Plant tissue culture as an important tool for the continuous production of active compounds including secondary metabolites and engineered molecules. Novel methods (gene editing, abiotic stress) can improve the technique. Humans have a long history of reliance on plants for a supply of food, shelter and, most importantly, medicine. Current-day pharmaceuticals are typically based on plant-derived metabolites, with new products being discovered constantly. Nevertheless, the consistent and uniform supply of plant pharmaceuticals has often been compromised. One alternative for the production of important plant active compounds is in vitro plant tissue culture, as it assures independence from geographical conditions by eliminating the need to rely on wild plants. Plant transformation also allows the further use of plants for the production of engineered compounds, such as vaccines and multiple pharmaceuticals. This review summarizes the important bioactive compounds currently produced by plant tissue culture and the fundamental methods and plants employed for their production.

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In vitro plant tissue culture: means for production of biological active compounds

Biotechnology is playing a vital alternative role in the production of pharmaceutical plant secondary metabolites to support industrial production and mitigate over-exploitation of natural sources. High-value pharmaceuticals that include alkaloids, flavonoids, terpenes, steroids, among others, are biosynthesized as a defensive strategy by plants in response to perturbations under natural environmental conditions. However, they can also be produced using plant cell, tissue, and organ culture techniques through the application of various in vitro approaches and strategies. In the past decades, efforts were on the clonal propagation, biomass and secondary metabolites production in the in vitro cultures of medicinally important plants that produce these molecules. In recent years, the effort has shifted towards optimizing culture conditions for their production through the application of cell line selection, elicitation, precursor feeding, two-phase co-culture among cell, tissue, and organ culture approaches. The efforts are made with the possibility to scale-up the production, meet pharmaceutical industry demand and conserve natural sources of the molecules. Applications of metabolic engineering and production from endophytes are also getting increasing attention but, the approaches are far from practical application in their industrial production.

Secondary metabolism of pharmaceuticals in the plant in vitro cultures: strategies, approaches, and limitations to achieving higher yield

Recently, plant secondary metabolites are considered as important sources of pharmaceuticals, food additives, flavours, cosmetics, and other industrial products. The accumulation of secondary metabolites in plant cell and organ cultures often occurs when cultures are subjected to varied kinds of stresses including elicitors or signal molecules. Application of exogenous jasmonic acid (JA) and methyl jasmonate (MJ) is responsible for the induction of reactive oxygen species (ROS) and subsequent defence mechanisms in cultured cells and organs. It is also responsible for the induction of signal transduction, the expression of many defence genes followed by the accumulation of secondary metabolites. In this review, the application of exogenous MJ elicitation strategies on the induction of defence mechanism and secondary metabolite accumulation in cell and organ cultures is introduced and discussed. The information presented here is useful for efficient large-scale production of plant secondary metabolites by the plant cell and organ cultures.

Methyl Jasmonate Induced Oxidative Stress and Accumulation of Secondary Metabolites in Plant Cell and Organ Cultures

Plant secondary metabolism evolved in the context of highly organized and differentiated cells and tissues, featuring massive chemical complexity operating under tight environmental, developmental and genetic control. Biotechnological demand for natural products has been continuously increasing because of their significant value and new applications, mainly as pharmaceuticals. Aseptic production systems of plant secondary metabolites have improved considerably, constituting an attractive tool for increased, stable and large-scale supply of valuable molecules. Surprisingly, to date, only a few examples including taxol, shikonin, berberine and artemisinin have emerged as success cases of commercial production using this strategy. The present review focuses on the main characteristics of plant specialized metabolism and their implications for current strategies used to produce secondary compounds in axenic cultivation systems. The search for consonance between plant secondary metabolism unique features and various in vitro culture systems, including cell, tissue, organ, and engineered cultures, as well as heterologous expression in microbial platforms, is discussed. Data to date strongly suggest that attaining full potential of these biotechnology production strategies requires being able to take advantage of plant specialized metabolism singularities for improved target molecule yields and for bypassing inherent difficulties in its rational manipulation.

