Stimulus-Responsive Peptide for Effective Delivery and Release of DNA in Plants

Cell-penetrating peptides for sustainable agriculture

Cell-penetrating peptides (CPPs) are short (typically 5-30 amino acids), cationic, amphipathic, or hydrophobic peptides that facilitate the cellular uptake of diverse cargo molecules by eukaryotic cells via direct translocation or endocytosis across the plasma membrane. CPPs can deliver a variety of bioactive cargos, including proteins, peptides, nucleic acids, and small molecules into the cell. Once inside, the delivered cargo may function in the cytosol, nucleus, or other subcellular compartments. Numerous CPPs have been used for studies and drug delivery in mammalian systems. Although CPPs have many potential uses in plant research and agriculture, the application of CPPs in plants remains limited. Here we review the structures and mechanisms of CPPs and highlight their potential applications for sustainable agriculture.

Polymeric Nanocarriers Autonomously Cross the Plant Cell Wall and Enable Protein Delivery for Stress Sensing

Delivery of proteins in plant cells can facilitate the design of desired functions by modulation of biological processes and plant traits but is currently limited by narrow host range, tissue damage, and poor scalability. Physical barriers in plants, including cell walls and membranes, limit protein delivery to desired plant tissues. Herein, a cationic high aspect ratio polymeric nanocarriers (PNCs) platform is developed to enable efficient protein delivery to plants. The cationic nature of PNCs binds proteins through electrostatic. The ability to precisely design PNCs' size and aspect ratio allowed us to find a cutoff of ≈14 nm in the cell wall, below which cationic PNCs can autonomously overcome the barrier and carry their cargo into plant cells. To exploit these findings, a reduction-oxidation sensitive green fluorescent protein (roGFP) is deployed as a stress sensor protein cargo in a model plant Nicotiana benthamiana and common crop plants, including tomato and maize. In vivo imaging of PNC-roGFP enabled optical monitoring of plant response to wounding, biotic, and heat stressors. These results show that PNCs can be precisely designed below the size exclusion limit of cell walls to overcome current limitations in protein delivery to plants and facilitate species-independent plant engineering.

Enhancing plant biotechnology by nanoparticle delivery of nucleic acids

Plant biotechnology plays a crucial role in developing modern agriculture and plant science research. However, the delivery of exogenous genetic material into plants has been a long-standing obstacle. Nanoparticle-based delivery systems are being established to address this limitation and are proving to be a feasible, versatile, and efficient approach to facilitate the internalization of functional RNA and DNA by plants. The nanoparticle-based delivery systems can also be designed for subcellular delivery and controlled release of the biomolecular cargo. In this review, we provide a concise overview of the recent advances in nanocarriers for the delivery of biomolecules into plants, with a specific focus on applications to enhance RNA interference, foreign gene transfer, and genome editing in plants.

Nanoplatforms for the Delivery of Nucleic Acids into Plant Cells

Nanocarriers are widely used for efficient delivery of different cargo into mammalian cells; however, delivery into plant cells remains a challenging issue due to physical and mechanical barriers such as the cuticle and cell wall. Here, we discuss recent progress on biodegradable and biosafe nanomaterials that were demonstrated to be applicable to the delivery of nucleic acids into plant cells. This review covers studies the object of which is the plant cell and the cargo for the nanocarrier is either DNA or RNA. The following nanoplatforms that could be potentially used for nucleic acid foliar delivery via spraying are discussed: mesoporous silica nanoparticles, layered double hydroxides (nanoclay), carbon-based materials (carbon dots and single-walled nanotubes), chitosan and, finally, cell-penetrating peptides (CPPs). Hybrid nanomaterials, for example, chitosan- or CPP-functionalized carbon nanotubes, are taken into account. The selected nanocarriers are analyzed according to the following aspects: biosafety, adjustability for the particular cargo and task (e.g., organelle targeting), penetration efficiency and ability to protect nucleic acid from environmental and cellular factors (pH, UV, nucleases, etc.) and to mediate the gradual and timely release of cargo. In addition, we discuss the method of application, experimental system and approaches that are used to assess the efficiency of the tested formulation in the overviewed studies. This review presents recent progress in developing the most promising nanoparticle-based materials that are applicable to both laboratory experiments and field applications.

