Regulatory networks of hormone-involved transcription factors and their downstream pathways during somatic embryogenesis of Arabidopsis thaliana

Somatic embryogenesis (SE) depends on a variety of developmental pathways that are influenced by several environmental factors. Therefore, it is important to understand the relationship between environmental and genetic factors by identifying the gene networks involved in SE through gene set enrichment analysis (GSEA). For determination of SE effective transcription factors, upstream sequences of core-enriched genes were analyzed. The results indicated that response to hormones is one of the biological pathways activated by the enriched TFs at all stages of somatic embryogenesis and about half of the hormonal pathways were enriched. On the fifth day after 2,4-Dichlorophenoxyacetic acid (2,4-D) treatment, the activity of hormone-affecting genes reached its maximum. At this time, more transcription factors regulated the enriched genes compared to the other stages of somatic embryogenesis. MYBs, AT-HOOKs, and HSFs are the main families of transcription factors which affect core-enriched genes during SE. CCA1, PRR7, and TOC1 and their related genes at the center of protein-protein interaction of SE-key transcription factors, involved in the regulation of the circadian clock. Gene expression analysis of CCA1, PRR7, and TOC1 revealed that the genes involved in circadian clock reached their maximum activity when embryonic cells formed. Also, auxin response elements were identified at the upstream of SE-circadian clock transcription factors, indicating that they might mediate between auxin signaling and SE-related hormonal pathways as well as SE marker genes such as AGL15, BBM, and LECs. Based on these results, it is possible that the cellular circadian rhythm activates various developmental pathways under the influence of auxin signal transduction and their interactions determine the induction of somatic embryogenesis. According to the results of this study, modifying pathways affected by SE-related transcription factors such as circadian rhythm may result in cell reprogramming and increase somatic embryogenesis efficiency.