Plant Stem Cells Research Articles

Deciphering the molecular logic of WOX5 function in the root stem cell organizer

AbstractPlant and animal stem cells receive signals from their surrounding cells to stay undifferentiated. In the Arabidopsis root, the quiescent center (QC) acts as a stem cell organizer, signaling to the neighboring stem cells. WOX5 is a central transcription factor regulating QC function. However, due to the scarcity of QC cells, WOX5 functions in the QC are largely unexplored at a genomic scale. Here, we unveil the transcriptional and epigenetic landscapes of the QC and the role of WOX5 within them. We find that WOX5 functions both as a transcriptional repressor and activator, affecting histone modifications and chromatin accessibility. Our data expand on known WOX5 functions, such as the regulation of differentiation, cell division, and auxin biosynthesis. We also uncover unexpected WOX5-regulated pathways involved in nitrate transport and the regulation of basal expression levels of genes associated with mature root tissues. These data suggest a role for QC cells as reserve stem cells and primed cells for prospective progenitor fates. Taken together, these findings offer insights into the role of WOX5 at the QC and provide a basis for further analyses to advance our understanding of the nature of plant stem cell organizers.

Heat stress-induced decapping of WUSCHEL mRNA enhances stem cell thermotolerance in Arabidopsis

The plasticity of stem cells in response to environmental change is critical for multicellular organisms. Here, we show that MYB3R-like directly activates the key plant stem cell regulator WUSCHEL (WUS) by recruiting the methyltransferase ROOT INITIATION DEFECTIVE 2 (RID2), which functions in m7G methylation at the 5’ cap of WUS mRNA to protect it from degradation. We demonstrated that protein-folding genes are repressed by WUS to maintain precise protein synthesis in stem cells by preventing the reuse of misfolded proteins. However, upon heat stress, the MYB3R-like/RID2 module is repressed to reduce WUS transcripts via the decapping of nascent WUS mRNA. This releases the inhibition of protein folding capacity in stem cells and protects plant stem cells from heat-shock by eliminating misfolded protein aggregation. Our results reveal a tradeoff strategy in plants by reducing the accuracy of protein synthesis in exchange for the survival of stem cells at high temperatures.

The WOX9-WUS modules are indispensable for the maintenance of stem cell homeostasis in Arabidopsis thaliana.

The dynamic balance between the self-renewal and differentiation of stem cells in plants is precisely regulated by a series of developmental regulated genes that exhibit spatiotemporal-specific expression patterns. Several studies have demonstrated that the WOX family transcription factors play critical roles in maintaining the identity of stem cells in Arabidopsis thaliana. In this study, we obtained amiR-WOX9 transgenic plants, which displayed terminating prematurely of shoot apical meristem (SAM) development, along with alterations in inflorescence meristem and flower development. The phenotype of amiR-WOX9 plants exhibited similarities to that of wus-101 mutant, characterized by a stop-and-go growth pattern. It was also found that the expression of WUS in amiR-WOX9 lines was decreased significantly, while in UBQ10::WOX9-GFP transgenic plants, the WUS expression was increased significantly despite no substantial alteration in meristem size compared to Col. Therefore, these data substantiated the indispensable role of WOX9 in maintaining the proper expression of WUS. Further investigations unveiled the direct binding of WOX9 to the WUS promoter via the TAAT motif, thereby activating its expression. It was also found that WUS recognized identical the same TAAT motif cis-elements in its own promoter, thereby repress self-expression. Next, we successfully identified a physical interaction between WOX9 and WUS, and verified that it was harmful to the expression of WUS. Finally, our experimental findings demonstrate that WOX9 was responsible for the direct activating of WUS, which however was interfered by the ways of WUS binding its own promoter and the interaction of WUS and WOX9, thereby ensuring the appropriate expression pattern of WUS and then the stem cell stability. This study contributes to an enhanced comprehension of the regulatory network of the WOX9-WUS module in maintaining the equilibrium of the SAM.

