Physiological and molecular mechanisms of radicle development of somatic embryos in Schisandra chinensis cultured in the dark

Somatic embryogenesis (SE) is a technique aimed at producing plant embryos in vitro and is considered a highly promising method for micropropagation. Here, we have established an efficient pathway for plant regeneration through somatic embryogenesis in S. chinensis. In the study, it was found that dark culture conditions significantly increased the rooting rate of plants through SE regeneration. Under dark conditions, radicle primordia were initiated during the globular embryo stage and developed from the heart-shaped to the torpedo-shaped embryo stages. The levels of IAA and ABA in somatic embryos subjected to the dark treatment were significantly lower (190.9 ng/g and 525.1 ng/g) from the globular to heart-shaped embryo stages compared to those in somatic embryos exposed to light (597.5 ng/g and 749.188 ng/g). Additionally, the concentrations of GA₃ and ZR were lower at all stages under light treatment. Transcriptome sequencing and bioinformatics analysis revealed that the pathways and processes predominantly enriched in differentially expressed genes in somatic embryos under dark conditions were plant hormone signaling, circadian rhythm and phenylpropanoid biosynthesis. QRT-PCR was employed to validate the expression of genes related to plant hormone signaling transduction. The results were consistent with the transcriptome sequencing results. This work has laid the foundation for applied research and could prove useful in future programs aimed at improving reluctant woody plants. Furthermore, the findings can potentially be extended to other species as well.