Strategies for delivery of CRISPR/Cas-mediated genome editing to obtain edited plants directly without transgene integration

Increased understanding of plant genetics and the development of powerful and easier-to-use gene editing tools over the past century have revolutionized humankind's ability to deliver precise genotypes in crops. Plant transformation techniques are well developed for making transgenic varieties in certain crops and model organisms, yet reagent delivery and plant regeneration remain key bottlenecks to applying the technology of gene editing to most crops. Typical plant transformation protocols to produce transgenic, genetically modified (GM) varieties rely on transgenes, chemical selection, and tissue culture. Typical protocols to make gene edited (GE) varieties also use transgenes, even though these may be undesirable in the final crop product. In some crops, the transgenes are routinely segregated away during meiosis by performing crosses, and thus only a minor concern. In other crops, particularly those propagated vegetatively, complex hybrids, or crops with long generation times, such crosses are impractical or impossible. This review highlights diverse strategies to deliver CRISPR/Cas gene editing reagents to regenerable plant cells and to recover edited plants without unwanted integration of transgenes. Some examples include delivering DNA-free gene editing reagents such as ribonucleoproteins or mRNA, relying on reagent expression from non-integrated DNA, using novel delivery mechanisms such as viruses or nanoparticles, using unconventional selection methods to avoid integration of transgenes, and/or avoiding tissue culture altogether. These methods are advancing rapidly and already enabling crop scientists to make use of the precision of CRISPR gene editing tools.

Technological Development and Application of Plant Genetic Transformation

Genetic transformation is an important strategy for enhancing plant biomass or resistance in response to adverse environments and population growth by imparting desirable genetic characteristics. Research on plant genetic transformation technology can promote the functional analysis of plant genes, the utilization of excellent traits, and precise breeding. Various technologies of genetic transformation have been continuously discovered and developed for convenient manipulation and high efficiency, mainly involving the delivery of exogenous genes and regeneration of transformed plants. Here, currently developed genetic transformation technologies were expounded and compared. Agrobacterium-mediated gene delivery methods are commonly used as direct genetic transformation, as well as external force-mediated ways such as particle bombardment, electroporation, silicon carbide whiskers, and pollen tubes as indirect ones. The regeneration of transformed plants usually involves the de novo organogenesis or somatic embryogenesis pathway of the explants. Ectopic expression of morphogenetic transcription factors (Bbm, Wus2, and GRF-GIF) can significantly improve plant regeneration efficiency and enable the transformation of some hard-to-transform plant genotypes. Meanwhile, some limitations in these gene transfer methods were compared including genotype dependence, low transformation efficiency, and plant tissue damage, and recently developed flexible approaches for plant genotype transformation are discussed regarding how gene delivery and regeneration strategies can be optimized to overcome species and genotype dependence. This review summarizes the principles of various techniques for plant genetic transformation and discusses their application scope and limiting factors, which can provide a reference for plant transgenic breeding.

Organelle-targeted gene delivery in plants by nanomaterials

Genetic engineering of plants has revolutionized agriculture and has had a significant impact on our everyday life. It has allowed for the production of crops with longer shelf lives, enhanced yields and resistance to pests and disease. The application of nanomaterials in plant genetic engineering has further augmented these programs with higher delivery efficiencies, biocompatibility and the potential for plant regeneration. In particular, subcellular targeting using nanomaterials has recently become possible with the cutting-edge developments within nanomaterials, but remains challenging despite the promise in organellar engineering for the introduction of useful traits and the elucidation of subcellular interactions. This feature article provides an overview of nanomaterial delivery within plants and highlights the application of recent progress in nanomaterials for subcellular organelle-targeted delivery.

Cell-Penetrating Peptides for Use in Development of Transgenic Plants

Genetically modified plants and crops can contribute to remarkable increase in global food supply, with improved yield and resistance to plant diseases or insect pests. The development of biotechnology introducing exogenous nucleic acids in transgenic plants is important for plant health management. Different genetic engineering methods for DNA delivery, such as biolistic methods, Agrobacterium tumefaciens-mediated transformation, and other physicochemical methods have been developed to improve translocation across the plasma membrane and cell wall in plants. Recently, the peptide-based gene delivery system, mediated by cell-penetrating peptides (CPPs), has been regarded as a promising non-viral tool for efficient and stable gene transfection into both animal and plant cells. CPPs are short peptides with diverse sequences and functionalities, capable of agitating plasma membrane and entering cells. Here, we highlight recent research and ideas on diverse types of CPPs, which have been applied in DNA delivery in plants. Various basic, amphipathic, cyclic, and branched CPPs were designed, and modifications of functional groups were performed to enhance DNA interaction and stabilization in transgenesis. CPPs were able to carry cargoes in either a covalent or noncovalent manner and to internalize CPP/cargo complexes into cells by either direct membrane translocation or endocytosis. Importantly, subcellular targets of CPP-mediated nucleic acid delivery were reviewed. CPPs offer transfection strategies and influence transgene expression at subcellular localizations, such as in plastids, mitochondria, and the nucleus. In summary, the technology of CPP-mediated gene delivery provides a potent and useful tool to genetically modified plants and crops of the future.

