Study of a Tobacco MADS-Box Gene Triggering Flower Formation

Recently, we have reported a rice MADS-box gene, OsMADS1, as a molecular factor triggering flower formation; this has been well studied in a heterologous system (Chung et al., 1994). In order to study whether the OsMADS1 homolog exists in other plant species, the OsMADS1 cDNA was used as a probe to screen a tobacco cDNA library, and a potential homolog, NtMADS3, was isolated. Sequence analysis revealed that the gene shares 56.1% identity in whole amino acids with OsMADS1. Like OsMADS1, the NtMADS3 gene starts to express at a very early stage of flower development, and the expression continues up to flower maturation. In the tobacco flower, the gene is expressed in whorl 2,3 and 4, corresponding to the petal, stamen, and carpel, respectively. Upon ectopic expression in the homologous system, NtMADS3 caused a trasition from inflorescence shoot meristem into floral meristem, reducing flowering time dramatically. These phenotypes strongly suggest the NtMADS3 gene is the OsMADS1 homolog of tobacco. Hybrids between the OsMADS1 and the NtMADS3 plants were also generated. The hybrids flowered even earlier than these two transgenic plants. The detailed studies are discussed here.