An efficient protocol for perennial ryegrass mesophyll protoplast isolation and transformation, and its application on interaction study between LpNOL and LpNYC1

Optimized protoplast isolation and transfection with a breakpoint: accelerating Cas9/sgRNA cleavage efficiency validation in monocot and dicot

The CRISPR-Cas genome editing tools are revolutionizing agriculture and basic biology with their simplicity and precision ability to modify target genomic loci. Software-predicted guide RNAs (gRNAs) often fail to induce efficient cleavage at target loci. Many target loci are inaccessible due to complex chromatin structure. Currently, there is no suitable tool available to predict the architecture of genomic target sites and their accessibility. Hence, significant time and resources are spent on performing editing experiments with inefficient guides. Although in vitro-cleavage assay could provide a rough assessment of gRNA efficiency, it largely excludes the interference of native genomic context. Transient in-vivo testing gives a proper assessment of the cleavage ability of editing reagents in a native genomic context. Here, we developed a modified protocol that offers highly efficient protoplast isolation from rice, Arabidopsis, and chickpea, using a sucrose gradient, transfection using PEG (polyethylene glycol), and validation of single guide RNAs (sgRNAs) cleavage efficiency of CRISPR-Cas9. We have optimized various parameters for PEG-mediated protoplast transfection and achieved high transfection efficiency using our protocol in both monocots and dicots. We introduced plasmid vectors containing Cas9 and sgRNAs targeting genes in rice, Arabidopsis, and chickpea protoplasts. Using dual sgRNAs, our CRISPR-deletion strategy offers straightforward detection of genome editing success by simple agarose gel electrophoresis. Sanger sequencing of PCR products confirmed the editing efficiency of specific sgRNAs. Notably, we demonstrated that isolated protoplasts can be stored for up to 24/48 h with little loss of viability, allowing a pause between isolation and transfection. This high-efficiency protocol for protoplast isolation and transfection enables rapid (less than 7 days) validation of sgRNA cleavage efficiency before proceeding with stable transformation. The isolation and transfection method can also be utilized for rapid validation of editing strategies, evaluating diverse editing reagents, regenerating plants from transfected protoplasts, gene expression studies, protein localization and functional analysis, and other applications.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42994-024-00139-7.

A protoplast-based transient gene expression assay for the identification of heat and oxidative stress-regulatory genes in perennial ryegrass

BACKGROUND

With the accumulating omics data, an efficient and time-saving transient assay to express target genes is desired. Mesophyll protoplasts, maintaining most stress-physiological responses and cellular activities as intact plants, offer an alternative transient assay to study target genes' effects on heat and oxidative stress responses.

RESULTS

In this study, a perennial ryegrass (Lolium perenne L.) mesophyll protoplast-based assay was established to effectively over- or down-regulate target genes. The relative expression levels of the target genes could be quantified using RT-qPCR, and the effects of heat and H2O2-induced oxidative stress on protoplasts' viability could be quantitatively measured. The practicality of the assay was demonstrated by identifying the potential thermos-sensor genes LpTT3.1/LpTT3.2 in ryegrass that over-expressing these genes significantly altered protoplasts' viability rates after heat stress.

CONCLUSION

This protoplast-based rapid stress regulatory gene identification assay was briefed as 'PRIDA' that will complement the stable genetic transformation studies to rapidly identify candidate stress-regulatory genes in perennial ryegrass and other grass species.

Genome-wide identification of bHLH transcription factors and functional analysis in salt gland development of the recretohalophyte sea lavender (Limonium bicolor)

Transcription factors with basic helix-loop-helix (bHLH) structures regulate plant growth, epidermal structure development, metabolic processes, and responses to stress extensively. Sea lavender (Limonium bicolor) is a recretohalophyte with unique salt glands in the epidermis that make it highly resistant to salt stress, contributing to the improvement of saline lands. However, the features of the bHLH transcription factor family in L. bicolor are largely unknown. Here, we systematically analyzed the characteristics, localization, and phylogenetic relationships of 187 identified bHLH family genes throughout the L. bicolor genome, as well as their cis-regulatory promoter elements, expression patterns, and key roles in salt gland development or salt tolerance by genetic analysis. Nine verified L. bicolor bHLH genes are expressed and the encoded proteins function in the nucleus, among which the proteins encoded by Lb2G14060 and Lb1G07934 also localize to salt glands. Analysis of CRISPR-Cas9-generated knockout mutants and overexpression lines indicated that the protein encoded by Lb1G07934 is involved in the formation of salt glands, salt secretion, and salt resistance, indicating that bHLH genes strongly influence epidermal structure development and stress responses. The current study lays the foundation for further investigation of the effects and functional mechanisms of bHLH genes in L. bicolor and paves the way for selecting salt-tolerance genes that will enhance salt resistance in crops and for the improvement of saline soils.

