Transgenic Sugarcane with a cry1Ac Gene Exhibited Better Phenotypic Traits and Enhanced Resistance against Sugarcane Borer

Transgenic early japonica rice: Integration and expression characterization of stem borer resistance Bt gene

BACKGROUND

Transgenic insect-resistant rice offers an environmentally friendly approach to mitigate yield losses caused by lepidopteran pests, such as stem borers. Bt (Bacillus thuringiensis) genes encode insecticidal proteins and are widely used to confer insect resistance to genetically modified crops. This study investigated the integration, inheritance, and expression characteristics of codon-optimised synthetic Bt genes, cry1C* and cry2A*, in transgenic early japonica rice lines.

METHODS

The early japonica rice cultivar, Songgeng 9 (Oryza sativa), was transformed with cry1C* or cry2A*, which are driven by the ubi promoter via Agrobacterium tumefaciens-mediated transformation. Molecular analyses, including quantitative PCR (qPCR), enzyme-linked immunosorbent assay (ELISA), and Southern blot analysis were performed to confirm transgene integration, inheritance, transcriptional levels, and protein expression patterns across different tissues and developmental stages.

RESULTS

Stable transgenic early japonica lines exhibiting single-copy transgene integration were established. Transcriptional analysis revealed variations in Bt gene expression among lines, tissues, and growth stages, with higher expression levels observed in leaves than in other organs. Notably, cry2A* exhibited consistently higher mRNA and protein levels than cry1C* across all examined tissues and developmental time points. Bt protein accumulation followed the trend of leaves > stem sheaths > young panicles > brown rice, with peak expression during the filling stage in the vegetative tissues.

CONCLUSIONS

Synthetic cry2A* displayed markedly elevated transcription and translation compared to cry1C* in the transgenic early japonica rice lines examined. Distinct spatiotemporal patterns of Bt gene expression were elucidated, providing insights into the potential insect resistance conferred by these genes in rice. These findings will contribute to the development of insect-resistant japonica rice varieties and facilitate the rational deployment of Bt crops.

Genetic Engineering for Enhancing Sugarcane Tolerance to Biotic and Abiotic Stresses

Sugarcane, a vital cash crop, contributes significantly to the world's sugar supply and raw materials for biofuel production, playing a significant role in the global sugar industry. However, sustainable productivity is severely hampered by biotic and abiotic stressors. Genetic engineering has been used to transfer useful genes into sugarcane plants to improve desirable traits and has emerged as a basic and applied research method to maintain growth and productivity under different adverse environmental conditions. However, the use of transgenic approaches remains contentious and requires rigorous experimental methods to address biosafety challenges. Clustered regularly interspaced short palindromic repeat (CRISPR) mediated genome editing technology is growing rapidly and may revolutionize sugarcane production. This review aims to explore innovative genetic engineering techniques and their successful application in developing sugarcane cultivars with enhanced resistance to biotic and abiotic stresses to produce superior sugarcane cultivars.

Factors affecting the production of sugarcane yield and sucrose accumulation: suggested potential biological solutions

Environmental stresses are the main constraints on agricultural productivity and food security worldwide. This issue is worsened by abrupt and severe changes in global climate. The formation of sugarcane yield and the accumulation of sucrose are significantly influenced by biotic and abiotic stresses. Understanding the biochemical, physiological, and environmental phenomena associated with these stresses is essential to increase crop production. This review explores the effect of environmental factors on sucrose content and sugarcane yield and highlights the negative effects of insufficient water supply, temperature fluctuations, insect pests, and diseases. This article also explains the mechanism of reactive oxygen species (ROS), the role of different metabolites under environmental stresses, and highlights the function of environmental stress-related resistance genes in sugarcane. This review further discusses sugarcane crop improvement approaches, with a focus on endophytic mechanism and consortium endophyte application in sugarcane plants. Endophytes are vital in plant defense; they produce bioactive molecules that act as biocontrol agents to enhance plant immune systems and modify environmental responses through interaction with plants. This review provides an overview of internal mechanisms to enhance sugarcane plant growth and environmental resistance and offers new ideas for improving sugarcane plant fitness and crop productivity.

Cell wall-localized Bt protein endows rice high resistance to Lepidoptera pests

BACKGROUND

The commercialized Bt (Bacillus thuringiensis) crops accumulate Bt protein within cells, but the intracellular interactions of foreign protein with endogenous protein inevitably result in large or small unintended effects. In this study, the Bt gene Cry1Ca was linked with the sequences of extracellular secretion signal peptide and carbohydrate binding module 11 to constitute a fusion gene SP-Cry1Ca-CBM11, and the fusion gene driven by constitutive promoters was used for secreting and anchoring onto the cell wall to minimize unintended effects.

RESULTS

The transient expression in tobacco leaves demonstrated that the fusion protein was anchored on cell walls. The Cry1Ca contents of five homozygous rice transformants of single-copy insertion were different and descended in the order leaf > root > stem. The maximum content of Cry1Ca was 17.55 μg g-1 in leaves of transformant 21H037. The bioassay results revealed that the transformants exhibited high resistance to lepidopteran pests. The corrected mortality of pink stem borer (Sesamia inferens) and striped stem borer (Chilo suppressalis) ranged from 96.33% to 100%, and from 83.32% to 100%, respectively, and the corrected mortality of rice leaf roller (Cnaphalocrocis medinalis) was 92.53%. Besides, the agronomic traits of the five transformants were normal and similar to that of the recipient, and the transformants were highly resistant to glyphosate at the germination and seedling stages.

