A biolistic-based genetic transformation system applicable to a broad-range of sugarcane and energycane varieties

Sugarcane productivity and sugar yield improvement: Selecting variety, nitrogen fertilizer rate, and bioregulator as a first-line treatment

The improvement of sugarcane productivity depends on the crop varieties, growth environments, and management practices. In particular, the selection of the most productive variety and the use of an optimal fertilizer rate and plant bioregulator are critical for increasing sugarcane productivity and sugar yield. This study aimed to determine the high-performing sugarcane variety, optimal nitrogen rate, and potential bioregulator for improved sugarcane production, juice quality, and sugar yield. Two sugarcane varieties (D42/58 and NCo-334), three nitrogen (N) fertilizer rates (0, 100, and 150 kg/ha), and two bioregulators (Agrostemin and Crops®) were used for the study. The study revealed that sugarcane variety had a significant effect on all growth, yield, and quality parameters. Plant height was significantly influenced by variety and bioregulators, while stalk population was significantly influenced by two- and three-way interactions of varieties, bioregulators, and N fertilizer rates. Cane weight was significantly affected by variety, N fertilizer rate, and bioregulators, whereas cane yield was significantly affected by variety, N fertilizer, and their interaction effects. Sugar yield was similarly influenced by variety, bioregulator, and their interaction. The three main factors, as well as their two- and three-way interactions, had a considerable influence on cane quality parameters. Sugarcane variety D42/58 significantly outperformed variety NCo-334 in terms of sprouting, number of tillers, plant height, number of millable canes, and sucrose percentage by 7.49%, 9.50%, 12.80%, 10.50%, and 9.10%, respectively. The use of the D42/58 variety with N fertilizer (at 100 kg/ha) and/or the Agrostemin bioregulator also led to higher performance in cane population (107126), cane yield (153.34 tons/ha), Pol % (15.81%), and sugar yield (10.25 tons/ha). Most sugarcane growth, yield, juice quality, and sugar yield parameters were positively correlated; hence, high-performing varieties, appropriate N rates, and plant bioregulators could boost sugarcane productivity and sugar yield. Overall, the selection and combination of sugarcane variety D42/58 with 100 kg N/ha and/or Agrostemin bioregulator could maximize sugarcane production, juice quality, and sugar yield. To confirm the current findings, however, more research needs to be conducted across different agroecologies and seasons.

A short review on sugarcane: its domestication, molecular manipulations and future perspectives

Sugarcane (Saccharum spp.) is a special crop plant that underwent anthropogenic evolution from a wild grass species to an important food, fodder, and energy crop. Unlike any other grass species which were selected for their kernels, sugarcane was selected for its high stem sucrose accumulation. Flowering in sugarcane is not favored since flowering diverts the stored sugar resources for the reproductive and developmental energy needs. Cultivars are vegetatively propagated and sugarcane breeding is still essentially focused on conventional methods, since the knowledge of sugarcane genetics has lagged that of other major crops. Cultivar improvement has been extremely challenging due to its polyploidy and aneuploidy nature derived from a few interspecific hybridizations between Saccharum officinarum and Saccharum spontaneum, revealing the coexistence of two distinct genome organization modes in the modern variety. Alongside implementation of modern agricultural techniques, generation of hybrid clones, transgenics and genome edited events will help to meet the ever-growing bioenergy needs. Additionally, there are two common biotechnological approaches to improve plant stress tolerance, which includes marker-assisted selection (MAS) and genetic transformation. During the past two decades, the use of molecular approaches has contributed greatly to a better understanding of the genetic and biochemical basis of plant stress-tolerance and in some cases, it led to the development of plants with enhanced tolerance to abiotic stress. Hence, this review mainly intends on the events that shaped the sugarcane as what it is now and what challenges ahead and measures taken to further improve its yield, production and maximize utilization to beat the growing demands.

Metabolic engineering of energycane to hyperaccumulate lipids in vegetative biomass

Background

The metabolic engineering of high-biomass crops for lipid production in their vegetative biomass has recently been proposed as a strategy to elevate energy density and lipid yields for biodiesel production. Energycane and sugarcane are highly polyploid, interspecific hybrids between Saccharum officinarum and Saccharum spontaneum that differ in the amount of ancestral contribution to their genomes. This results in greater biomass yield and persistence in energycane, which makes it the preferred target crop for biofuel production.

Results

Here, we report on the hyperaccumulation of triacylglycerol (TAG) in energycane following the overexpression of the lipogenic factors Diacylglycerol acyltransferase1-2 (DGAT1-2) and Oleosin1 (OLE1) in combination with RNAi suppression of SUGAR-DEPENDENT1 (SDP1) and Trigalactosyl diacylglycerol1 (TGD1). TAG accumulated up to 1.52% of leaf dry weight (DW,) a rate that was 30-fold that of non-modified energycane, in addition to almost doubling the total fatty acid content in leaves to 4.42% of its DW. Pearson’s correlation analysis showed that the accumulation of TAG had the highest correlation with the expression level of ZmDGAT1-2, followed by the level of RNAi suppression for SDP1.

Conclusions

This is the first report on the metabolic engineering of energycane and demonstrates that this resilient, high-biomass crop is an excellent target for the further optimization of the production of lipids from vegetative tissues.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12896-022-00753-7.