HSFA3 functions as a positive regulator of HSFA2a to enhance thermotolerance in perennial ryegrass

Perennial ryegrass (Lolium perenne) is a widely used cool season turfgrass with outstanding turf quality and grazing tolerance. High temperature is the key factor restricting the distribution of perennial ryegrass in temperate and sub-tropic regions. In this study, we found that one HEAT SHCOK TRANSCRIPTION FACOTR (HSF) class A gene from perennial ryegrass, LpHSFA3, was highly induced by heat stress. LpHSFA3 is localized in nucleus and functions as a transcription factor. Ectopic overexpression of LpHSFA3 in Arabidopsis improved thermotolerance and rescued heat sensitive deficiency of athsfa3 mutant. Overexpression of LpHSFA3 in perennial ryegrass enhanced heat tolerance and increased survival rate in summer season as evidenced by decreased EL and MDA, increased number of green leaves and total chlorophyll content. LpHSFA3 binds to the HSE region in LpHSFA2a promoter to constitutively activate the expression of LpHSFA2a and downstream heat stress responsive genes. Ectopic overexpression of LpHSFA2a consequently rescued thermal sensitivity of athsfa3 mutant and enhanced thermotolerance of athsfa2 mutant. Perennial ryegrass protoplasts with overexpression of LpHSFA3 and LpHSFA2a exhibited induction of similar subsets of heat responsive genes. These results indicated that transcription factor LpHSFA3 functions as positive regulator of LpHSFA2a to improve thermotolerance of perennial ryegrass, providing further evidence to understand the regulatory networks of plant heat stress response.

Optimization of preparation and transformation of protoplasts from Populus simonii × P. nigra leaves and subcellular localization of the major latex protein 328 (MLP328)

BACKGROUND

Populus simonii × P. nigra is an ideal material for studying the molecular mechanisms of woody plants. In recent years, research on Populus simonii × P. nigra has increasingly focused on the application of transgenic technology to improve salt tolerance. However, the rapid characterization of gene functions has been hampered by the long growth cycle and exceedingly poor transformation efficiency. Protoplasts are an important tool for plant gene engineering, which can assist with challenging genetic transformation and the protracted growth cycle of Populus simonii × P. nigra. This study established an optimized system for the preparation and transformation of protoplasts from Populus simonii × P. nigra leaves, making genetic research on Populus simonii × P. nigra faster and more convenient. Major Latex Protein (MLP) family genes play a crucial role in plant salt stress response. In the previous study, we discovered that PsnMLP328 can be induced by salt treatment, which suggested that this gene may be involved in response to salt stress. Protein localization is a suggestion for its function. Therefore, we conducted subcellular localization analysis using protoplasts of Populus simonii × P. nigra to study the function of the PsnMLP328 gene preliminarily.

RESULTS

This study established an optimized system for the preparation and transformation of Populus simonii × P. nigra protoplasts. The research results indicate that the optimal separation scheme for the protoplasts of Populus simonii × P. nigra leaves included 2.5% cellulase R-10, 0.6% macerozyme R-10, 0.3% pectolyase Y-23, and 0.8 M mannitol. After enzymatic digestion for 5 h, the yield of obtained protoplasts could reach up to 2 × 107 protoplasts/gFW, with a high viability of 98%. We carried out the subcellular localization analysis based on the optimized transient transformation system, and the results indicated that the MLP328 protein is localized in the nucleus and cytoplasm; thereby proving the effectiveness of the transformation system.

CONCLUSION

In summary, this study successfully established an efficient system for preparing and transforming leaf protoplasts of Populus simonii × P. nigra, laying the foundation for future research on gene function and expression of Populus simonii × P. nigra.

