Targeted DNA demethylation produces heritable epialleles in rice

Inheritance of acquired adaptive cold tolerance in rice through DNA methylation

Epigenetic pathways could provide a mechanistic explanation for the inheritance of acquired characteristics, as proposed by Lamarck in 1802, but epigenetic alterations that endow adaptive hereditary traits have rarely been observed. Here, in cultivated Asian rice (Oryzasativa L.), we identified an epiallele conferring acquired and heritable cold tolerance, an adaptive trait enabling northward spread from its tropical origins. We subjected cold-sensitive rice to multigenerational cold stress and identified a line with acquired stable inheritance of cold tolerance. DNA-hypomethylation variation in the acquiredcoldtolerance 1 (ACT1) promoter region rendered its expression insensitive to cold. This change is, in large part, responsible for the acquired cold tolerance, as confirmed by DNA-methylation editing. Natural variation in ACT1 DNA hypomethylation is associated with cold tolerance and rice geographic distribution. Hypomethylation at ACT1 triggers adaptive cold tolerance, presenting a route to epigenetic-variation-driven inheritance of acquired characteristics.

The generation of novel epialleles in plants: the prospective behind re-shaping the epigenome

Chromatin organization is a relevant layer of control of gene expression during plant development. Chromatin states strictly depend on associated features such as DNA methylation, histone modifications and histone variants. Thus, epigenome editing has become of primary interest to alter gene expression without disrupting genomic sequences. Different tools have been developed to address this challenge, starting with modular Zinc Finger Proteins (ZFPs) and Transcription Activator Like Effectors (TALEs). However, the discovery of CRISPR/Cas9 system and the adaptability of technologies based on enzymatically dead Cas9 (dCas9) have paved the way towards a reliable and adaptable epigenome editing in a great variety of organisms. In this review, we will focus on the application of targeted epigenome editing technologies in plants, summarizing the most updated advances in this field. The promising results obtained by altering the expression state of targets involved in flowering time and abiotic stress resistance are crucial not only for elucidating the molecular interactions that underly chromatin dynamics, but also for future applications in breeding programs as an alternative route to genetic manipulation towards the achievement of higher quality crops particularly in terms of nutritional properties, yield and tolerance.

Enhancing nature's palette through the epigenetic breeding of flower color in chrysanthemum

Flower color is an important character of ornamental plants and one of the main target traits for variety innovation. We previously identified a CmMYB6 epigenetic allele that affects the flower color in chrysanthemum, and changes in flower color are caused by the DNA methylation level of this gene. However, it is still unknown which DNA methyltransferases are involved in modifying the DNA methylation levels of this gene. Here, we used dead Cas9 (dCas9) together with DNA methyltransferases that methylate cytosine residues in the CHH context to target the CmMYB6 promoter through transient and stable transformation methods. We found that CmDRM2a increased the DNA methylation level of the CmMYB6 promoter, the expression of CmMYB6 decreased and a lighter flower color resulted. By contrast, both CmDRM2b and CmCMT2 enhanced DNA methylation levels of the CmMYB6 promoter, the expression of CmMYB6 increased and a deeper flower color resulted. Furthermore, the regulatory mechanism of DNA methyltransferase in the formation of chrysanthemum flower color was investigated, pointing to a new strategy for silencing or activating CmMYB6 epiallele to regulate anthocyanin synthesis. This lays a solid foundation for regulating flower color in chrysanthemum through epigenetic breeding.

Wheat2035: Integrating pan-omics and advanced biotechnology for future wheat design

Wheat (Triticum aestivum) production is vital for global food security, providing energy and protein to millions of people worldwide. Recent advancements in wheat research have led to significant increases in production, fueled by technological and scientific innovation. Here, we summarize the major advancements in wheat research, particularly the integration of biotechnologies and a deeper understanding of wheat biology. The shift from multi-omics to pan-omics approaches in wheat research has greatly enhanced our understanding of the complex genome, genomic variations, and regulatory networks to decode complex traits. We also outline key scientific questions, potential research directions, and technological strategies for improving wheat over the next decade. Since global wheat production is expected to increase by 60% in 2050, continued innovation and collaboration are crucial. Integrating biotechnologies and a deeper understanding of wheat biology will be essential for addressing future challenges in wheat production, ensuring sustainable practices and improved productivity.

