Original URL: http://www.mpiz-koeln.mpg.de/~theissen/grouphome/maize.html
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MADS-Box Genes in Maize Inflorescence Development
Advances in understanding the molecular genetic basis of floral
organ patterning can provide new approaches to understanding these homologies.
Maize is a monocotyledonous plant species and belongs to the grass family
It is monoecious, the male inflorescence (tassel) develops in
a terminal position, whereas the female inflorescences (ears) grow in the
axil of vegetative leaves.
The inflorescences, as typical for grasses, are composed of spikelets.
In the case of maize
each spikelet contains two florets (the grass flower) enclosed by
a pair of bracts (inner and outer glume).
Each floret consists of two enclosing bracts (lemma and palea), two
lodicules (scale-like organs, prominent only in male flowers), three stamens
and a central pistil enclosing a single ovule.
The grass flower is sufficiently different from a typical angiosperm flower.
The latter is composed of concentric whorls of sepals and petals
enclosing whorls of stamens and pistils.
The homologies of the angiosperm flower-tissues
to those of the grass floret have been debated for more than 200 years.
Moreover, since the lineages that led to monocots and eudicots have already
separated about 200 million years ago (), a comparison of MADS-box
gene structure and function between both taxa might tell a great deal about
the conservation as well as the variability of the molecular control of
A few years ago, a critical question was whether the MADS-box genes of monocots
are structurally similar and
functional equivalent to those of the dicotyledonous model plants.
Meanwhile, we and a few other laboratories have demonstrated that monocotyledonous plants
such as maize and rice have indeed MADS-box genes that are orthologous to those of dicots
(Schmidt et al. 1993; Mena et al. 1995,1996; Theißen et al. 1995,1996; Fischer et al. 1995a,b;
Chung et al. 1994, 1995; Kang et al. 1995; Kang and An 1997; Greco et al. 1997). Studying the
transcription of a fraction of the genes that have been isolated in our lab by in situ
revealed in some cases expression patterns very similar to those of floral homeotic genes
from dicotyledonous plants.
For example, the genes ZMM2 and ZMM7 are expressed in developing
stamens and carpels, or in developing carpels only (Cacharrón et al. 1995,1998). Thus these
two genes probably fall into the category of floral organ identity genes, which is well known
from Arabidopsis and Antirrhinum.
To fully develop the agronomic potential of the MADS-box gene family of maize we have
initiated a comprehensive isolation and characterization of its members. We are currently
cloning and sequencing as many maize MADS-box genes as possible. The expression of the genes will
be determined by Northern and in situ hybridizations. Further studies will be carried out in
cooperation with industrial partners. Together we will determine the map positions of the genes
in order to find out whether they coincide with known loci of mutant genes. Information about
the functions of the genes will be obtained by the analysis of such mutants, transgenic
studies or reverse genetics. The data that we are going to accumulate will help us to find those
genes that are most suitable for a "radical crop design" by transgenic technology, as defined
In the maize-project are taking part:
Günter Theissen, Thomas Münster, Zheng Meng, Susanne Werth, Wolfram Faigl,
Wim Deleu, Luzie Ursula Wingen
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