Vincetoxicum spirale, known locally in Rajasthan as Aakari Bel or Doodhli, is far from an obscure botanical curiosity. In the Little Rann of Kachchh, a unique salt-marsh landscape in Gujarat, it is regarded as one of the region’s life-supporting plants, valued as food for both people and cattle. The plant carries a substantial chemical arsenal, including an acyclic diterpene ester, bergenin, ferulic acid, quercetin derivatives, squalene and triterpenes. Traditional medicine has exploited these constituents for their alterative, astringent, cooling, emetic, purgative, anti-inflammatory, antimicrobial and antifungal properties, deploying the plant against gonorrhoea, fever, indigestion, dysentery and muscular troubles. Native to Eritrea and Yemen and distributed across the dry shrublands of Africa, Australia and Asia, the species is already listed as threatened in the Karachi region of Pakistan, and ecological niche modelling predicts a high risk of habitat destruction in southeastern Sindh by 2050.

The obstacles to natural regeneration are formidable. The plant propagates by small, brown, winged seeds, but seed availability, germination and seedling establishment are all unreliable, and drought stress, overgrazing and mechanized agriculture compound the losses. Against this backdrop, the research team, led by Ashok Kumar Patel with Deepika Lodha, Sumitra Kumari Choudhary and N. S. Shekhawat, set out to build a regeneration system from scratch. Their strategy relied on indirect organogenesis, the process by which differentiated plant cells first dedifferentiate into an unorganized callus and then re-differentiate into shoots through newly formed meristematic centres. The process unfolds in three recognized stages: dedifferentiation, in which the explant responds to organogenetic signals; induction, in which cells commit to producing shoots or roots; and realization, when visible organs emerge.

The team began by comparing four types of explants: leaf, node, internode and root segments, all collected from a wild source plant near the village of Mogra in Jodhpur district. After surface sterilization with the systemic fungicide Bavistin followed by mercuric chloride, the explants were placed on Murashige and Skoog medium fortified with sucrose and varying concentrations of the synthetic auxins NAA or 2,4-dichlorophenoxyacetic acid. The verdict was unambiguous. Leaf explants cultured on medium containing 2.0 milligrams per litre of 2,4-D produced the highest callus induction rate, 76.7 percent, and the greatest fresh weight, about 747 milligrams after five weeks. Internodal explants performed respectably at 63.3 percent, while node and root explants lagged far behind, and root cultures suffered the heaviest contamination. The authors note that the midrib and veins of a leaf are extensions of the stem’s vascular bundles, surrounded by unspecialized parenchyma cells that are particularly competent to respond to growth regulators.

The choice of auxin proved decisive. While 2,4-D at 2.0 milligrams per litre produced cottony-white, proliferative and partially organized callus, the same concentration of NAA yielded brown, slow-growing, compact callus with a response of only 24.6 percent, and higher NAA levels pushed the tissue toward hard, rhizogenic growth. The researchers attribute 2,4-D’s potency to its role in reprogramming cells and driving cell division, effects that involve the control of endogenous auxin metabolism, DNA methylation and the induction of specific proteins. Yet callus induced on 2,4-D would not proliferate indefinitely on the same medium, because the synthetic auxin is metabolized slowly and can accumulate to toxic levels. The solution was to transfer the tissue to medium containing a reduced dose of 1.0 milligram per litre of 2,4-D combined with 0.5 milligrams per litre of the cytokinin Kinetin. This combination produced morphogenic, competent, light yellow-green, friable callus with a callus proliferation coefficient of 7.49, meaning the tissue nearly seven-and-a-half-folded in mass over five weeks, compared with just 3.01 on auxin alone.