Epigenetic control of plant abiotic stress responses

On top of genetic information, organisms have evolved complex and sophisticated epigenetic regulation to adjust gene expression in response to developmental and environmental signals. Key epigenetic mechanisms include DNA methylation, histone modifications and variants, chromatin remodeling, and chemical modifications of RNAs. Epigenetic control of environmental responses is particularly important for plants, which are sessile and unable to move away from adverse environments. Besides enabling plants to rapidly respond to environmental stresses, some stress-induced epigenetic changes can be maintained, providing plants with a pre-adapted state to recurring stresses. Understanding these epigenetic mechanisms offers valuable insights for developing crop varieties with enhanced stress tolerance. Here, we focus on abiotic stresses and summarize recent progress in characterizing stress-induced epigenetic changes and their regulatory mechanisms and roles in plant abiotic stress resistance.

Development of an inducible DNA barcoding system to understand lineage changes in Arabidopsis regeneration

Plants demonstrate a high degree of developmental plasticity, capable of regenerating entire individuals from detached somatic tissues-a regenerative phenomenon rarely observed in metazoa. Consequently, elucidating the lineage relationship between somatic founder cells and descendant cells in regenerated plant organs has long been a pursuit. In this study, we developed and optimized both DNA barcode- and multi-fluorescence-based cell-lineage tracing toolsets, employing an inducible method to mark individual cells in Arabidopsis donor somatic tissues at the onset of regeneration. Utilizing these complementary methods, we scrutinized cell identities at the single-cell level and presented compelling evidence that all cells in the regenerated Arabidopsis plants, irrespective of their organ types, originated from a single progenitor cell in the donor somatic tissue. Our discovery suggests a single-cell passage directing the transition from multicellular donor tissue to regenerated plants, thereby creating opportunities for cell-cell competition during plant regeneration-a strategy for maximizing survival.

Targeted genome-modification tools and their advanced applications in crop breeding

Crop improvement by genome editing involves the targeted alteration of genes to improve plant traits, such as stress tolerance, disease resistance or nutritional content. Techniques for the targeted modification of genomes have evolved from generating random mutations to precise base substitutions, followed by insertions, substitutions and deletions of small DNA fragments, and are finally starting to achieve precision manipulation of large DNA segments. Recent developments in base editing, prime editing and other CRISPR-associated systems have laid a solid technological foundation to enable plant basic research and precise molecular breeding. In this Review, we systematically outline the technological principles underlying precise and targeted genome-modification methods. We also review methods for the delivery of genome-editing reagents in plants and outline emerging crop-breeding strategies based on targeted genome modification. Finally, we consider potential future developments in precise genome-editing technologies, delivery methods and crop-breeding approaches, as well as regulatory policies for genome-editing products.

Targeted gene regulation through epigenome editing in plants

The precise targeted gene regulation in plants is essential for improving plant traits and gaining a comprehensive understanding of gene functions. The regulation of gene expression in eukaryotes can be achieved through transcriptional and epigenetic mechanisms. Over the last decade, advancements in gene-targeting technologies, along with an expanded understanding of epigenetic gene regulation mechanisms, have significantly contributed to the development of programmable gene regulation tools. In this review, we will discuss the recent progress in targeted plant gene regulation through epigenome editing, emphasizing the role of effector proteins in modulating target gene expression via diverse mechanisms, including DNA methylation, histone modifications, and chromatin remodeling. Additionally, we will also briefly review targeted gene regulation by transcriptional regulation and mRNA modifications in plants.