CONCLUSION

The fusion Bt protein was accumulated on cell walls and endowed the rice with high resistance to lepidopteran pests without unintended effects in agronomic traits. © 2023 Society of Chemical Industry.

Developing new sugarcane varieties suitable for mechanized production in China: principles, strategies and prospects

The sugar industry, which relates to people's livelihood, is strategic and fundamental in the development of agricultural economy. In China, sugar derived from sugarcane accounts for approximately 85% of total sugar production. Mechanization is the "flower" of sugarcane industry. As the saying goes "when there are blooming flowers, there will be sweet honey." However, due to limitations in land resources, technology, equipment, organization, and management, mechanization throughout the sugarcane production process has not yet brought about the economic benefits that a mechanized system should provide and has not reached an ideal yield through the integration of agricultural machinery and agronomic practice. This paper briefly describes how to initiate the mechanization of Chinese sugarcane production to promote the sound, healthy, and rapid development of the sugarcane industry, and how to ultimately achieve the transformation of sugarcane breeding in China and the modernization of the sugarcane industry from three perspectives, namely, requirements of mechanized production for sugarcane varieties, breeding strategies for selecting new sugarcane varieties suitable for mechanized production, and screening for sugarcane varieties that are suitable for mechanization and diversification in variety distribution or arrangement in China. We also highlight the current challenges surrounding this topic and look forward to its bright prospects.

Integrating the Soil Microbiota and Metabolome Reveals the Mechanism through Which Controlled Release Fertilizer Affects Sugarcane Growth

Root-soil underground interactions mediated by soil microorganisms and metabolites are crucial for fertilizer utilization efficiency and crop growth regulation. This study employed a combined approach of soil microbial community profiling and non-targeted metabolomics to investigate the patterns of root-associated microbial aggregation and the mechanisms associated with metabolites under varying controlled-release fertilizer (CRF) application rates. The experimental treatments included five field application rates of CRF (D1: 675 kg/ha; D15: 1012.5 kg/ha; D2: 1350 kg/ha; D25: 1687.5 kg/ha; and D3: 2025 kg/ha) along with traditional fertilizer as a control (CK: 1687.5 kg/ha). The results indicated that the growth of sugarcane in the field was significantly influenced by the CRF application rate (p < 0.05). Compared with CK, the optimal field application of CRF was observed at D25, resulting in a 16.3% to 53.6% increase in sugarcane yield. Under the condition of reducing fertilizer application by 20%, D2 showed a 13.3% increase in stem yield and a 6.7% increase in sugar production. The bacterial ACE index exhibited significant differences between D25 and D1, while the Chao1 index showed significance among the D25, D1, and CK treatments. The dominant bacterial phyla in sugarcane rhizosphere aggregation included Proteobacteria, Actinobacteriota, and Acidobacteriota. Fungal phyla comprised Rozellomycota, Basidiomycota, and Ascomycota. The annotated metabolic pathways encompassed biosynthesis of secondary metabolites, carbohydrate metabolism, and lipid metabolism. Differential analysis and random forest selection identified distinctive biomarkers including Leotiomycetes, Cercospora, Anaeromyxobacter, isoleucyl-proline, and methylmalonic acid. Redundancy analysis unveiled soil pH, soil organic carbon, and available nitrogen as the primary drivers of microbial communities, while the metabolic profiles were notably influenced by the available potassium and phosphorus. The correlation heatmaps illustrated potential microbial-metabolite regulatory mechanisms under CRF application conditions. These findings underscore the significant potential of CRF in sugarcane field production, laying a theoretical foundation for sustainable development in the sugarcane industry.

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.

New methods for sorghum transformation in temperate climates

Sorghum (Sorghum bicolor) is an emerging cereal crop in temperate climates due to its high drought tolerance and other valuable traits. Genetic transformation is an important tool for the improvement of cereals. However, sorghum is recalcitrant to genetic transformation which is almost only successful in warmer climates. Here, we test the application of two new techniques for sorghum transformation in temperate climates, namely transient transformation by Agrobacterium tumefaciens-mediated agroinfiltration and stable transformation using gold particle bombardment and leaf whorls as explants. We optimized the transient transformation method, including post-infiltration incubation of plants in the dark and using Agrobacterium grown on plates with a high cell density (OD₆₀₀ = 2.0). Expression of the green fluorescence protein (GFP)-tagged endogenous sorghum gene SbDHR2 was achieved with low transformation efficiency, and our results point out a potential weakness in using this approach for localization studies. Furthermore, we succeeded in the production of callus and somatic embryos from leaf whorls, although no genetic transformation was accomplished with this method. Both methods show potential, even if they seem to be influenced by climatic conditions and therefore need further optimization to be applied routinely in temperate climates.

Correlation of microbiomes in "plant-insect-soil" ecosystem

Introduction

Traditional chemical control methods pose a damaging effect on farmland ecology, and their long-term use has led to the development of pest resistance.

