Work in our group relates
to key issues in Molecular Plant Science. Our research interest is
focussed on the role of Chloroplasts (and other Plastid types) in
the gene-regulatory network of entire cells, tissues and organs,
which is involved in fundamental activities such
as photosynthesis, growth and development, and defence against
stress conditions and disease. None of these activities can happen
without chloroplast gene regulation and hence this aspect
of "green life" holds promise both for basic and applied
See "Best of Botany" (samples from G.L. lecture) here .
The following two projects pursued
in our group both are aimed at a better understanding of chloroplast
gene expression, with a focus on gene transcription (RNA synthesis).
Both projects mutually complement each other, and they both extend into
other (post-)transcriptional areas of gene regulation:
studies of transcription regulation in plants:
chloroplast sigma factors and
Chloroplasts are essential sites of biosynthesis and gene activity in
plants. Transcription, the first step in plastid gene expression, has
recently become more fully understood despite its inherent complexity:
At least two different organellar RNA polymerases are involved, i.e.
NEP, the nucleus-encoded single-subunit (T7-like) enzyme, and PEP, the
multi-subunit bacterial-type enzyme initially thought to be entirely
coded by chloroplast genes. It has become clear, however, that this is
true only for the subunits of the catalytic core, i.e. the equivalents
of bacterial alpha, beta, and beta-prime. In contrast, regulatory
components of the plastid transcription apparatus including a set of
sigma initiation factors are encoded by the nucleus, thus placing the
chloroplast under nuclear control at this key level.
Our research efforts are centered on the plastid sigma factors and
their genes, which have partially overlapping and specialized functions
during plant development and in response to environmental and stress
conditions. Moreover, sigma activity is under phosphorylation control
by a master regulator named plastid transcription kinase (PTK), which
is a CK2 kinase associated with the plastid transcription machinery.
Current work is based on mutational function analyses of both sigma
factor and kinase genes in bacterial cells and transgenic Arabidopsis
plants. Switching on or off these genes in a controlled manner is
expected to provide new insights into their roles both in a
developmental and environmental context.
of chloroplast transcription
provide the basis for most life on earth by the process widely known as
photosynthesis. It has become clear that these unique plant cell
organelles have their own gene expression system in close physical
proximity to the photosynthetic apparatus, which is an ideal
requirement for mutual regulation of these two macromolecular systems.
Photosynthesis proteins such as those of the reaction centers are
subject to accelerated turnover and degradation in response to light
intensity and other environmental conditions and hence there is a need
for controlled replenishment by gene expression. A key player
identified in our group is a redox-
responsive Ser/Thr protein kinase of the CK2 type, which is a
functional part of the chloroplast transcription apparatus. Following
the cloning and characterization of this redox mediator our current
interest centers on the interaction partners, both upstream and
downstream along the redox signaling pathway, its target genes, and the
molecuar phenotype of CK2 knockout vs. wildtype plants
and redox stress conditions. In combination with a broader analysis of
redox-active components involved in chloroplast gene expression, this
can be expected to provide a better picture of redox control in this
important plant cell organelle.