Genome-wide identification of DREB1 transcription factors in perennial ryegrass and functional profiling of LpDREB1H2 in response to cold stress

Perennial ryegrass (Lolium perenne L.) is an outstanding turfgrass and forage cultivated in temperate regions worldwide. However, poor tolerance to extreme cold, heat, or drought limits wide extension and cultivation. DEHYDRATION-RESPONSIVE ELEMENT BINDING FACTOR1s (DREB1s) play a vital role in enhancing plant tolerance to abiotic stress, specifically for low-temperature stress. In this study, a total of 24 LpDREB1 family members were identified from the released genome of perennial ryegrass. Phylogenetic analysis showed that the LpDREB1 genes are divided into 7 groups that have close relationships with rice homologues. Conserved motif analysis revealed that members within the same group have similar conserved motif compositions. All LpDREB1s lack introns, and the promoter sequences of LpDREB1 genes contain multiple cis-acting elements associated with stress response, phytohormone signal transduction and plant growth and development. The majority of LpDREB1 genes were upregulated by drought, submergence, heat and cold stress treatments, including LpDREB1H2. Further investigation showed that LpDREB1H2 is localized in the nucleus. Overexpression of LpDREB1H2 in Arabidopsis induced the expression of cold-responsive (COR) genes, increased the levels of osmotic adjusting substances, and enhanced antioxidant enzyme activities, thus improving the cold tolerance of Arabidopsis. This study lays a foundation for further understanding the function of LpDREB1 genes in perennial ryegrass and provides insights for plant stress tolerance breeding.

Cotyledon peeling method for passion fruit protoplasts: a versatile cell system for transient gene expression in passion fruit (Passiflora edulis)

Passion fruit (Passiflora edulis) is a perennial evergreen vine that grows mainly in tropical and subtropical regions due to its nutritional, medicinal and ornamental values. However, the molecular biology study of passion fruit is extremely hindered by the lack of an easy and efficient method for transformation. The protoplast transformation system plays a vital role in plant regeneration, gene function analysis and genome editing. Here, we present a new method ('Cotyledon Peeling Method') for simple and efficient passion fruit protoplast isolation using cotyledon as the source tissue. A high yield (2.3 × 107 protoplasts per gram of fresh tissues) and viability (76%) of protoplasts were obtained upon incubation in the enzyme solution [1% (w/v) cellulase R10, 0.25% (w/v) macerozyme R10, 0.4 M mannitol, 10 mM CaCl2, 20 mM KCl, 20 mM MES and 0.1% (w/v) BSA, pH 5.7] for 2 hours. In addition, we achieved high transfection efficiency of 83% via the polyethylene glycol (PEG)-mediated transformation with a green fluorescent protein (GFP)-tagged plasmid upon optimization. The crucial factors affecting transformation efficiency were optimized as follows: 3 μg of plasmid DNA, 5 min transfection time, PEG concentration at 40% and protoplast density of 100 × 104 cells/ml. Furthermore, the established protoplast system was successfully applied for subcellular localization analysis of multiple fluorescent organelle markers and protein-protein interaction study. Taken together, we report a simple and efficient passion fruit protoplast isolation and transformation system, and demonstrate its usage in transient gene expression for the first time in passion fruit. The protoplast system would provide essential support for various passion fruit biology studies, including genome editing, gene function analysis and whole plant regeneration.

Protoplast isolation and transient transformation system for Ginkgo biloba L

Ginkgo biloba L. has a unique evolutionary status. Owing to its high medicinal and ornamental value, ginkgo has also recently become a research hotspot. However, the large genome and long juvenile period, as well as the lack of an effective genetic transformation system, have hindered gaining a full understanding of the comprehensive functions of ginkgo genes. At present, heterologous expression of genes in model plants is the primary method used in ginkgo-related research; however, these distant plant model relatives limit reliable interpretation of the results for direct applications in ginkgo breeding. To overcome these limitations, in this study, an efficient isolation and transient expression system for ginkgo protoplasts was established. A large number of intact and homogeneous ginkgo mesophyll protoplasts were isolated using 2% cellulase and 0.25% pectinase in 0.4 M mannitol. The activity of these protoplasts remained above 90% even after 24 h. Furthermore, when the concentration of the polyethylene glycol 4000 solution was 30%-40% (w/v), the transformation efficiency of the protoplasts reached 40%. Finally, the reliability of the system was verified using subcellular localization, transient overexpression, and protein interaction experiments with ginkgo genes, thereby providing a technical platform for the identification and analysis of ginkgo gene functions. The proposed method partially compensates for the limitations associated with the lack of a genetic transformation system and provides technical support to expand research on elucidating the functions of ginkgo genes.

Direct leaf-peeling method for areca protoplasts: a simple and efficient system for protoplast isolation and transformation in areca palm (Areca catechu)

BACKGROUND

Areca palm (Areca catechu) is a woody perennial plant of both economical and medicinal importance grown in tropical and subtropical climates. Yet, the molecular biology study of areca palm is extremely impeded by its unavailability of a transformation method. An efficient protoplast isolation and transformation system could be highly desirable to overcome this barrier.