Specialized Plant Metabolism Characteristics and Impact on Target Molecule Biotechnological Production.

We examined the effects of abiotic (methyl jasmonate [MeJA] and salicylic acid [SA]) and biotic (yeast extract and chitosan) elicitors for improvement of bioactive compounds production on adventitious root cultures in Polygonum multiflorum. The application of yeast extract resulted in significantly (p ≤ 0.05) higher dry root biomass (9.98 g/L) and relative growth rate versus the control. Cultures treated with abiotic elicitors showed higher percentage of dry weight than the other samples. Low concentrations of all elicitors (50 μM MeJA and SA, and 50 mg/L yeast extract) improved secondary metabolite production except for chitosan, whose performance was worse than that of the control. HPLC analysis of various bioactive compounds revealed significantly higher elicitation efficiency for MeJA than for the other treatments, with an approximately 2-fold increase in root dry weight (22.08 mg/g DW) under 50 μM MeJA treatment versus the control (10.35 mg/g DW). We also investigated the feasibility of scaling up the production process by comparing shake flask cultures with 3- and 5-L balloon type bubble bioreactors (BTBB) using 50 μM MeJA as an elicitor. Growth and metabolite accumulation increased in BTBB compared with shake flask cultures. We detected a non-significant difference in biomass productivity between 3 and 5-L BTBB, but the efficiency of bioactive compound accumulation decreased with increasing volume. These findings will be useful for developing a pilot-scale P. multiflorum adventitious root cultivation process for high biomass and bioactive compound production to meet the demands for natural ingredients by the pharmaceutical and cosmetic industries without affecting the natural habitat of this plant.

Improvement of biosynthesis and accumulation of bioactive compounds by elicitation in adventitious root cultures of Polygonum multiflorum.

Polygonum multiflorum Thunb. is an important medicinal plant that synthesizes an array of phenolic compounds. Its roots are used in a variety of pharmacological and cosmetic formulations, notably as hair dye. In the present study, the inoculum density (3–15 g/L) and culture period (1–7 weeks) were optimized in a 3 L bioreactor. High root biomass (14.18 g/L dry weight (DW)) was recorded with an inoculum of 7 g/L (p ≤ 0.05), which is consistent with the results for 5 and 10 g/L. However, significantly higher yield of bioactive compounds (53.87 mg/g DW total phenolics and 27.96 mg/g DW total flavonoids) with high free radical scavenging activity was obtained in root samples from 5 g/L inoculum density. A 4 week culture period was sufficient for optimum root growth and metabolite production. The optimized conditions were used for large-scale (5 and 20 L) and pilot-scale (500 L) studies. Considering that the continuous aeration of root cultures may lead to oxidative stress, antioxidant enzyme activity and lipid peroxidation also were studied. The results revealed high catalase (CAT) and guaiacol peroxidase (G-POD) activities, and low malondialdehyde (MDA) production, with increasing culture scale (20 and 500 L), which may indicate low-level oxidative damage to the cultures. An optimal yield of 4.01 kg dry root biomass with 287.12 mg/L of total phenolic productivity was achieved in a 500 L pilot-scale bioreactor. This work can pave the way for commercial production of biomass and secondary metabolites at the industrial level, and meet the rising demand for natural ingredients, especially in the pharmaceutical and cosmetic industries.

Adventitious root culture of Polygonum multiflorum for phenolic compounds and its pilot-scale production in 500 L-tank

