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Complexes of MADS-box proteins are sufficient to convert leaves into floral organs


Genetic studies, using floral homeotic mutants, have led to the ABC model of flower development. This model proposes that the combinatorial action of three sets of genes, the A, B and C function genes, specify the four floral organs (sepals, petals, stamens and carpels) in the concentric floral whorls1,2. However, attempts to convert vegetative organs into floral organs by altering the expression of ABC genes have been unsuccessful3,4,5. Here we show that the class B proteins of Arabidopsis, PISTILLATA (PI) and APETALA3 (AP3), interact with APETALA1 (AP1, a class A protein) and SEPALLATA3 (SEP3, previously AGL9), and with AGAMOUS (AG, a class C protein) through SEP3. We also show that vegetative leaves of triply transgenic plants, 35S::PI;35S::AP3;35S::AP1 or 35S::PI;35S::AP3;35S::SEP3, are transformed into petaloid organs and that those of 35S::PI; 35S::AP3;35S::SEP3;35S::AG are transformed into staminoid organs. Our findings indicate that the formation of ternary and quaternary complexes of ABC proteins may be the molecular basis of the ABC model, and that the flower-specific expression of SEP3 restricts the action of the ABC genes to the flower.

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Figure 1: Interactions among MADS proteins in yeast and in vitro.
Figure 2: AP3::GUS expression in the transgenic plants.
Figure 3: Phenotypes of triply and quadruply transgenic plants.


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We are grateful to M. Yanofsky for communicating data before publication, and to D. Weigel for providing the cDNA library. We also thank J. Bowman, T. Ito and H. Tsukaya for critical reading of the manuscript. This work was supported by grants from the Monbusho and JSPS.

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Correspondence to Koji Goto.

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Institute for Chemical Research, Kyoto University, Uji, 611-0011, Japan

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Honma, T., Goto, K. Complexes of MADS-box proteins are sufficient to convert leaves into floral organs. Nature 409, 525–529 (2001).

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