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B and C floral organ identity functions require SEPALLATA MADS-box genes


Abnormal flowers have been recognized for thousands of years, but only in the past decade have the mysteries of flower development begun to unfold. Among these mysteries is the differentiation of four distinct organ types (sepals, petals, stamens and carpels), each of which may be a modified leaf1. A landmark accomplishment in plant developmental biology is the ABC model of flower organ identity2,3. This simple model provides a conceptual framework for explaining how the individual and combined activities of the ABC genes produce the four organ types of the typical eudicot flower. Here we show that the activities of the B and C organ-identity genes require the activities of three closely related and functionally redundant MADS-box genes, SEPALLATA1/2/3 (SEP1/2/3). Triple mutant Arabidopsis plants lacking the activity of all three SEP genes produce flowers in which all organs develop as sepals. Thus SEP1/2/3 are a class of organ-identity genes that is required for development of petals, stamens and carpels.

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Figure 1: Models for flower organ identity in Arabidopsis.
Figure 2: Phenotype of sep1 sep2 sep3 triple mutants.
Figure 3: AP3, PI and AG are activated normally in sep1 sep2 sep3 mutants.

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We thank J. Bowman for the pi ag double mutant photograph, K. Goto for sharing unpublished results, C. Wiley, C. Kawashima and T. Kawashima for technical assistance, D. Weigel, S. Liljegren, J. Bowman, D. Smyth and E. Meyerowitz for comments on the manuscript; and T. Casper and DuPont for access to pooled T-DNA insertion lines. S.P. was supported in part by the Human Frontiers Science Program Organization, and this work was supported by grants from the National Science Foundation and the National Institutes of Health (M.Y.).

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Correspondence to Martin F. Yanofsky.

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Pelaz, S., Ditta, G., Baumann, E. et al. B and C floral organ identity functions require SEPALLATA MADS-box genes. Nature 405, 200–203 (2000).

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