Molecular study of the MADS-box genes involved in flower induction

A rice MADS-box gene, OsMADS1 and two tobacco MADS-box genes, NtMADS1 and NtMADS3 were studied. OsMADS1 is flower specific in rice and not expressed in any other vegetative organs. RNA blot analysis revealed that the gene is continuously expressed during the entire flower development from its floral identity to the further organ development. In situ hybridization supported the RNA blot analysis with specific localizations of the transcript in rice primodia and in developing flower, especially in palea/lemma and carpel. RNA blot analysis of the transcript with total RNA isolated from the transgenic plants that undergo ectopic expression of the OsMADS1 gene showed that expression of the gene induces early flowering with reduced apical dominance (dwarfism) which causes lateral branching. Early flowering and dwarfing phenotypes are important traits that can be applied to agricultural and also horticultural crop species.;In order to study whether the OsMADS1 homolog exists in dicot, two tobacco clones NtMADS1 and NtMADS3 were isolated and their functions were studied by transgenic plant approach. NtMADS1 shares 50.8% identity with OsMADS1 in amino acids, whereas NtMADS3 shares 56.1% identity with the proteins. The two tobacco MADS-box genes were transformed into tobacco plant in both sense and antisense orientations of the transgenes. Interestingly, overexpression of the NtMADS3 gene in tobacco showed early flowering and reduced apical dominance with several lateral branches as observed in the OsMADS1 transgenic plant, suggesting that the NtMADS3 gene might be the OsMADS1 homolog of tobacco. The detail studies of the two tobacco MADS-box genes are discussed.