A Sugarcane G-Protein-Coupled Receptor, ShGPCR1, Confers Tolerance to Multiple Abiotic Stresses

Sugarcane (Saccharum spp.) is a prominent source of sugar and serves as bioenergy/biomass feedstock globally. Multiple biotic and abiotic stresses, including drought, salinity, and cold, adversely affect sugarcane yield. G-protein-coupled receptors (GPCRs) are components of G-protein-mediated signaling affecting plant growth, development, and stress responses. Here, we identified a GPCR-like protein (ShGPCR1) from sugarcane and energy cane (Saccharum spp. hybrids) and characterized its function in conferring tolerance to multiple abiotic stresses. ShGPCR1 protein sequence contained nine predicted transmembrane (TM) domains connected by four extracellular and four intracellular loops, which could interact with various ligands and heterotrimeric G proteins in the cells. ShGPCR1 sequence displayed other signature features of a GPCR, such as a putative guanidine triphosphate (GTP)-binding domain, as well as multiple myristoylation and protein phosphorylation sites, presumably important for its biochemical function. Expression of ShGPCR1 was upregulated by drought, salinity, and cold stresses. Subcellular imaging and calcium (Ca²⁺) measurements revealed that ShGPCR1 predominantly localized to the plasma membrane and enhanced intracellular Ca²⁺ levels in response to GTP, respectively. Furthermore, constitutive overexpression of ShGPCR1 in sugarcane conferred tolerance to the three stressors. The stress-tolerance phenotype of the transgenic lines corresponded with activation of multiple drought-, salinity-, and cold-stress marker genes, such as Saccharum spp. LATE EMBRYOGENESIS ABUNDANT, DEHYDRIN, DROUGHT RESPONSIVE 4, GALACTINOL SYNTHASE, ETHYLENE RESPONSIVE FACTOR 3, SALT OVERLY SENSITIVE 1, VACUOLAR Na+/H+ ANTIPORTER 1, NAM/ATAF1/2/CUC2, COLD RESPONSIVE FACTOR 2, and ALCOHOL DEHYDROGENASE 3. We suggest that ShGPCR1 plays a key role in conferring tolerance to multiple abiotic stresses, and the engineered lines may be useful to enhance sugarcane production in marginal environments with fewer resources.

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.

High-Level Production of Recombinant Snowdrop Lectin in Sugarcane and Energy Cane

Sugarcane and energy cane (Saccharum spp. hybrids) are ideal for plant-based production of recombinant proteins because their high resource-use efficiency, rapid growth and efficient photosynthesis enable extensive biomass production and protein accumulation at a cost-effective scale. Here, we aimed to develop these species as efficient platforms to produce recombinant Galanthus nivalis L. (snowdrop) agglutinin (GNA), a monocot-bulb mannose-specific lectin with potent antiviral, antifungal and antitumor activities. Initially, GNA levels of 0.04% and 0.3% total soluble protein (TSP) (0.3 and 3.8 mg kg^–1 tissue) were recovered from the culms and leaves, respectively, of sugarcane lines expressing recombinant GNA under the control of the constitutive maize ubiquitin 1 (Ubi) promoter. Co-expression of recombinant GNA from stacked multiple promoters (pUbi and culm-regulated promoters from sugarcane dirigent5-1 and Sugarcane bacilliform virus) on separate expression vectors increased GNA yields up to 42.3-fold (1.8% TSP or 12.7 mg kg^–1 tissue) and 7.7-fold (2.3% TSP or 29.3 mg kg^–1 tissue) in sugarcane and energy cane lines, respectively. Moreover, inducing promoter activity in the leaves of GNA transgenic lines with stress-regulated hormones increased GNA accumulation to 2.7% TSP (37.2 mg kg^–1 tissue). Purification by mannose-agarose affinity chromatography yielded a functional sugarcane recombinant GNA with binding substrate specificity similar to that of native snowdrop-bulb GNA, as shown by enzyme-linked lectin and mannose-binding inhibition assays. The size and molecular weight of recombinant GNA were identical to those of native GNA, as determined by size-exclusion chromatography and MALDI-TOF mass spectrometry. This work demonstrates the feasibility of producing recombinant GNA at high levels in Saccharum species, with the long-term goal of using it as a broad-spectrum antiviral carrier molecule for hemopurifiers and in related therapeutic applications.

Unprecedented enhancement of recombinant protein production in sugarcane culms using a combinatorial promoter stacking system

Plants represent a safe and cost-effective platform for producing high-value proteins with pharmaceutical properties; however, the ability to accumulate these in commercially viable quantities is challenging. Ideal crops to serve as biofactories would include low-input, fast-growing, high-biomass species such as sugarcane. The objective of this study was to develop an efficient expression system to enable large-scale production of high-value recombinant proteins in sugarcane culms. Bovine lysozyme (BvLz) is a potent broad-spectrum antimicrobial enzyme used in the food, cosmetics and agricultural industries. Here, we report a novel strategy to achieve high-level expression of recombinant proteins using a combinatorial stacked promoter system. We demonstrate this by co-expressing BvLz under the control of multiple constitutive and culm-regulated promoters on separate expression vectors and combinatorial plant transformation. BvLz accumulation reached 1.4% of total soluble protein (TSP) (10.0 mg BvLz/kg culm mass) in stacked multiple promoter:BvLz lines, compared to 0.07% of TSP (0.56 mg/kg) in single promoter:BvLz lines. BvLz accumulation was further boosted to 11.5% of TSP (82.5 mg/kg) through event stacking by re-transforming the stacked promoter:BvLz lines with additional BvLz expression vectors. The protein accumulation achieved with the combinatorial promoter stacking expression system was stable in multiple vegetative propagations, demonstrating the feasibility of using sugarcane as a biofactory for producing high-value proteins and bioproducts.