Early gene expression in dedifferentiating Nicotiana glauca pith

Dedifferentiation in vitro of pith explants of Nicotiana glauca requires early de novo transcription. We have identified two genes which are up-regulated following transfer of explants to callus-inducing medium. edeA and edeB mRNAs increase about 57 and 8-fold during the first eight hours after transfer and then decline. The edeA and edeB genes are present at low copy numbers in the N. glauca genome; homologues are present in the genomes of various higher plant species, yeast and possibly mammals. Contrary to N. glauca pith explants, those from a tumorous hybrid of N. glauca and N. langsdorffii can initiate dedifferentiation in the presence of Actinomycin D and can apparently overcome the requirement for early de novo transcription.