Methods

Here, we analyzed the correlations and differences in the microbiome present in the plant and soil of sugarcane cultivars exhibiting different insect resistance to investigate the role played by microbiome in crop insect resistance. We evaluated the microbiome of stems, topsoil, rhizosphere soil, and striped borers obtained from infested stems, as well as soil chemical parameters.

Results and Discussion

Results showed that microbiome diversity was higher in stems of insect-resistant plants, and contrast, lower in the soil of resistant plants, with fungi being more pronounced than bacteria. The microbiome in plant stems was almost entirely derived from the soil. The microbiome of insect-susceptible plants and surrounding soil tended to change towards that of insect-resistant plants after insect damage. Insects' microbiome was mainly derived from plant stems and partly from the soil. Available potassium showed an extremely significant correlation with soil microbiome. This study validated the role played by the microbiome ecology of plant-soil-insect system in insect resistance and provided a pre-theoretical basis for crop resistance control.

Genetic engineering: an efficient approach to mitigating biotic and abiotic stresses in sugarcane cultivation

Abiotic stresses are the foremost limiting factors for crop productivity. Crop plants need to cope with adverse external pressure caused by various environmental conditions with their intrinsic biological mechanisms to keep their growth, development, and productivity. Climate-resilient, high-yielding crops need to be developed to maintain sustainable food supply. Over the last decade, understanding of the genetic complexity of agronomic traits in sugarcane has prompted the integrated application of genetic engineering to address specific biological questions. Genes for adaptation to environmental stress and yield enhancement traits are being determined and introgressed to develop elite sugarcane cultivars with improved characteristics through genetic engineering approaches. Here, we discuss the advancement to provide a reference for future sugarcane (Saccharum spp.) genetic engineering.

Overexpression of the AGL42 gene in cotton delayed leaf senescence through downregulation of NAC transcription factors

Premature leaf senescence negatively influences the physiology and yield of cotton plants. The conserved IDLNL sequence in the C-terminal region of AGL42 MADS-box determines its repressor potential for the down regulation of senescence-related genes. To determine the delay in premature leaf senescence, Arabidopsis AGL42 gene was overexpressed in cotton plants. The absolute quantification of transgenic cotton plants revealed higher mRNA expression of AGL42 compared to that of the non-transgenic control. The spatial expression of GUS fused with AGL42 and the mRNA level was highest in the petals, abscission zone (flower and bud), 8 days post anthesis (DPA) fiber, fresh mature leaves, and senescenced leaves. The mRNA levels of different NAC senescence-promoting genes were significantly downregulated in AGL42 transgenic cotton lines than those in the non-transgenic control. The photosynthetic rate and chlorophyll content were higher in AGL42 transgenic cotton lines than those in the non-transgenic control. Fluorescence in situ hybridization of the AG3 transgenic cotton line revealed a fluorescent signal on chromosome 1 in the hemizygous form. Moreover, the average number of bolls in the transgenic cotton lines was significantly higher than that in the non-transgenic control because of the higher retention of floral buds and squares, which has the potential to improve cotton fiber yield.

Expression Analysis and Interaction Protein Screening of CRY1 in Strawberry

Cryptochrome 1 (CRY1), a main blue light receptor protein, plays a significant role in several biological processes. However, the expression patterns and function of CRY1 in strawberry have not been identified. Here, the expression profile of CRY1 in different tissues and developmental stages of strawberry fruit, and expression patterns response to abiotic stresses (low temperature, salt and drought) were analyzed. Its subcellular localization, interaction proteins and heterologous overexpression in tobacco were also investigated. The results showed that CRY1 was mainly expressed in leaves and fruits with an expression peak at the initial red stage in strawberry fruit. Abiotic stresses could significantly induce the expression of CRY1. The CRY1 protein was located in both nucleus and cytoplasm. Five proteins (CSN5a-like, JAZ5, eIF3G. NF-YC9, and NDUFB9) interacting with CRY1 were discovered. Genes related flowering times, such as HY5 and CO, in three overexpressed FaCRY1 tobacco lines, were significantly upregulated. Taken together, our results suggested CRY1 have a broad role in biological processes in strawberry.

A highly efficient stratagem for protoplast isolation and genetic transformation in filamentous fungus Colletotrichum falcatum

Red rot of sugarcane caused by the hemi-biotrophic fungal pathogen, Colletotrichum falcatum, is a major threat to sugarcane cultivation in many tropical countries such as India, Bangladesh, and Pakistan. With the accumulating information on pathogenicity determinants, namely, effectors and pathogen-associated molecular patterns (PAMPs) of C. falcatum, it is of paramount importance to decipher the functional role of these molecular players that may ultimately decide upon the outcome of sugarcane-C. falcatum interaction. Since C. falcatum is a multinucleated filamentous fungus, the conventional Agrobacterium-mediated transformation method could not be effectively utilized for targeted manipulation of genomic DNA. Hence, we developed a highly efficient protoplast-based transformation method for the virulent pathotype of C. falcatum - Cf671, which involves isolation of protoplast, polyethylene glycol (PEG)-mediated transformation, and regeneration of transformed protoplasts into hyphal colonies. In this study, germinating conidiospores of Cf671 were treated with different enzyme-osmoticum combinations, out of which 20 mg/mL lysing enzyme with 5 mg/mL β-glucanase in an osmoticum of 1.2 mol/L MgSO₄ yielded maximum number of viable protoplasts. The resultant protoplasts were transformed with pAsp shuttle vector. Transformed protoplasts were regenerated into hyphal colonies under hygromycin selection and observed for GFP fluorescence. This protocol resulted in a transformation efficiency of > 130 transformants per μg of plasmid DNA. This method of transformation is rapid, simple, and more efficient for gene knockout, site-directed mutagenesis, ectopic expression, and other genetic functional characterization experiments in C. falcatum, even with large vectors (> 10 kb) and can also be applied for other filamentous fungi.