With proliferating callus in hand, the team turned to the heart of the protocol: coaxing shoots to form. Proliferated callus was moved to media containing the cytokinins BAP or Kinetin, alone or with low levels of the auxins NAA or IAA. BAP outperformed Kinetin, and the two cytokinins together worked better than either alone, with a trace of NAA further boosting differentiation. The winning formula combined 0.5 milligrams per litre of BAP, 0.25 milligrams per litre of Kinetin and 0.1 milligrams per litre of NAA, supplemented with adenine sulphate, L-arginine and citric acid at 25 milligrams per litre each, ascorbic acid at 50 milligrams per litre, and 100 milligrams per litre of activated charcoal. This cocktail yielded an average of 30.17 shoots per culture, each about 6.26 centimetres long, after six weeks. Each additive earns its place: adenine sulphate is a purine precursor in cytokinin biosynthesis, L-arginine supplies extra reduced nitrogen, citric acid chelates and suppresses the phenolic browning that plagues many cultures, ascorbic acid acts as an enzyme cofactor and antioxidant, and activated charcoal adsorbs inhibitory metabolites while releasing growth-favouring substances.

Perhaps the most commercially significant step is what the researchers did next. Instead of rooting the microshoots in sterile laboratory medium, they pulse-treated the cut bases with concentrated auxin solutions and planted them directly into solid substrates, a one-step strategy known as ex vitro rooting and concurrent acclimatization, or EVRCA. Dipping shoots in 300 milligrams per litre of NAA for exactly five minutes produced rooting in more than 75 percent of shoots, with an average of 4.45 roots per shoot reaching 5.58 centimetres within three weeks. Timing mattered: five minutes beat seven, three and nine minute treatments. Among the substrates tested, the porous, water-retentive Soilrite outperformed cocopeat and ordinary soil, both of which impede the delicate juvenile roots. Because EVRCA eliminates the entire in vitro rooting stage, it cuts chemical use, labour and time, reduces microbial contamination, and produces root systems with lateral root hairs and good vascular connectivity that resemble those of mother plants. About 70 percent of the rooted plantlets survived transplantation into polybags, and the cultures themselves were maintained for two years of subculturing without any decline in vigour.

The study’s second strand reaches into molecular territory. To understand why some callus regenerates and some does not, the team compared the total soluble protein profiles of non-regenerative callus, harvested from the induction medium, and regenerative callus, harvested from the shoot differentiation medium, using sodium dodecyl sulfate polyacrylamide gel electrophoresis with silver staining. Total protein content rose from 34 micrograms per milligram fresh weight in non-regenerative callus to 42 in regenerative callus. The gels resolved 16 bands in the non-regenerative sample and 19 in the regenerative one, with significant differences at eleven polypeptide positions unique to the regenerative callus and three unique to the non-regenerative one, plus intensity variations at four further bands. Notably, the low molecular weight polypeptides labelled P17, P18 and P19 appeared only in regenerative tissue, suggesting they may underpin the callus’s capacity to build shoots. Protein expression is known to shift with developmental phase as structural and regulatory genes switch on and off, influenced by media composition, explant type and culture conditions, echoing earlier findings in sweet orange, where 2,4-D-responsive proteins revealed extensive gene reprogramming during somatic embryogenesis.

The implications extend well beyond a single species. Because the callus originates from mature leaf tissue, the system opens a door to secondary metabolite production in bioreactors, sidestepping the need to harvest wild plants. Indirect organogenesis through callus is also the gateway for genetic transformation, making the protocol a prerequisite for future CRISPR-Cas genome editing and molecular breeding aimed at improving the plant’s therapeutic traits. The authors are careful to frame the protein work as a first step: identifying and characterizing the specific regeneration-linked proteins will require further study, but the differential profiles provide the initial molecular map. In the broader picture, the study aligns with United Nations Sustainable Development Goal 15, which calls for the conservation of terrestrial ecosystems and the protection of threatened species. For a climber that has sustained desert communities for generations, science has now supplied a way to ensure it survives them.

