How do plants regenerate

One of the main cause of controversies is the mixing of the genetic and developmental biology viewpoints of cellular differentiation. All multicellular organism is characterized by a given number of genes, but none of their cells express all but only a portion of them and as such can be considered as genetically differentiated.

In consequence, a genetically fully dedifferentiated cell would express all the genes coded in the genome. Such cell obviously does not exist. Even the zygote having the highest developmental potency have a well-defined gene expression pattern Sprunck et al. From a developmental biology perspective, the zygote is the origo of the cell differentiation process.

Despite their high developmental potencies, stem cells are also differentiated: the specific cells of the shoot or root meristems have well defined gene expression patterns depending on meristem identity factors e. Stem cells have the function to sense and respond to stem cell niche signals, express cell fate determinants, segregate those into specific cellular regions and then divide asymmetrically to ensure self-renewal and the production of progenitor cells.

These are specific functions that require the action of a specific set of genes, what was ensured by cell differentiation yet allowing a high developmental potency. Dedifferentiation, similarly, to differentiation, is a transient process that governs cells from one differentiated state to another. A cell can only be regarded as differentiated or dedifferentiated in relation to another one, namely to the one it derived from. As differentiation results in various specialized cell types, dedifferentiation, the opposite process, does the same.

In the terminology of plant cell and tissue culture, however, dedifferentiation is collectively used for all processes resulting in increased developmental potencies Figure 1. It is not surprising, if we consider that cell lineages are less important in plant than in animal development and plant somatic cells can be more easily reprogrammed Gaillochet and Lohmann, Callus formation can rather be considered as a type of transdifferentiation Sugimoto et al.

Recent transcriptomic data support the view that calli can be formed via various initial pathways which converge on the same gene regulatory network coordinating stress, hormone, and developmental responses. Nevertheless, the gene sets expressed in various types of calli only partly overlap.

Auxin-induced incubation on callus-induction medium, CIM; Valvekens et al. This type of callus was shown to express root meristem pluripotency markers in a more-or-less correct temporal and spatial organization Sugimoto et al. Similarly, to lateral root primordia LRPs , auxin-induced callus formation initiates in pericycle cell-like stem cells and there is no requirement for preceding dedifferentiation of differentiated somatic cells Atta et al.

This callus type at the early developmental phase might be considered as an over proliferating lateral root primordium. Most remarkably, these characteristics of the calli were independent of the type of the explant either root or aerial organs excluding also the possibility of dedifferentiation in a strict sense within cell lineage.

Table 1. Common up-regulated genes in various auxin-induced callus tissues see Figure 2B for details. In two independent experiments, and genes were found to be regulated, respectively, during auxin-induced callus formation from root explants after the fourth day of culture Che et al.

Only of the genes showed an overlap in the two studies. Considering callus formation from different explants, seedling roots were compared to aerial parts hypocotyls and cotyledons by Xu et al.

There were upregulated genes that were present in both datasets, while gene was upregulated only in the aerial tissue-derived calli and in the root-derived ones Xu et al. Comparison of these data sets to those obtained from auxin-induced leaf- Lee et al. The above numbers indicate that the type of explant and the other experimental conditions have considerable effects on the number and specificity of genes that are regulated during auxin-induced callus development.

Figure 2. The overlaps among various gene expression data sets obtained form analyses of auxin-induced calli. A Comparison of up-regulated genes in root and aerial explants hypocotyl and cotyledon at the time of initial callus formation at 4 days on callus-induction medium in relation to the initial explant the data were obtained from the experiments of Xu et al. B Comparison of up-regulated genes in root only the genes that were found to be up-regulated by both Xu et al.

In addition to auxin, callus may also form in response to other hormones or wounding for review, Ikeuchi et al. Wounding up-regulates cytokinin biosynthesis and signaling, leading to the activation of cell proliferation and callus formation Iwase et al. Interestingly, endogenous auxin accumulation or activation of auxin response could not be detected at the wound site and the auxin signaling mutant solitary root had no defects in wound-induced callus formation Iwase et al.

Therefore, exogenous auxin and wounding triggers callus formation in different ways. Iwase et al. There was a significant gene expression overlap among the WIND1- and auxin-induced calli genes while genes were upregulated only in response to WIND1 but not for 2,4-D and genes were regulated in the opposite way Iwase et al. The above comparison of gene expression data based on a few time points and inducing agents allows only limited conclusions about the genetic nature of callus tissues in general.