Epigenome editing for targeted DNA (de)methylation: a new perspective in modulating gene expression

Traditionally, it has been believed that inheritance is driven as phenotypic variations resulting from changes in DNA sequence. However, this paradigm has been challenged and redefined in the contemporary era of epigenetics. The changes in DNA methylation, histone modification, non-coding RNA biogenesis, and chromatin remodeling play crucial roles in genomic functions and regulation of gene expression. More importantly, some of these changes are inherited to the next generations as a part of epigenetic memory and play significant roles in gene expression. The sum total of all changes in DNA bases, histone proteins, and ncRNA biogenesis constitutes the epigenome. Continuous progress in deciphering epigenetic regulations and the existence of heritable epigenetic/epiallelic variations associated with trait of interest enables to deploy epigenome editing tools to modulate gene expression. DNA methylation marks can be utilized in epigenome editing for the manipulation of gene expression. Initially, genome/epigenome editing technologies relied on zinc-finger protein or transcriptional activator-like effector protein. However, the discovery of clustered regulatory interspaced short palindromic repeats CRISPR)/deadCRISPR-associated protein 9 (dCas9) enabled epigenome editing to be more specific/efficient for targeted DNA (de)methylation. One of the major concerns has been the off-target effects, wherein epigenome editing may unintentionally modify gene/regulatory element which may cause unintended change/harmful effects. Moreover, epigenome editing of germline cell raises several ethical/safety issues. This review focuses on the recent developments in epigenome editing tools/techniques, technological limitations, and future perspectives of this emerging technology in therapeutics for human diseases as well as plant improvement to achieve sustainable developmental goals.

Heritable responses to stress in plants

Most plants are adapted to their environments through generations of exposure to all elements. The adaptation process involves the best possible response to fluctuations in the environment based on the genetic and epigenetic make-up of the organism. Many plant species have the capacity to acclimate or adapt to certain stresses, allowing them to respond more efficiently, with fewer resources diverted from growth and development. However, plants can also acquire protection against stress across generations. Such a response is known as an intergenerational response to stress; typically, plants lose most of the tolerance in the subsequent generation when propagated without stress. Occasionally, the protection lasts for more than one generation after stress exposure and such a response is called transgenerational. In this review, we will summarize what is known about inter- and transgenerational responses to stress, focus on phenotypic and epigenetic events, their mechanisms and ecological and evolutionary meaning.

An epi-allele of SMS causes Sanming dominant genic male sterility in rice

Male sterility is an important trait in rice for hybrid rice (Oryza sativa) breeding. However, the factors involved in dominant male sterility are largely unknown. Here, we identified a gene from Sanming dominant genic male sterile rice, named Sanming dominant male sterility (SMS), and reported that an epi-allele of this locus contributes to male sterility. Segregation analysis attributed dominant male sterility to a single locus, SMS, which we characterized using a male-sterile near isogenic line (NIL) of rice cultivar 93-11. The SMS locus was heterozygous in the male-sterile 93-11 NIL, containing an epi-allele identical to that in 93-11, and an epi-allele identical to that in rice cultivar Nipponbare, which we refer to as SMS9 and SMSN, respectively. SMS9 is silent and hyper-methylated, whereas SMSN is expressed and hypo-methylated in the 93-11 NIL. Overexpressing SMSN led to male sterility. Mutations in SMS rescued the male sterility of the 93-11 NIL. Interestingly, we observed the duplication of SMSN in Nipponbare, but did not observe the duplication of SMS9 in 93-11. Together, these findings suggest that the reduced methylation and enhanced expression of the SMSN epi-allele in the 93-11 NIL is responsible for its role in conferring dominant male sterility.

Optimized prime editing in monocot plants using PlantPegDesigner and engineered plant prime editors (ePPEs)

Prime editors (PEs), which can install desired base edits without donor DNA or double-strand breaks, have been used in plants and can, in principle, accelerate crop improvement and breeding. However, their editing efficiency in plants is generally low. Optimizing the prime editing guide RNA (pegRNA) by designing the sequence on the basis of melting temperature, using dual-pegRNAs and engineering PEs have all been shown to enhance PE efficiency. In addition, an automated pegRNA design platform, PlantPegDesigner, has been developed on the basis of rice prime editing experimental data. In this protocol, we present detailed protocols for designing and optimizing pegRNAs using PlantPegDesigner, constructing engineered plant PE vectors with enhanced editing efficiency for prime editing, evaluating prime editing efficiencies using a reporter system and comparing the effectiveness and byproducts of PEs by deep amplicon sequencing. Using this protocol, researchers can construct optimized pegRNAs for prime editing in 4-7 d and obtain prime-edited rice or wheat plants within 3 months.