Subject of Research: Indirect organogenesis and protein profiling in callus cultures of the threatened medicinal climber Vincetoxicum spirale

Article Title: Indirect organogenesis, ex vitro rooting, and protein profiling of callus cultures of Vincetoxicum spirale: a threatened climber

Article References: Indirect organogenesis, ex vitro rooting, and protein profiling of callus cultures of Vincetoxicum spirale: a threatened climber. (n.d.). https://doi.org/10.1007/s44340-025-00009-y

Image Credits: AI Generated

DOI: 10.1007/s44340-025-00009-y

Keywords: Vincetoxicum spirale, indirect organogenesis, plant tissue culture, callus, 2,4-D, BAP, ex vitro rooting, SDS-PAGE, protein profiling, plant conservation, Asclepiadoideae, micropropagation

The classic experimental system for studying plant regeneration is the two-step tissue culture protocol. Explants, small pieces of plant tissue, are first placed on a callus induction medium containing a balanced ratio of the plant hormones auxin and cytokinin. Under these conditions, a subset of cells re-enters the cell cycle and proliferates into callus, a disorganized mass of cells that resembles lateral root primordia more than any mature tissue. When the callus is then transferred to a shoot induction medium rich in cytokinin, some cells adopt shoot identity and form a shoot apical meristem, the self-renewing stem cell hub that generates leaves, stems, and eventually flowers. Understanding the molecular switches that govern each of these transitions has become one of the central questions in plant developmental biology.

At the heart of the process lies hormonal control. Auxin, arguably the most influential player, drives dedifferentiation and callus formation, and its signaling operates through transport inhibitor response 1 receptors and auxin response factors that directly regulate reprogramming genes. Work in Arabidopsis thaliana has shown that auxin upregulates LEAFY COTYLEDON 1 and 2, transcription factors central to somatic embryogenesis. Studies in rice further revealed that local auxin gradients determine whether regenerating tissues form roots or shoots: high auxin with low cytokinin favors roots, while the opposite combination promotes shoots. PIN-FORMED transport proteins channel auxin directionally to specific sites, initiating de novo root organogenesis with remarkable spatial precision.

Cytokinin acts as auxin’s counterweight. It sustains cell division and, at high concentrations, promotes shoot primordia formation, while lower levels favor roots or somatic embryos. Cytokinin signaling flows through the Arabidopsis response regulator family, and type-B regulators such as ARR1, ARR2, ARR10, and ARR12 bind directly to the promoter of WUSCHEL, the master gene that maintains stem cell activity in the shoot apical meristem. Cytokinin also suppresses auxin accumulation through the YUCCA biosynthetic pathway, and remarkably, it reaches into the epigenetic machinery by modulating histone acetyltransferases, thereby making meristem maintenance genes more accessible for transcription. Mutations in type-B response regulators impair shoot regeneration, whereas overexpressing ARR12 enhances it, and WUSCHEL overexpression can rescue defective regeneration in double mutants, underscoring the centrality of this regulatory module.

Other hormones fine-tune the process. Gibberellins do not initiate reprogramming but sustain proliferation and maturation once cells have been redirected, promoting the elongation of somatic embryos into functional plantlets. Brassinosteroids, acting through the BRI1 receptor, synergize with auxin and cytokinin to boost cell division in callus and support organ formation. Abscisic acid, the stress hormone, plays the antagonist: elevated levels suppress cell division and organogenesis, inducing a dormancy-like state that prevents cells from reverting to totipotency under unfavorable conditions. ABA and cytokinin act antagonistically in shoot regeneration, illustrating how plants calibrate their regenerative responses against environmental risk.

Beneath the hormonal layer sits an elaborate gene regulatory network. Callus formation begins with the division of xylem pole pericycle cells, a process sharing molecular logic with lateral root initiation. The ALF4 protein initiates pericycle division, and root meristem genes including WOX5, WOX11, SCARECROW, PLETHORA 1 and 2, and SHORT ROOT become strongly upregulated. Mutant analyses confirm their importance: plt3plt5plt7 mutants lose shoot progenitor regeneration, and lbd16 mutants show reduced expression of WOX5 and PLETHORA genes with diminished shoot regeneration. On shoot induction medium, CUC1 and CUC2 transcription factors mark pre-meristematic zones, recruit PIN1 polarization, and activate SHOOT MERISTEMLESS to define future shoot progenitors, while ESR1 and ESR2 act upstream to promote the process. A transient root stem cell niche, marked by WOX5 expression, appears to be a prerequisite for the subsequent switch to shoot identity.

