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SYSTEMS BIOLOGY, MOLECULAR BIOLOGY, AND GENE REGULATION

Involvement of the MADS-Box Gene ZMM4 in Floral Induction and Inflorescence Development in Maize^1,[W],[OA]

Pioneer Hi-Bred International, Inc., a DuPont Company, Johnston, Iowa 50131 (O.N.D., X.M., D.A.S., P.H., R.G., E.V.A., M.G.M.); DuPont Crop Genetics Research, Experimental Station, Wilmington, Delaware 19880–0353 (S.D.); and Althea Technologies, San Diego, California 92121 (G.V.)

The switch from vegetative to reproductive growth is marked by the termination of vegetative development and the adoption of floral identity by the shoot apical meristem (SAM). This process is called the floral transition. To elucidate the molecular determinants involved in this process, we performed genome-wide RNA expression profiling on maize (Zea mays) shoot apices at vegetative and early reproductive stages using massively parallel signature sequencing technology. Profiling revealed significant up-regulation of two maize MADS-box (ZMM) genes, ZMM4 and ZMM15, after the floral transition. ZMM4 and ZMM15 map to duplicated regions on chromosomes 1 and 5 and are linked to neighboring MADS-box genes ZMM24 and ZMM31, respectively. This gene order is syntenic with the vernalization1 locus responsible for floral induction in winter wheat (Triticum monococcum) and similar loci in other cereals. Analyses of temporal and spatial expression patterns indicated that the duplicated pairs ZMM4-ZMM24 and ZMM15-ZMM31 are coordinately activated after the floral transition in early developing inflorescences. More detailed analyses revealed ZMM4 expression initiates in leaf primordia of vegetative shoot apices and later increases within elongating meristems acquiring inflorescence identity. Expression analysis in late flowering mutants positioned all four genes downstream of the floral activators indeterminate1 (id1) and delayed flowering1 (dlf1). Overexpression of ZMM4 leads to early flowering in transgenic maize and suppresses the late flowering phenotype of both the id1 and dlf1 mutations. Our results suggest ZMM4 may play roles in both floral induction and inflorescence development.

² Present address: Department of Genetics, Development and Cell Biology, 2156 MBB, Iowa State University, Ames, IA 50011.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Olga N. Danilevskaya (olga.danilevskaya{at}pioneer.com).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.115261

^* Corresponding author; e-mail olga.danilevskaya{at}pioneer.com.

Received December 21, 2007; accepted May 31, 2008; published June 6, 2008.

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