Plant Stem Cells Research Articles

Transcriptomic and Metabolomic Investigation on Leaf Necrosis Induced by ZmWus2 Transient Overexpression in Nicotiana benthamiana.

WUSCHEL (WUS) is a crucial transcription factor in regulating plant stem cell development, and its expression can also improve genetic transformation. However, the ectopic expression of WUS always causes pleiotropic effects during genetic transformation, making it important to understand the regulatory mechanisms underlying these phenomena. In our study, we found that the transient expression of the maize WUS ortholog ZmWus2 caused severe leaf necrosis in Nicotiana benthamiana. We performed transcriptomic and non-target metabolomic analyses on tobacco leaves during healthy to wilted states after ZmWus2 transient overexpression. Transcriptomic analysis revealed that ZmWus2 transformation caused active metabolism of inositol trisphosphate and glycerol-3-phosphate, while also upregulating plant hormone signaling and downregulating photosystem and protein folding pathways. Metabolomic analysis mainly identified changes in the synthesis of phenylpropanoid compounds and various lipid classes, including steroid synthesis. In addition, transcription factors such as ethylene-responsive factors (ERFs), the basic helix-loop-helix (bHLH) factors, and MYBs were found to be regulated by ZmWus2. By integrating these findings, we developed a WUS regulatory model that includes plant hormone accumulation, stress responses, lipid remodeling, and leaf necrosis. Our study sheds light on the mechanisms underlying WUS ectopic expression causing leaf necrosis and may inform the development of future genetic transformation strategies.

Identification and Evolutionary Analysis of Cotton (Gossypium hirsutum) WOX Family Genes and Their Potential Function in Somatic Embryogenesis.

WUSCHEL-related homeobox (WOX) proteins participate profoundly in plant development and stress responses. As the difficulty of somatic embryogenesis severely constrains cotton genetic modification, in this study, we identified and comprehensively analyzed WOX genes in cotton. As a result, 40 WOX genes were identified in the upland cotton genome. All these cotton WOX genes were classified into three clades, ancient, intermediate, and modern clades, based on the phylogenetic analysis of previous studies. The majority (24) of the cotton WOX genes belonged to the modern clade, in which all gene members contain the vital functional domain WUS-box, which is necessary for plant stem cell regulation and maintenance. Collinearity analysis indicated that the WOX gene family in cotton expanded to some degree compared to Arabidopsis, especially in the modern clade. Genome duplication and segmental duplication may greatly contribute to expansion. Hormone-response- and abiotic-stress-response-related cis-acting regulatory elements were widely distributed in the promoter regions of cotton WOX genes, suggesting that the corresponding functions of stress responses and the participation of development processes were involved in hormone responses. By RNA sequencing, we profiled the expression patterns of cotton WOX genes in somatic embryogenesis. Only about half of cotton WOX genes were actively expressed during somatic embryogenesis; different cotton WOX genes may function in different development stages. The most representative, GhWOX4 and GhWOX13, may function in almost all stages of somatic embryogenesis; GhWOX2 and GhWOX9 function in the late stages of embryo patterning and embryo development during cotton somatic embryogenesis. Co-expression analysis showed that the cotton WOXs co-expressed with genes involved in extensive genetic information processing, including DNA replication, DNA repair, homologous recombination, RNA transport, protein processing, and several signaling and metabolism pathways, in which plant hormones signal transduction, MAPK signaling pathways, phosphatidylinositol signaling systems, and ABC transporters, as well as the metabolism of fatty acid; valine, leucine, and isoleucine biosynthesis; and cutin, suberine, and wax biosynthesis, were most significantly enriched. Taken together, the present study provides useful information and new insights into the functions of cotton WOX genes during somatic embryogenesis. The specific regulatory roles of some WOX genes in somatic embryogenesis are worthy of further functional research.

Plant stem cells under low oxygen: metabolic rewiring by phytoglobin underlies stem cell functionality.