Recently, Ikeuchi and co-workers followed a more straightforward approach to delineate a gene regulatory network underlying callus formation. They established regulatory relationships among transcription factors and 48 promoters using a systematic yeast one-hybrid screening approach.

It was found that the auxin- and wound-induced callus formation pathways converge on the same gene regulation network, the core elements of which are the PLT3, ESR1, and HSFB1 transcription factors Ikeuchi et al.

This study also highlights that specialized callus functions including developmental potencies rely on the cooperative action of defined sets of transcription factors and not merely on the loss of differentiated functions.

Gain- or loss-of-function of many cell cycle or developmental regulators might also result in callus formation Ikeuchi et al. Whether these pathways overriding cell differentiation also converge on the above gene regulatory node is an interesting question to be investigated.

Furthermore, it also needs to be investigated how genetically homogeneous a callus tissue is? Callus seems to be rather heterogenous during its formation e. Only certain cells of calli but not all of them can be involved in organ regeneration or embryogenesis, supporting a heterogenous organization. It must be emphasized here that developmental potency is a cellular term and, therefore, a callus cannot be pluri- or totipotent but can have pluri- or totipotent cells see also further.

Long-term callus cultures become more and more homogenous often with parallel loss of developmental potencies, especially in liquid culture cell suspension cultures. In addition to callus formation, protoplast isolation is also strongly believed to be associated with plant cell dedifferentiation Zhao et al.

During protoplast isolation, the tissues are wounded, the cells are exposed to cell wall-digesting enzymes, separated from each other, and released into an artificial medium. As a result, the stressed cells lose their developmental and hormonal constrains and differentiated functions Williams et al. These events as well as the associated gene expression changes are rather similar to those characterizing cellular senescence Damri et al. In agreement, these protoplasts die in a hormone-free medium.

It is hypothesized that senescing leaf cells go through dedifferentiation similarly to isolated protoplasts Damri et al. However, in the absence of proper developmental signals, protoplast-derived cells cannot be reverted to mesophyll cells; they develop to elongated or proliferating parenchymatic callus cells in the presence of auxin or auxin and cytokinin, respectively Grafi, The continuous presence of the two hormones finally leads to the formation of callus tissue.

The formed calli express 18 transcription factors also expressed during lateral root initiation Chupeau et al. This supports the view that auxin-induced calli have a well-defined gene expression pattern irrespective of the explant and further indicate that callus formation from protoplast-derived cells is not a proof of their dedifferentiation.

Rather, senescing leaf cells respond to the artificial hormone treatment with proliferation. Overproliferation of the protoplast-derived cells results in callus formation in the continuous presence of exogenous or endogenous, in habituated cultures auxin and cytokinin.

Grafi and co-workers Grafi, ; Damri et al. This is, however, a very loose interpretation of stem cell-ness and developmental potency. Callus tissues of various origin can express a wide variety of genes which discriminate them, especially at the early phases of their development.

Despite the fact that calli can be formed via various initial pathways, established callus tissues seem to be characterized by a network of transcription factors that facilitate cell fate switch and regeneration. Based on this, the callus is a transient tissue, similarly to the blastema of animals, but can be long maintained under artificial conditions.

In the first and stricter sense, only zygotes or one-celled embryos are totipotent. In the second and wider sense cells which can develop to all the various cell types of an organism but under different condition each, are also totipotent. Based on this second definition, embryonic animal stem cells that can produce a wide range but not all!

However, plant regeneration from a totipotent cell must fulfill two main criteria: i it must be initiated in an individual cell since totipotency is a cellular term Condic, ; ii it must proceed autonomously as a single process Verdeil et al. Whole plants are regenerated from in vitro cultured plant cells either directly or indirectly intervened by callus formation via organogenesis or somatic embryogenesis.

These processes are not autonomous but needs to be induced! Therefore, one could say, at best, that plant cells can re gain totipotency but they are not totipotent per se. Plant regeneration via several steps obviously does not fulfill the criterium of autonomous development.

For example, plant regeneration via organogenesis includes at least two stages: either shoot or root is regenerated from the initial cell and a second induction step is required to regenerate the missing plant part.

Not the same cell is forming the shoot and the root! The direct de novo formation of stem cells from single differentiated somatic cells is widely believed to take place but hardly evidenced Gaillochet and Lohmann, ; Perez-Garcia and Moreno-Risueno, Root formation on leaf explants detached from Arabidopsis plants might represent an example Liu et al.