Control of DNA demethylation by superoxide anion in plant stem cells.

Superoxide anion is thought to be a natural by-product with strong oxidizing ability in all living organisms and was recently found to accumulate in plant meristems to maintain stem cells in the shoot and undifferentiated meristematic cells in the root. Here we show that the DNA demethylase repressor of silencing 1 (ROS1) is one of the direct targets of superoxide in stem cells. The Fe-S clusters in ROS1 are oxidized by superoxide to activate its DNA glycosylase/lyase activity. We demonstrate that superoxide extensively participates in the establishment of active DNA demethylation in the Arabidopsis genome and that ARABIDOPSIS RESPONSE REGULATOR 12 acts downstream of ROS1-mediated superoxide signaling to maintain stem cell fate. Our results provide a mechanistic framework for superoxide control of the stem cell niche and demonstrate how redox and DNA demethylation interact to define stem cell fate in plants.

Stem cells of Impatiens tinctoria A.Rich tuber and antioxidant activity of their extracts

The use of plant stem cell extracts as active ingredients in cosmetic formulations has gained popularity recently, highlighting the need to establish Impatiens tinctoria A. Rich in vitro cultures in order to prepare bioactive stem cell extracts. This study is aimed at establishing cell suspension culture and evaluates the antioxidant activity of the stem cell extract. In order to initiate callus and cell suspension cultures, tuber explants were inoculated onto Murashige and Skoog (MS) media containing 2,4-D (0.5–2 mg/L) and BAP (0–2 mg/L). Optimal hormone concentrations of 2 mg/L 2,4-D and 1.5 mg/L BAP were sufficient to produce callus. The obtained callus was utilized as the inoculum to start a cell suspension culture for the production of stem cell extracts. High biomass accumulation was obtained at 30 g/L sucrose concentration and 6g inoculum size. The stem cell extract had a total phenolic content of 4.6 µgGAE/mL and a flavonoid content of 190.96 µgQE/mL. DPPH scavenging activity of 95.82% and the IC50 value of 37.54 µg/mL was detected for the stem cell extract. The study indicated that the suspension cultures of I. tinctoria A. Rich have the potential to produce stem cell extracts with increased flavonoids content and antioxidant activity.

Potential of Plant Stem Cells as Helpful Agents for Skin Disorders—A Narrative Review

Recently, cellular senescence has been of great interest due to its pleiotropic nature and association with both physiological (e.g., aging) and pathological conditions. Excessive accumulation of reactive oxygen species (ROS) can induce inflammation, which accelerates skin aging (also premature aging) and may cause several dermatoses. It has been postulated that plant-derived antioxidants, especially plant stem cells, may prevent cell damage by preserving stemness and reducing cellular senescence by ROS targeting. Therefore, this paper aims to review and summarize recent developments and innovative techniques associated with plant-derived stem cells in relation to skin senescence. This review also presents the possible pathways involved in this process. Particular attention was paid to the potential applications of plant stem cells as senostatics/senomorphics produced by modern plant biotechnology methods. Furthermore, the advantages, limitations, and future directions of this technology are also discussed. This knowledge allows the development of personalized strategies to create a healthy balance in skin care. Plant stem cells could be a more feasible and practical approach to combating the adverse effects of skin senescence processes.

Methionine Synthase 2 Represses Stem Cell Maintenance of Arabidopsis thaliana in Response to Salt Stress.

