1. Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA
2. USDA, ARS and Department of Plant Breeding, Cornell University, Ithaca, New York 14850, USA
3. †Present addresses: Department of Genetics, Development and Cell Biology, Iowa State University, Ames, Iowa 50011, USA (E.V.). Department of Botany and Plant Science, Center for Plant Cell Biology, University of California, Riverside, California 92521, USA (P.S.). The Boston Consulting Group, 1 Exchange Place, Boston, Massachusetts 02109, USA (L.G.)

Correspondence to: Robert Martienssen¹ Correspondence and requests for materials should be addressed to R.M. (Email: martiens@cshl.org).

Abstract

The external appearance of flowering plants is determined to a large extent by the forms of flower-bearing branch systems, known as inflorescences, and their position in the overall structure of the plant. Branches and branching patterns are produced by tissues called shoot apical meristems. Thus, inflorescence architecture reflects meristem number, arrangement and activity, and the duration of meristem activity correlates with branch length. The inflorescences of maize, unlike those of related grasses such as rice and sorghum, predominantly lack long branches, giving rise to the tassel and familiar corncob. Here we report the isolation of the maize ramosa1 gene and show that it controls inflorescence architecture. Through its expression in a boundary domain near the nascent meristem base, ramosa1 imposes short branch identity as branch meristems are initiated. A second gene, ramosa2, acts through ramosa1 by regulating ramosa1 gene expression levels. ramosa1 encodes a transcription factor that appears to be absent in rice, is heterochronically expressed in sorghum, and may have played an important role in maize domestication and grass evolution.

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