Root growth in maize (Zea mays L.) is regulated by the activity of the quiescent center (QC) stem cells located within the root apical meristem. Here, we show that despite being highly hypoxic under normal oxygen tension, QC stem cells are vulnerable to hypoxic stress, which causes their degradation with subsequent inhibition of root growth. Under low oxygen, QC stem cells became depleted of starch and soluble sugars and exhibited reliance on glycolytic fermentation with the impairment of the TCA cycle through the depressed activity of several enzymes, including pyruvate dehydrogenase (PDH). This finding suggests that carbohydrate delivery from the shoot might be insufficient to meet the metabolic demand of QC stem cells during stress. Some metabolic changes characteristic of the hypoxic response in mature root cells were not observed in the QC. Hypoxia-responsive genes, such as PYRUVATE DECARBOXYLASE (PDC) and ALCOHOL DEHYDROGENASE (ADH), were not activated in response to hypoxia, despite an increase in ADH activity. Increases in phosphoenolpyruvate (PEP) with little change in steady-state levels of succinate were also atypical responses to low-oxygen tensions. Overexpression of PHYTOGLOBIN 1 (ZmPgb1.1) preserved the functionality of the QC stem cells during stress. The QC stem cell preservation was underpinned by extensive metabolic rewiring centered around activation of the TCA cycle and retention of carbohydrate storage products, denoting a more efficient energy production and diminished demand for carbohydrates under conditions where nutrient transport may be limiting. Overall, this study provides an overview of metabolic responses occurring in plant stem cells during oxygen deficiency.

Cytosolic isocitrate dehydrogenase regulates plant stem cell maintenance in response to nutrient deficiency.

WUSCHEL (WUS) and WUSCHEL-RELATED HOMEOBOX (WOX) proteins determine stem cell maintenance for continual plant growth and development under changing environmental conditions. Nutrient availability is an environmental factor that substantially controls plant growth and development. However, how plant stem cell homeostasis is regulated under nutrient deficiency remains to be elucidated. Here, we showed that cytosolic isocitrate dehydrogenase (ICDH) plays an important role in nutrient sensing of stem cells in Arabidopsis (Arabidopsis thaliana). Nutrient deficiency induced the cytoplasmic-to-nuclear translocation of cytosolic ICDH protein. ICDH can interact with WUS/WOX protein as a complex that further promotes WUS/WOX expression by binding to its promoter. WUS/WOX expression in the icdh-2 mutant was lower than that of wild-type plants under nutrient deficiency. Consistently, loss of ICDH function caused a more serious growth repression under nutrient deficiency that was independent of ICDH's catalytic activity. Therefore, cytosolic ICDH regulates stem cell homeostasis of plants in response to nutrient deficiency.

Clinical and Radiographic Evaluation of Locally Delivered Plant Stem Cells for Treatment of Periodontitis: Randomized Clinical Trial.

Periodontitis causes the destruction of soft and hard tissues. Stem cells have immense potential in regenerative cellular therapy. This clinical trial aimed to evaluate clinically and radiographically the effectiveness of the local application of Edelweiss stem cells as a nonsurgical treatment for stage III periodontitis. The trial included 40 periodontal pockets in participants who have stage III periodontitis with probing pocket depth (PPD) ≥5 mm and clinical attachment loss (CAL) ≥5 mm. Pockets were randomly divided into two groups Group 1: was given oral hygiene instruction, scaling, root planing, and subgingival application of plant stem cells on gel foam carrier after that a periodontal dressing was applied. The procedures were repeated after 2 weeks. Group 2: was treated only by scaling and root planing. Gingival index, CAL, and PPD were measured at baseline and 3 months' posttherapy. The radiographical evaluation was done by digital long-cone parallel periapical radiographs at baseline and 6 months posttherapy. Clinical parameters for both groups showed a statistically significant improvement. Regarding radiographic evaluation, there was a significant increase in bone density in favor of the study group. Locally applied Edelweiss stem cells can be considered a promising nonsurgical treatment modality for periodontal regeneration.