Convergence of Bar and Cry1Ac Mutant Genes in Soybean Confers Synergistic Resistance to Herbicide and Lepidopteran Insects

Soybean is a globally important crop species, which is subject to pressure by insects and weeds causing severe substantially reduce yield and quality. Despite the success of transgenic soybean in terms of Bacillus thuringiensis (Bt) and herbicide tolerance, unforeseen mitigated performances have still been inspected due to climate changes that favor the emergence of insect resistance. Therefore, there is a need to develop a biotech soybean with elaborated gene stacking to improve insect and herbicide tolerance in the field. In this study, new gene stacking soybean events, such as bialaphos resistance (bar) and pesticidal crystal protein (cry)1Ac mutant 2 (M#2), are being developed in Vietnamese soybean under field condition. Five transgenic plants were extensively studied in the herbicide effects, gene expression patterns, and insect mortality across generations. The increase in the expression of the bar gene by 100% in the leaves of putative transgenic plants was a determinant of herbicide tolerance. In an insect bioassay, the cry1Ac-M#2 protein tested yielded higher than expected larval mortality (86%), reflecting larval weight gain and weight of leaf consumed were less in the T1 generation. Similarly, in the field tests, the expression of cry1Ac-M#2 in the transgenic soybean lines was relatively stable from T0 to T3 generations that corresponded to a large reduction in the rate of leaves and pods damage caused by Lamprosema indicata and Helicoverpa armigera. The transgenic lines converged two genes, producing a soybean phenotype that was resistant to herbicide and lepidopteran insects. Furthermore, the expression of cry1Ac-M#2 was dominant in the T1 generation leading to the exhibit of better phenotypic traits. These results underscored the great potential of combining bar and cry1Ac mutation genes in transgenic soybean as pursuant of ensuring resistance to herbicide and lepidopteran insects.

Novel approaches to circumvent the devastating effects of pests on sugarcane

Sugarcane (Saccharum officinarum L.) is a cash crop grown commercially for its higher amounts of sucrose, stored within the mature internodes of the stem. Numerous studies have been done for the resistance development against biotic and abiotic stresses to save the sucrose yields. Quality and yield of sugarcane production is always threatened by the damages of cane borers and weeds. In current study two problems were better addressed through the genetic modification of sugarcane for provision of resistance against insects and weedicide via the expression of two modified cane borer resistant CEMB-Cry1Ac (1.8 kb), CEMB-Cry2A (1.9 kb) and one glyphosate tolerant CEMB-GTGene (1.4 kb) genes, driven by maize Ubiquitin Promoter and nos terminator. Insect Bio-toxicity assays were carried out for the assessment of Cry proteins through mortality percent of shoot borer Chilo infuscatellus at 2nd instar larvae stage. During V0, V1 and V2 generations young leaves from the transgenic sugarcane plants were collected at plant age of 20, 40, 60, 80 days and fed to the Chilo infuscatellus larvae. Up to 100% mortality of Chilo infuscatellus from 80 days old transgenic plants of V2 generation indicated that these transgenic plants were highly resistant against shoot borer and the gene expression level is sufficient to provide complete resistance against target pests. Glyphosate spray assay was carried out for complete removal of weeds. In V1-generation, 70-76% transgenic sugarcane plants were found tolerant against glyphosate spray (3000 mL/ha) under field conditions. While in V2-generation, the replicates of five selected lines 4L/2, 5L/5, 6L/5, L8/4, and L9/6 were found 100% tolerant against 3000 mL/ha glyphosate spray. It is evident from current study that CEMB-GTGene, CEMB-Cry1Ac and CEMB-Cry2A genes expression in sugarcane variety CPF-246 showed an efficient resistance against cane borers (Chilo infuscatellus) and was also highly tolerant against glyphosate spray. The selected transgenic sugarcane lines showed sustainable resistance against cane borer and glyphosate spray can be further exploited at farmer's field level after fulfilling the biosafety requirements to boost the sugarcane production in the country.