Temperature-Responsive Bottlebrush Polymers Deliver a Stress-Regulating Agent In Vivo for Prolonged Plant Heat Stress Mitigation

Anticipated increases in the frequency and intensity of extreme temperatures will damage crops. Methods that efficiently deliver stress-regulating agents to crops can mitigate these effects. Here, we describe high aspect ratio polymer bottlebrushes for temperature-controlled agent delivery in plants. The foliar-applied bottlebrush polymers had near complete uptake into the leaf and resided in both the apoplastic regions of the leaf mesophyll and in cells surrounding the vasculature. Elevated temperature enhanced the in vivo release of spermidine (a stress-regulating agent) from the bottlebrushes, promoting tomato plant (Solanum lycopersicum) photosynthesis under heat and light stress. The bottlebrushes continued to provide protection against heat stress for at least 15 days after foliar application, whereas free spermidine did not. About 30% of the ∼80 nm short and ∼300 nm long bottlebrushes entered the phloem and moved to other plant organs, enabling heat-activated release of plant protection agents in phloem. These results indicate the ability of the polymer bottlebrushes to release encapsulated stress relief agents when triggered by heat to provide long-term protection to plants and the potential to manage plant phloem pathogens. Overall, this temperature-responsive delivery platform provides a new tool for protecting plants against climate-induced damage and yield loss.

What is missing to advance foliar fertilization using nanotechnology?

An urgent challenge within agriculture is to improve fertilizer efficiency in order to reduce the environmental footprint associated with an increased production of crops on existing farmland. Standard soil fertilization strategies are often not very efficient due to immobilization in the soil and losses of nutrients by leaching or volatilization. Foliar fertilization offers an attractive supplementary strategy as it bypasses the adverse soil processes, but implementation is often hampered by a poor penetration through leaf barriers, leaf damage, and a limited ability of nutrients to translocate. Recent advances within bionanotechnology offer a range of emerging possibilities to overcome these challenges. Here we review how nanoparticles can be tailored with smart properties to interact with plant tissue for a more efficient delivery of nutrients.

Imaging tools for plant nanobiotechnology

The successful application of nanobiotechnology in biomedicine has greatly changed the traditional way of diagnosis and treating of disease, and is promising for revolutionizing the traditional plant nanobiotechnology. Over the past few years, nanobiotechnology has increasingly expanded into plant research area. Nanomaterials can be designed as vectors for targeted delivery and controlled release of fertilizers, pesticides, herbicides, nucleotides, proteins, etc. Interestingly, nanomaterials with unique physical and chemical properties can directly affect plant growth and development; improve plant resistance to disease and stress; design as sensors in plant biology; and even be used for plant genetic engineering. Similarly, there have been concerns about the potential biological toxicity of nanomaterials. Selecting appropriate characterization methods will help understand how nanomaterials interact with plants and promote advances in plant nanobiotechnology. However, there are relatively few reviews of tools for characterizing nanomaterials in plant nanobiotechnology. In this review, we present relevant imaging tools that have been used in plant nanobiotechnology to monitor nanomaterial migration, interaction with and internalization into plants at three-dimensional lengths. Including: 1) Migration of nanomaterial into plant organs 2) Penetration of nanomaterial into plant tissues (iii)Internalization of nanomaterials by plant cells and interactions with plant subcellular structures. We compare the advantages and disadvantages of current characterization tools and propose future optimal characterization methods for plant nanobiotechnology.