The capability for de novo meristem formation is mostly confined to callus tissues Perez-Garcia and Moreno-Risueno, During these regeneration processes, appropriate hormonal gradients are established in the callus tissue leading to stem cell niche formation and stem cell differentiation Perez-Garcia and Moreno-Risueno, Therefore, the new meristem does not have a clear single cell origin. Moreover, only the newly formed stem cells but not all cells of the callus tissue can be regarded as pluripotent.

Somatic embryogenesis is believed to be the definitive proof for the totipotency of somatic plant cells. Indeed, single cells forming embryos embryogenic cells are totipotent by definition since embryos can autonomously develop to whole plants. If all plant cells are totipotent, all plant cells could be able to form somatic embryos.

This is obviously not the case. Although somatic embryogenesis is prevalent, it is confined to defined genotypes, developmental states, and explants. Similarly, to organogenesis, somatic embryogenesis needs induction.

This means that although certain somatic cells might re gain totipotency under appropriate conditions, they are not totipotent per se. Furthermore, somatic embryo formation not necessarily involves neither dedifferentiated somatic nor totipotent cells.

Such as callus formation and organogenesis, initiation of embryos from cells surrounding the veins often referred as procambial cells was frequently observed Guzzo et al. In carrot, somatic embryo formation could be tracked back to single cells or small cell clusters of perivascular origin in the fresh liquid culture of hypocotyl explants Schmidt et al. In the presence of auxin 2,4-D , these cells form proembryogenic cell masses PEMs as a transitional stage toward embryogenesis.

It is a second signal, the removal of auxin, that triggers embryo formation from PEMs de Vries et al. These series of events question the direct autonomous development of somatic embryos from the single embryogenic cells. However, PEMs themselves might be regarded as overproliferating somatic embryos losing their organization for review, Dudits et al.

Recent observations indicate that indirect embryogenesis progresses on surfaces of embryogenic calli via the reorganization of cell clusters instead of developing from single totipotent cells for review, Su and Zhang, Several cellular and molecular steps of embryo formation have been revealed in the case of embryogenic Arabidopsis calli Su et al.

The following model could be established using fluorescent gene expression markers and confocal laser scanning microscopy Su et al. Embryogenic calli form in the 2,4-D-containing culture medium. Momoko Ikeuchi Momoko Ikeuchi. This site. Google Scholar. Yoichi Ogawa , Yoichi Ogawa. Akira Iwase , Akira Iwase. Keiko Sugimoto Author and article information.

Yoichi Ogawa. Akira Iwase. Competing interests The authors declare no competing or financial interests. Online Issn: Published by The Company of Biologists Ltd. Development 9 : — Cite Icon Cite. View large Download slide. Molecular physiology of adventitious root formation in Petunia hybrida cuttings: involvement of wound response and primary metabolism. Genes involved in organ separation in Arabidopsis: an analysis of the cup-shaped cotyledon mutant.

Role of cytokinin and auxin in shaping root architecture: regulating vascular differentiation, lateral root initiation, root apical dominance and root gravitropism. Improved tissue culture response of an elite maize inbred through backcross breeding, and identification of chromosomal regions important for regeneration by RFLP analysis.

Spatially selective hormonal control of RAP2. Pluripotency of Arabidopsis xylem pericycle underlies shoot regeneration from root and hypocotyl explants grown in vitro. Factors effecting adventitious shoot regeneration from leaf explants of quince Cydonia oblonga. Anatomical and biochemical events during in vitro rooting of microcuttings from juvenile and mature phases of chestnut. Overexpression of Arabidopsis ESR1 induces initiation of shoot regeneration. Age and physiological condition of donor plants affect in vitro morphogenesis in leaf explants of Passiflora edulis f.

Ben Amer. Developmental events and shoot apical meristem gene expression patterns during shoot development in Arabidopsis thaliana. Incipient stem cell niche conversion in tissue culture: using a systems approach to probe early events in WUSCHEL-dependent conversion of lateral root primordia into shoot meristems.

Global and hormone-induced gene expression changes during shoot development in Arabidopsis. Gene expression programs during shoot, root, and callus development in Arabidopsis tissue culture. Developmental steps in acquiring competence for shoot development in Arabidopsis tissue culture. Characterization of the early events leading to totipotency in an Arabidopsis protoplast liquid culture by temporal transcript profiling. When stress and development go hand in hand: main hormonal controls of adventitious rooting in cuttings.

High efficiency plant regeneration from cotyledons of watermelon Citrullus vulgaris Schrad. Flores Berrios. The transcription factor FUSCA3 controls developmental timing in Arabidopsis through the hormones gibberellin and abscisic acid. Ghasemi Bezdi. Effects of genotype, explant type and nutrient medium components on canola Brassica napus L.