RESULTS

Here, we described a simple and efficient method for protoplast isolation and transformation from the perennial plant areca palm. A high yield of protoplasts (2.5 × 10⁷ protoplasts per gram of fresh leaf tissues) was obtained from the fresh light green leaflet from the newly-emerged leaf digested overnight in the enzyme solution [2% (w/v) cellulase R10, 0.5% (w/v) macerozyme R10, 0.7 M mannitol, 10 mM CaCl₂, 20 mM KCl, 20 mM MES and 0.1% (w/v) BSA, pH 5.7] by the direct leaf-peeling method. The isolated areca protoplasts maintain viability of 86.6% and have been successfully transformed with a green fluorescent protein (GFP)-tagged plasmid (pGreen0029-GFP, 6.0 kb) via the polyethylene glycol (PEG)-mediated transformation. Moreover, the mannitol concentration (optimal: 0.7 M) was determined as a key factor affecting areca protoplast isolation. We also demonstrated that the optimal density of areca protoplast for efficient transformation was at 1.0-1.5 × 10⁶ cells/ml. With the optimization of transformation parameters, we have achieved a relatively high transformation efficiency of nearly 50%.

CONCLUSION

We have established the first efficient protocol for the high-yield isolation and transformation of areca palm protoplasts. This method shall be applied in various biological studies of areca palm, such as gene function analysis, genome editing, protein trafficking and localization and protein-protein interaction. In addition, the protoplast system offers a great genetic transformation approach for the woody perennial plant-areca palm. Moreover, the established platform may be applied in protoplast isolation and transformation for other important species in the palm family, including oil palm and coconut.

Application of a novel strong promoter from Chinese fir (Cunninghamia lanceolate) in the CRISPR/Cas mediated genome editing of its protoplasts and transgenesis of rice and poplar

Novel constitutive promoters are essential for plant biotechnology. Although in angiosperms, a number of promoters were applied in monocots or dicots genetic engineering, only a few promoters were used in gymnosperm. Here we identified two strong promoters (Cula11 and Cula08) from Chinese fir (C. lanceolate) by screening the transcriptomic data and preliminary promoter activity assays in tobacco. By using the newly established Chinese fir protoplast transient expression technology that enables in vivo molecular biology studies in its homologous system, we compared the activities of Cula11 and Cula08 with that of the commonly used promoters in genetic engineering of monocots or dicots, such as CaM35S, CmYLCV, and ZmUbi, and our results revealed that Cula11 and Cula08 promoters have stronger activities in Chinese fir protoplasts. Furthermore, the vector containing Cas gene driven by Cula11 promoter and sgRNA driven by the newly isolated CulaU6b polyIII promoters were introduced into Chinese fir protoplasts, and CRISPR/Cas mediated gene knock-out event was successfully achieved. More importantly, compared with the commonly used promoters in the genetic engineering in angiosperms, Cula11 promoter has much stronger activity than CaM35S promoter in transgenic poplar, and ZmUbi promoter in transgenic rice, respectively, indicating its potential application in poplar and rice genetic engineering. Overall, the novel putative constitutive gene promoters reported here will have great potential application in gymnosperm and angiosperm biotechnology, and the transient gene expression system established here will serve as a useful tool for the molecular and genetic analyses of Chinese fir genes.

Protoplast isolation and transient gene expression in different petunia cultivars

The protocol optimized for Petunia hybrida cv. Mirage Rose produced high protoplast yields in 3 out of other 11 cultivars (Damask White, Dreams White, and Opera Supreme White). Factors optimized in the protoplast transfection process showed that the best transfection efficiency (80%) was obtained using 2.5 × 10⁵ protoplast density, 40% polyethylene glycol (PEG) concentration, 10 µg plasmid DNA, and 15 min of transfection time. Assessing the usability of the protocol for other cultivars (Damask White, Dreams White, and Opera Supreme White), a reasonable protoplast transfection efficiency (⁓50%) was observed in the cultivars Dreams White and Opera Supreme White, with lower efficiency (⁓50%) observed in the cv. Damask White. The transient expression of enhanced green fluorescent protein (eGFP) in the nucleus of the transfected protoplasts of all cultivars was confirmed using PCR. This system could be valuable for genome editing of unwanted genes in petunias using the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated 9 (Cas9) technology. Furthermore, it could contribute to other studies on protein subcellular localization, protein-protein interactions, and functional gene expression in the petunias.

