75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

181 Active cell-to-cell transport and depletion of Arabidopsis TTG1 determines epidermal
trichome patterning
Daniel Bouyer 1 , Friedrich Kragler 2 , Arp Schnittger 3 , Martin Huelskamp 1
1
Botany III, University Cologne, Germany, 2 University of Vienna, Department of Biochemistry - Max F. Perutz
Laboratories, Austria, 3 Max-Planck-Institut fur Zuchtungsforschung (MPIZ), Cologne, Germany
In plants intercellular communication by moving transcription factors is important for development (1, 2). Epidermal
trichome patterning in Arabidopsis involves mobile trichome inhibiting MYB-like proteins and trichome promoting
factors including the WD40 repeat protein TRANSPARENT TESTA GLABRA1 (TTG1) (3).
Here we demonstrate by clonal analysis using the CRE-LOX system that unexpectedly the trichome promoting factor
TTG1 can act non-cell autonomously. While TTG1 is expressed ubiquitously TTG1 protein accumulates in trichomes and
is depleted in the surrounding cells. The accumulation in trichomes is also seen when using other ubiquitous (CaMV-35S)
or even subepidermis-specific promoters.
Microinjection experiments indicate that TTG1 protein actively utilizes plasmodesmata to gain access to neighboring
cells. Finally we provide evidence that biasing TTG1 mobility affects patterning.
Taken together our data provide evidence that TTG1 is involved in a substrate-depletion mechanism which accounts
for lateral inhibtion of trichome-neighboring cells.
References:
T. Kurata, K. Okada, T. Wada, Curr Opin Plant Biol. 8, 600 (2005)
W. J. Lucas and J. Y. Lee, Nat Rev Mol Cell Biol 5, 712 (2004)
J. C. Larkin, M. L. Brown and J. Schiefelbein, Annu. Rev. Plant Biol. 54, 403 (2003)
182 Transcriptional Networks of Plant Stem Cell Control
Wolfgang Busch, Jan Lohmann
Max-Planck-Institute for Developmental Biology
In contrast to animals, plants develop mostly postembryonically and continuously form new organs during their
entire life cycle. The cellular basis for this mode of development is the continuous presence of stem-cell pools in the
apical meristems of shoot and root, which are the growing points of a plant. The size of the stem-cell pool has to be
tightly regulated to avoid ill effects for the organism. In Arabidopsis thaliana, several key factors of stem cell control
have previously been identified by genetic approaches. Since most of them are transcription factors, we have set out to
elucidate the regulatory network of stem-cell control by means of transcriptional profiling. Focusing on the shoot apical
meristem and the floral meristem, we have used loss-of-function mutants, as well as inducible overexpression lines of
several key factors including WUSCHEL (WUS), CLAVATA3 (CLV3) and LEAFY (LFY) to identify common and unique
targets. By conducting meta-analysis on our expression data and screening for transcripts that follow the genetically
defined regulatory logic, such as the negative feedback loop between WUS and CLV3, we were able to identify several
high priority targets. Promoter regions of these targets are used for regulatory element searches, with the aim to identify
previously unknown sites. Currently we verify the microarray data by quantitative rtPCR and study their spatial expression
domains and dynamics by in situ hybridization. Furthermore, we use chromatin immunoprecipitation techniques to study
the interaction of the transcription factor WUS with its target genes in vivo. With these diverse approaches we hope
not only to gain insight into the in vivo function of target genes, but also into the regulatory logic of stem-cell control.
Ultimately, we want to establish a comprehensive model of stem cell homoeostasis with predictive power.