Salt stress represses the growth and development of plants that mainly depend on the continual propagation and differentiation of stem cells. WUSCHEL (WUS)/WUSCHEL-RELATED HOMEOBOX (WOX) family proteins determine stem cell fate in plants under ever-changing environments. It is not yet known how plant stem cell homeostasis is regulated under salt stress. Methionine synthase catalyzes the formation of methionine by methylating homocysteine in the one-carbon metabolism pathway. In this work, we investigated the role of Arabidopsis METHIONINE SYNTHASE 2 (AtMS2) in stem cell homeostasis under salt stress. The results showed that AtMS2 represses the stem cell maintenance of Arabidopsis in response to salt stress. Under normal growth conditions, AtMS2 is mainly localized in the cytoplasm. However, under salt stress, it exhibits significant accumulation in the nucleus. AtMS2 interacts with the WUS/WOX protein, and, together, they repress WUS/WOX expression by binding to its promoter. The mutation in AtMS2 resulted in enhanced salt tolerance. Therefore, AtMS2 might act as a key negative regulator to repress the stem cell maintenance and growth of Arabidopsis under salt stress.

(Invited) Carbon Nanodots for Improved Plant Genetic Engineering

Anthropogenic climate change has made the need for more nutritious and stress-tolerant plants indisputable for providing food security. Climate change has decreased the global agricultural productivity by 21% since 1961, and will continue to drop crop yields by 7.4% for every degree-Celsius increase in temperature. CRISPR genetic engineering can enable previously inaccessible crop tolerances to meet the demand for nutritionally-balanced and high-yielding crops. However, plant biomolecule delivery and transformation are two important bottlenecks that prevent plant genetic engineering from reaching its full potential.Nanomaterials have already shown promise to deliver genetic cargoes into plant somatic cells for transient expression of proteins1. For most applications in agriculture, however, biomolecules need to be delivered to cells that can give rise to next generation of edited plants, such as germ or stem cells. These cell types are extremely challenging to penetrate and deliver cargoes using traditional approaches, hence forcing researchers to use undifferentiated tissues to transform and go through an arduous regeneration process in tissue culture. This time consuming, inefficient, and highly species dependent approach has been a critical obstacle in plant biology and bioengineering.We have synthesized small (~3 nm) and positively charged (+35 mV) carbon nanodots (CNDs) from glycerol and polyethyleneimine (PEI) using the microwave method. These CNDs showed high entry efficiency into plant stem cells and ability to deliver DNA cargoes into a model plant Nicotiana benthamiana without affecting stem cell viability and differentiation capability. This is a first-time demonstration of nanoparticle uptake by plant stem cells and cargo expression in these cell types. Once we perform CRISPR gene editing in these stem cells, the edited germ cells and seeds will develop automatically from the stem cells, facilitating the creation of edited and improved new plant varieties.

Appreciating animal induced pluripotent stem cells to shape plant cell reprogramming strategies.

Animals and plants have developed resilience mechanisms to effectively endure and overcome physical damage and environmental challenges throughout their life span. To sustain their vitality, both animals and plants employ mechanisms to replenish damaged cells, either directly, involving the activity of adult stem cells, or indirectly, via dedifferentiation of somatic cells that are induced to revert to a stem cell state and subsequently redifferentiate. Stem cell research has been a rapidly advancing field in animal studies for many years, driven by its promising potential in human therapeutics, including tissue regeneration and drug development. A major breakthrough was the discovery of induced pluripotent stem cells (iPSCs), which are reprogrammed from somatic cells by expressing a limited set of transcription factors. This discovery enabled the generation of an unlimited supply of cells that can be differentiated into specific cell types and tissues. Equally, a keen interest in the connection between plant stem cells and regeneration has been developed in the last decade, driven by the demand to enhance plant traits such as yield, resistance to pathogens, and the opportunities provided by CRISPR/Cas-mediated gene editing. Here we discuss how knowledge of stem cell biology benefits regeneration technology, and we speculate on the creation of a universal genotype-independent iPSC system for plants to overcome regenerative recalcitrance.