Comparisons between Plant and Animal Stem Cells Regarding Regeneration Potential and Application

Regeneration refers to the process by which organisms repair and replace lost tissues and organs. Regeneration is widespread in plants and animals; however, the regeneration capabilities of different species vary greatly. Stem cells form the basis for animal and plant regeneration. The essential developmental processes of animals and plants involve totipotent stem cells (fertilized eggs), which develop into pluripotent stem cells and unipotent stem cells. Stem cells and their metabolites are widely used in agriculture, animal husbandry, environmental protection, and regenerative medicine. In this review, we discuss the similarities and differences in animal and plant tissue regeneration, as well as the signaling pathways and key genes involved in the regulation of regeneration, to provide ideas for practical applications in agriculture and human organ regeneration and to expand the application of regeneration technology in the future.

Plant Stem Cells: The Source of Plant Vitality and Persistent Growth.

Plant Stem Cells: The Source of Plant Vitality and Persistent Growth.

Plant stem cell extract from Coffea canephora shows antioxidant, anti-inflammatory, and skin regenerative properties mediated by suppression of nuclear factor-κB.

Plant cell cultures have become a promising production platform of bioactive compounds for biomedical and cosmetic uses in the last decades. However, the success so far has been limited. The study aimed to evaluate the effectiveness of this unique biotechnology process to obtain a bioactive stem cell extract of Coffea canephora (SCECC) with antioxidant, anti-inflammatory, and regenerative properties. Total phenolic and flavonoid contents were determined in the SCECC by spectrophotometry. The chemical composition of the extracts was characterized by mass spectrometry. Antioxidant activity was evaluated using the colorimetric methods of free radical scavenging 2,2'-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) and the ferric reducing ability of plasma (FRAP). The anti-inflammatory activity was determined in lipopolysaccharide-stimulated RAW 264.7 macrophages through the production of superoxide anion (O2•-), nitric oxide (NO), tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and the activity of nuclear factor kappa B (NF-κB). Moreover, the ability of SCECC to stimulate the proliferation and migration of fibroblasts was assessed. Five compounds were tentatively identified, two flavonoids, two phenolic acids, and one sugar. High phenolic content and antioxidant activity were observed in the SCECC. SCECC promoted the proliferation and migration of fibroblasts and suppressed the pro-inflammatory mediators O2•-, NO, TNF-α, and IL-6 in a dose-dependent manner. Moreover, SCECC inhibited the NF-κB transcription factor. Therefore, we obtained evidence that the extract from C. canephora stem cells can be used as a natural agent against skin damage. Hence, it could be of interest in cosmetics for preventing skin aging.

Genome-Wide Identification and Expression Profile Analysis of the WUSCHEL-Related Homeobox (WOX) Genes in Woodland Strawberry (Fragaria vesca)

The WUSCHEL-related homeobox (WOX) is a unique transcription factor family belonging to plants. Its members play important roles in regulation of plant stem cell division and differentiation or dynamic balance of the organ development. In this study, 16 Fragaria vesca WOX members (FvWOXs) were identified in the woodland strawberry (Fragaria vesca) genome. According to the phylogenetic analysis, FvWOX proteins can be classified into three clades: the ancient clade, the WUS clade and the intermediate clade. The gene structure and protein motif analysis showed that FvWOXs are highly conserved to each other in their respective clades. Chromosome location analysis revealed that FvWOXs are unevenly distributed in the Fragaria vesca chromosomes. Expression analysis showed that FvWOX genes are widely expressed in various tissues of Fragaria vesca. Moreover, when treated with 6-benzylaminopurine (6-BA) or gibberellin (GA3), expression level changes of the genes highly expressed in crowns were detected at 48 h after treatment. The subcellular localization of FvWUSb was determined in tobacco leaves, indicating that the protein is located in the nucleus. This study enlarged our recognition about the WUSCHEL-related homeobox genes in Fragaria vesca, and laid a foundation for further researches about this gene family in strawberry.

