Secreted molecules as modulators of somatic embryogenesis efficiency - an overview

Somatic embryogenesis (SE) is a biological process in which somatic cells undergo molecular reprogramming, leading to embryo formation. SE is considered the most efficient plant propagation system, supporting breeding programs that use genetic engineering/editing and omics-based research. However, its success depends on a complex interaction between internal and external factors, including biomolecules released by explants into the culture medium. The use of nurse cell cultures, established decades ago, exemplifies this process. Nevertheless, few studies have characterised the secreted molecules involved or investigated their role in SE efficiency. This review compiles current knowledge on molecules released during SE, focusing on secreted proteins and metabolites. In addition, the involvement of extracellular vesicles (EVs) as modulators of SE response is hypothesised, emphasising their capacity to mediate targeted communication during the early stages of embryogenic reprogramming. EVs transport regulatory biomolecules and may participate in coordinating the cellular responses triggered by SE-inducing stimuli, as supported by the recurrent identification of EVs-associated proteins linked to stress perception and developmental signalling. Understanding how these extracellular factors interface with intracellular pathways could advance efforts to optimise SE and broaden its biotechnological applications.