Warm Temperature Promotes Shoot Regeneration in Arabidopsis thaliana

The roles of epigenetic regulators in plant regeneration: Exploring patterns amidst complex conditions

Plants possess remarkable capability to regenerate upon tissue damage or optimal environmental stimuli. This ability not only serves as a crucial strategy for immobile plants to survive through harsh environments, but also made numerous modern plant improvements techniques possible. At the cellular level, this biological process involves dynamic changes in gene expression that redirect cell fate transitions. It is increasingly recognized that chromatin epigenetic modifications, both activating and repressive, intricately interact to regulate this process. Moreover, the outcomes of epigenetic regulation on regeneration are influenced by factors such as the differences in regenerative plant species and donor tissue types, as well as the concentration and timing of hormone treatments. In this review, we focus on several well-characterized epigenetic modifications and their regulatory roles in the expression of widely studied morphogenic regulators, aiming to enhance our understanding of the mechanisms by which epigenetic modifications govern plant regeneration.

Injection-based hairy root induction and plant regeneration techniques in Brassicaceae

BACKGROUND

Hairy roots constitute a valuable tissue culture system for species that are difficult to propagate through conventional seed-based methods. Moreover, the generation of transgenic plants derived from hairy roots can be facilitated by employing carefully designed hormone-containing media.

RESULTS

We initiated hairy root formation in the rare crucifer species Asperuginoides axillaris via an injection-based protocol using the Agrobacterium strain C58C1 harboring a hairy root-inducing (Ri) plasmid and successfully regenerated plants from established hairy root lines. Our study confirms the genetic stability of both hairy roots and their derived regenerants and highlights their utility as a permanent source of mitotic chromosomes for cytogenetic investigations. Additionally, we have developed an effective embryo rescue protocol to circumvent seed dormancy issues in A. axillaris seeds. By using inflorescence primary stems of Arabidopsis thaliana and Cardamine hirsuta as starting material, we also established hairy root lines that were subsequently used for regeneration studies.

CONCLUSION

We developed efficient hairy root transformation and regeneration protocols for various crucifers, namely A. axillaris, A. thaliana, and C. hirsuta. Hairy roots and derived regenerants can serve as a continuous source of plant material for molecular and cytogenetic analyses.

Plant grafting: Molecular mechanisms and applications

People have grafted plants since antiquity for propagation, to increase yields, and to improve stress tolerance. This cutting and joining of tissues activates an incredible regenerative ability as different plants fuse and grow as one. For over a hundred years, people have studied the scientific basis for how plants graft. Today, new techniques and a deepening knowledge of the molecular basis for graft formation have allowed a range of previously ungraftable combinations to emerge. Here, we review recent developments in our understanding of graft formation, including the attachment and vascular formation steps. We analyze why plants graft and how biotic and abiotic factors influence successful grafting. We also discuss the ability and inability of plants to graft, and how grafting has transformed both horticulture and fundamental plant science. As our knowledge about plant grafting improves, new combinations and techniques will emerge to allow an expanded use of grafting for horticultural applications and to address fundamental research questions.

Illuminating the path to shoot meristem regeneration: Molecular insights into reprogramming cells into stem cells

Plant cells possess the ability to dedifferentiate and reprogram into stem cell-like populations, enabling the regeneration of new organs. However, the maintenance of stem cells relies on specialized microenvironments composed of distinct cell populations with specific functions. Consequently, the regeneration process necessitates the orchestrated regulation of multiple pathways across diverse cellular populations. One crucial pathway involves the transcription factor WUSCHEL HOMEOBOX 5 (WOX5), which plays a pivotal role in reprogramming cells into stem cells and promoting their conversion into shoot meristems through WUSCHEL (WUS). Additionally, cell and tissue mechanics, including cell wall modifications and mechanical stress, critically contribute to de novo shoot organogenesis by regulating polar auxin transport. Furthermore, light signaling emerges as a key regulator of plant regeneration, directly influencing expression of meristem genes and potentially influencing aforementioned pathways as well.

Morphological and physio-biochemical responses under heat stress in cotton: Overview

Cotton is an important cash crop in addition to being a fiber commodity, and it plays an essential part in the economies of numerous nations. High temperature is the most critical element affecting its yield from fertilization to harvest. The optimal temperature for root formation is 30 C -35 °C; however, root development ends around 40 °C. Increased temperature, in particular, influences different biochemical and physiological processes associated with cotton plant, resulting in low seed cotton production. Many studies in various agroecological zones used various agronomic strategies and contemporary breeding techniques to reduce heat stress and improve cotton productivity. To attain desired traits, cotton breeders should investigate all potential possibilities, such as generating superior cultivars by traditional breeding, employing molecular techniques and transgenic methods, such as using genome editing techniques. The main objective of this review is to provide the recent information on the environmental factors, such as temperature, heat and drought, influence the growth and development, morphology and physio-chemical alteration associated with cotton. Furthermore, recent advancement in cotton breeding to combat the serious threat of drought and heat stress.

3D imaging reveals apical stem cell responses to ambient temperature

Plant growth is driven by apical meristems at the shoot and root growth points, which comprise continuously active stem cell populations. While many of the key factors involved in homeostasis of the shoot apical meristem (SAM) have been extensively studied under artificial constant growth conditions, only little is known how variations in the environment affect the underlying regulatory network. To shed light on the responses of the SAM to ambient temperature, we combined 3D live imaging of fluorescent reporter lines that allowed us to monitor the activity of two key regulators of stem cell homeostasis in the SAM namely CLAVATA3 (CLV3) and WUSCHEL (WUS), with computational image analysis to derive morphological and cellular parameters of the SAM. Whereas CLV3 expression marks the stem cell population, WUS promoter activity is confined to the organizing center (OC), the niche cells adjacent to the stem cells, hence allowing us to record on the two central cell populations of the SAM. Applying an integrated computational analysis of our data we found that variations in ambient temperature not only led to specific changes in spatial expression patterns of key regulators of SAM homeostasis, but also correlated with modifications in overall cellular organization and shoot meristem morphology.

