Sugarcane Internode Research Articles

Metabolic Control of Sugarcane Internode Elongation and Sucrose Accumulation

The relationship between metabolic changes occurring in the developing internodes of sugarcane and the final yield and sugar characteristics is poorly understood due to the lack of integration between phenotypic and metabolic data. To address this issue, a study was conducted where sugarcane metabolism was modeled based on the measurement of cellular components in the top internodes, at two stages of crop development. The study also looked at the effects of Trinexapac-ethyl (Moddus®) on growth inhibition. The metabolome was measured using GC-analysis, while LC-MS/MS was used to measure proteome changes in the developing internodes. These data were then integrated with the metabolic rates. Regardless of the growth rate, internode elongation was restricted to the top five internodes. In contrast, sucrose and lignin accumulation was sensitive to the growth rate. Crossover plots showed that sucrose accumulation only occurred once the cell wall synthesis had slowed down. These data suggest that sucrose accumulation controlled a reduction in sucrose breakdown for metabolic activity and a reduction in demand for carbon for cell wall polysaccharide synthesis. This study also found that nucleotide sugar metabolism appears to be a key regulator in regulating carbon flow during internode development.

Chemical and histological characterization of internodes of sugarcane and energy-cane hybrids throughout plant development

Sugarcane and energy-cane are important Saccharum spp. hybrids that encompass desirable features for energy production. Their stem lignocellulose can be used as the raw material for the second-generation ethanol industry, contributing to accelerated fossil-fuel replacement. However, knowledge on the internode composition and saccharification of these hybrids is still needed to optimize their uses, especially in energy-cane. In this work, the agronomical, chemical, and histological internode features and saccharification potential were analyzed in sugarcane and energy-cane hybrids across four critical developmental stages (tillering, grand growth, early ripening and late ripening) and several internode positions along the stem. Except for galactose content that was higher in the sugarcane hybrid compared to the energy-cane, cell-wall composition was fairly similar in both types of cane across the growing cycle. Among main cell-wall components, maximum crystalline cellulose and matrix polysaccharides contents were observed at tillering and late ripening, respectively. Lignin concentrated towards upper internode positions and advanced developmental stages. Saccharification potential augmented towards apical internodes and early developmental stages, and negatively correlated to lignin and xylose contents. The energy-cane hybrid showed lower number of vascular bundles and metaxylem diameter and its lignin deposition was more extended towards the parenchymal tissue, when compared to the commercial sugarcane throughout the growth cycle. Taken together, these findings demonstrate that developmental stage and internode position largely affect cell-wall composition and its recalcitrance to enzymatic degradation. The use of sugarcane/energy-cane lignocellulose from early developmental stages could be beneficial for the second generation ethanol production. Novel management practices for that usage should consider economic, social and environmental sustainability standards under a sugar/ethanol production scheme.

Effect of pheromone blend sources and loadings on sugarcane internode borer moth catches in Sri Lanka

The internode borer, Chilo sacchariphagus indicus Kapur is an important moth borer on sugarcane in South Asia including India and Sri Lanka. Collaborative studies to evolve locally optimum sex pheromone trapping system for this pest were undertaken in Sri Lanka during 2019-20. The first study comparing alternative pheromone blend sources showed significant differences in moth catches, with the best source consistently attracting twice or more moths than the others. The next study on pheromone lure loadings showed non-significant differences in moth catches, clarifying the adequacy of the widely adopted loading (3 mg/ septa). While these findings could guide in adopting locally optimum blend source and loading for pheromone trapping of the borer moths, the scope of future R&D to further enhance the impact potential of pheromone-based mass trapping of sugarcane internode borer moths in Sri Lanka is indicated.

Enhancement of healthful novel sugar contents in genetically engineered sugarcane juice integrated with molecularly characterized ThSyGII (CEMB-SIG2)