Genetic Engineering Approaches for Enhanced Insect Pest Resistance in Sugarcane

Sugarcane (Saccharum officinarum), a sugar crop commonly grown for sugar production all over the world, is susceptible to several insect pests attack in addition to bacterial, fungal and viral infections leading to substantial reductions in its yield. The complex genetic makeup and lack of resistant genes in genome of sugarcane have made the conventional breeding a difficult and challenging task for breeders. Using pesticides for control of the attacking insects can harm beneficial insects, human and other animals and the environment as well. As alternative and effective strategy for control of insect pests, genetic engineering has been applied for overexpression of cry proteins, vegetative insecticidal proteins (vip), lectins and proteinase inhibitors (PI). In addition, the latest biotechnological tools such as host-induced gene silencing (HIGS) and CRISPR/Cas9 can be employed for sustainable control of insect pests in sugarcane. In this review overexpression of the cry, vip, lectins and PI genes in transgenic sugarcane and their disease resistance potential is described.

hRNAi-mediated knock-down of Sphenophorus levis V-ATPase E in transgenic sugarcane (Saccharum spp interspecific hybrid) affects the insect growth and survival

Transgenic sugarcane expressing V-ATPase subunit E dsRNA affects growth and survival of Sphenophorus levis. Plants being sessile organisms are constantly confronted with several biotic and abiotic stresses. Sugarcane (Saccharum spp) is a major tropical crop widely cultivated for its sugar and other by-products. In Brazil, sugarcane plantations account for significant production losses due to Sphenophorus levis (sugarcane weevil) infestations. With the existing control measures being less effective, there arises a necessity for advanced strategies. Our bioassay injection experiments with V-ATPase E dsRNA in S. levis larvae showed significant mortality and reduction in transcription levels. Furthermore, we down-regulated the V-ATPase E gene of S. levis in transgenic sugarcane using an RNAi approach. The resultant RNAi transgenic lines exhibited reduction in larval growth and survival, without compromising plant performance under controlled environment. Our results illustrate that RNAi-mediated down-regulation of key genes is a promising approach in imparting resistance to sugarcane weevil.

Improvement of sugarcane for borer resistance using Agrobacterium mediated transformation of cry1Ac gene

The sugarcane (Saccharum X officinarum) is one of the most important crops used to produce sugar and raw material for biofuel in the world. One of the main causes for sucrose content and yield losses is the attack by insect. In this investigation, cry1Ac gene was introduced into sugarcane variety GT54-9(C9) using the Agrobacterium tumefaciens transformation method for transgenic sugarcane production presenting insect-resistance. The A. tumefaciens strain GV1303 including pARTcry1Ac vector was used for the production of transformed sugarcane. The Bacillus thuringiensis cry gene were successfully used to produce transgenic plants used for the improvement of both agronomic efficiency and product quality by acquiring insect resistance. PCR and Southern hybridization techniques were used to confirm the cry1Ac gene incorporation into sugarcane genome. Transformation percentage was 22.2% using PCR analysis with specific primers for cry1Ac and npt-II (Neomycin phosphotransferase) genes. The expression of cry1Ac gene was determined using reverse transcriptase polymerase chain reaction (RT-PCR), QuickStix test, and insect bioassays. Bioassays for transformed sugarcane plants showed high level of toxicity to Sesamia cretica giving 100% mortality of the larvae. Sugarcane insect resistance was improved significantly by using cry1Ac gene transformation.

Genetic Transformation of Sugarcane, Current Status and Future Prospects

Sugarcane (Saccharum spp.) is a tropical and sub-tropical, vegetative-propagated crop that contributes to approximately 80% of the sugar and 40% of the world's biofuel production. Modern sugarcane cultivars are highly polyploid and aneuploid hybrids with extremely large genomes (>10 Gigabases), that have originated from artificial crosses between the two species, Saccharum officinarum and S. spontaneum. The genetic complexity and low fertility of sugarcane under natural growing conditions make traditional breeding improvement extremely laborious, costly and time-consuming. This, together with its vegetative propagation, which allows for stable transfer and multiplication of transgenes, make sugarcane a good candidate for crop improvement through genetic engineering. Genetic transformation has the potential to improve economically important properties in sugarcane as well as diversify sugarcane beyond traditional applications, such as sucrose production. Traits such as herbicide, disease and insect resistance, improved tolerance to cold, salt and drought and accumulation of sugar and biomass have been some of the areas of interest as far as the application of transgenic sugarcane is concerned. Although there have been much interest in developing transgenic sugarcane there are only three officially approved varieties for commercialization, all of them expressing insect-resistance and recently released in Brazil. Since the early 1990's, different genetic transformation systems have been successfully developed in sugarcane, including electroporation, Agrobacterium tumefaciens and biobalistics. However, genetic transformation of sugarcane is a very laborious process, which relies heavily on intensive and sophisticated tissue culture and plant generation procedures that must be optimized for each new genotype to be transformed. Therefore, it remains a great technical challenge to develop an efficient transformation protocol for any sugarcane variety that has not been previously transformed. Additionally, once a transgenic event is obtained, molecular studies required for a commercial release by regulatory authorities, which include transgene insertion site, number of transgenes and gene expression levels, are all hindered by the genomic complexity and the lack of a complete sequenced reference genome for this crop. The objective of this review is to summarize current techniques and state of the art in sugarcane transformation and provide information on existing and future sugarcane improvement by genetic engineering.

