Repression of Carotenoid Accumulation by Nitrogen and NH4+ Supply in Carrot Callus Cells In Vitro

Nitrogen availability modulates carotene biosynthesis, chromoplast biogenesis, and cell wall composition in carrot callus

KEY MESSAGE

Carrot callus grown on a medium with increased nitrogen have reduced carotenoid accumulation, changed gene expression, high amount of vesicular plastids and altered cell wall composition. Carotenoid biosynthesis is vital for plant development and quality, yet its regulation under varying nutrient conditions remains unclear. To explore the effects of nitrogen (N) availability, we used carrot (Daucus carota L.) model callus cultures in vitro as a controlled system for studying nutrient-regulated metabolic processes. Two mineral media differing in N content and NO₃⁻/NH₄⁺ ratios were used. Comprehensive analyses, HPLC, transmission electron microscopy, immunochemistry, and RNA sequencing, revealed notable cellular and molecular responses to N treatments. The results demonstrated that N supplementation reduced carotenoid content by 50%, particularly β-carotene and α-carotene. The composition of chromoplast types shifted, with vesicular chromoplasts dominating (55%), followed by a globular type (23%), while in the control callus, globular and crystalline types predominated (57% and 33%, respectively). Immunohistochemistry showed increased presence of high-esterified pectins and arabinogalactan proteins in N-treated cells. Transcriptomic analysis identified 1704 differentially expressed genes (DEGs), including only two in the carotenoid biosynthesis pathway: phytoene synthase 2 (PSY2) and zeaxanthin epoxidase (ZEP). PSY2, which encodes the carotenoid rate-limiting enzyme, showed expression levels that corresponded with reduced carotene content. Other DEGs included 15 involved in nitrogen transport, 1 in nitrogen assimilation, 40 in cell wall biosynthesis and modification, and 9 in phenylpropanoid/flavonoid pathways. N-treated callus exhibited altered expression of MADS-box, NLP, bZIP, and ethylene-responsive transcription factors. These findings reveal how nitrogen availability disrupts carotenoid biosynthesis and triggers extensive chromoplast and cell wall remodeling, providing a cellular framework for understanding nutrient-regulated metabolic shifts.

In Vitro vs. In Vivo Transcriptomic Approach Revealed Core Pathways of Nitrogen Deficiency Response in Tea Plant (Camellia sinensis (L.) Kuntze)

For the first time, we used an in vitro vs. in vivo experimental design to reveal core pathways under nitrogen deficiency (ND) in an evergreen tree crop. These pathways were related to lignin biosynthesis, cell redox homeostasis, the defense response to fungus, the response to Karrikin, amino acid transmembrane transport, the extracellular region, the cellular protein catabolic process, and aspartic-type endopeptidase activity. In addition, the mitogen-activated protein kinase pathway and ATP synthase (ATP)-binding cassette transporters were significantly upregulated under nitrogen deficiency in vitro and in vivo. Most of the MAPK downstream genes were related to calcium signaling (818 genes) rather than hormone signaling (157 genes). Moreover, the hormone signaling pathway predominantly contained auxin- and abscisic acid-related genes, indicating the crucial role of these hormones in ND response. Overall, 45 transcription factors were upregulated in both experiments, 5 WRKYs, 3 NACs, 2 MYBs, 2 ERFs, HD-Zip, RLP12, bHLH25, RADIALIS-like, and others, suggesting their ND regulation is independent from the presence of a root system. Gene network reconstruction displayed that these transcription factors participate in response to fungus/chitin, suggesting that nitrogen response and pathogen response have common regulation. The upregulation of lignin biosynthesis genes, cytochrome genes, and strigalactone response genes was much more pronounced under in vitro ND as compared to in vivo ND. Several cell wall-related genes were closely associated with cytochromes, indicating their important role in flavanols biosynthesis in tea plant. These results clarify the signaling mechanisms and regulation of the response to nitrogen deficiency in evergreen tree crops.