Enhancement of sugar contents and yielding healthful sugar products from sugarcane demand high profile scientific strategies. Previous efforts to foster manipulation in metabolic pathways or triggering sugar production through combating abiotic stresses fail to yield high sugar recovery in Saccharum officinarum L. Novel sucrose isomers trehalulose (TH) and isomaltulose (IM) are naturally manufactured in microbial sources. In pursuance of novel scientific methodology, codon optimized sucrose isomerase gene, Trehalulose synthase gene II(CEMB-SIG2) cloned under dual combined stem specific constitutive promoters in pCAMBIA1301 expression vector integrated with Vacuole targeted signal peptide (VTS) to concentrate gene product into the vacuole. The resultant mRNA expression obtained by Real Time PCR validated extremely increased transgene expression in sugarcane culms than leaf tissues. Overall sugar estimation from transgenic sugarcane lines was executed through refractometer. HPLC based quantifications of Trehalulose (TH) alongside different internodes of transgenic sugarcane confirmed the enhancement of boosted sugar concentrations in mature sugarcane culms. Trehalulose synthase gene II receptive sugarcane lines indicated the unprecedented impressions of duly combined constitutive stem regulated promoters. Transgenic sugarcane lines produce highest sugar recovery percentages, 14.9% as compared to control lines (8.5%). The increased sugar recovery percentage in transgenic sugarcane validated the utmost performance and expression of ThSyGII gene .High Profile Liquid chromatography based sugar contents estimation of Trehalulose (TH) and Isomaltulose (IM) yielded unprecedented improvement in the whole sugar recovery percentage as compared to control lines.⁠

Comparison of the root, leaf and internode transcriptomes in sugarcane (Saccharum spp. hybrids)

• The organs of sugarcane use carbon in different ways, leading to differing ratios of insoluble and soluble compounds • Transcription aligned closely with differences in the biomass makeup of insoluble and soluble components. • Large transcriptional differences were observed among organs, and smaller differences we observed according to maturity. • This study may support efforts to develop sugarcane with biomass composition better suited to various end uses. The major carbon source and sink organs (roots, leaves and internodes) of sugarcane ( Saccharum spp. hybrids) have different roles and consequently different apportioning of carbon into the major components of these organs. This study performed RNA-seq on two leaves, three internodes (of differing maturity) and roots in two similar commercial sugarcane genotypes to determine the patterns of gene expression associated with differences in carbon partitioning. A total of 18 RNA-seq libraries (in triplicate) were generated per genotype, thus yielding ∼0.6 billion high quality reads, with an average length of 125 bp, covering 90% of the long-read SUGIT transcriptome. RNA-seq, differential gene expression analysis, annotation and pathway analysis were performed. Transcript expression in active source organs (1st and 5th visible dewlap leaves) displayed higher expression in photosynthetic transcripts and some protein and respiratory transcripts, and low expression of most transcripts associated with cell-wall synthesis. Additionally, the transcription of some sucrose synthetic transcripts (sucrose phosphate synthase and sucrose phosphate phosphatase) was significantly higher than that in all other organs. Storage sinks (middle and bottom internodes) displayed lower expression of transcripts associated with UDP-glucose synthesis from sucrose and UDP-glucose conversion into cell-wall components than did meristematic sinks (immature internodes and root). Both meristematic sinks displayed lower transcript expression related to photosynthesis, and far higher expression of protein, cell-wall and respiratory-related transcripts, particularly in relation to source organs. Interestingly, transcription was higher for transcripts associated with lignin and hemicellulose synthesis in the roots but not immature internodes. Transcription closely aligned with differences in the biomass makeup of insoluble and soluble components in sugarcane organs. Similar transcriptional profiles observed across internodes of differing maturity, i.e., between immature and mature internodes, suggested that transcriptional changes in select sets of genes influence changes in the direction of carbon partitioning during maturation. This finding contrasts with the large transcriptional differences observed among major organ types. This knowledge may support efforts to develop sugarcane with biomass composition better suited to various end uses.

Global transcriptome changes of elongating internode of sugarcane in response to mepiquat chloride

BackgroundMepiquat chloride (DPC) is a chemical that is extensively used to control internode growth and create compact canopies in cultured plants. Previous studies have suggested that DPC could also inhibit gibberellin biosynthesis in sugarcane. Unfortunately, the molecular mechanism underlying the suppressive effects of DPC on plant growth is still largely unknown.ResultsIn the present study, we first obtained high-quality long transcripts from the internodes of sugarcane using the PacBio Sequel System. A total of 72,671 isoforms, with N50 at 3073, were generated. These long isoforms were used as a reference for the subsequent RNA-seq. Afterwards, short reads generated from the Illumina HiSeq 4000 platform were used to compare the differentially expressed genes in both the DPC and the control groups. Transcriptome profiling showed that most significant gene changes occurred after six days post DPC treatment. These genes were related to plant hormone signal transduction and biosynthesis of several metabolites, indicating that DPC affected multiple pathways, in addition to suppressing gibberellin biosynthesis. The network of DPC on the key stage was illustrated by weighted gene co-expression network analysis (WGCNA). Among the 36 constructed modules, the top positive correlated module, at the stage of six days post spraying DPC, was sienna3. Notably, Stf0 sulfotransferase, cyclin-like F-box, and HOX12 were the hub genes in sienna3 that had high correlation with other genes in this module. Furthermore, the qPCR validated the high accuracy of the RNA-seq results.ConclusionTaken together, we have demonstrated the key role of these genes in DPC-induced growth inhibition in sugarcane.