Isolation, purification and PEG-mediated transient expression of mesophyll protoplasts in Camellia oleifera

BACKGROUND

Camellia oleifera (C. oleifera) is a woody edible oil crop of great economic importance. Because of the lack of modern biotechnology research, C. oleifera faces huge challenges in both breeding and basic research. The protoplast and transient transformation system plays an important role in biological breeding, plant regeneration and somatic cell fusion. The objective of this present study was to develop a highly efficient protocol for isolating and purifying mesophyll protoplasts and transient transformation of C. oleifera. Several critical factors for mesophyll protoplast isolation from C. oleifera, including starting material (leaf age), pretreatment, enzymatic treatment (type of enzyme, concentration and digestion time), osmotic pressure and purification were optimized. Then the factors affecting the transient transformation rate of mesophyll protoplasts such as PEG molecular weights, PEG4000 concentration, plasmid concentration and incubation time were explored.

RESULTS

The in vitro grown seedlings of C. oleifera 'Huashuo' were treated in the dark for 24 h, then the 1st to 2nd true leaves were picked and vacuumed at - 0.07 MPa for 20 min. The maximum yield (3.5 × 10⁷/g·FW) and viability (90.9%) of protoplast were reached when the 1st to 2nd true leaves were digested in the enzymatic solution containing1.5% (w/v) Cellulase R-10, 0.5% (w/v) Macerozyme R-10 and 0.25% (w/v) Snailase and 0.4 M mannitol for 10 h. Moreover, the protoplast isolation method was also applicable to the other two cultivars, the protoplast yield for 'TXP14' and 'DP47' was 1.1 × 10⁷/g·FW and 2.6 × 10⁷/g·FW, the protoplast viability for 'TXP14' and 'DP47' was 90.0% and 88.2%. The purification effect was the best when using W buffer as a cleaning agent by centrifugal precipitation. The maximum transfection efficiency (70.6%) was obtained with the incubation of the protoplasts with 15 µg plasmid and 40% PEG4000 for 20 min.

CONCLUSION

In summary, a simple and efficient system for isolation and transient transformation of C. oleifera mesophyll protoplast is proposed, which is of great significance in various aspects of C. oleifera research, including the study of somatic cell fusion, genome editing, protein function, signal transduction, transcriptional regulation and multi-omics analyses.

Genome-wide identification of heat shock transcription factor families in perennial ryegrass highlights the role of LpHSFC2b in heat stress response

Perennial ryegrass (Lolium perenne) is a cool-season turf and forage grass. Heat shock transcription factors (HSFs) play an important role in regulating plant abiotic stress. However, HSFs in perennial ryegrass have rarely been characterized. Here, 25 LpHSFs were identified from the perennial ryegrass genome. Phylogenetic analysis showed that the LpHSFs could be classified into 12 subclasses. Gene structure analysis showed that 22 LpHSFs have only one intron. Cis-acting elements analysis revealed that the promoter of 15 LpHSFs contained hormone-responsive and abiotic stress-responsive elements. Expression profile analysis indicated that 24 LpHSFs were differentially expressed under submerge, drought, heat, and cold stresses. In addition, a subclass C2 gene, LpHSFC2b, was significantly induced by abiotic stresses. The LpHSFC2b protein is localized to the nucleus, and heterologous expression of LpHSFC2b in Arabidopsis improves plant thermotolerance. This study provides insights useful for the breeding of stress tolerance in perennial ryegrass.

Callus Induction from Diverse Explants and Genotypes Enables Robust Transformation of Perennial Ryegrass (Lolium perenne L.)

Genetic transformation of perennial ryegrass (Lolium perenne L.) is critical for fundamental and translational research in this important grass species. It often relies on Agrobacterium-mediated transformation of callus tissue. However, callus induction is restricted to a few genotypes that respond well to tissue culture. Here, we report callus induction from different perennial ryegrass genotypes and explants, such as shoot tips, seeds, and anthers, which were transformed with several plasmids for functional genomics. β-glucuronidase (GUS) histochemical staining showed the LmdsRNAbp promoter sequence was active in stigmas, spikelets, anthers, and leaves. We also transformed calli with plasmids allowing gene silencing and gene knock-out using RNA interference and CRISPR/Cas9, respectively, for which genotypic and phenotypic investigations are ongoing. Using 19 different constructs, 262 transgenic events were regenerated. Moreover, the protocol regenerated a doubled haploid transgenic event from anther-derived calli. This work provides a proof-of-concept method for expanding the range of genotypes amenable to transformation, thus, serving research and breeding initiatives to improve this important grass crop for forage and recreation.