Extensive modulation of the transcription factor transcriptome during somatic embryogenesis in Arabidopsis thaliana.

Pattern formation during de novo assembly of the Arabidopsis shoot meristem. Reprogramming of H3K27me3 is critical for acquisition of pluripotency from cultured Arabidopsis tissues. Regeneration of transgenic plants expressing the GFP gene from rape cotyledonary and leaf explants: effects of the genotype and ABA.

Levels of endogenous abscisic acid and indoleacetic acid influence shoot organogenesis in callus cultures of rice subjected to osmotic stress. Establishment of a reproducible tissue culture system for the induction of Arabidopsis somatic embryos. Stress-induced somatic embryogenesis in vegetative tissues of Arabidopsis thaliana. Control of plant cell differentiation by histone modification and DNA methylation.

Physcomitrella cyclin-dependent kinase A links cell cycle reactivation to other cellular changes during reprogramming of leaf cells. Arabidopsis WIND1 induces callus formation in rapeseed, tomato, and tobacco. WIND1-based acquisition of regeneration competency in Arabidopsis and rapeseed. Stress induced somatic embryogenesis in carrot and its application to synthetic seed production.

Shoot regeneration from stem and leaf explants of Dendranthema grandiflora Tzvelev syn. Chrysanthemum morifolium Ramat. Life without a cell membrane: regeneration of protoplasts from disintegrated cells of the marine green alga Bryopsis plumosa.

Developmental plasticity of glandular trichomes into somatic embryogenesis in Tilia amurensis. Characterization and mapping of a gene controlling shoot regeneration in tomato. Dynamic regulation of H3K27 trimethylation during Arabidopsis differentiation. The histone deacetylase inhibitor trichostatin a promotes totipotency in the male gametophyte. Auxin polar transport is essential for the establishment of bilateral symmetry during early plant embryogenesis.

WOX11 and 12 are involved in the first-step cell fate transition during de novo root organogenesis in Arabidopsis. The tomato Solanum lycopersicum cv. Micro-Tom natural genetic variation Rg1 and the DELLA mutant procera control the competence necessary to form adventitious roots and shoots. Improved efficiency of somatic embryogenesis and plant regeneration in tissue cultures of maize Zea mays L. Isolation of an embryogenic line from non-embryogenic Brassica napus cv.

Westar through microspore embryogenesis. Androgenic switch: an example of plant embryogenesis from the male gametophyte perspective. A developmental framework for graft formation and vascular reconnection in Arabidopsis thaliana. CUC2 as an early marker for regeneration competence in Arabidopsis root explants. Adventitious shoot regeneration and micropropagation of Chirita flavimaculata W. Wang, C. The shoot regeneration capacity of excised Arabidopsis cotyledons is established during the initial hours after injury and is modulated by a complex genetic network of light signalling.

Phytochrome-mediated regulation of cell division and growth during regeneration and sporeling development in the liverwort Marchantia polymorpha. Isolation of a rice regeneration quantitative trait loci gene and its application to transformation systems. Organogenic responses in tissue culture of srd mutants of Arabidopsis thaliana.

Adventitious rooting declines with the vegetative to reproductive switch and involves a changed auxin homeostasis. Microsurgical and laser ablation analysis of interactions between the zones and layers of the tomato shoot apical meristem. Organ regeneration does not require a functional stem cell niche in plants. Chemical regulation of growth and organ formation in plant tissues cultured in vitro.

Skip to main content Thank you for visiting nature. Atom RSS Feed Plant regeneration Definition Plant regeneration refers to the physiological renewal, repair, or replacement of tissue in plants. Research 02 October Open Access The genetic framework of shoot regeneration in Arabidopsis comprises master regulators and conditional fine-tuning factors Robin Lardon et al.

Communications Biology 3 , Nature Plants 6 , Research 03 August Local auxin biosynthesis is required for root regeneration after wounding When root stem cells are destroyed, the remaining neighbour cells accumulate auxin to prepare for regeneration.

Nature Plants 1 , It may also prove to be medically relevant if it turns out that the process behind tissue regeneration in plants is related to the regeneration of body structures in animals. Go directly to: Content Search box Breadcrumb. Stem cells Extensive medical research has been done on retinoblastoma protein in its role as a tumour suppressor and an inhibitor of cell division. Twitter Whatsapp Linkedin Email.