Differential gene expression during floral transition in an orchid hybrid Dendrobium Madame Thong-In

We have developed an in vitro orchid (Dendrobium grex Madame Thong-In) system as a model for investigating gene expression during floral transition. Total RNA was isolated from vegetative shoot apical meristems (VSAM) and transitional shoot apical meristems (TSAM). Using the mRNA differential display method, we identified 53 cDNA clones differentially expressed in VSAMs and 16 cDNA fragments specifically expressed in TSAMs. Northern blot analysis confirmed that, on the basis of their transcripts, 12 cDNAs decreased and 8 cDNAs increased during floral transition. Sequence analysis suggested that 5 clones are likely to be transcription factors, including one MADS-box gene of the AGL2 subfamily, one class 1 knox gene and one homolog of the Drosophila seven-up gene. Other clones showed homology with those coding for Arabidopsis SOD copper chaperone, CKI and the tobacco 21D7 protein.