The plant stem-cell niche and pluripotency: 15 years of an epigenetic perspective.

Pluripotent stem-cells are slowly dividing cells giving rise to daughter cells that can either differentiate to new tissues and organs, or remain stem-cells. In plants, stem-cells are located in specific niches of the shoot and root apical meristems (SAMs and RAMs). After ablation of stem-cell niches, pluripotent meristematic cells can establish new stem-cells, whereas the removal of the whole meristem destructs the regeneration process. In tissue cultures, after detached plant organs are transferred to rooting or callus induction medium (G5 or CIM), vasculature-associated pluripotent cells (VPCs) immediately start proliferation to form adventitious roots or callus, respectively, while other cell types of the organ explants basically play no part in the process. Hence, in contrast to the widely-held assumption that all plant cells have the ability to reproduce a complete organism, only few cell types are pluripotent in practice, raising the question how pluripotent stem-cells differ from differentiated cells. It is now clear that, in addition to gene regulatory networks of pluripotency factors and phytohormone signaling, epigenetics play a crucial role in initiation, maintenance and determination of plant stem-cells. Although, more and more epigenetic regulators have been shown to control plant stem-cell fate, only a few studies demonstrate how they are recruited and how they change the chromatin structure and transcriptional regulation of pluripotency factors. Here, we highlight recent breakthroughs but also revisited classical studies of epigenetic regulation and chromatin dynamics of plant stem-cells and their pluripotent precursor-cells, and point out open questions and future directions.

Liposomal stem cell extract formulation from Coffea canephora shows outstanding anti-inflammatory activity, increased tissue repair, neocollagenesis and neoangiogenesis.

Coffea canephora plant stem cells can have bioactive compounds with tissue repairing and anti-inflammatory action. This study aimed to develop a liposomal stem cell extract formulation obtained from the leaves of C. canephora (LSCECC) and to investigate its capacity to contribute to the dynamic mechanisms of tissue repair. The liposome cream was developed and characterized through the dynamic light scattering technique, atomic force microscopy, and transmission electron microscopy. The excisional full-thickness skin wound model was used and daily topically treated with the LSCECC formulation or vehicle control. On days 2, 7, 14, and 21 after wounding, five rats from each group were euthanized and the rates of wound closure and re-epithelialization were evaluated using biochemical and histological tests. LSCECC resulted in faster re-epithelialization exhibiting a significant reduction in wound area of 36.4, 42.4, and 87.5% after 7, 10, and 14days, respectively, when compared to vehicle control. LSCECC treated wounds exhibited an increase in granular tissue and a proper inflammatory response mediated by the reduction of pro-inflammatory cytokines like TNF-α and IL-6 and an increase of IL-10. Furthermore, wounds treated with LSCECC showed an increase in the deposition and organization of collagen fibers at the wound site and improved scar tissue quality due to the increase in transforming growth factor-beta and vascular endothelial growth factor. Our data showed that LSCECC improves wound healing, the formation of extracellular matrix, modulates inflammatory response, and promotes neovascularization being consider a promising bioactive extract to promote and support healthy skin. The graphical presents the action of LSCECC in all four phases of wound healing and tissue repair. The LSCECC can reduce the inflammatory infiltrate in the inflammatory phase by decreasing the pro-inflammatory cytokines like IL-6 and TNF-α, in addition to maintaining this modulation through lesser activation and recruitment of macrophages. The LSCECC can also increase the release of IL-10, an anti-inflammatory cytokine, decreasing local edema. The increase in VEGF provides neovascularization and the supply of nutrients to newly repaired tissue. Finally, signaling via TGF-β increases the production and organization of collagen fibers in the remodeling phase.