The peptidase DA1 cleaves and destabilizes WUSCHEL to control shoot apical meristem size

Stem cells in plants and animals are the source of new tissues and organs. In plants, stem cells are maintained in the central zone (CZ) of multicellular meristems, and large shoot meristems with an increased stem cell population hold promise for enhancing yield. The mobile homeodomain transcription factor WUSCHEL (WUS) is a central regulator of stem cell function in plant shoot meristems. Despite its central importance, the factors that directly modulate WUS protein stability have been a long-standing question. Here, we show that the peptidase DA1 physically interacts with and cleaves the WUS protein, leading to its destabilization. Furthermore, our results reveal that cytokinin signaling represses the level of DA1 protein in the shoot apical meristem, thereby increasing the accumulation of WUS protein. Consistent with these observations, loss of DA1 function results in larger shoot apical meristems with an increased stem cell population and also influences cytokinin-induced enlargement of shoot apical meristem. Collectively, our findings uncover a previously unrecognized mechanism by which the repression of DA1 by cytokinin signaling stabilizes WUS, resulting in the enlarged shoot apical meristems with the increased stem cell number during plant growth and development.

PagPXYs improve drought tolerance by regulating reactive oxygen species homeostasis in the cambium of Populus alba × P. glandulosa

PXY (Phloem intercalated with xylem) is a receptor kinase required for directional cell division during the development of plant vascular tissue. Drought stress usually affects plant stem cell division and differentiation thereby limiting plant growth. However, the role of PXY in cambial activities of woody plants under drought stress is unclear. In this study, we analyzed the biological functions of two PXY genes (PagPXYa and PagPXYb) in poplar growth and development and in response to drought stress in a hybrid poplar (Populus alba × P. glandulosa, ‘84K’). Expression analysis indicated that PagPXYs, similar to their orthologs PtrPXYs in Populus trichocarpa, are mainly expressed in the stem vascular system, and related to drought. Interestingly, overexpression of PagPXYa and PagPXYb in poplar did not have a significant impact on the growth status of transgenic plants under normal condition. However, when treated with 8 % PEG6000 or 100 mM H2O2, PagPXYa and PagPXYb overexpressing lines consistently exhibited more cambium cell layers, fewer xylem cell layers, and enhanced drought tolerance compared to the non-transgenic control ‘84K’. In addition, PagPXYs can alleviate the damage caused by H2O2 to the cambium under drought stress, thereby maintaining the cambial division activity of poplar under drought stress, indicating that PagPXYs play an important role in plant resistance to drought stress. This study provides a new insight for further research on the balance of growth and drought tolerance in forest trees.

Response of agronomic and physiological traits of flue-cured tobacco (Nicotiana tabacum L.) to plant stem cell soil amendments

Black shank disease is an important factor limiting the yield of flue-cured tobacco. Soil amendments have the potential to improve soil health and increase crop yield and quality. However, the application effects of soil amendments have not been elucidated in flue-cured tobacco. Here, we conducted field experiments in the major tobacco planting area, Exploring the effects of plant stem cell soil amendments at different levels on the occurrence and physiological growth of tobacco black shank disease, The purpose is to evaluate the effectiveness of plant stem cell soil amendments and recommend feasible applied rates. Plant stem cell soil amendments are applied at four levels: T0 (0 kg ha−1), T1 (1500 kg ha−1), T2 (2250 kg ha−1), and T3 (3000 kg ha−1). Nutrient absorption, agronomic traits, dry matter quality, chemical composition, and economic benefits of flue-cured tobacco black shank disease were explored. The results showed that the application of plant stem cell soil amendments effectively reduced the incidence rate of tobacco black shank disease, and significantly improved the agronomic traits (leaf number, plant height, leaf length, and width) and dry matter quality of flue-cured tobacco. At the same time, the nutrient content (N, P, and K), the proportion of high-quality tobacco leaves, and the content of coordinated chemical components (total nitrogen, total plant alkali, total sugar, reducing sugar, potassium and chlorine) of flue-cured tobacco plants were increased. In addition, the application rate of stem cell soil amendment at 3000 kg ha−1 showed the best effect on reducing the occurrence of black shank disease, which resulted in improved tobacco yields and economic benefits to the greatest extent of flue-cured tobacco. The study indicates that plant stem cell soil amendments can significantly enhance the yield and quality of flue-cured tobacco and offers an effective method for sustainable crop production in the tobacco industry.