A Rapid and Efficient Method for Isolation and Transformation of Cotton Callus Protoplast

Protoplasts, which lack cell walls, are ideal research materials for genetic engineering. They are commonly employed in fusion (they can be used for more distant somatic cell fusion to obtain somatic hybrids), genetic transformation, plant regeneration, and other applications. Cotton is grown throughout the world and is the most economically important crop globally. It is therefore critical to study successful extraction and transformation efficiency of cotton protoplasts. In the present study, a cotton callus protoplast extraction method was tested to optimize the ratio of enzymes (cellulase, pectinase, macerozyme R-10, and hemicellulase) used in the procedure. The optimized ratio significantly increased the quantity and activity of protoplasts extracted. We showed that when enzyme concentrations of 1.5% cellulase and 1.5% pectinase, and either 1.5% or 0.5% macerozyme and 0.5% hemicellulase were used, one can obtain increasingly stable protoplasts. We successfully obtained fluorescent protoplasts by transiently expressing fluorescent proteins in the isolated protoplasts. The protoplasts were determined to be suitable for use in further experimental studies. We also studied the influence of plasmid concentration and transformation time on protoplast transformation efficiency. When the plasmid concentration reaches 16 µg and the transformation time is controlled within 12–16 h, the best transformation efficiency can be obtained. In summary, this study presents efficient extraction and transformation techniques for cotton protoplasts.

The NAC factor LpNAL delays leaf senescence by repressing two chlorophyll catabolic genes in perennial ryegrass

Expression of chlorophyll (Chl) catabolic genes during leaf senescence is tightly controlled at the transcriptional level. Here, we identified a NAC family transcription factor, LpNAL, involved in regulating Chl catabolic genes via the yeast one-hybrid system based on truncated promoter analysis of STAYGREEN (LpSGR) in perennial ryegrass (Lolium perenne L.). LpNAL was found to be a transcriptional repressor, directly repressing LpSGR as well as the Chl b reductase gene, NONYELLOWING COLORING1. Perennial ryegrass plants over-expressing LpNAL exhibited delayed leaf senescence or stay-green phenotypes, whereas knocking down LpNAL using RNA interference accelerated leaf senescence. Comparative transcriptome analysis of leaves at 30 d after emergence in wild-type, LpNAL-overexpression, and knock-down transgenic plants revealed that LpNAL-regulated stay-green phenotypes possess altered light reactions of photosynthesis, antioxidant metabolism, ABA and ethylene synthesis and signaling, and Chl catabolism. Collectively, the transcriptional repressor LpNAL targets both Chl a and Chl b catabolic genes and acts as a brake to fine-tune the rate of Chl degradation during leaf senescence in perennial ryegrass.

Zoysia japonica Chlorophyll b Reductase Gene NOL Participates in Chlorophyll Degradation and Photosynthesis

The degradation of chlorophyll is of great significance to plant growth. The chlorophyll b reductase NOL (NYC1-like) is in charge of catalyzing the degradation of chlorophyll b and maintaining the stability of the photosystem. However, the molecular mechanisms of NOL-mediated chlorophyll degradation, senescence, and photosynthesis and its functions in other metabolic pathways remain unclear, especially in warm-season turfgrass. In this study, ZjNOL was cloned from Zoysia japonica. It is highly expressed in senescent leaves. Subcellular localization investigation showed ZjNOL is localized in the chloroplast and the bimolecular fluorescence complementation (BiFC) results proved ZjNOL interacts with ZjNYC1 in vivo. ZjNOL promoted the accumulation of abscisic acid (ABA) and carbohydrates, and the increase of SAG14 at the transcriptional level. ZjNOL simultaneously led to the excessive accumulation of reactive oxygen species (ROS), the activation of antioxidant enzymes, and the generation of oxidative stress, which in turn accelerated senescence. Chlorophyll fluorescence assay (JIP-test) analysis showed that ZjNOL inhibited photosynthetic efficiency mainly through damage to the oxygen-evolving complex. In total, these results suggest that ZjNOL promotes chlorophyll degradation and senescence and negatively affects the integrity and functionality of the photosystem. It could be a valuable candidate gene for genome editing to cultivate Z. japonica germplasm with prolonged green period and improved photosynthesis efficiency.

