Establishment of a Protocol for the Characterization of Secreted Biomolecules in Somatic Embryogenic Cultures of Olea europaea L.

Somatic embryogenesis (SE) involves the formation of embryo-like structures from somatic cells without fertilization and is widely used for clonal propagation and genetic transformation. However, in olive (Olea europaea sp. europaea), SE remains challenging due to the recalcitrant behavior of adult tissues when used as initial explants. Bioactive molecules released into the culture medium (conditioned medium, CM) by embryogenic cultures have been identified as modulators of the SE response. However, their potential role in enhancing SE efficiency in olive and overcoming tissue recalcitrance remains largely unexplored. To investigate the role of these biomolecules in olive SE, a protocol was established using SE cultures of cv. ‘Galega Vulgar’. Proteins and metabolites were separated by filtration, concentrated through lyophilization, and precipitated using three methods: Acetone, TCA/Acetone, and Methanol/Chloroform. The efficiency of these methods was evaluated through total protein quantification and via SDS-PAGE electrophoresis. LC-MS/MS was employed to analyze secretome composition using the TCA/Acetone precipitation method. Additionally, metabolite profiles were analyzed using 1H NMR spectroscopy. The results led to the identification of 1096 (526 protein groups) Olea europaea proteins, including well-known SE biomarkers such as kinases and peroxidases. NMR spectroscopy identified several metabolites secreted into the medium or resulting from the metabolic activity of secreted enzymes, confirming the applicability of the procedure. Although extracting secreted biomolecules from the culture medium presents significant challenges, the protocol established in this study successfully enabled the isolation and identification of both proteins and metabolites, revealing a valuable workflow for future in-depth analyses of secreted biomolecules in olive SE.