Applying Molecular Phenotyping Tools to Explore Sugarcane Carbon Potential

Sugarcane (Saccharum spp.), a C₄ grass, has a peculiar feature: it accumulates, gradient-wise, large amounts of carbon (C) as sucrose in its culms through a complex pathway. Apart from being a sustainable crop concerning C efficiency and bioenergetic yield per hectare, sugarcane is used as feedstock for producing ethanol, sugar, high-value compounds, and products (e.g., polymers and succinate), and bioelectricity, earning the title of the world's leading biomass crop. Commercial cultivars, hybrids bearing high levels of polyploidy, and aneuploidy, are selected from a large number of crosses among suitable parental genotypes followed by the cloning of superior individuals among the progeny. Traditionally, these classical breeding strategies have been favoring the selection of cultivars with high sucrose content and resistance to environmental stresses. A current paradigm change in sugarcane breeding programs aims to alter the balance of C partitioning as a means to provide more plasticity in the sustainable use of this biomass for metabolic engineering and green chemistry. The recently available sugarcane genetic assemblies powered by data science provide exciting perspectives to increase biomass, as the current sugarcane yield is roughly 20% of its predicted potential. Nowadays, several molecular phenotyping tools can be applied to meet the predicted sugarcane C potential, mainly targeting two competing pathways: sucrose production/storage and biomass accumulation. Here we discuss how molecular phenotyping can be a powerful tool to assist breeding programs and which strategies could be adopted depending on the desired final products. We also tackle the advances in genetic markers and mapping as well as how functional genomics and genetic transformation might be able to improve yield and saccharification rates. Finally, we review how "omics" advances are promising to speed up plant breeding and reach the unexplored potential of sugarcane in terms of sucrose and biomass production.

Particle bombardment technology and its applications in plants

Particle bombardment, or biolistics, has emerged as an excellent alternative approach for plant genetic transformation which circumvents the limitations of Agrobacterium-mediated genetic transformation. The method has no biological constraints and can transform a wide range of plant species. Besides, it has been the most efficient way to achieve organelle transformation (for both chloroplasts and mitochondria) so far. Along with the recent advances in genome editing technologies, conventional gene delivery tools are now being repurposed to deliver targeted gene editing reagents into the plants. One of the key advantages is that the particle bombardment allows DNA-free gene editing of the genome. It enables the direct delivery of proteins, RNAs, and RNPs into plants. Owing to the versatility and wide-range applicability of the particle bombardment, it will likely remain one of the major genetic transformation methods in the future. This article provides an overview of the current status of particle bombardment technology and its applications in the field of plant research and biotechnology.

The complete mitochondrial genome and phylogenetic analysis of sugarcane (Saccharum spp. hybrids) line 15a-53

The complete mitogenome of Saccharum spp. hybrid 15a-53 was determined in this study, which contains two distinct circular chromosomes, Chromosome 1 and 2. The length of Chromosome 1 is 300,848 bp with the GC content of 43.93%, while Chromosome 2 is 144,713 bp in length with the GC content of 43.57%. In Chromosome 1, 7.14% of the genome (21,468 nucleotides) is coding DNA and 92.86% (279,380 nucleotides) are intergenic region, while in Chromosome 2, 8.20% of genome (11,865 nucleotides) are coding DNA and 91.80% (132,848 nucleotides) are intergenic region. Chromosome 1 contains 20 protein-coding genes (three atp genes, three ccm genes, two cox genes, one mat gene, one mtt gene, six nad genes, and four rps genes), and 21 non-coding genes (15 tRNA and six rRNAs), while in Chromosome 2, there are 13 protein-coding genes (four nad genes, three rps genes, two atp genes, one ccm gene, one cob gene, one cox gene, and one rpl gene) and five tRNA genes. Maximum Likelihood phylogenetic analysis indicated that 15a-53 is close to S. spp. hybrid ROC22, S. spp. hybrid FN15 and S. officinarum Khon Kaen 3. The complete mitochondrial genome herein will provide useful sequence information for phylogenetic and evolutionary studies for Saccharum and Poaceae.

Resistance to Chilo infuscatellus (Lepidoptera: Pyraloidea) in transgenic lines of sugarcane expressing Bacillus thuringiensis derived Vip3A protein

Sustainable agriculture requires management of insect pests through resistance development. The biological potential of Cry toxins and Vip protein, derived from Bacillus species, is widely recognized in this context. The identification, evaluation of new insecticidal protein genes with different mode of action and entomotoxicity against sugarcane stem borer (Chilo infuscatellus) is important to overcome evolved insect resistance. In this study, we reported the generation of transgenic sugarcane lines expressing Vip3A toxin driven by polyubiquitin promoter for resistance against sugarcane stem borer. The V₀ transgenic sugarcane plants were initially characterized by GUS histochemical staining, PCR and Southern blot assays that confirmed genetic transformation of twelve independent sugarcane lines. Variable transgene expression was found among transgenic sugarcane lines when revealed through Realtime quantitative PCR (RT-qPCR) with highest in S10 line while minimum was observed in V5 line. A similar expression pattern was observed in transgenic sugarcane lines for Vip3A protein concentration which ranged from 5.35 to 8.89 µg/mL. A direct correlation was observed between the Vip3A protein and Vip3A transgene expression in the transgenic sugarcane lines. In in-vitro insect bioassay on V₁, Vip3A transgenic sugarcane lines exhibited high resistance to C. infuscatellus with upto 100% mortality compared to the control sugarcane line. Our findings suggest that a single copy insertion of Vip3A gene in transgenic sugarcane lines render them resistant to borer and these lines can be potentially used for generation of insect resistant transgenic sugarcane and could also be employed in gene pyramiding with Bt toxin to prolong resistance.