Calcium signaling in coordinating plant development, circadian oscillations and environmental stress responses in plants

Calcium (Ca 2+ ) is an intracellular second messenger involved in many signal transduction pathways in plants. The perception of environmental and internal cues leads to alterations in the cytosolic Ca 2+ signatures which translate into changes in gene expression and cellular functions. Herein, we review the novel roles of Ca 2+ signalling in coordinating plant stem cell niche homeostasis for root and shoot development. We also summarize the regulatory networks between Ca 2+ signalling and other plant signalling pathways which commence into activation or repression of genes involved in regulating vegetative to reproductive phase transition and light-mediated plant growth responses. The possible functions of Ca 2+ in the input pathway as a second messenger, external stimuli and the output of the clock regulating the rhythmicity of the plant circadian system are being reviewed. Additionally, we have also highlighted the new insights into the roles of Ca 2+ signalling components in the perception and regulation of abiotic/ biotic stress responses in plants. • Ca 2+ signalling integrates several signalling pathways in response to various environmental stimuli in plants. • Nuclear Ca 2+ signalling correlates cell activity, plant development, developmental phase transition, and hormonal homeostasis. • Ca 2+ signalling plays crucial roles in coordinating phosphorylation-mediated photoacclimation processes in plants. • Cytosolic-free Ca 2+ oscillations regulate circadian clocks in plants through Ca 2+ dependent calcium binding proteins. • Spatiotemporal regulation of Ca 2+ binding proteins couple biotic/abiotic stress responses contributing towards plant adaptation.

Cell- and noncell-autonomous AUXIN RESPONSE FACTOR3 controls meristem proliferation and phyllotactic patterns.

In cell-cell communication, noncell-autonomous transcription factors play vital roles in controlling plant stem cell fate. We previously reported that AUXIN RESPONSE FACTOR3 (ARF3), a member of the ARF family with critical roles in floral meristem maintenance and determinacy, has a distinct accumulation pattern that differs from the expression domain of its encoding gene in the shoot apical meristem (SAM). However, the biological meaning of this difference is obscure. Here, we demonstrate that ARF3 expression in Arabidopsis (Arabidopsis thaliana) is mainly activated at the periphery of the SAM by auxin where ARF3 cell autonomously regulates the expression of meristem-organ boundary-specific genes, such as CUP-SHAPED COTYLEDON1-3 (CUC1-3), BLADE ON PETIOLE1-2 (BOP1-2), and TARGETS UNDER ETTIN CONTROL3 (TEC3) to regulate the arrangement of organs in regular pattern, a phenomenon referred to as phyllotaxis. We also show that ARF3 is translocated into the organizing center where it represses cytokinin activity and WUSCHEL expression to regulate meristem activity noncell-autonomously. Therefore, ARF3 acts as a molecular link that mediates the interaction of auxin and cytokinin signaling in the SAM while coordinating the balance between meristem maintenance and organogenesis. Our findings reveal an ARF3-mediated coordination mechanism through cell-cell communication in dynamic SAM maintenance.

Uncovering a Phenomenon of Active Hormone Transcriptional Regulation during Early Somatic Embryogenesis in Medicago sativa.

Somatic embryogenesis (SE) is a developmental process in which somatic cells undergo dedifferentiation to become plant stem cells, and redifferentiation to become a whole embryo. SE is a prerequisite for molecular breeding and is an excellent platform to study cell development in the majority of plant species. However, the molecular mechanism involved in M. sativa somatic embryonic induction, embryonic and maturation is unclear. This study was designed to examine the differentially expressed genes (DEGs) and miRNA roles during somatic embryonic induction, embryonic and maturation. The cut cotyledon (ICE), non-embryogenic callus (NEC), embryogenic callus (EC) and cotyledon embryo (CE) were selected for transcriptome and small RNA sequencing. The results showed that 17,251 DEGs, and 177 known and 110 novel miRNAs families were involved in embryonic induction (ICE to NEC), embryonic (NEC to EC), and maturation (EC to CE). Expression patterns and functional classification analysis showed several novel genes and miRNAs involved in SE. Moreover, embryonic induction is an active process of molecular regulation, and hormonal signal transduction related to pathways involved in the whole SE. Finally, a miRNA–target interaction network was proposed during M. sativa SE. This study provides novel perspectives to comprehend the molecular mechanisms in M. sativa SE.