EXPERIENCE OF USING STEM CELLS IN PATIENTS WITH ATOPIC DERMATITIS

Recent research in this area has shown that in many tissues, including skin, stem cells become dormant as they mature, slowing down their rate of division and not responding as effectively to stimulation [1]. A decrease in the activity of stem cells leads to the fact that the rate of skin renewal slows down and defects begin to accumulate in it; the skin ages [2]. Recently, the attention of scientists has been attracted by plant stem cells, which produce a complex of molecular regulators that are universal. These regulators are capable of changing the functioning of human skin stem cells, partially returning them the energy of youth [3]. One of the most popular ingredients today is Swiss apple stem cells. Each adult apple stem cell can independently generate new cells and, in a concentration of just 0.1%, stimulate the division of human stem cells by 80% [4]. Phytostem (plant) cells were discovered relatively recently - only in the second half of the 20th century [5]. And the most effective in influencing human cells are considered to be plant stem cells, green apple phytostem cells. Scientists have proven that they are active biostimulators of human cells [6]. Plant cell preparations are absolutely hypoallergenic, unlike those obtained from animal or human tissues.

Extreme restructuring of cis-regulatory regions controlling a deeply conserved plant stem cell regulator.

A striking paradox is that genes with conserved protein sequence, function and expression pattern over deep time often exhibit extremely divergent cis-regulatory sequences. It remains unclear how such drastic cis-regulatory evolution across species allows preservation of gene function, and to what extent these differences influence how cis-regulatory variation arising within species impacts phenotypic change. Here, we investigated these questions using a plant stem cell regulator conserved in expression pattern and function over ~125 million years. Using in-vivo genome editing in two distantly related models, Arabidopsis thaliana (Arabidopsis) and Solanum lycopersicum (tomato), we generated over 70 deletion alleles in the upstream and downstream regions of the stem cell repressor gene CLAVATA3 (CLV3) and compared their individual and combined effects on a shared phenotype, the number of carpels that make fruits. We found that sequences upstream of tomato CLV3 are highly sensitive to even small perturbations compared to its downstream region. In contrast, Arabidopsis CLV3 function is tolerant to severe disruptions both upstream and downstream of the coding sequence. Combining upstream and downstream deletions also revealed a different regulatory outcome. Whereas phenotypic enhancement from adding downstream mutations was predominantly weak and additive in tomato, mutating both regions of Arabidopsis CLV3 caused substantial and synergistic effects, demonstrating distinct distribution and redundancy of functional cis-regulatory sequences. Our results demonstrate remarkable malleability in cis-regulatory structural organization of a deeply conserved plant stem cell regulator and suggest that major reconfiguration of cis-regulatory sequence space is a common yet cryptic evolutionary force altering genotype-to-phenotype relationships from regulatory variation in conserved genes. Finally, our findings underscore the need for lineage-specific dissection of the spatial architecture of cis-regulation to effectively engineer trait variation from conserved productivity genes in crops.

Plant Stem Cell Informatics Database (PSCIdb): A comprehensive computational platform for identifying and analyzing genes related to plant stem cells

Plant Stem Cell Informatics Database (PSCIdb): A comprehensive computational platform for identifying and analyzing genes related to plant stem cells

Transcription Factor MdPLT1 Involved Adventitious Root Initiation in Apple Rootstocks