Foreign cry1Ac gene integration and endogenous borer stress-related genes synergistically improve insect resistance in sugarcane

BACKGROUND

Sugarcane (Saccharum spp. hybrids) is considered the most globally important sugar-producing crop and raw material for biofuel. Insect attack is a major issue in sugarcane cultivation, resulting in yield losses and sucrose content reductions. Stem borer (Diatraea saccharalis F.) causes serious yield losses in sugarcane worldwide. However, insect-resistant germplasms for sugarcane are not available in any collections all over the world, and the molecular mechanism of insect resistance has not been elucidated. In this study, cry1Ac transgenic sugarcane lines were obtained and the biological characteristics and transgene dosage effect were investigated and a global exploration of gene expression by transcriptome analysis was performed.

RESULTS

The transgene copies of foreign cry1Ac were variable and random. The correlation between the cry1Ac protein and cry1Ac gene copies differed between the transgenic lines from FN15 and ROC22. The medium copy lines from FN15 showed a significant linear relationship, while ROC22 showed no definite dosage effect. The transgenic lines with medium copies of cry1Ac showed an elite phenotype. Transcriptome analysis by RNA sequencing indicated that up/down regulated differentially expressed genes were abundant among the cry1Ac sugarcane lines and the receptor variety. Foreign cry1Ac gene and endogenous borer stress-related genes may have a synergistic effect. Three lines, namely, A1, A5, and A6, were selected for their excellent stem borer resistance and phenotypic traits and are expected to be used directly as cultivars or crossing parents for sugarcane borer resistance breeding.

CONCLUSIONS

Cry1Ac gene integration dramatically improved sugarcane insect resistance. The elite transgenic offspring contained medium transgene copies. Foreign cry1Ac gene integration and endogenous borer stress-related genes may have a synergistic effect on sugarcane insect resistance improvement.

Particle Bombardment of the cry2A Gene Cassette Induces Stem Borer Resistance in Sugarcane

Sugarcane borer is the most common and harmful pest in Chinese sugarcane fields, and can cause damage to the whole plant during the entire growing season. To improve borer resistance in sugarcane, we constructed a plant expression vector pGcry2A0229 with the bar gene as the marker and the cry2A gene as the target, and introduced it into embryogenic calli of most widely cultivated sugarcane cultivar ROC22 by particle bombardment. After screening with phosphinothricin in vitro and Basta spray, 21 resistance-regenerated plants were obtained, and 10 positive transgenic lines harboring the cry2A gene were further confirmed by conventional PCR detection. Real-time quantitative PCR (RT-qPCR) analysis showed that the copy number of the cry2A gene varied among different transgenic lines but did not exceed four copies. Quantitative ELISA analysis showed that there was no linear relationship with copy number but negatively correlated with the percentage of borer-infested plants. The analysis of industrial and agronomic traits showed that the theoretical sugar yields of transgenic lines TR-4 and TR-10 were slightly lower than that of the control in both plant cane and ratoon cane; nevertheless, TR-4 and TR-10 lines exhibited markedly lower in frequency of borer-infested plants in plant cane and in the ratoon cane compared to the control. Our results indicate that the introduction of the cry2A gene via bombardment produces transgenic lines with obviously increased stem borer resistance and comparable sugar yield, providing a practical value in direct commercial cultivation and crossbreeding for ROC22 has been used as the most popular elite genitor in various breeding programs in China.

Application of droplet digital PCR to determine copy number of endogenous genes and transgenes in sugarcane

Droplet digital PCR combined with the low copy ACT allele as endogenous reference gene, makes accurate and rapid estimation of gene copy number in Q208 ^A and Q240 ^A attainable. Sugarcane is an important cultivated crop with both high polyploidy and aneuploidy in its 10 Gb genome. Without a known copy number reference gene, it is difficult to accurately estimate the copy number of any gene of interest by PCR-based methods in sugarcane. Recently, a new technology, known as droplet digital PCR (ddPCR) has been developed which can measure the absolute amount of the target DNA in a given sample. In this study, we deduced the true copy number of three endogenous genes, actin depolymerizing factor (ADF), adenine phosphoribosyltransferase (APRT) and actin (ACT) in three Australian sugarcane varieties, using ddPCR by comparing the absolute amounts of the above genes with a transgene of known copy number. A single copy of the ACT allele was detected in Q208 ^A , two copies in Q240 ^A , but was absent in Q117. Copy number variation was also observed for both APRT and ADF, and ranged from 9 to 11 in the three tested varieties. Using this newly developed ddPCR method, transgene copy number was successfully determined in 19 transgenic Q208 ^A and Q240 ^A events using ACT as the reference endogenous gene. Our study demonstrates that ddPCR can be used for high-throughput genetic analysis and is a quick, accurate and reliable alternative method for gene copy number determination in sugarcane. This discovered ACT allele would be a suitable endogenous reference gene for future gene copy number variation and dosage studies of functional genes in Q208 ^A and Q240 ^A .