Functional peptide-mediated plastid transformation in tobacco, rice, and kenaf

In plant engineering, plastid transformation is more advantageous than nuclear transformation because it results in high levels of protein expression from multiple genome copies per cell and is unaffected by gene silencing. The common plastid transformation methods are biolistic bombardment that requires special instruments and PEG-mediated transformation that is only applicable to protoplast cells. Here, we aimed to establish a new plastid transformation method in tobacco, rice, and kenaf using a biocompatible fusion peptide as a carrier to deliver DNA into plastids. We used a fusion peptide, KH-AtOEP34, comprising a polycationic DNA-binding peptide (KH) and a plastid-targeting peptide (AtOEP34) to successfully deliver and integrate construct DNA into plastid DNA (ptDNA) via homologous recombination. We obtained transformants in each species using selection with spectinomycin/streptomycin and the corresponding resistance gene aadA. The constructs remained in ptDNA for several months after introduction even under non-selective condition. The transformants normally flowered and are fertile in most cases. The offspring of the transformants (the T₁ generation) retained the integrated construct DNA in their ptDNA, as indicated by PCR and DNA blotting, and expressed GFP in plastids from the integrated construct DNA. In summary, we successfully used the fusion peptide method for integration of foreign DNA in tobacco, rice, and kenaf ptDNA, and the integrated DNA was transmitted to the next generations. Whereas optimization is necessary to obtain homoplasmic plastid transformants that enable stable heterologous expression of genes, the plastid transformation method shown here is a novel nanomaterial-based approach distinct from the conventional methods, and we propose that this easy method could be used to target a wide variety of plants.

Nanomaterials coupled with microRNAs for alleviating plant stress: a new opening towards sustainable agriculture

Plant growth and development is influenced by their continuous interaction with the environment. Their cellular machinery is geared to make rapid changes for adjusting the morphology and physiology to withstand the stressful changes in their surroundings. The present scenario of climate change has however intensified the occurrence and duration of stress and this is getting reflected in terms of yield loss. A number of breeding and molecular strategies are being adopted to enhance the performance of plants under abiotic stress conditions. In this context, the use of nanomaterials is gaining momentum. Nanotechnology is a versatile field and its application has been demonstrated in almost all the existing fields of science. In the agriculture sector, the use of nanoparticles is still limited, even though it has been found to increase germination and growth, enhance physiological and biochemical activities and impact gene expression. In this review, we have summarized the use and role of nanomaterial and small non-coding RNAs in crop improvement while highlighting the potential of nanomaterial assisted eco-friendly delivery of small non-coding RNAs as an innovative strategy for mitigating the effect of abiotic stress.

Nanotechnology Strategies for Plant Genetic Engineering

Plant genetic engineering is essential for improving crop yield, quality, and resistance to abiotic/biotic stresses for sustainable agriculture. Agrobacterium-, biolistic bombardment-, electroporation-, and poly(ethylene glycol) (PEG)-mediated genetic-transformation systems are extensively used in plant genetic engineering. However, these systems have limitations, including species dependency, destruction of plant tissues, low transformation efficiency, and high cost. Recently, nanotechnology-based gene-delivery methods have been developed for plant genetic transformation. This nanostrategy shows excellent transformation efficiency, good biocompatibility, adequate protection of exogenous nucleic acids, and the potential for plant regeneration. However, the nanomaterial-mediated gene-delivery system in plants is still in its infancy, and there are many challenges for its broad applications. Herein, the conventional genetic transformation techniques used in plants are briefly discussed. After that, the progress in the development of nanomaterial-based gene-delivery systems is considered. CRISPR-Cas-mediated genome editing and its combined applications with plant nanotechnology are also discussed. The conceptual innovations, methods, and practical applications of nanomaterial-mediated genetic transformation summarized herein will be beneficial for promoting plant genetic engineering in modern agriculture.

Emerging landscape of cell-penetrating peptide-mediated nucleic acid delivery and their utility in imaging, gene-editing, and RNA-sequencing

The safety issues like immunogenicity and unacceptable cancer risk of viral vectors for DNA/mRNA vaccine delivery necessitate the development of non-viral vectors with no toxicity. Among the non-viral strategies, cell-penetrating peptides (CPPs) have been a topic of interest recently because of their ability to cross plasma membranes and facilitate nucleic acids delivery both in vivo and in vitro. In addition to the application in the field of gene vaccine and gene therapy, CPPs based nucleic acids delivery have been proved by its potential application like gene editing, RNA-sequencing, and imaging. Here, we focus on summarizing the recent applications and progress of CPPs-mediated nucleic acids delivery and discuss the current problems and solutions in this field.

