Ectopic expression of tobacco MADS genes modulates flowering time and plant architecture

MADS genes encode regulatory factors that are involved in various developmental steps of the plant life cycle. During flower development, they regulate the early step of specifying floral meristem identity as well as the later step of determining the fate of floral organ primordia. Here, we report the isolation of two cDNA clones, NsMADS2 and NsMADS3, from a long-day tobacco species, Nicotiana sylvestris, which encode MADS domain-containing proteins. The NsMADS2 amino acid sequence showed 66% identity to SQUA and 64% to AP1. NsMADS3 showed a high degree of amino acid identity with FBP2 (98%), DEFH 72 (89%), DEFH 200 (88%), and AGL9 (76%). RNA blot analyses of NsMADS2 and NsMADS3 revealed that both transcripts were present in floral organs, but not in vegetative organs such as the leaf, root, stem, and 10 d old seedlings. The NsMADS2 transcript was localized in all four whorls and the NsMADS3 transcript was restricted in the three inner whorls of floral organs. The ectopic expression of NsMADS2 using the CaMV 35S promoter caused early flowering and lengthened internode length in transgenic tobacco plants. The ectopic expression of NsMADS3 also caused early flowering phenotype in transgenic tobacco plants, but the plants exhibited reduced apical dominance. Possible implications of these results in relation to the functions of NsMADS2 and NsMADS3 are discussed.