Genetic characteristics of polycistronic system‑mediated randomly‑inserted multi‑transgenes in miniature pigs and mice

Multi-transgenic technology is superior to single transgenic technology in biological and medical research. Multi-transgene insertion mediated by a polycistronic system is more effective for the integration of polygenes. The multi-transgene insertion patterns and manners of inheritance are not completely understood. Copy number quantification is one available approach for addressing this issue. The present study determined copy numbers in two multi-transgenic mice (K3 and L3) and two multi-transgenic miniature pigs (Z2 and Z3) using absolute quantitative polymerase chain reaction analysis. For the F0 generation, a given transgene was able to exhibit different copy number integration capacities in different individuals. For the F1 generation, the most notable characteristic was that the copy number proportions were different among pedigrees (P<0.05). The results of the present study demonstrated that transgenes within the same vector exhibited the same integration trend between the F0 and F1 generations. In conclusion, intraspecific consistency and intergenerational copy numbers were compared and the integration capacity of each specific transgene differed in multi-transgenic animals. In particular, the copy number of one transgene may not be used to represent other transgenes in polycistronic vector-mediated multi-transgenic organisms. Consequently, in multi-transgenic experimental animal disease model research or breeding, copy numbers provide an important reference. Therefore, each transgene in multi-transgenic animals must be separately screened to prevent large copy number differences, and inconsistent expression between transgenes and miscellaneous data, in subsequent research.

Development and Characterization of Transgenic Sugarcane with Insect Resistance and Herbicide Tolerance

Genetically modified crops which had been commercial applied extensively majorly are the insect resistance and herbicide tolerance events. In this study, the Bt insecticidal gene Cry1Ab, the glyphosate-tolerant gene EPSPS, and the selection marker gene PMI were combined into a single transferred DNA fragment and introduced into sugarcane by Agrobacterium-mediated transformation. Thirty-three resistant plantlets were obtained after selection using a PMI/mannose selection system. Thirty of these resistant plantlets were PCR positive for the three target genes. Southern blot assay revealed that the copy number of the integrated fragment in the transformed plantlets varied from 1 to 7. ELISA analysis showed that 23 of the 33 resistant plantlets expressed Cry1Ab and EPSPS protein. Five single-copy and ELISA-positive transgenic lines were tested under laboratory and field conditions to determine their resistance to insects and herbicides, and also evaluated their agronomic characteristics and industrial traits. Results showed that larvae fed with fodder mixture containing stem tissues from single-copy transgenic lines were weak and small, moreover, pupation and eclosion were delayed significantly during voluntary feeding bioassays. None of transgenic sugarcane was destroyed by cane borer while more than 30% of wild type sugarcane was destroyed by cane borer. For herbicide resistance, the transgenic plantlets grew healthy even when treated with up to 0.5% roundup while wild type plantlets would die off when treated with 0.1% roundup. Thus demonstrate that these transgenic lines showed strong insect resistance and glyphosate tolerance under both laboratory and field conditions. But in the field most of the transgenic plants were shorter and more slender than non-transformed control plants. So they presented poor agronomic characteristics and industrial traits than non-transformed control plants. Thus, a considerable number of embryogenic calli should be infected to obtain transgenic lines with potential for commercial use.

Isolation and Characterization of ScGluD2, a New Sugarcane beta-1,3-Glucanase D Family Gene Induced by Sporisorium scitamineum, ABA, H2O2, NaCl, and CdCl2 Stresses

Beta-1,3-glucanases (EC 3.2.1.39), commonly known as pathogenesis-related (PR) proteins, play an important role not only in plant defense against fungal pathogens but also in plant physiological and developmental processes. However, only a limited number of sugarcane beta-1,3-glucanase genes have been isolated. In the present study, we identified and characterized a new beta-1,3-glucanase gene ScGluD2 (GenBank Acc No. KF664181) from sugarcane. An X8 domain was present at the C terminal region of ScGluD2, suggesting beta-1,3-glucan-binding function. Phylogenetic analysis showed that the predicted ScGluD2 protein was classified into subfamily D beta-1,3-glucanase. Localization of the ScGluD2 protein in the plasma membrane was determined by tagging it with green fluorescent protein. The expression of ScGluD2 was more up-regulated in sugarcane smut-resistant cultivars in the early stage (1 or 3 days) than in the susceptible ones after being challenged by the smut pathogen, revealing that ScGluD2 may be involved in defense against the invasion of Sporisorium scitamineum. Transient overexpression of ScGluD2 in Nicotiana benthamiana leaves induced a defense response and exhibited antimicrobial action on the tobacco pathogens Pseudomonas solanacearum and Botrytis cinerea, further demonstrating that ScGluD2 was related to the resistance to plant pathogens. However, the transcripts of ScGluD2 partially increased (12 h) under NaCl stress, and were steadily up-regulated from 6 to 24 h upon ABA, H2O2, and CdCl2 treatments, suggesting that ABA may be a signal molecule regulating oxidative stress and play a role in the salt and heavy metal stress-induced stimulation of ScGluD2 transcripts. Taken together, ScGluD2, a novel member of subfamily D beta-1,3-glucanase, was a stress-related gene of sugarcane involved in plant defense against smut pathogen attack and salt and heavy metal stresses.