Establishment of Stem Cell-like Cells of Sida hermaphrodita (L.) Rusby from Explants Containing Cambial Meristems.

The in vitro cultures of plant stem cells and stem cell-like cells can be established from tissues containing meristematic cells. Chemical compounds—as well as their production potential—is among the emerging topics of plant biotechnology. We induced the callus cell biomass growth and characterized the parameters indicating the presence of stem cells or stem cell-like cells. Four types of explants (stem, petiole, leaf, root) from Sida hermaphrodita (L.) Rusby and various combinations of auxins and cytokinins were tested for initiation of callus, growth of sub-cultivated callus biomass, and establishment of stem cells or stem cell-like cells. Induction of callus and its growth parameters were significantly affected both by the explant type and the combination of used plant growth hormones and regulators. The responsibility for callus initiation and growth was the highest in stem-derived explants containing cambial meristematic cells. Growth parameters of callus biomass and specific characteristics of vacuoles confirmed the presence of stem cells or stem cell-like cells in sub-cultivated callus cell biomass. Establishment of in vitro stem cell or stem cell-like cell cultures in S. hermaphrodita can lead to the development of various applications of in vitro cultivation systems as well as alternative applications of this crop.

Construction strategies and prospect of the Global Medicinal Plant Stem Cell Bank

Medicinal plant stem cells are separated from the meristem and vascular cambium of medicinal plants, which can produce active components for preventing and treating diseases and improving body physical functions under certain conditions. Medicinal plant stem cells come from a broad category of medicinal plants, including ethnic medicinal plants, folk medicinal plants, original plants of health products, vegetables, fruits, and other potential medicinal plants. At present, the techniques for the isolation, identification, preservation and culture of medicinal plant stem cells have become increasingly mature, and the mechanism of stem cell differentiation, growth and regulation of secondary metabolites has been studied in depth. Medicinal plant stem cells have a broad application prospect in medicine, health food, food and medical beauty products. As a strategic resource, the construction of the "Global Medicinal Plant Stem Cell Bank" was first proposed to preserve various kinds of medicinal plant resources in the world, and it will go global relying on the internationalization strategy of traditional Chinese medicine. The bank should follow safety, environmental protection, advanced and practical design principles. The main construction contents include the original plant bank, stem cell bank, component resource bank, gene bank, database and resource sharing system, with genetic and data resources incorporated into the scope of protection and utilization. The bank will establish a new strategy for medicinal plant resources protection and regeneration, and provide a new resource for natural products drug discovery and a technology sharing platform for various medicinal plant stem cells. As a resource treasury, a source of innovative technologies and a center of cooperation, it will become the core driving force of the global medicinal plant stem cell industry.

Cell Fate Decisions Within the Vascular Cambium-Initiating Wood and Bast Formation.

Precise coordination of cell fate decisions is a hallmark of multicellular organisms. Especially in tissues with non-stereotypic anatomies, dynamic communication between developing cells is vital for ensuring functional tissue organization. Radial plant growth is driven by a plant stem cell niche known as vascular cambium, usually strictly producing secondary xylem (wood) inward and secondary phloem (bast) outward, two important structures serving as much-needed CO2 depositories and building materials. Because of its bidirectional nature and its developmental plasticity, the vascular cambium serves as an instructive paradigm for investigating principles of tissue patterning. Although genes and hormones involved in xylem and phloem formation have been identified, we have a yet incomplete picture of the initial steps of cell fate transitions of stem cell daughters into xylem and phloem progenitors. In this mini-review perspective, we describe two possible scenarios of cell fate decisions based on the current knowledge about gene regulatory networks and how cellular environments are established. In addition, we point out further possible research directions.

