Proteome analysis of secondary somatic embryogenesis in cassava (Manihot esculenta)

Using histological analysis of the induction of secondary somatic embryogenesis (SSE) in cassava (Manihot esculenta Crantz) as a guide, we performed 2-DE for protein separation and matrix-assisted laser desorption ionization-time of flight-tandem mass spectrometry (MALDI-TOF-TOF-MS) for protein identification in cotyledons of cassava somatic embryos undergoing SSE. Reference map obtained by 2-DE within a pH range of 3–10 and a size range of 6–97 kDa revealed approximately 410 eletrophoretically resolved spots populated primarily by acidic (pI < 7) proteins with molecular masses between 30 and 75 kDa. Tryptic digestion of 163 of the most abundant spots led to the identification of 86 proteins with a protein identification success rate of 53%. In total, 43% of the identified proteins were involved in metabolism and energy and 11.6% in protein destination and storage. Others are, disease/defense (11.6%), transcription and protein synthesis (7%), signal transduction (5.8%), cell growth/division (3.5%), transporters (3.5%), cell structure (2.3%), secondary metabolism (1.2%) and other functional classes (10.5%). Our studies demonstrate that 2-DE-based proteomic approaches combined with histological studies can serve as tools for identifying protein markers for the developmental stages of cassava SE while providing clues on the underlying causes of the low rate of conversion of cassava somatic embryos into mature plants.