Proteome study of embryogenic competence acquisition in the callus cultures of Nothapodytes nimmoniana (J. Graham) Mabberly

Among the alternative plant sources of camptothecin (CPT), Nothapodytes nimmoniana is regarded as the most convenient source for large-scale isolation of the monoterpenoid indole anticancer alkaloid. As a result, CPT annual trade value has grossed over billion US Dollars in recent years. Somatic embryogenesis (SE) offers potential application in the rapid clonal propagation of the tree and production of the alkaloid, so as to mitigate indiscriminate harvest of its endangered natural population to meet industrial demand. However, response to the production of embryogenic callus (EC) in the in vitro cultures of N. nimmoniana is poor to scant. In the present study, two-dimensional electrophoresis (2-DE) and mass spectrometry (MaSp/MaSp) were employed in studying proteome expression changes between EC and non-embryogenic callus (NEC) of the forest tree. The results of the study showed higher metabolic and physiological processes associated with embryogenic competence acquisition in the callus cultures; high cellular oxidative stress, energy metabolism, protein synthesis, and other metabolic processes played a key role in upregulated expression of the identified proteins in EC over NEC. Putative role of the expressed proteins during embryogenic competence acquisition by N. nimmoniana callus cultures has provided some insight into the physiology of the competence acquisition through cellular roles played by oxidative stress and metabolic processes. Further studies on metabolic physiological processes associated with EC production could have application in optimizing culture conditions for mass propagation through the SE, so as to mitigate the indiscriminate harvest of endangered N. Nimmoniana natural population for CPT.