Different Approaches to Cyclize a Cell-Penetrating Peptide and to Tether Bioactive Payloads

Cell-penetrating peptides (CPPs) are versatile tools to deliver various molecules into different cell types. The majority of CPPs are usually represented by linear structures, but numerous recent studies demonstrated cyclization to be an effective strategy leading to favorable biological activities. Here we describe two different methods for the side chain and backbone cyclization of CPPs . Furthermore, we highlight straightforward procedures for the covalent coupling of fluorophores or cytotoxic payloads.

Lanthanum(III) triggers AtrbohD- and jasmonic acid-dependent systemic endocytosis in plants

Trivalent rare earth elements (REEs) are widely used in agriculture. Aerially applied REEs enter leaf epidermal cells by endocytosis and act systemically to improve the growth of the whole plant. The mechanistic basis of their systemic activity is unclear. Here, we show that treatment of Arabidopsis leaves with trivalent lanthanum [La(III)], a representative of REEs, triggers systemic endocytosis from leaves to roots. La(III)-induced systemic endocytosis requires AtrbohD-mediated reactive oxygen species production and jasmonic acid. Systemic endocytosis impacts the accumulation of mineral elements and the development of roots consistent with the growth promoting effects induced by aerially applied REEs. These findings provide insights into the mechanistic basis of REE activity in plants.

Synthetic Mitochondria-Targeting Peptides Incorporating α-Aminoisobutyric Acid with a Stable Amphiphilic Helix Conformation in Plant Cells

In the genetic modification of plant cells, the mitochondrion is an important target in addition to the nucleus and plastid. However, gene delivery into the mitochondria of plant cells has yet to be established by conventional methods, such as particle bombardment, because of the small size and high mobility of mitochondria. To develop an efficient mitochondria-targeting signal (MTS) that functions in plant cells, we designed the artificial peptide (LURL)₃ and its analogues, which periodically feature hydrophobic α-aminoisobutyric acid (Aib, U) and cationic arginine (R), considering the consensus motif recognized by the mitochondrial import receptor Tom20. Circular dichroism measurements and molecular dynamics simulation studies revealed that (LURL)₃ had a propensity to form a stable α-helix in 0.1 M phosphate buffer solution containing 1.0 wt % sodium dodecyl sulfate. After internalization into plant cells via particle bombardment, (LURL)₃ revealed highly selective accumulation in the mitochondria, whereas its analogue (LARL)₃ was predominantly located in the vacuoles in addition to mitochondria. The high selectivity of (LURL)₃ can be attributed to the incorporation of Aib, which promotes the hydrophobic interaction between the MTS and Tom20 by increasing the hydrophobicity and helicity of (LURL)₃. The present study provided a prospective mitochondrial targeting system using the simple design of artificial peptides.

Endosome-escaping micelle complexes dually equipped with cell-penetrating and endosome-disrupting peptides for efficient DNA delivery into intact plants

The delivery of DNA to plants is crucial for enhancing their ability to produce valuable compounds and adapt to climate change. Peptides can provide a versatile tool for delivering DNA to a specific target organelle in various plant species without the use of specialized equipment. However, peptide-mediated DNA delivery suffers from endosomal entrapment and subsequent vacuolar degradation of the DNA cargo, which leads to poor transfection efficiency. To overcome the lack of a reliable approach for bypassing vacuolar degradation in plants, we herein present an endosome-escaping micelle. The micelle surface is dually modified with cell-penetrating (CPP) and endosome-disrupting peptides (EDP) and the core is composed of plasmid DNA condensed with cationic peptides. Due to the functions of CPP and EDP, the dual peptide-modified micelles efficiently undergo endocytic internalization and escape from endosomes to the cytosol, thereby achieving significantly enhanced transfection of intact plants with negligible cytotoxicity. The present study offers a robust strategy for efficient intracellular DNA delivery to plants without vacuolar degradation, and can facilitate plant bioengineering for diverse biotechnological applications.

