15th International Conference on Arabidopsis Research - TAIR

T02-001
Root Hair Tip Growth Requires the Arabidopsis COW1
Gene which Encodes a Phosphatidyl Inositol Transfer
Protein
Karen Böhme(1), Yong Li(2), Florence Charlot(1), Claire Grierson(3), Katia
Marrocco(2), Kyotaka Okada(4), Michel Laloue(2), Fabien Nogué(1)
1-Station de Génétique et d'Amélioration des Plantes, INRA, Route de St Cyr, 78026 Versailles,
France
2-Laboratoire de Biologie Cellulaire, INRA, Route de St Cyr, 78026 Versailles, France
3-School of Biological Sciences, University of Bristol, Woodland Road, Bristol, BS8 1UG, UK
4-Department of Botany, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-cho,
Sakyo-ku, Kyoto 606-8502, Japan
Root hairs present an important model system for development studies in
higher plants, since root hairs are a major site for the uptake of water and
nutrients into plants, and their tip growth is a major requirement for growing.
The cow1 mutant in Arabidopsis thaliana is impaired in root hair tip growth.
The N-terminus of the COW1 protein is 32% identical to an essential
phosphatidylinositol transfer protein (PITP), the yeast Sec14 protein (sec14p),
while the C-terminus is 34.5% identical to a late nodulin of Lotus japonicus,
Nlj16. In good agreement with the role of Nlj16 in Lotus japonicus we show
that GFP fusion with the COW1 protein is targeted to the plasma membrane
of root hairs.
Furthermore, the growth defect associated with Sec14p dysfunction in yeast
is complemented by expression of the COW1 lipid-binding domain in our
studies. PITPs play important roles in promoting the activities of various
inositol lipid-signaling pathways by regulating the production of certain
phosphoinositides.
We conclude that the COW1 protein is essential for proper root hair growth,
that it has a PITP function, and that it is targeted to the plasma membrane.
The potential role of COW1 in PLC signaling required for the tip Ca2+ gradient
will be discussed.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin
T02-002
Natural genetic variation in Arabidopsis identifies
BREVIS RADIX, a novel regulator of cell proliferation
and elongation in the root
Céline F. Mouchel(1), Georgette C. Briggs(1), Christian S. Hardtke(1)
1-McGill University, Biology Department, 1205 Docteur Penfield Avenue, Montréal, Québec H3A
1B1, Canada
In an attempt to isolate novel factors that modulate quantitative aspects
of root development and are responsible for intra-specific morphological
variation, we exploited natural genetic variation in the model plant Arabidopsis
thaliana. Quantitative trait locus analysis of a cross between isogenized
accessions revealed that a single locus is responsible for approximately 80%
of the variance of the observed difference in root length. We succeeded in
isolating the corresponding gene, which we named BREVIS RADIX (BRX), by
map-based cloning. BRX controls the extent of cell proliferation and elongation
in the growth zone of the root tip and is a member of a small group
of highly conserved genes. This family of BRX-like genes is only found in multicellular
plants. Analyses of Arabidopsis single and double mutants suggest
that BRX is the only gene of this family with a role in root development. The
BRX protein is nuclear localized and activates transcription in a heterologous
yeast system. BRX family proteins contain three distinct highly conserved domains
that are predicted to form alpha-helical structures. Two of the domains
are highly similar to each other and appear to mediate the transcriptional
activation in the yeast system. The combined data indicate that BRX family
proteins might represent a novel class of transcription factors. Further details
on the genetics and biochemistry of this gene family will be reported.
T02 Development 2 (Shoot, Root)