Regulatory effects and mechanisms of hormones on the growth and rosmarinic acid synthesis in the suspension-cultured cells of Origanum vulgare

Plant cell suspension culture has many advantages such as short production cycle and independence of natural conditions, and therefore shows a good application prospect in the production of plant secondary metabolite. In this paper, the regulatory effects of hormones on the growth and RosA (rosmarinic acid) synthesis of the cultured O. vulgare cells were comprehensively investigated, meanwhile, the mechanisms of the regulation were explored using integrated multi-omics analysis. The hormone screening and optimization tests revealed that 6-BA and NAA showed a significant promotion effect on cell growth, but 2,4-D displayed an inhibitory effect on growth, while KT, TDZ, ZT and IBA had no significant effect. The preferred hormone combination for cell growth was 4.0 mg/L NAA and 0.5 mg/L 6-BA, under which cell biomass was up to 20.25 g/L. Nine hormones, including KT, ZT, TDZ, 2,4-D, IBA, GA3, ETH, MeJA, and Spm, inhibited the synthesis of RosA in the cells, while ABA exhibited a significant promotion on the synthesis. The yield of RosA reached 283.54 mg/L under ABA induction, which was 3.47 times higher than that of the control. The integrated transcriptome and metabolome analysis showed that the expression levels of TFs (transcriptional regulators) such as GT-3A, MYB61, and WRKY72A were significantly up-regulated under ABA treatment, which in turn significantly promoted the expression of key genes for RosA synthesis like 4-coumarate CoA-ligase, cytochrome P450 monooxygenase, hydroxyphenylpyruvate reductase, abscisic-aldehyde oxidase and xanthoxin dehydrogenase, ultimately leading to a significant increase in RosA synthesis in cells.