Imaging of the Entry Pathway of a Cell-Penetrating Peptide-DNA Complex From the Extracellular Space to Chloroplast Nucleoids Across Multiple Membranes in Arabidopsis Leaves

Each plant cell has hundreds of copies of the chloroplast genome and chloroplast transgenes do not undergo silencing. Therefore, chloroplast transformation has many powerful potential agricultural and industrial applications. We previously succeeded in integrating exogenous genes into the chloroplast genome using peptide-DNA complexes composed of plasmid DNA and a fusion peptide consisting of a cell-penetrating peptide (CPP) and a chloroplast transit peptide (cpPD complex). However, how cpPD complexes are transported into the chloroplast from outside the cell remains unclear. Here, to characterize the route by which these cpPD complexes move into chloroplasts, we tracked their movement from the extracellular space to the chloroplast stroma using a fluorescent label and confocal laser scanning microscopy (CLSM). Upon infiltration of cpPD complexes into the extracellular space of Arabidopsis thaliana leaves, the complexes reached the chloroplast surface within 6h. The cpPD complexes reached were engulfed by the chloroplast outer envelope membrane and gradually integrated into the chloroplast. We detected several cpPD complexes localized around chloroplast nucleoids and observed the release of DNA from the cpPD. Our results thus define the route taken by the cpPD complexes for gene delivery from the extracellular space to the chloroplast stroma.

Nanoparticle-mediated gene transformation strategies for plant genetic engineering

Plant genetic engineering, a recent technological advancement in the field of plant science, is an important tool used to improve crop quality and yield, to enhance secondary metabolite content in medicinal plants or to develop crops for sustainable agriculture. A new approach based on nanoparticle-mediated gene transformation can overcome the obstacle of the plant cell wall and accurately transfer DNA or RNA into plants to produce transient or stable transformation. In this review, several nanoparticle-based approaches are discussed, taking into account recent advances and challenges to hint at potential applications of these approaches in transgenic plant improvement programs. This review also highlights challenges in implementing the nanoparticle-based approaches used in plant genetic engineering. A new technology that improves gene transformation efficiency and overcomes difficulties in plant regeneration has been established and will be used for the de novo production of transgenic plants, and CRISPR/Cas9 genome editing has accelerated crop improvement. Therefore, we outline future perspectives based on combinations of genome editing, nanoparticle-mediated gene transformation and de novo regeneration technologies to accelerate crop improvement. The information provided here will assist an effective exploration of the technological advances in plant genetic engineering to support plant breeding and important crop improvement programs.

Peptides as a material platform for gene delivery: Emerging concepts and converging technologies

Successful gene therapies rely on methods that safely introduce DNA into target cells and enable subsequent expression of proteins. To that end, peptides are an attractive materials platform for DNA delivery, facilitating condensation into nanoparticles, delivery into cells, and subcellular release to enable protein expression. Peptides are programmable materials that can be designed to address biocompatibility, stability, and subcellular barriers that limit efficiency of non-viral gene delivery systems. This review focuses on fundamental structure-function relationships regarding peptide design and their impact on nanoparticle physical properties, biologic activity, and biocompatibility. Recent peptide technologies utilize multi-dimensional structures, non-natural chemistries, and combinations of peptides with lipids to achieve desired properties and efficient transfection. Advances in DNA cargo design are also presented to highlight further opportunities for peptide-based gene delivery. Modern DNA designs enable prolonged expression compared to traditional plasmids, providing an additional component that can be synergized with peptide carriers for improved transfection. Peptide transfection systems are poised to become a flexible and efficient platform incorporating new chemistries, functionalities, and improved DNA cargos to usher in a new era of gene therapy.

Development of Reactive Oxygen Species-Triggered Degradable Nanoparticles Using Oligoproline-Containing Peptides

Oligoproline-containing peptides, GPPG and GPPPG, were designed and developed for nanoparticle-based delivery platforms, and their degradation is triggered by reactive oxygen species (ROS). Peptides containing more than two consecutive proline residues were found to be cleavable in 1 mM of ROS generated by hydrogen peroxide in the presence of CuSO₄, which corresponds to plant cells under photosynthetic conditions. The nanoparticles formed by the peptides were also ROS-degradable and efficiently encapsulated a hydrophobic dye. The hydrophobic cargo in the peptide nanoparticles was released into the cytosol of plant leaf cells in response to the ROS generated in chloroplasts by light irradiation. Furthermore, local laser irradiation enabled the peptide nanoparticles to release their cargo at only the irradiated cell, promising site-selective cargo release triggered by irradiation.

