (a GST), and Ban (LAR) in bHLH mutants, ttg1 mutant,
and wt plants. Also, bHLH, PAP Myb, and TTG1 gene expression levels were
analyzed in various mutants and in light vs. dark grown wt seedlings to test
for the possible light-regulation of these anthocyanin regulators.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin
T07-094
Functional analysis of sterol-C24-methyltransferase
in arabidopsis
Pierrette Bouvier-Navé(1), Félix Muller(1), Aurélie Schaeffer(1), Vincent
Compagnon(1), Pierre Benveniste(1), Hubert Schaller(1)
1-IBMP/CNRS, Isoprenoid Department, Strasbourg, France
S-adenosyl-methionine sterol C-methyltransferases are involved in two
distinct and non consecutive methyl group transfers in phytosterol biosynthesis.
SMT1 catalyses preferentially the C24 methylation of cycloartenol
whereas SMT2 catalyses preferentially the C241 methylation of 24-methylene
lophenol. SMT2 acts at a branchpoint of the sterol pathway defining
then two biosynthetic segments: the 24-methyl sterol (campesterol) and
the 24-ethyl sterol (sitosterol) segments. Polypeptides of the first and the
second class of SMTs share around 40% identity. The Arabidopsis genome
contains three genes encoding SMTs. The biochemical and physiological
functions of AtSMT1, AtSMT2;1 and AtSMT2;2 were examined using a set of
mutants or transgenic plants in which the expression of one of each SMTs
was modulated. These plant lines were characterized by a high cholesterol,
high campesterol or high sitosterol profile. Expression analysis (RT-PCR, GUS
fusions, in situ) showed transcription patterns for all three genes. However, a
knock-out in SMT2;2 did not show any dramatic phenotypic variations compared
with the wild-type. Modulation of the expression of the two other SMTs
had an impact on sterol profile and morphology; certain organs or tissues
were more responsive to modified ratios of 24-methyl to 24-ethyl sterols
than others. Behaviour of smt lines in adverse environmental conditions was
studied: high sitosterol plants displayed an increased tolerance to salt stress
compared to the wild-type. Regulation of the Arabidopsis sterol metabolism
and its physiological implications will be further discussed in the view of
transcription profile analysis.
T07 Metabolism (Primary, Secondary, Cross-Talk and Short Distance Metabolite Transport)