The induction of adventitious roots is a key factor restricting the vegetative propagation of apple dwarf rootstocks. PLETHORA (PLT) transcription factors are involved in the regulation of plant stem cell niche and adventitious root development. In this study, we identified the PLT1 gene in apples by bioinformatics and analyzed its evolutionary relationship. The MdPLT1 gene was cloned from M9-T337 to verify its subcellular localization and analyze its function in transgenic tobacco. The MdPLT1 protein contained two conserved AP2 domains which may be similar to those of poplar the PtrPLT2a and PtrPLT2b with 85% support. The CDS sequence of the MdPLT1 gene was 1638 bp, encoding 545 amino acids. The transcription factor MdPLT1 was localized in the nucleus. The number of adventitious roots of tobacco plants overexpressing MdPLT1 significantly increased. In the adventitious roots of MdPLT1-overexpressed plants, the expression levels of genes related to the NtPINs family and the NtYUCCAs family were significantly increased. The results showed that MdPLT1 positively regulated adventitious root formation. This study provided a theoretical basis for the establishment of the fast vegetative propagation of apple dwarf rootstocks.

Suspension culture of stem cells established of Calendula officinalis L.

Plant stem cell cultures have so far been established in only a few plant species using cambial meristematic cells. The presence of stem cells or stem cell-like cells in other organs and tissues of the plant body, as well as the possibility of de novo generation of meristematic cells from differentiated cells, allow to consider the establishment of stem cell cultures in a broader range of species. This study aimed to establish a stem cell culture of the medicinal plant Calendula officinalis L. Callus tissues were induced from leaf and root explants, and already at this stage, stem and dedifferentiated cells could be identified. The cell suspension cultures established both from the root- and leaf-derived calli contained a high proportion of stem cells (92–93% and 72–73%, respectively). The most effective combination of growth regulators for the development of stem cells in calli as well as cell cultures was 1.0 mg/L 2,4-D and 0.5 mg/L BAP. The highest amount of stem cells (5.60–5.72 × 105) was in cell suspension derived from the roots. An effective protocol for the establishment of marigold stem cell suspension culture was developed. The ratio of root-derived stem cells against dedifferentiated cells exceeded 90%.

Nitric oxide controls shoot meristem activity via regulation of DNA methylation

Despite the importance of Nitric Oxide (NO) as signaling molecule in both plant and animal development, the regulatory mechanisms downstream of NO remain largely unclear. Here, we show that NO is involved in Arabidopsis shoot stem cell control via modifying expression and activity of ARGONAUTE 4 (AGO4), a core component of the RNA-directed DNA Methylation (RdDM) pathway. Mutations in components of the RdDM pathway cause meristematic defects, and reduce responses of the stem cell system to NO signaling. Importantly, we find that the stem cell inducing WUSCHEL transcription factor directly interacts with AGO4 in a NO dependent manner, explaining how these two signaling systems may converge to modify DNA methylation patterns. Taken together, our results reveal that NO signaling plays an important role in controlling plant stem cell homeostasis via the regulation of de novo DNA methylation.

Condensation: A new mechanism underlying STM function in plant stem cell activity

Condensation: A new mechanism underlying STM function in plant stem cell activity

Salicylic acid and RNA interference mediate antiviral immunity of plant stem cells

Stem cells are essential for the development and organ regeneration of multicellular organisms, so their infection by pathogenic viruses must be prevented. Accordingly, mammalian stem cells are highly resistant to viral infection due to dedicated antiviral pathways including RNA interference (RNAi). In plants, a small group of stem cells harbored within the shoot apical meristem generate all postembryonic above-ground tissues, including the germline cells. Many viruses do not proliferate in these cells, yet the molecular bases of this exclusion remain only partially understood. Here, we show that a plant-encoded RNA-dependent RNA polymerase, after activation by the plant hormone salicylic acid, amplifies antiviral RNAi in infected tissues. This provides stem cells with RNA-based virus sequence information, which prevents virus proliferation. Furthermore, we find RNAi to be necessary for stem cell exclusion of several unrelated RNA viruses, despite their ability to efficiently suppress RNAi in the rest of the plant. This work elucidates a molecular pathway of great biological and economic relevance and lays the foundations for our future understanding of the unique systems underlying stem cell immunity.