Dissecting the natural phytochemical diversity of carrot roots with its colour using high performance liquid chromatography and UV-Visible spectrophotometry

The research provides insights into the phytoconstituents of black, orange and red carrots (Daucus carota subsp. Sativus (Hoffm.) Schübl. & G. Martens), a highly nutritious food crop widely appreciated across age groups. Recognising carrots as a repository of health-promoting compounds, our study employs UV-Visible spectrophotometric and HPLC methods to discern significant variations in bioactive components among carrot varieties. Black carrots emerge as potent contenders, displaying the highest levels of total phenolics (2660 ± 2.29 mg GAE/100 g F W.), total flavonoids (831 ± 1.74 mg QE/100 g F W.), proanthocyanins (10910 ± 1.11 mg CE/100 g F W.), and tannins (713 ± 0.84 mg/100 g F W.). Red carrots, conversely, showcase higher anthocyanin content (6870 ± 1.85 mg CyGE/100 g F W.) by UV-Vis spectrophotometry. Additionally, orange carrots exhibit heightened β-carotene levels, confirmed at 0.03 μg/mg through HPLC. HPLC analysis unveils substantial chlorogenic acid variability (1.29 μg/mg) in black carrots, accompanied by the discovery of unique compounds such as cryptochlorogenic acid (0.05 μg/mg), caffeic acid (0.01 μg/mg), ferulic acid (0.11 μg/mg), methyl caffeate (0.01 μg/mg), and quercetin (0.02 μg/mg), marking the first detection of methyl caffeate in black carrots. The analytical methodology was meticulously validated encompassing optimal parameters such as linearity, precision, limit of detection, limit of quantification, accuracy, and robustness, within the range. In conclusion, our study underscores the health benefits of black carrots due to their rich polyphenolic content and endorses orange carrots for elevated β-carotene levels. These findings contribute to a deeper understanding of the diverse phytoconstituents in carrots, aid in informed dietary choices for improved health.

Seed endophytic bacterium Lysinibacillus sp. (ZM1) from maize (Zea mays L.) shapes its root architecture through modulation of auxin biosynthesis and nitrogen metabolism

Seed endophytic bacteria have been shown to promote the growth and development of numerous plants. However, the underlying mechanism still needs to be better understood. The present study aims to investigate the role of a seed endophytic bacterium Lysinibacillus sp. (ZM1) in promoting plant growth and shaping the root architecture of maize seedlings. The study explores how bacteria-mediated auxin biosynthesis and nitrogen metabolism affect plant growth promotion and shape the root architecture of maize seedlings. The results demonstrate that ZM1 inoculation significantly enhances root length, root biomass, and the number of seminal roots in maize seedlings. Additionally, the treated seedlings exhibit increased shoot biomass and higher levels of photosynthetic pigments. Confocal laser scanning microscopy (CLSM) analysis revealed extensive colonization of ZM1 on root hairs, as well as in the cortical and stellar regions of the root. Furthermore, LC-MS analysis demonstrated elevated auxin content in the roots of the ZM1 treated maize seedlings compared to the uninoculated control. Inoculation with ZM1 significantly increased the levels of endogenous ammonium content, GS, and GOGAT enzyme activities in the roots of treated maize seedlings compared to the control, indicating enhanced nitrogen metabolism. Furthermore, inoculation of bacteria under nitrogen-deficient conditions enhanced plant growth, as evidenced by increased root shoot length, fresh and dry weights, average number of seminal roots, and content of photosynthetic pigments. Transcript analysis indicated upregulation of auxin biosynthetic genes, along with genes involved in nitrogen metabolism at different time points in roots of ZM1-treated maize seedlings. Collectively, our findings highlight the positive impact of Lysinibacillus sp. ZM1 inoculation on maize seeds by improving root architecture through modulation of auxin biosynthesis and affecting various nitrogen metabolism related parameters. These findings provide valuable insights into the potential utilization of seed endophytic bacteria as biofertilizers to enhance plant growth and yield in nutrient deficient soils.

Strategies, Achievements, and Potential Challenges of Plant and Microbial Chassis in the Biosynthesis of Plant Secondary Metabolites

Diverse secondary metabolites in plants, with their rich biological activities, have long been important sources for human medicine, food additives, pesticides, etc. However, the large-scale cultivation of host plants consumes land resources and is susceptible to pest and disease problems. Additionally, the multi-step and demanding nature of chemical synthesis adds to production costs, limiting their widespread application. In vitro cultivation and the metabolic engineering of plants have significantly enhanced the synthesis of secondary metabolites with successful industrial production cases. As synthetic biology advances, more research is focusing on heterologous synthesis using microorganisms. This review provides a comprehensive comparison between these two chassis, evaluating their performance in the synthesis of various types of secondary metabolites from the perspectives of yield and strategies. It also discusses the challenges they face and offers insights into future efforts and directions.

