Architecture of floral branch systems in maize and related grasses

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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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Figure 1: Maize inflorescences.
Figure 2: Transposon tagging, expression and sequence of the ra1 gene.
Figure 3: ra1 gene expression pattern.
Figure 4: Developmental genetics of long branch pathways.
Figure 5: Comparative development and ra1 expression in Panicoid grasses.
Figure 6: A model for heterochronic modulation of inflorescence and plant architecture.


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We thank T. Mulligan for plant care, Z. Lippman and C. Kopec for help with in situ hybridization and SEM, R. J. Schmidt for producing and sharing the ra1-RS allele, D. Jackson for discussions and V. Irish for commenting on the manuscript. E.V. was a DOE-Energy Biosciences postdoctoral fellow of the Life Sciences Research Foundation. L.G. was supported by the Cold Spring Harbor Undergraduate Research Program. Grant support was provided by the Agricultural Research Service of the USDA (to E.S.B.), the National Research Initiative of the USDA CSREES (to R.M.), and by the NSF Plant Genome Research Program (to E.S.B. and R.M.).

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Correspondence to Robert Martienssen.

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Competing interests

DNA sequences reported here have been deposited in GenBank under accession numbers AY957396–AY957399 and DQ013174–DQ013203. Reprints and permissions information is available at The authors declare no competing financial interests.

Supplementary information

Supplementary Table S1

This Microsoft Word format file contains a table with statistics of nucleotide diversity and HKA tests. (DOC 30 kb)

Supplementary Methods

This Microsoft Word format file contains text that summarizes genetic methods for cosegregation analysis of mutable, Spm-induced alleles of ramosa1. (DOC 24 kb)

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Vollbrecht, E., Springer, P., Goh, L. et al. Architecture of floral branch systems in maize and related grasses. Nature 436, 1119–1126 (2005) doi:10.1038/nature03892

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