Original URL: http://www.mpiz-koeln.mpg.de/~theissen/grouphome/maize.html

MADS-Box Genes in Maize Inflorescence Development

Young maize plants in the greenhouse

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.

Advances in understanding the molecular genetic basis of floral organ patterning can provide new approaches to understanding these homologies.

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 flower development.

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 hybridization 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 above.

In the maize-project are taking part:

Günter Theissen, Thomas Münster, Zheng Meng, Susanne Werth, Wolfram Faigl, Wim Deleu, Luzie Ursula Wingen

Please direct questions or remarkes to wingen@mpiz-koeln.mpg.de

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