Plant Tissue Culture and Secondary Metabolites Production

Plants have developed a complex biochemical system for interacting and coping with dynamic environmental challenges throughout their whole life [...].

Biotechnological production of β-carotene using plant in vitro cultures

β-carotene is biologically active compound widely distributed in plants. The use of plant in vitro cultures and genetic engineering is a promising strategy for its sustainable production. β-carotene is an orange carotenoid often found in leaves as well as in fruits, flowers, and roots. A member of the tetraterpene family, this 40-carbon isoprenoid has a conjugated double-bond structure, which is responsible for some of its most remarkable properties. In plants, β-carotene functions as an antenna pigment and antioxidant, providing protection against photooxidative damage caused by strong UV-B light. In humans, β-carotene acts as a precursor of vitamin A, prevents skin damage by solar radiation, and protects against several types of cancer such as oral, colon and prostate. Due to its wide spectrum of applications, the global market for β-carotene is expanding, and the demand can no longer be met by extraction from plant raw materials. Considerable research has been dedicated to finding more efficient production alternatives based on biotechnological systems. This review provides a detailed overview of the strategies used to increase the production of β-carotene in plant in vitro cultures, with particular focus on culture conditions, precursor feeding and elicitation, and the application of metabolic engineering.

Overexpression of LT, an Oncoprotein Derived from the Polyomavirus SV40, Promotes Somatic Embryogenesis in Cotton

Although genetic transformation has opened up a new era for cotton molecular breeding, it still suffers from the limitation problem of long transformation periods, which slows down the generation of new cotton germplasms. In this study, LT gene (SV40 large T antigen), which promotes the transformation efficiency of animal cells, was codon-optimized. Its overexpression vector was transformed into cotton. It was observed that EC (embryogenic callus) formation period was 33% shorter and transformation efficiency was slightly higher in the LT T0 generation than that of control. RNA-seq data of NEC (non-embryonic callus) and EC from LT and control revealed that more DEGs (differential expression genes) in NEC were identified than that of EC, indicating LT mainly functioned in NEC. Further KEGG, GO, and transcription factor analyses showed that DEGs were significantly enriched in brassinosteroid biosynthesis pathways and that bHLH, MYB, and AP2/ERF were the top three gene families, which are involved in EC formation. In addition, the key genes related to the auxin pathway were differentially expressed only in LT overexpression NEC, which caused early response, biosynthesis, and transportation of the hormone, resulting in EC earlier formation. In summary, the results demonstrated that LT can promote somatic embryogenesis in cotton, which provides a new strategy for improving cotton transformation and shortening EC formation time.

Optimization of Biomass Accumulation and Production of Phenolic Compounds in Callus Cultures of Rhodiola rosea L. Using Design of Experiments

Rhodiola rosea L. is a valuable medicinal plant with adaptogenic, neuroprotective, antitumor, cardioprotective, and antidepressant effects. In this study, design of experiments methodology was employed to analyze and optimize the interacting effects of mineral compounds (concentration of NO₃⁻ and the ratio of NH₄⁺ to K⁺) and two plant growth regulators [total 6-benzylaminopurine (BAP) and α-naphthylacetic acid (NAA) concentration and the ratio of BAP to NAA] on the growth and the production of total phenolic compounds (TPCs) in R. rosea calluses. The overall effect of the model was highly significant (p < 0.0001), indicating that NH₄⁺, K⁺, NO₃⁻, BAP, and NAA significantly affected growth. The best callus growth (703%) and the highest production of TPCs (75.17 mg/g) were achieved at an NH₄⁺/K⁺ ratio of 0.33 and BAP/NAA of 0.33, provided that the concentration of plant growth regulators was 30 μM and that of NO₃⁻ was ≤40 mM. According to high-performance liquid chromatography analyses of aerial parts (leaves and stems), in vitro seedlings and callus cultures of R. rosea contain no detectable rosarin, rosavin, rosin, and cinnamyl alcohol. This is the first report on the creation of an experiment for the significant improvement of biomass accumulation and TPC production in callus cultures of R. rosea.