15th International Conference on Arabidopsis Research - TAIR

T07-075
Genome wide analysis of Arabidopsis gene
expression under sulfur starvation reveals the
involvement of key transcription factors controlling
sulfur assimilation metabolism
Bertrand Gakière(1), Tilbert Kosmehl(1), Monika Adamik(1), Stefan Kempa(1),
Holger Hesse(1), Rainer Hoefgen(1)
1-Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, 14476 Golm,
Germany. Tel +49 (0) 331 567 8222. Fax +49 (0) 331 567 8408. Email: gakiere@mpimp-golm.
mpg.de
Sulfur, a macronutrient that is essential to plant growth, is contained in a variety
of cellular components and plays critical biochemical roles in a number of
cellular processes, such as redox cycles, detoxification of heavy metals and
xenobiotics, and metabolism of secondary products (Hell, 1997). In a cascade
of enzymatic steps inorganic sulfur is converted to the nutritionnaly important
sulfur-containing amino acids cysteine and methionine ( Ravanel et al., 1998,
Droux et al., 2000).
Currently, no knowledge is available concerning the regulatory elements,
such as transcription factors, controlling sulfur assimilation and metabolism
in plants. Therefore, we see a necessity to screen for transcription factors
responding to nutrient alterations, especially sulfate.
Recently, the application of genomic tools as transcriptomics has provided
further insight using seedlings or hydroponically grown plants under sulfur
starvation (Nikiforova et al., 2003, Maruyama-Natkashita et al., 2003, Hirai
et al., 2003). However, because of the astonishingly high number of genes
responding to sulfur starvation, the main question is the specificity of the
response. This is probably because the stress was too strong or present for a
too long period, leading to many secondary answers.
For this reason we applied a moderate sulfate starvation on a short period
to Arabidopsis hydroponics, roots and leaves being harvested separately. We
also resupplemented the starved plants and applied in parallel to other plants
signalling metabolites. This allowed us to eliminate most of the unspecific or
secondary reactions. Differential expression was scored using full genome
Affymetrix Genechips. Indeed, it indicates a low number of genes responding
to sulfate depletion, and marker genes as metabolites measured evidence for
a sulfur starvation of the plants.
We selected a set of candidate genes encoding transcription factors that may
be involved in the control of sulfur metabolism in plants. The corresponding
Arabidopsis mutants analysis are in progress.
Droux M et al., 2000. In Sulfur Nutrition and Sulfur Assimilation in Higher Plants (Brunold C, ed).
Bern: Paul Haupt, pp. 73-92.
Hell R, 1997. Planta 202, 138-148.
Hirai MY et al., 2003. Plant J. 33, 651-663.
Maruyama-Natkashita A et al., 2003. Plant Physiol. 132, 597-605.
Nikiforova V et al., 2003. Plant J. 33, 633-650.
Ravanel S et al., 1998. Proc. Natl. Acad. Sci. USA 95, 7805-7812.
T07 Metabolism (Primary, Secondary, Cross-Talk and Short Distance Metabolite Transport)
T07-076
Multiple regulations on the antagonistic crosstalks
between jasmonate- and salicylate-signaling
pathways
Hwang Bae Sohn(1), Song Yion Yeu(1), Yeon Jong Koo(1), Myeong Ae Kim(1), Eun
Hye Kim(2), Sang Ik Song(2), Ju-Kon Kim(2), Jong Seob Lee(3), Jong-Joo Cheong(1),
Yang Do Choi(1)
1-School of Agricultural Biotechnology, Seoul National University, Seoul 151-742, Korea
2-Department of Biological Sciences, Myongji University, Yongin 449-728, Korea
3-School of Biological Sciences, Seoul National University, Seoul 151-742, Korea
It was reported that MPK4 kinase activity is required to repress salicylic acid
(SA)-induced systemic acquired resistance (SAR) and to activate jasmonic
acid (JA)-responsive gene expression. We have generated a transgenic Arabidopsis
transformed with AtMPK4, and observed that the plant constitutively
expresses jasmonate-responsive genes such as JR2, PDF1.2 and ERF1. In
parallel with the experiment, we have isolated the AtHMGA gene encoding an
AT-hook transcription factor binding to the promoter of JMT, a JA-inducible
gene. A transgenic Arabidopsis over-producing the gene contained elevated
level of SA and constitutively expressed SA-responsive genes, PR1 and
PR2. By contrast, JA-response genes JR2 and AOS were highly expressed
in AtHMGA-suppressing mutants. Thus, AtHMGA transcription factor may
act as an activator for the SA-responsive genes, and as a repressor for the
JA-responsive genes. In another set of experiments, we found that PR1 was
not induced by SA treatment in a transgenic Arabidopsis integrating a rice
SA methyltransferase gene OsSAMT. It was recently reported that the SAMT
gene AtBSMT1 was activated by JA treatment. Taken together, JA-induction
of SA methylation might be responsible for the antagonistic effect of jasmonates
on SA-mediated gene activation. Overall, our data suggest that the two
signaling pathways cross-talk at multiple regulatory points; signal transduction,
transcriptional regulation, and SA inactivation.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin