Differences in Gene Expression and Regulation during Ontogenetic Phase Change in Apple Seedlings

A woody perennial plant has to undergo a gradual and continuous process of transition from juvenility to reproductive maturity. To better understand the underlying mechanism of ontogenesis, our aim in this study was to identify differentially expressed genes between juvenile phase and adult phase not only among different seedlings but also among different hybrid crosses. Two reciprocal subtracted cDNA libraries of juvenile versus adult phases were constructed using suppression subtractive hybridization (SSH) in an apple (Malus domestica Borkh.) hybrid seedling (Jonathan x Golden Delicious). The expression uniformity of genes between the two ontogenetic phases was reconfirmed by real-time PCR (RT-qPCR) in three seedlings from the same population and also in three seedlings from different hybrid populations. Some potential post-transcriptional regulated genes were confirmed by semi-quantitative PCR. Eighty-five expressed sequence tags (ESTs) were up-regulated in the juvenile phase, and 103 ESTs were up-regulated in the adult phase. The transcription of genes associated with lipid metabolism, chloroplast protein metabolism and secondary metabolism was up-regulated in the adult phase; however, the expression of some phytohormone responsive genes was up-regulated during the juvenile phase. Several ontogenetic differential genes, such as rbcS, differed in sequences or elements in mRNA 3' untranslated region (3' UTR). In summary, the ontogenetic variations are probably under both transcriptional and post transcriptional regulation. The expression of redox related genes differed between juvenile and adult phase, indicating that redox homeostasis may play a role in vegetative phase change and floral transition.