Knock down of NON-YELLOW COLOURING 1-like gene or chlorophyllin application enhanced chlorophyll accumulation with antioxidant roles in suppressing heat-induced leaf senescence in perennial ryegrass

Loss of chlorophyll and oxidative damage co-occur during heat-induced leaf senescence. This study aimed to determine the functions of a chlorophyll catabolic gene, NON-YELLOW COLOURING 1 (NYC1)-like (NOL), in regulating heat-induced leaf senescence and to characterize antioxidant roles of a chlorophyll derivative, sodium copper chlorophyllin (SCC), in suppressing heat-induced leaf senescence. In two separate experiments, one by comparing NOL RNAi transgenic and wild-type plants, and the other by analysing the effects of SCC treatment, perennial ryegrass (Lolium perenne) was exposed to heat stress (38/35 °C, day/night) or optimal temperature (25/20 °C). Results showed that both knock down of LpNOL and application of SCC suppressed heat-induced leaf senescence, as manifested by increased chlorophyll content, reduced electrolyte leakage, down-regulation of chlorophyll-catabolic genes and senescence-related genes, as well as enhanced antioxidant capacity in the peroxidase pathway for H2O2 scavenging. Ex vivo SCC incubation protected membranes from H2O2 damage in mesophyll protoplasts of perennial ryegrass. The suppression of leaf senescence by knocking down NOL or chlorophyllin application was associated with enhanced chlorophyll accumulation playing antioxidant roles in protecting leaves from heat-induced oxidative damage.

Protoplast Isolation and Transfection in Wheat

Wheat is one of the major staple crops around the world. A transient expression system is crucial for gene functional studies in wheat as stable transfection is still difficult in most cultivars. Protoplasts could serve as a versatile transient expression tool in wheat research. Here, we describe protocols for wheat protoplast isolation and transfection that are enabled by cellulase R-10 and macerozyme R-10 containing enzymatic solution and polyethylene glycol-mediated method, respectively. In addition, we show an example of efficiency evaluation of the emerging base editors in wheat protoplasts. These protocols are of wide use in both conventional gene functional analysis and reagent functionality evaluation of genome editing in wheat.

NOL-mediated functional stay-green traits in perennial ryegrass (Lolium perenne L.) involving multifaceted molecular factors and metabolic pathways regulating leaf senescence

Loss of chlorophyll (Chl) is a hallmark of leaf senescence, which may be regulated by Chl catabolic genes, including NON-YELLOW COLORING 1 (NYC1)-like (NOL). The objective of this study was to determine molecular factors and metabolic pathways underlying NOL regulation of leaf senescence in perennial grass species. LpNOL was cloned from perennial ryegrass (Lolium perenne L.) and found to be highly expressed in senescent leaves. Transient overexpression of LpNOL accelerated leaf senescence and Chl b degradation in Nicotiana benthamiana. LpNOL RNA interference (NOLi) in perennial ryegrass not only significantly blocked Chl degradation in senescent leaves, but also delayed initiation and progression of leaf senescence. This study found that NOL, in addition to functioning as a Chl b reductase, could enact the functional stay-green phenotype in perennial grass species, as manifested by increased photosynthetic activities in NOLi plants. Comparative transcriptomic analysis revealed that NOL-mediated functional stay-green in perennial ryegrass was mainly achieved through the modulation of Chl catabolism, light harvesting for photosynthesis, photorespiration, cytochrome respiration, carbohydrate catabolism, oxidative detoxification, and abscisic acid biosynthesis and signaling pathways.

Transfection of Arctic Bryum sp. KMR5045 as a Model for Genetic Engineering of Cold-Tolerant Mosses

Mosses number about 13,000 species and are an important resource for the study of the plant evolution that occurred during terrestrial colonization by plants. Recently, the physiological and metabolic characteristics that distinguish mosses from terrestrial plants have received attention. In the Arctic, in particular, mosses developed their own distinct physiological features to adapt to the harsh environment. However, little is known about the molecular mechanisms by which Arctic mosses survive in extreme environments due to the lack of basic knowledge and tools such as genome sequences and genetic transfection methods. In this study, we report the axenic cultivation and transfection of Arctic Bryum sp. KMR5045, as a model for bioengineering of Arctic mosses. We also found that the inherent low-temperature tolerance of KMR5045 permitted it to maintain slow growth even at 2°C, while the model moss species Physcomitrium patens failed to grow at all, implying that KMR5045 is suitable for studies of cold-tolerance mechanisms. To achieve genetic transfection of KMR5045, some steps of the existing protocol for P. patens were modified. First, protoplasts were isolated using 1% driselase solution. Second, the appropriate antibiotic was identified and its concentration was optimized for the selection of transfectants. Third, the cell regeneration period before transfer to selection medium was extended to 9 days. As a result, KMR5045 transfectants were successfully obtained and confirmed transfection by detection of intracellular Citrine fluorescence derived from expression of a pAct5:Citrine transgene construct. This is the first report regarding the establishment of a genetic transfection method for an Arctic moss species belonging to the Bryaceae. The results of this study will contribute to understanding the function of genes involved in environmental adaptation and to application for production of useful metabolites derived from stress-tolerant mosses.