본 연구는 약용식물인 적하수오의 부정근과 생리활성물질 대량생산을 위해 생물반응기 배양 조건을 확립하고자 실시되었다. 이를 위하여 생물반응기 배양 시 배지 내 무기물 함량과, auxin의 종류와 농도, sucrose 농도가 적하수오 부정근의 생장과 총 phenolics와 flavonoids 함량에 미치는 영향을 조사하였으며, 배양 중 methyl jasmonate (MeJA)와 salicylic acid (SA)의 첨가가 생리활성물질 축적에 미치는 영향을 조사하였다. 그 결과 $9.84{\mu}M$ IBA와 50 g/L sucrose가 첨가된 1배 MS배지에서 최적의 부정근 생장이 이루어졌으며 생리활성물질 축적도 가장 높았다. MeJA와 SA 처리시 적하수오 부정근의 생장과 생리활성물질 축적은 오히려 감소하였다. 본 연구 결과는 산업적 목적을 위한 적하수오의 부정근과 생리활성물질 대량생산시 기초자료로 활용될 수 있을 것으로 기대된다. 【This study was conducted to investigate the productivity of biomass and antioxidant compounds in Polygonum multiflorum by culturing explants in air-lift bioreactor containing Murashige and Skoog (MS) medium, by adding different concentrations of auxins [indole-3-butyric acid (IBA) and naphthalene acetic acid (NAA)], sucrose, methyl jasmonate (MeJA), and salicylic acid (SA). Results of this study revealed that the explants culturing on the medium supplemented with $9.84{\mu}M$ IBA and 50 g/L sucrose were observed to have higher productivity of biomass and bioactive compound than other treatments used. Thus, we expect that these results will be helpful for large-scale production of biomass and antioxidant compounds from Polygonum multiflorum.】

Production of biomass and bioactive compounds from adventitious root cultures of Polygonum multiflorum using air-lift bioreactors

Sumoylation is a post-translational modification that mediates several regulatory processes in plants. It is associated with developmental processes such as cellular division, expansion and differentiation, and vegetative and reproductive growth. The primary function of SUMO E3 ligases is to control the mitotic cycle and maintain meristematic cells. Arabidopsis thaliana HIGH PLOIDY2 (HPY2), a SUMO E3 ligase, might therefore be expected to promote cell division and increase organ size when overexpressed in the model ornamental plant Petunia multiflora. One month after Agrobacterium-mediated transformation, nine putative transgenic P. multiflora plants were regenerated on selection medium, and were found to have high expression levels of AtHPY2. The proportion of cells in G2M phase, length of in vitro-cultivated plantlets, and trichome length all increased in transgenic lines compared with the wild type (WT). Transgenic petunia lines also exhibited increased growth, leaf and flower area, and flower number. Flowering time was also faster in transgenic P. multiflora than in the WT, and flower numbers increased. These results suggest that AtHPY2 overexpression stimulates cell division. This finding may be useful in controlling plant and flower size, and flowering timing and abundance in P. multiflora and other ornamentals.

Overexpression of SUMO E3 ligase HPY2 regulates the cell cycle in petunia development

An efficient regeneration protocol for stem disc culture of Populus euramericana, which is important species for bioenergy resource in agroforestry, was established. The number of explants that were obtained and the number of explants that regenerated varied with the genotypes. However, in all the genotypes, stem disc culture produced more regenerated shoots than did in axillary bud culture. A comparison of the effects of cytokinin type and concentration on shoot regeneration in different explants (i.e., petiole, leaf, and root segments of P. euramericana) revealed that a concentration of 0.002 mg l-1 thidiazuron (TDZ) used on petiole segments resulted in the greatest shoot regeneration (95.83%). The hormonal requirements for the greatest shoot regeneration in the three explant types varied. Different concentrations of AgNO3 and CoCl2 were added separately to the medium to stop the yellowing and subsequent necrosis of the regenerated shoots. Lower concentrations (3 and 5 mg l-1) of these compounds improved shoot regeneration and elongation, compared with the control. The in vitro-regenerated shoots were transferred to rooting medium and subsequently acclimatized. The highly efficient regeneration system of P. euramericana reported here can be used for mass propagation of this recalcitrant for regeneration, economically important tree species.

Kyung-Ju Lee

Papers

Adventitious root culture of Polygonum multiflorum for phenolic compounds and its pilot-scale production in 500 L-tank

Production of biomass and bioactive compounds from adventitious root cultures of Polygonum multiflorum using air-lift bioreactors

Overexpression of SUMO E3 ligase HPY2 regulates the cell cycle in petunia development

High-frequency regeneration by stem disc culture in selected clones of Populus euramericana