Dynamic Changes in Reactive Oxygen Species in the Shoot Apex Contribute to Stem Cell Death in Arabidopsis thaliana.

In monocarpic plants, stem cells are fated to die. However, the potential mechanism of stem cell death has remained elusive. Here, we reveal that the levels of two forms of reactive oxygen species (ROS), superoxide anion free radical () and hydrogen peroxide (H2O2), show dynamic changes in the shoot apex during the plant life cycle of Arabidopsis thaliana. We found that the level of decreased and disappeared at four weeks after bolting (WAB), while H2O2 appeared at 3 WAB and showed a burst at 5 WAB. The timing of dynamic changes in and H2O2 was delayed for approximately three weeks in clv3-2, which has a longer lifespan. Moreover, exogenous application of H2O2 inhibited the expression of the stem cell determinant WUSCHEL (WUS) and promoted the expression of the developmentally programmed cell death (dPCD) marker gene ORESARA 1 (ORE1). These results indicate that H2O2 triggers an important signal inducing dPCD in stem cells. Given that plays roles in maintaining WUS expression and stem cell activity, we speculate that the dynamic shift from to H2O2 in the shoot apex results in stem cell death. Our findings provide novel insights for understanding ROS-mediated regulation during plant stem cell death.

Dynamic evolution of small signalling peptide compensation in plant stem cell control

Gene duplications are a hallmark of plant genome evolution and a foundation for genetic interactions that shape phenotypic diversity1-5. Compensation is a major form of paralogue interaction6-8 but how compensation relationships change as allelic variation accumulates is unknown. Here we leveraged genomics and genome editing across the Solanaceae family to capture the evolution of compensating paralogues. Mutations in the stem cell regulator CLV3 cause floral organs to overproliferate in many plants9-11. In tomato, this phenotype is partially suppressed by transcriptional upregulation of a closely related paralogue12. Tobacco lost this paralogue, resulting in no compensation and extreme clv3 phenotypes. Strikingly, the paralogues of petunia and groundcherry nearly completely suppress clv3, indicating a potent ancestral state of compensation. Cross-species transgenic complementation analyses show that this potent compensation partially degenerated in tomato due to a single amino acid change in the paralogue and cis-regulatory variation that limits its transcriptional upregulation. Our findings show how genetic interactions are remodelled following duplications and suggest that dynamic paralogue evolution is widespread over short time scales and impacts phenotypic variation from natural and engineered mutations.

Abscisic acid switches cell division modes of asymmetric cell division and symmetric cell division in stem cells of protonemal filaments in the moss Physcomitrium patens.

Multicellular organisms regulate cell numbers and cell fate by using asymmetric cell division (ACD) and symmetric cell division (SCD) during their development and to adapt to unfavorable environmental conditions. A stem cell self-renews and generates differentiated cells. In plants, various types of cells are produced by ACD or SCD; however, the molecular mechanisms of ACD or SCD and the cell division mode switch are largely unknown. The moss Physcomitrium (Physcomitrella) patens is a suitable model to study plant stem cells due to its simple anatomy. Here, we report the cell division mode switch induced by abscisic acid (ABA) in P. patens. ABA is synthesized in response to abiotic stresses and induces round-shape cells, called brood cells, from cylindrical protonemal cells. Although two daughter cells with distinct sizes were produced by ACD in a protonemal stem cell on ABA-free media, the sizes of two daughter cells became similar with ABA treatment. Actin microfilaments were spatially localized on the apices of apical stem cells in protonemata on ABA-free media, but the polar accumulation was lost under the condition of ABA treatment. Moreover, ABA treatment conferred an identical cell fate to the daughter cells in terms of cell division activity. Collectively, the results indicate ABA may suppress the ACD characteristics but evoke SCD in cells. We also noticed that ABA-induced brood cells not only self-renewed but regenerated protonemal cells when ABA was removed from the media, suggesting that brood cells are novel stem cells that are induced by environmental signals in P. patens.