Characterization of MdMADS2, a member of the SQUAMOSA subfamily of genes, in apple

A MADS-box gene, MdMADS2, was isolated from the apple (Malus x domestica Bo rkh.) var Fuji and its developmental expression pattern was studied during flower development. MdMADS2 shares a high degree of amino acid sequence ide ntity with the SQUAMOSA subfamily of genes. RNA blot analysis showed that M dMADS2 is transcribed through all stages of flower development, and its tra nscription was seen in the four floral organs. RNA in situ hybridization re vealed that the MdMADS2 mRNA is expressed both in the inflorescence meriste m and in the floral meristem. The MdMADS2 transcript was detected at all st ages of flower development. Protein localization analysis showed that MdMAD S2 protein was excluded from the stamen and carpel primordia, in which a co nsiderable MdMADS2 mRNA signal was detected. This indicates that posttanscr iptional regulation may be involved in the MdMADS2-mediated control of flow er development. Transgenic tobacco expressing the MdMADS2 gene from the cau liflower mosaic virus 35S promoter showed early flowering and shorter bolts , but did not show any homeotic changes in the floral organs. These results suggest that MdMADS2 plays an important role during early stages of flower development.