Insights into the conversion potential of Theobroma cacao L. somatic embryos using quantitative proteomic analysis

Somatic embryogenesis (SE) has been routinely used as mass micropropagation technique, and as a model system for investigating the structural, physiological, and molecular events occurring during somatic embryo development. Successful in vitro SE is related to the quality and yield of somatic embryos obtained. In cacao (Theobroma cacao L.) SE, the efficiency of somatic embryo production has improved with secondary SE. However, the low number of somatic embryos able to conversion into viable plantlets is still low. Then, two morphological types of normal mature somatic embryos can be identified during cacao secondary SE. The first type shows white appearance and high conversion potential (75%), while the second type shows translucent appearance and exhibit low conversion potential (15%). In order to investigate the proteins that can be associated to conversion potential in cacao somatic embryos, the mass spectrometry HDMSE proteomic approach was used. At least 60 proteins showed differences in abundance levels in cacao white somatic embryos, when compared to translucent. An increased abundance of Beta-glucosidase, NAD(P)-linked oxidoreductase and Electron transfer flavoprotein proteins were observed in white somatic embryos. Moreover, in translucent somatic embryos were observed an increased abundance of Cytochrome P450 and Pathogenesis-related proteins. Using white somatic embryos as a model, we suggest that carbohydrate metabolism process and the redox regulation are involved in the control/regulation of somatic embryo quality. These new findings may improve cacao SE protocol, as well as the understanding of the role of pivotal metabolic pathways associated to this in vitro morphogenetic route.