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First published online August 6, 2004; 10.1104/pp.104.045039 Plant Physiology 135:2207-2219 (2004) © 2004 American Society of Plant Biologists Functional Characterization of OsMADS18, a Member of the AP1/SQUA Subfamily of MADS Box Genes1,[w] enicová2,3Dipartimento di Biologia (F.F., L.P., N.P., S.C., L.C.) and Dipartimento di Scienze Biomolecolari e Biotecnologie (S.M., Z.L-D., M.M.K.), Università degli Studi di Milano, 20133 Milan, Italy; and Dipartimento di Biologia Vegetale, Università La Sapienza, 00185 Rome, Italy (G.F., M.M.A.)
MADS box transcription factors controlling flower development have been isolated and studied in a wide variety of organisms. These studies have shown that homologous MADS box genes from different species often have similar functions. OsMADS18 from rice (Oryza sativa) belongs to the phylogenetically defined AP1/SQUA group. The MADS box genes of this group have functions in plant development, like controlling the transition from vegetative to reproductive growth, determination of floral organ identity, and regulation of fruit maturation. In this paper we report the functional analysis of OsMADS18. This rice MADS box gene is widely expressed in rice with its transcripts accumulated to higher levels in meristems. Overexpression of OsMADS18 in rice induced early flowering, and detailed histological analysis revealed that the formation of axillary shoot meristems was accelerated. Silencing of OsMADS18 using an RNA interference approach did not result in any visible phenotypic alteration, indicating that OsMADS18 is probably redundant with other MADS box transcription factors. Surprisingly, overexpression of OsMADS18 in Arabidopsis caused a phenotype closely resembling the ap1 mutant. We show that the ap1 phenotype is not caused by down-regulation of AP1 expression. Yeast two-hybrid experiments showed that some of the natural partners of AP1 interact with OsMADS18, suggesting that the OsMADS18 overexpression phenotype in Arabidopsis is likely to be due to the subtraction of AP1 partners from active transcription complexes. Thus, when compared to AP1, OsMADS18 during evolution seems to have conserved the mechanistic properties of protein-protein interactions, although it cannot complement the AP1 function.
1 This work was supported in part by the EU grants Cereal Gene Tags (QLG2–CT–2001–01453) and Conflow (QLK5–CT–2001–01412) and by the national grants Cofin '98 and Ateneo 2003. L.P. was supported by a European Community postdoctoral fellowship (QLK5–CT–2000–52129). 2 These authors contributed equally to the paper. 3 Present address: DSM Food Specialties, P.O. Box 1, 2600 MA Delft, The Netherlands. 4 Present address: Max-Planck-Institute für Züchtungforschung, Carl-von-Linne-Weg 10, 50829 Köln, Germany. 5 Present address: Plant Development and Reproduction, Plant Research International B.V., P.O. Box 16, 6700 AA Wageningen, the Netherlands. [w] The online version of this article contains Web-only data. Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.045039. * Corresponding author; e-mail martin.kater{at}unimi.it; fax 0039–02–50315044. Received April 22, 2004; returned for revision May 25, 2004; accepted May 25, 2004. This article has been cited by other articles:
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