15th International Conference on Arabidopsis Research - TAIR

T12-007
Wox gene phylogeny and expression in Maize and
Arabidopsis: A comparison of embryonic pattern
formation
Judith Nardmann(1), Wolfgang Werr(1)
1-Institut fuer Entwicklungsbiologie, Universitaet zu Koeln, Gyrhofstr. 17, 50931 Koeln
Although plant morphology exhibits tremendous variability, the basic principles
of development, e.g. those based on meristem function, are conserved
between plant species. Comparative approaches should therefore allow the
discrimination of common mechanisms from species-specific pecularities.
Within the angiosperms, the divergence of monocots and dicots is estimated
to have occurred over 150 million years ago (1). The difference giving
rise to the name, single (mono) or two (di) cotyledons is already manifested
during early embryogenesis and is related to the formation of the anlage
of the shoot apical meristem (SAM). In contrast to an apical position in the
Arabidopsis globular embryo, the SAM anlage is established at a lateral
position of the transition stage maize embryo. Therefore, genes associated
with SAM function are attractive candidates as molecular markers to
compare patterning between monocot and dicot embryos. One of the earliest
markers associated with the Arabidopsis SAM anlage is the WUSCHEL (WUS)
gene, which promotes stem cell fate and antagonizes the CLAVATA signalling
pathway restricting the number of pluripotent stem cells in the SAM. WUS
encodes a homeodomain transcription factor and is a member of a subfamily
consisting of about 20 genes in Arabidopsis. Many of these so-called WOX
genes have been isolated recently and show informative expression patterns
during embryogenesis (2). Another member of this gene family is PRESSED
FLOWER (PRS; 3).
The availability of the Arabidopsis genome sequence allows a phylogenetic
approach to be taken to directly compare sequence homologies between
maize and Arabidopsis and search for orthologous gene functions. Using this
approach, we have isolated and characterized several WUS-like homeobox
genes in maize. A comparison of the expression patterns of these genes
reveal informative similarities and differences during embryonic patterning
between maize and Arabidopsis.
For example, Narrow sheath1 and 2 (NS1, NS2) both represent maize
orthologues of PRS (Nardmann et al., in press). A comparison of the prs and
ns mutant phenotypes and the expression patterns of the corresponding
genes indicates that the development of the maize coleoptile and not of the
scutellum is similar to that of the Arabidopsis cotelydons. The isolation and
characterization of two putative WUS-orthologues from maize and their implication
on the conservation of the WUSCHEL-CLAVATA pathway in monocots
will also be discussed
(1) Wikstrom N. and Kenrick P. (2001)
(2) Haecker et al. (2004)
(3) Matsumoto N. and Okada K. (2001)
T12 Non-Arabidopsis (Limitations of the Arabidopsis Model)
T12-008
Tobacco functional genomics: Uncovering the
importance of "-like" and "unknown" genes for plant
fitness
Wolfgang Lein(1), Mark Stitt(1), Frederik Börnke(2), Uwe Sonnewald(2), Thomas
Ehrhardt(3), Andreas Reindl(3)
1-Max-Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, D-14476 Golm
2-Institut for Plant Genetics and Crop Plant Research, Corrensstr. 3, D-06466 Gatersleben
3-BASF-AG, D-67056 Ludwigshafen
The sequencing of full genomes has revealed that we know little or nothing
about the function of the majority of genes that they contain. One of the largest
challenges for post-genomics research is to improve our understanding
of genes whose function is poorly understood or completely unknown. Here
we describe the identification of genes that play a key role in plants by using
an unbiased high-throughput random post-transcriptional gene silencing
(PTGS)-approach. The advantage of this technology is that there is typically
a residual expression of 5-40% at the protein level when gene expression is
inhibited by either “sense”- or “antisense”-constructs. This is a more rigorous
way to identify key genes than the prevalent paradigm of knock-out mutants,
which may miss some absolutely essential genes because knock-outs in
them are lethal. At present, more then 90 cDNAs have already passed the
validation process (a second independent transformation). This number can
be predicted to rise to >120 (corresponds to 0,6% of the 20.000 genes
tested). Moreover, the ongoing work uncovers a substantial subset of poorly
annotated genes, for which quantitative changes in their expression levels
have major impact on plant health and performance.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin