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

183 Genetic Analysis of Vascular Patterning of the Arabidopsis Root
Annelie Carlsbecker 1, 2 , Anne Honkanen 1 , Ove Lindgren 1 , Siripong Tithamadee 1 , Yka Helariutta 1
1
Institute of Biotechnology, University of Helsinki, Finland, 2 Dept. of Physiological Botany, Evolutionary
Biology Centre, Uppsala University, Sweden
The vasculature of plants is of immense importance as it provides paths for the transport of water, sugars, hormones
and other signalling molecules through the phloem and xylem, in addition to providing physical support to the plant
through the lignified cell walls of the xylem and fibres associated with the vasculature. Despite its importance, little
is known about the regulation of the development of the tissues making up the vasculature. The influence of various
hormones have been emphasized by several studies, but few regulatory factors have been identified, and only one, APL,
has been shown to determine phloem identity (Bonke et al., 2003, Nature 426:181-186), and the VND6 and 7 genes to
determine xylem cell identity (Kubo et al., 2005, Genes & Dev. 19:1855-1860). Furthermore, the genes of the class III
HD-ZIP and KANADI families have been shown to influence the patterning of the vasculature in the shoot (Engstrom
et al., 2004, Plant Phys. 135:685-694). In order to identify novel components influencing the vascular patterning of the
Arabidopsis root, we have performed a genetic screen for mutants miss-expressing the phloem marker AtSUC2::GFP
(Imlau A et al., 1999, Plant Cell 11:309-322). This screen resulted in the identification of a set of novel mutants with
patterning and/or cell proliferation defects specific to the stele. We named these mutants distorted root vascular pattern1-
6 (dva1-6). Collectively, these mutants have short primary roots, display a lack of AtSUC2::GFP expression at the root
tip, accompanied by a delayed and distorted phloem development, and develop ectopic xylem in the pericycle along
the xylem axis. Interestingly the dva1 and dva2 mutants has a reduced expression of APL, suggesting that they may act
upstream of APL. Currently, we are analysing various other cell- or tissue specific markers to characterize theses mutants
further and to position them in relation to known factors influencing vascular development.
184 Mutations in the TORNADO2 Gene Enlarge the Peripheral Zone Relative to the Stem Cell
Zone in the Shoot Apical Meristem of Arabidopsis thaliana
Wei-Hsin Chiu, John Chandler, Wolfgang Werr
Department of Developmental Biology, University of Cologne, Gyrhofstrasse 17, D-50923 Cologne, Germany
The SHOOTMERISTEMLESS (STM) gene is essential for the correct initiation and maintenance of the shoot apical
meristem (SAM). An EMS mutagenesis effector screen performed with the STM:GUS marker line in Arabidopsis thaliana
identified a new tornado2 allele, trn2(3010). The histological and genetic analyses implicate TRN2 in SAM function,
whereby in trn2(3010) mutants, the peripheral zone is enlarged relative to the central stem cell zone. The trn2(3010)
mutant allele partially rescues vegetative stm mutant phenotypes but behaves epistatically to wus1 and clv3-2 alleles
during the vegetative phase and in the outer floral whorls. The development of carpels in trn2(3010) wus1 flowers
indicates that pluripotent cells persist in floral meristems in the absence of TRN2 function and can be recruited for carpel
anlagen. The data implicate a role for a membrane-bound plant tetraspanin protein in cellular decisions in the peripheral
zone of the SAM.