Dual Peptide-Based Gene Delivery System for the Efficient Transfection of Plant Callus Cells

Owing to their diverse functions and tunable physicochemical properties, peptides are promising alternatives to the conventional gene delivery tools that are available for plant systems. However, peptide-mediated gene delivery is limited by low transfection efficiency in plants because of the insufficient cytosolic translocation of DNA cargo. Here, we report a dual peptide-based gene delivery system for the efficient transfection of plant callus cells. This system is based on the combination of an artificial peptide composed of cationic cell-penetrating and hydrophobic endosomal escape domains with a gene carrier peptide composed of amphiphilic cell-penetrating and cationic DNA-binding domains. Cellular internalization and transfection studies revealed that this dual peptide-based system enables more efficient transfection of callus cells than does a carrier peptide alone by enhancing the endocytic uptake and subsequent cytosolic translocation of a carrier peptide/DNA complex. The present strategy will expand the utility of peptide-mediated plant gene delivery for a wide range of applications and basic research.

Computational study on the polymerization reaction of d-aminopeptidase for the synthesis of d-peptides

Almost all natural proteins are composed exclusively of l-amino acids, and this chirality influences their properties, functions, and selectivity. Proteases can recognize proteins composed of l-amino acids but display lower selectivity for their stereoisomers, d-amino acids. Taking this as an advantage, d-amino acids can be used to develop polypeptides or biobased materials with higher biostability. Chemoenzymatic peptide synthesis is a technique that uses proteases as biocatalysts to synthesize polypeptides, and d-stereospecific proteases can be used to synthesize polypeptides incorporating d-amino acids. However, engineered proteases with modified catalytic activities are required to allow the incorporation of d-amino acids with increased efficiency. To understand the stereospecificity presented by proteases and their involvement in polymerization reactions, we studied d-aminopeptidase. This enzyme displays the ability to efficiently synthesize poly d-alanine-based peptides under mild conditions. To elucidate the mechanisms involved in the unique specificity of d-aminopeptidase, we performed quantum mechanics/molecular mechanics simulations of its polymerization reaction and determined the energy barriers presented by the chiral substrates. The enzyme faces higher activation barriers for the acylation and aminolysis reactions with the l-stereoisomer than with the d-substrate (10.7 and 17.7 kcal mol-1 higher, respectively). The simulation results suggest that changes in the interaction of the substrate with Asn155 influence the stereospecificity of the polymerization reaction.

Efficient callus induction and a temperature condition for flowering and seed setting in kenaf Hibiscus cannabinus

Kenaf, Hibiscus cannabinus, is a fiber-enriched plant belonging to Malvaceae and is an important fiber crop. The features of kenaf of being fast-growing and fiber-enriched suggest the potential for the use of kenaf in biomass and materials. Here, we modified procedures for regeneration from kenaf explants in order to establish efficient genetic modification for improving the property of kenaf as a material. We tested several tissues of kenaf seedlings for callus induction and subsequent shoot regeneration by supplying several combinations of plant growth factors. We show the cotyledons to be the best tissue for efficient callus induction, and the rate for callus induction reached ∼98% on an improved callus inducing medium. We also show the efficient regeneration of kenaf from cotyledon-derived calli achieved by shoot induction on a shoot-inducing medium. We also achieved seed setting of the regenerated kanaf plants under a regulated growth condition in a chamber. Our efficient regeneration method and seed setting condition will enable the production of stably transformed kenaf that can improve the properties of kenaf as a material.

Native protein delivery into rice callus using ionic complexes of protein and cell-penetrating peptides

Direct protein delivery into intact plants remains a challenge for the agricultural and plant science fields. Cell-penetrating peptide (CPP)-mediated protein delivery requires the binding of CPPs to a protein to carry the protein into the cell through the cell wall and lipid bilayer. Thus, we prepared ionic complexes of a CPP-containing carrier peptide and a cargo protein, namely, Citrine yellow fluorescent protein, and subsequently studied their physicochemical properties. Two types of carrier peptides, BP100(KH)₉ and BP100CH₇, were investigated for delivery efficiency into rice callus. Both BP100(KH)₉ and BP100CH₇ successfully introduced Citrine protein into rice callus cells under pressure and vacuum treatment. Moreover, delivery efficiency varied at different growth stages of rice callus; 5-day rice callus was a more efficient recipient for Citrine than 21-day callus.