Organelle Visualization With Multicolored Fluorescent Markers in Bamboo

Bamboo is an important model plant to study the molecular mechanisms of rapid shoot growth and flowering once in a lifetime. However, bamboo research about protein functional characterization is largely lagged behind, mainly due to the lack of gene transformation platforms. In this study, a protoplast transient gene expression system in moso bamboo has been first established. Using this reliable and efficient system, we have generated a set of multicolored fluorescent markers based on the targeting sequences from endogenous proteins, which have been validated by their comparative localization with Arabidopsis organelle markers, in a combination with pharmaceutical treatments. Moreover, we further demonstrated the power of this multicolor marker set for rapid, combinatorial analysis of the subcellular localization of uncharacterized proteins, which may play potential functions in moso bamboo flowering and fast growth of shoots. Finally, this protoplast transient gene expression system has been elucidated for functional analysis in protein-protein interaction by fluorescence resonance energy transfer (FRET) and co-immunoprecipitation analysis. Taken together, in combination with the set of moso bamboo organelle markers, the protoplast transient gene expression system could be used for subcellular localization and functional study of unknown proteins in bamboo and will definitely promote rapid progress in diverse areas of research in bamboo plants.

Genetic Transformation of Protoplasts Isolated from Leaves of Lolium temulentum and Lolium perenne

Transient expression of inserted recombinant DNA in plant protoplasts is a widely used tool for functional genomics research. Recently it has been utilized to screen potential sgRNA guides for CRISPR-mediated genome editing. However, little research has been conducted into the use of transient expression of protoplasts in Lolium perenne (a globally important pasture, hay, and amenity grass), and no studies have been conducted into Lolium temulentum (a weed in cereal crops but a potentially useful model species for Lolium research). In this chapter, we describe a methodology of protoplast extraction and transformation from 14-day-old leaf mesophyll cells from L. perenne and L. temulentum. We believe this is the first report of a procedure for obtaining high density, viable protoplasts from L. temulentum. The method of polyethylene glycol (PEG)-mediated transformation is also described to achieve genetic transformation of protoplasts.

Simple protoplast isolation system for gene expression and protein interaction studies in pineapple (Ananas comosus L.)

Background

An efficient transformation protocol is a primary requisite to study and utilize the genetic potential of any plant species. A quick transformation system is also crucial for the functional analysis of genes along with the study of proteins and their interactions in vivo. Presently, however, quick and effective transformation systems are still lacking for many plant species including pineapple. This has limited the full exploration of the genetic repository of pineapple as well as the study of its genes, protein localization and protein interactions.

Results

To address the above limitations, we have developed an efficient system for protoplast isolation and subcellular localization of desired proteins using pineapple plants derived from tissue culture. A cocktail of 1.5% (W/V) Cellulase R-10 and 0.5% (W/V) Macerozyme R-10 resulted in 51% viable protoplasts with 3 h digestion. Compared to previously reported protocols, our protoplast isolation method is markedly faster (saving 4.5 h), requires only a small quantity of tissue sample (1 g of leaves) and has high yield (6.5 × 105). The quality of the isolated protoplasts was verified using organelle localization in protoplasts with different organelle markers. Additionally, colocalization analysis of two pineapple Mg2+ transporter genes in pineapple protoplasts was consistent with the results in a tobacco transient expression system, confirming that the protoplast isolation method can be used to study subcellular localization. Further findings showed that the system is also suitable for protein-protein interaction studies.

Conclusion

Based on our findings, the presently described method is an efficient and effective strategy for pineapple protoplast isolation and transformation; it is convenient and time saving and provides a greater platform for transformation studies.

An Efficient Protocol for Model Legume Root Protoplast Isolation and Transformation

Transient gene expression systems using protoplasts have been widely used for rapid functional characterization of genes and high-throughput analysis in many model and crop species. Here, we describe a simplified and highly efficient root protoplast isolation and transient expression system in the model legumes Lotus japonicus and Medicago truncatula. Firstly, we presented an efficient protocol for isolating protoplasts from L. japonicus and M. truncatula roots. We then established an efficient transient expression system in these legumes root protoplasts. Using this protocol, the subcellular localization of two symbiosis related proteins (SYMRK and ERN1) were visualized in the plasma membrane and nuclei, respectively. Collectively, this efficient protoplast isolation and transformation protocol is sufficient for studies on protein subcellular localization, and should be suitable for many other molecular biology applications.