15th International Conference on Arabidopsis Research - TAIR

T02-087
Regulation of LATERAL SUPPRESSOR ¯ a gene
involved in the formation of axillary meristems
Andrea Eicker(1), Thomas Greb(1), Klaus Theres(1)
1-Max Planck Institute for Plant Breeding Research, Cologne
The architecture of plants is determined by the number, arrangement and
growth intensity of their sideshoots. Sideshoots are initiated by the formation
of axillary meristems in the axils of leaves. We are interested to understand
at the molecular level the mechanisms which control the formation of axillary
meristems.
The las-4 mutant of Arabidopsis fails to initiate axillary meristems during
vegetative development, whereas in the reproductive phase sideshoots are
formed in the axils of cauline leaves. The LAS gene belongs to the GRAS
gene family and encodes a putative transcription factor. RNA in situ hybridization
experiments have demonstrated that LAS is expressed in the axils of
all primordia originating from the SAM. The aim of our work is to identify and
characterize upstream regulators that delimit the LAS expression domain.
To understand the control of LAS expression we are analyzing the LAS promoter.
Complementation experiments with deletion constructs indicated that
at least 820 bp upstream of the ATG are necessary for a restoration of the
wildtype phenotype. In addition, T-DNA insertion lines were characterized to
identify important regulatory elements in the promoter region. Currently these
cis regulatory elements are being used to screen for trans acting factors .
Greb T. et al., (2003) Genes Dev.;
Schumacher K. et al., (1999) Proc Natl Acad Sci USA
T02 Development 2 (Shoot, Root)
T02-088
Genetic analysis of procambial development in the
Arabidopsis root
Annelie Carlsbecker(1), Ove Lindgren(1), Martin Bonke(1), Siripong Thitamadee(1,
2), Sari Tähtiharju(1), Ykä Helariutta(1)
1-Institute of Biotechnology, P.O.Box 56 (Viikinkaari 4d), FIN-00014, University of Helsinki, Finland
2-Laboratory of Plant Molecular Biology, The Rockefeller University, 1230 York Avenue, New York,
NY 10021, USA
We have determined the cell lineage relationships for phloem and xylem
during procambial development in Arabidopsis root. Subsequently, we have
been searching for and characterizing mutations that are informative for
formative and/or proliferative functions related to procambial development. A
recessive mutation, wooden leg (wol), in the CRE1/WOL/AHK4 gene coding
for a cytokinin receptor, results in reduced cell proliferation and exclusive
xylem differentiation (1). This indicates the involvement of a specific cytokinin
mediated morphogenetic pathway during early stages of vascular development.
Another recessive mutation, altered phloem development (apl) results
in defective phloem related asymmetric cell divisions as well as differentiation
(2). APL encodes a MYB-like transcription factor active specifically in
developing phloem cells, consistent with a key role as a regulator of phloem
development. Furthermore, ectopic APL expression in the stele results in
inhibition of xylem development. We present a model of procambial development
involving cytokinin signaling and the phloem promotive and xylem
repressive functions of APL. We also discuss current forward and reverse
genetics approaches to identify new key pathways in phloem and xylem cell
differentiation.
1 Mähönen et al. 2000, Genes Dev 14:2938; 2 Bonke et al. 2003, Nature 426:181.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin