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.