Proteomic Analysis of Callus Development in Vanilla planifolia Andrews

The orchid Vanilla planifolia has long been cultivated for its flavoured pods. Plant regeneration via an intermediary callus phase remains difficult, partially attributed to a low frequency of callus formation from various explants. In this study, a two-dimensional gel electrophoresis (2-DE) gel-based proteomic approach was taken to investigate the molecular mechanisms involved in callus formation and development. Protein extracts from 15-day-old callus with a mean weight of 20-30 mg (CS-1) and 45-day-old callus with a mean weight of 50-60 mg (CS-2) induced from nodal explants (NC) of V. planifolia were extracted and analysed using 2-DE. Protein spots detected on 2-D gels from NC, CS-1 and CS-2 were 265, 179 and 223 protein spots, respectively, with the majority being distributed across the isoelectric focusing point (pI) range of 5.0-6.9 and with molecular masses between 25-100 kDa. Of these, 73 protein spots showed significantly differential expression, and 23 proteins were successfully identified. The majority of proteins differing between nodal explants and callus tissues were classified as defence and stress response, metabolism, protein synthesis, transport, transcription, iron storage, photosynthesis and organ-specific proteins. The largest group of proteins identified were stress response proteins, indicating their effects on callus formation.