Cytokinins - regulators of de novo shoot organogenesis

Plants, unlike animals, possess a unique developmental plasticity, that allows them to adapt to changing environmental conditions. A fundamental aspect of this plasticity is their ability to undergo postembryonic de novo organogenesis. This requires the presence of regulators that trigger and mediate specific spatiotemporal changes in developmental programs. The phytohormone cytokinin has been known as a principal regulator of plant development for more than six decades. In de novo shoot organogenesis and in vitro shoot regeneration, cytokinins are the prime candidates for the signal that determines shoot identity. Both processes of de novo shoot apical meristem development are accompanied by changes in gene expression, cell fate reprogramming, and the switching-on of the shoot-specific homeodomain regulator, WUSCHEL. Current understanding about the role of cytokinins in the shoot regeneration will be discussed.

A network of CLAVATA receptors buffers auxin-dependent meristem maintenance

Plant body plans are elaborated in response to both environmental and endogenous cues. How these inputs intersect to promote growth and development remains poorly understood. During reproductive development, central zone stem cell proliferation in inflorescence meristems is negatively regulated by the CLAVATA3 (CLV3) peptide signalling pathway. In contrast, floral primordia formation on meristem flanks requires the hormone auxin. Here we show that CLV3 signalling is also necessary for auxin-dependent floral primordia generation and that this function is partially masked by both inflorescence fasciation and heat-induced auxin biosynthesis. Stem cell regulation by CLAVATA signalling is separable from primordia formation but is also sensitized to temperature and auxin levels. In addition, we uncover a novel role for the CLV3 receptor CLAVATA1 in auxin-dependent meristem maintenance in cooler environments. As such, CLV3 signalling buffers multiple auxin-dependent shoot processes across divergent thermal environments, with opposing effects on cell proliferation in different meristem regions.

WUSCHEL-RELATED HOMEOBOX 13 suppresses de novo shoot regeneration via cell fate control of pluripotent callus

Plants can regenerate their bodies via de novo establishment of shoot apical meristems (SAMs) from pluripotent callus. Only a small fraction of callus cells is eventually specified into SAMs but the molecular mechanisms underlying fate specification remain obscure. The expression of WUSCHEL (WUS) is an early hallmark of SAM fate acquisition. Here, we show that a WUS paralog, WUSCHEL-RELATED HOMEOBOX 13 (WOX13), negatively regulates SAM formation from callus in Arabidopsis thaliana. WOX13 promotes non-meristematic cell fate via transcriptional repression of WUS and other SAM regulators and activation of cell wall modifiers. Our Quartz-Seq2-based single cell transcriptome revealed that WOX13 plays key roles in determining cellular identity of callus cell population. We propose that reciprocal inhibition between WUS and WOX13 mediates critical cell fate determination in pluripotent cell population, which has a major impact on regeneration efficiency.

The dynamics of chromatin states mediated by epigenetic modifications during somatic cell reprogramming

Somatic cell reprogramming (SCR) is the conversion of differentiated somatic cells into totipotent or pluripotent cells through a variety of methods. Somatic cell reprogramming also provides a platform to investigate the role of chromatin-based factors in establishing and maintaining totipotency or pluripotency, since high expression of totipotency- or pluripotency-related genes usually require an active chromatin state. Several studies in plants or mammals have recently shed light on the molecular mechanisms by which epigenetic modifications regulate the expression of totipotency or pluripotency genes by altering their chromatin states. In this review, we present a comprehensive overview of the dynamic changes in epigenetic modifications and chromatin states during reprogramming from somatic cells to totipotent or pluripotent cells. In addition, we illustrate the potential role of DNA methylation, histone modifications, histone variants, and chromatin remodeling during somatic cell reprogramming, which will pave the way to developing reliable strategies for efficient cellular reprogramming.

REGENOMICS: A web-based application for plant REGENeration-associated transcriptOMICS analyses

In plants, differentiated somatic cells exhibit an exceptional ability to regenerate new tissues, organs, or whole plants. Recent studies have unveiled core genetic components and pathways underlying cellular reprogramming and de novo tissue regeneration in plants. Although high-throughput analyses have led to key discoveries in plant regeneration, a comprehensive organization of large-scale data is needed to further enhance our understanding of plant regeneration. Here, we collected all currently available transcriptome datasets related to wounding responses, callus formation, de novo organogenesis, somatic embryogenesis, and protoplast regeneration to construct REGENOMICS, a web-based application for plant REGENeration-associated transcriptOMICS analyses. REGENOMICS supports single- and multi-query analyses of plant regeneration-related gene-expression dynamics, co-expression networks, gene-regulatory networks, and single-cell expression profiles. Furthermore, it enables user-friendly transcriptome-level analysis of REGENOMICS-deposited and user-submitted RNA-seq datasets. Overall, we demonstrate that REGENOMICS can serve as a key hub of plant regeneration transcriptome analysis and greatly enhance our understanding on gene-expression networks, new molecular interactions, and the crosstalk between genetic pathways underlying each mode of plant regeneration. The REGENOMICS web-based application is available at http://plantregeneration.snu.ac.kr.