The Formation of Early Norway Spruce Somatic Embryos: The Role of AILs, LAFLs, WOXs, PKL and VAL Transcription Factors

The use of somatic embryogenesis (SE) technology for the large-scale production of conifers demands a comprehensive understanding of its molecular basis. In this study, we identified and functionally characterized genes encoding key transcription factors (TFs) regulating SE (AILs, LAFLs, WOXs, PKL, VAL) in Picea abies (L.) H. Karst. genome. The expression profiles and patterns of the selected genes were determined by qRT-PCR in three distinct stages: (1) the formation of PEM from a zygotic embryo, (2) the initiation of ESM formation on the surface of a zygotic embryo, and (3) the proliferation of ESMs differing in morphology (white and light-yellow) and culture duration. It was determined that the prolonged subculturing of embryonal-suspensor masses (ESMs) on a medium containing plant growth regulators resulted in a decrease in the expression of identified genes. The molecular markers (among genes regulating SE) during ESM proliferation (outside the influence of the zygotic embryo) differ from those active at the embryogenic culture initiation stage. The present study proposes molecular markers of embryogenic competence of proliferating cell cultures. In silico analysis of cis-regulatory elements in promoter regions of genes revealed a total of 105 cis-elements. The most significant group, both in terms of the number of individual motifs and their occurrence, is associated with the influence of various abiotic factors. Furthermore, the investigation revealed the presence of motifs that function as binding sites for transcription factors (TFs) associated with auxin and auxin-related signaling pathways within the promoters of all the genes studied.