Shoot-root signal circuit: Phytoremediation of heavy metal contaminated soil

High concentrations of heavy metals in the environment will cause serious harm to ecosystems and human health. It is urgent to develop effective methods to control soil heavy metal pollution. Phytoremediation has advantages and potential for soil heavy metal pollution control. However, the current hyperaccumulators have the disadvantages of poor environmental adaptability, single enrichment species and small biomass. Based on the concept of modularity, synthetic biology makes it possible to design a wide range of organisms. In this paper, a comprehensive strategy of "microbial biosensor detection - phytoremediation - heavy metal recovery" for soil heavy metal pollution control was proposed, and the required steps were modified by using synthetic biology methods. This paper summarizes the new experimental methods that promote the discovery of synthetic biological elements and the construction of circuits, and combs the methods of producing transgenic plants to facilitate the transformation of constructed synthetic biological vectors. Finally, the problems that should be paid more attention to in the remediation of soil heavy metal pollution based on synthetic biology were discussed.

Targeted DNA demethylation of the Arabidopsis genome using the SunTag-dCpf1-TET1cd system

DNA methylation is a stable and heritable epigenetic mark, and it plays an important role in regulation of gene expression and transposon silencing. Here we developed a CRISPR/dCpf1-based targeted demethylation system using the catalytic domain of the human demethylase TEN-ELEVEN TRANSLOCATION1 (TET1cd) and a SunTag system. The SunTag-dCpf1-TET1cd system is able to achieve targeted DNA demethylation and up-regulate gene expression when guided to the FWA or CACTA1 loci in Arabidopsis thaliana . Our study provides tools for targeted removal of DNA cytosine methylation, and activation of protein-coding genes or transposons expression.

Plant synthetic epigenomic engineering for crop improvement

Efforts have been directed to redesign crops with increased yield, stress adaptability, and nutritional value through synthetic biology-the application of engineering principles to biology. A recent expansion in our understanding of how epigenetic mechanisms regulate plant development and stress responses has unveiled a new set of resources that can be harnessed to develop improved crops, thus heralding the promise of "synthetic epigenetics." In this review, we summarize the latest advances in epigenetic regulation and highlight how innovative sequencing techniques, epigenetic editing, and deep learning-driven predictive tools can rapidly extend these insights. We also proposed the future directions of synthetic epigenetics for the development of engineered smart crops that can actively monitor and respond to internal and external cues throughout their life cycles.

Transgenerationally Transmitted DNA Demethylation of a Spontaneous Epialleles Using CRISPR/dCas9-TET1cd Targeted Epigenetic Editing in Arabidopsis

CRISPR/dCas9 is an important DNA modification tool in which a disarmed Cas9 protein with no nuclease activity is fused with a specific DNA modifying enzyme. A previous study reported that overexpression of the TET1 catalytic domain (TET1cd) reduces genome-wide methylation in Arabidopsis. A spontaneous naturally occurring methylation region (NMR19-4) was identified in the promoter region of the PPH (Pheophytin Pheophorbide Hydrolase) gene, which encodes an enzyme that can degrade chlorophyll and accelerate leaf senescence. The methylation status of NMR19-4 is associated with PPH expression and leaf senescence in Arabidopsis natural accessions. In this study, we show that the CRISPR/dCas9-TET1cd system can be used to target the methylation of hypermethylated NMR19-4 region to reduce the level of methylation, thereby increasing the expression of PPH and accelerating leaf senescence. Furthermore, hybridization between transgenic demethylated plants and hypermethylated ecotypes showed that the demethylation status of edited NMR19-4, along with the enhanced PPH expression and accelerated leaf senescence, showed Mendelian inheritance in F1 and F2 progeny, indicating that spontaneous epialleles are stably transmitted trans-generationally after demethylation editing. Our results provide a rational approach for future editing of spontaneously mutated epialleles and provide insights into the epigenetic mechanisms that control plant leaf senescence.