Arabinogalactan protein-rare earth element complexes activate plant endocytosis

Endocytosis is essential to all eukaryotes, but how cargoes are selected for internalization remains poorly characterized. Extracellular cargoes are thought to be selected by transmembrane receptors that bind intracellular adaptors proteins to initiate endocytosis. Here, we report a mechanism for clathrin-mediated endocytosis (CME) of extracellular lanthanum [La(III)] cargoes, which requires extracellular arabinogalactan proteins (AGPs) that are anchored on the outer face of the plasma membrane. AGPs were colocalized with La(III) on the cell surface and in La(III)-induced endocytic vesicles in Arabidopsis leaf cells. Superresolution imaging showed that La(III) triggered AGP movement across the plasma membrane. AGPs were then colocalized and physically associated with the μ subunit of the intracellular adaptor protein 2 (AP2) complexes. The AGP-AP2 interaction was independent of CME, whereas AGP's internalization required CME and AP2. Moreover, we show that AGP-dependent endocytosis in the presence of La(III) also occurred in human cells. These findings indicate that extracellular AGPs act as conserved CME cargo receptors, thus challenging the current paradigm about endocytosis of extracellular cargoes.

Block Copolymer/Plasmid DNA Micelles Postmodified with Functional Peptides via Thiol-Maleimide Conjugation for Efficient Gene Delivery into Plants

Introducing exogenous genes into plant cells is essential for a wide range of applications in agriculture and plant biotechnology fields. Cationic peptide carriers with cell-penetrating and DNA-binding domains successfully deliver exogenous genes into plants. However, their cell-penetrating activity may be attenuated by undesired electrostatic interactions between the cell-penetrating peptide (CPP) domain and DNA cargo, resulting in limited gene delivery efficiency. Here, we developed the block copolymer maleimide-conjugated tetra(ethylene glycol) and poly(l-lysine) (MAL-TEG-PLL). Through electrostatic interactions with plasmid DNA (pDNA), MAL-TEG-PLL formed a micelle that presented maleimide groups on its surface. The micelle enabled postmodification with cysteine-containing functional peptides, including a CPP (BP100-Cys) and nuclear localization signal (Cys-NLS) via thiol-maleimide conjugation, thereby avoiding undesired interactions. According to a comparison of gene delivery efficiencies among the peptide-postmodified micelles, the amount of BP100-Cys on the micelle surface was key for efficient gene delivery. The BP100-postmodified micelle showed more efficient delivery compared with that of the BP100-premodified micelle. Thus, postmodification of polymeric micelles with functional peptides opens the door to designing highly efficient plant gene delivery systems.

Vacuum/Compression Infiltration-mediated Permeation Pathway of a Peptide-pDNA Complex as a Non-Viral Carrier for Gene Delivery in Planta

Non-viral gene carriers have been extensively investigated as alternatives to viral vectors for gene delivery systems into animal and plant cells. A non-viral gene carrier containing a cell-penetrating peptide and a cationic sequence was previously developed for use in intact plants and plant cells; however, the permeation pathway of the gene carrier into plant cells is yet to be elucidated, which would facilitate the improvement of the gene delivery efficiency. Here, we identified the vacuum/compression infiltration-mediated permeation pathway of a non-viral gene carrier into plant tissues and cells using a complex of plasmid DNA and a peptide-based gene carrier. This complex was taken up via the hydathodes in Arabidopsis thaliana, and from root hairs in Nicotiana benthamiana. Remarkably, these structurally weak tissues are also routes of bacterial invasion in nature, suggesting that peptide-pDNA complexes invade intact plants through similar pathways as bacterial pathogens.

Gene Delivery to Tobacco Root Cells with Single-Walled Carbon Nanotubes and Cell-Penetrating Fusogenic Peptides

Development of efficient, easy, and safe gene delivery methods is of great interest in the field of plant biotechnology. Considering the limitations of the usual transfection methods (such as transgene size and plant type), several new techniques have been tested for replacement. The success of some biological and synthetic nanostructures such as cell-penetrating peptides and carbon nanotubes in transferring macromolecules (proteins and nucleic acids) into mammalian cells provoked us to assess the ability of an engineered chimeric peptide and also arginine functionalized single-walled carbon nanotube in gene delivery to intact tobacco (Nicotiana tabacum var. Virginia) root cells. It was suggested that the engineered peptide with its special cationic and hydrophobic domains and the arginine functionalized single-walled carbon nanotube due to its nano-cylindrical shape can pass plant cell barriers while plasmid DNA (which codes green fluorescent protein) has been condensed on them. The success of gene delivery to tobacco root cells was confirmed by fluorescence microscopy and western blotting analysis.