Transcriptome dynamics of cork oak (Quercus suber) somatic embryogenesis reveals active gene players in transcription regulation and phytohormone homeostasis of embryo development

Cork oak (Quercus suber L.) is one of the most important Mediterranean forest tree species. The last decades have been marked by a decline in this species. Implementation of breeding programs is fundamental to revert this trend. Somatic embryogenesis is the system of choice for clonal propagation, constituting a valuable tool for embryo production and improved genotype testing. In this study, the cork oak transcriptome during somatic embryogenesis was characterized in four stages of development to identify relevant genes in the process and to understand the molecular and biochemical events occurring in each specific stage. A total 66,693 candidate coding regions were predicted from the generated de novo transcriptome assembly. Differential gene expression analysis identified 11,507 genes distributed in 30 clusters with distinct gene expression patterns and enriched in various biological process GO terms. Results show 1159 differentially expressed genes coding for transcription regulators, namely transcription factors (76%) with important roles in embryogenesis, like orthologous of AINTEGUMENTA-like, PLETHORA, CYTOKININ RESPONSE FACTOR, GATA transcription factors, and AUXIN RESPONSE FACTORs genes. Results also show 250 differentially expressed phytohormone-related genes involved in important aspects of embryogenesis as tissue specification, differentiation, and embryogenesis competence. Finally, we identified a group of genes with functions in cellular protection and abiotic stress tolerance coding for LATE EMBRYOGENESIS ABUNDANT proteins. Cork oak embryogenesis transcriptome characterization represents a tool for future biotechnological applications. Our results provide a molecular insight into embryo development, establishing a basis for further research towards improvement of somatic embryogenesis in cork oak.