High- and low- embryogenic Taxodium hybrid ‘zhongshanshan’ cell lines reveal involvement of redox homeostasis in somatic embryogenesis

• Genotype with higher embryogenesis efficiency exhibited larger head cells and denser stalk cells. • Significant differences in the expression of genes related to redox regulation between the high- and low-embryogenic cell lines. • The antioxidant system of high embryogenic cell line was stronger. • Addition of 0.1 mg L –1 ETH could effectively promote somatic embryo induction. Taxodium hybrid ‘zhongshanshan’ is a valuable horticultural ornamental tree species in China. SE (somatic embryogenesis) technology can regenerate numerous plantlets in a short period and thus has great commercial value for this species. However, the SE efficiency of Taxodium hybrid ‘zhongshanshan’ is highly genotype-dependent, and the mechanisms remain largely unclear so far. Here, we investigated morphological disparities, transcriptional profiles and physiological indices between high- and low-embryogenic cell lines. Our findings suggested that high-embryogenic cell line exhibited promising potential for long-term and robust division maintenance. Additionally, high-embryogenic cell line demonstrated a higher efficacy in inducing somatic embryos compared to low-embryogenic cell line. Discernible variations in cellular architecture between the two cell lines were found and RNA-seq analysis identified a total of 1169 DEGs (differentially expressed genes). Accordingly, DEGs were enriched in tyrosine metabolism, brassinosteroid biosynthesis, glutathione metabolism, phenylpropanoid biosynthesis, galactose metabolism and flavonoid biosynthesis. Physiological measurements indicated that cell line with appropriate endogenous H 2 O 2 (hydrogen peroxide) and a stronger antioxidant system may be conducive to somatic embryo development. Additionally, the exogenous addition of 0.1 mg L –1 ETH (ethylene) could effectively promote somatic embryo induction of Taxodium hybrid ‘zhongshanshan’. Taken together, we highlighted the redox homeostasis effects on SE of Taxodium hybrid ‘zhongshanshan’. Our findings provided theoretical references for understanding the mechanism of SE efficiency and served as experimental foundations for the breeding and rapid propagation of Taxodium hybrid ‘zhongshanshan’.