Small RNAs add another layer of temporal and spatial control. The miR156-SPL module explains why regeneration efficiency declines with plant age: juvenile plants with high miR156 repress SPL transcripts, keeping cytokinin responses active, whereas older plants accumulate SPL proteins that suppress type-B response regulators and reduce regeneration. miR165/166 promotes shoot formation, and the ARGONAUTE10 protein sequesters these microRNAs, with ago10 mutants showing elevated miR165/166 and enhanced regeneration. Meanwhile, a miR160-ARF10-ARR15 cascade fine-tunes the early balance between auxin and cytokinin signaling during callus formation, demonstrating how microRNA circuits integrate hormonal cues across developmental stages.

Perhaps the most striking insight from the review is that reprogramming is governed less by genetic change than by epigenetic rewiring. Global DNA hypomethylation is a hallmark of callus formation across species. In Arabidopsis, MET1 maintains CG methylation, and its loss increases WUSCHEL transcription and accelerates shoot formation; met1 mutants produce more shoots. Yet local hypermethylation also matters, silencing organ identity genes such as GSTU10, MAPK12, and BXL1 to help establish an undifferentiated cell mass. Histone marks are equally dynamic: H3K9ac and global H3 acetylation rise during callus formation, activating sugar metabolism, peptide signaling, and hormone transport genes while repressing photosynthesis programs. The demethylase JMJ30 removes repressive H3K9me3 marks from LBD16 and LBD29 promoters to enable callus formation, while ATX4 deposits activating H3K4me3 at shoot identity genes. Loss of the deacetylase HDA19 suppresses shoot regeneration, showing that both writing and erasing these marks is essential.

Proteomic studies, though still limited in number, reveal consistent patterns. Embryogenic cells accumulate heat-shock proteins as molecular chaperones, elevated glutathione-S-transferases that detoxify auxin, and cytoskeletal components such as tubulin and actin that establish cell polarity during division. Carbohydrate metabolism enzymes, photosynthetic proteins that appear as embryos mature, and nuclear import factors like importin all shift in abundance, reflecting the massive metabolic and architectural reorganization that accompanies the acquisition of pluripotency. Reactive oxygen species homeostasis intersects with auxin signaling during dedifferentiation, linking stress physiology directly to developmental potential.

New technologies are transforming the field’s resolution. Single-cell RNA sequencing has mapped the cellular composition of Arabidopsis and rice roots, revealed hormone signaling variation across cell clusters, and, when combined with ATAC-seq, identified WUSCHEL and DORNROESCHEN as crucial factors for regenerating mesophyll cells. CRISPR-based activation has been used to enhance somatic embryogenesis in tomato by targeting the SlWRKY29 gene, and CRISPR-dCas9 systems now allow precise transcriptional tuning of master regulators. Even artificial intelligence has entered the tissue culture lab: machine learning models, including neural networks and gradient boosting algorithms, have successfully predicted optimal media compositions for callus induction in carrot, micropropagation of lavender, and callogenesis in saffron, cutting both cost and experimental time. Together, these tools point toward a future in which regeneration efficiency can be engineered rather than stumbled upon, with implications for crop improvement, the propagation of recalcitrant and endangered species, and a deeper understanding of how any cell, given the right molecular instructions, can be persuaded to start over.

Subject of Research: Molecular mechanisms of cell fate reprogramming during de novo organogenesis in plants

Article Title: Understanding the molecular landscape of de novo organogenesis: insights into cell fate reprogramming

Article References: Nath, J., Kumari, A., Joshi, S., Gusain, S., Kumari, K., Yadav, S. K., & Joshi, R. (2025). Understanding the molecular landscape of de novo organogenesis: insights into cell fate reprogramming. Discover Biotechnology, 2(1), Article 27. https://doi.org/10.1007/s44340-025-00035-w

Image Credits: AI Generated

DOI: 10.1007/s44340-025-00035-w

Keywords: de novo organogenesis, cell fate reprogramming, auxin, cytokinin, WUSCHEL, epigenetics, DNA methylation, histone modification, callus, single-cell RNA sequencing, CRISPR, plant regeneration