Seasonal incidence of sugarcane internode borer, Chilo sacchariphagus indicus in popular sugarcane varieties in Mandya

A study on seasonal incidence of sugarcane internode borer, Chilo sacchariphagus indicus (Kapur) (Crambidae: Lepidoptera) revealed high infestation of C. Sacchariphagus indicus in the sugarcane crop planted in the months of June and July. The correlation studies on the incidence of internode borer with weather parameters showed significant positive relationship with maximum, minimum and mean temperature and sunshine hours. But, there was a significant negative correlation with morning, evening and mean relative humidity and rainfall.

Enhanced Activity of Genes Associated With Photosynthesis, Phytohormone Metabolism and Cell Wall Synthesis Is Involved in Gibberellin-Mediated Sugarcane Internode Growth.

Internode elongation is an important trait in sugarcane as it affects the sugarcane yield. Gibberellin (GA) is a key modulator of internode elongation in sugarcane. Understanding the gene expression features of GA-mediated internode elongation has both scientific and practical significance. This study aimed to examine the transcriptomic changes in the internode elongation of sugarcane following GA treatment. Eighteen cDNA libraries from the internode tissues on days of 0, 3, and 6 in control and GA treatment groups were sequenced and their gene expression were studied. RNA-seq analysis revealed 1,338,723,248 reads and 70,821 unigenes from elongating internodes of sugarcane. Comparative studies discovered a large number of transcripts that were differentially expressed in GA-treated samples compared to the control. Further analysis revealed that the differentially expressed genes were enriched in the metabolic process, one-carbon compound transport, and single-organism process. Kyoto Encyclopedia of Genes and Genomes pathway annotation showed significant enrichment in photosynthesis and plant hormone signal transduction, indicating its involvement in internode elongation. The function analysis suggested that metabolic pathways and biosynthesis of secondary metabolites, plant hormones, and cell wall components were enriched in the internodes of the GA-treated plants. The hub genes were identified, with the function of cellulose synthesis. The results of this study provide a global view of mRNA changes during sugarcane internode elongation and extend our knowledge of the GA-mediated cellular processes involved in sugarcane stem growth.

Instar determination for sugarcane internode borer Chilo sacchariphagus indicus (Kapur) (Lepidoptera: Crambidae)

• Sugarcane internode borer (INB) passes through five larval instars to become a pupa. • Frequency distribution of head capsule widths is reliable in instar fixation in INB. • Dyar’s ratios and regression analyses confirmed that no instar has been overlooked. • The probability of misclassifying an INB instar into another is remote (0.16–1.97%). Internode borer (INB), Chilo sacchariphagus indicus has been a serious threat to sugarcane cultivation for more than six decades. We have determined the number of instars for INB through frequency distribution analysis of cast head capsule widths. This is the first report, which proves that the INB of sugarcane passes through five larval instars to attain its pupal stage. The number of instars determined by kernel density estimation was in corroboration with the number of instars observed in the laboratory. The mean Dyar’s ratios for both the instar-wise observed data on head capsule widths and the theoretical data derived from the frequency distribution analysis were one and the same (1.46). Linear regression (R 2 > 0.998) between the instar numbers and their corresponding mean head capsule widths reaffirmed that no instar has been overlooked. Further, the theoretical misclassification probabilities of 0.16–1.97% indicates that the chance of misidentifying an INB instar into its preceding or succeeding one is very remote. Since the determination of the exact number of instars in a pest species is a pre-requisite for developing appropriate management strategies, the outcome of this study holds great promise in managing the most notorious Crambid borer of sugarcane.

The sugarcane ShMYB78 transcription factor activates suberin biosynthesis in Nicotiana benthamiana.

A sugarcane MYB present in the culm induces suberin biosynthesis and is involved both with fatty acid and phenolics metabolism. Few transcription factors have been described as regulators of cell wall polymers deposition in C4 grasses. Particularly, regulation of suberin biosynthesis in this group of plants remains poorly understood. Here, we showed that the sugarcane MYB transcription factor ShMYB78 is an activator of suberin biosynthesis and deposition. ShMYB78 was identified upon screening genes whose expression was upregulated in sugarcane internodes undergoing suberization during culm development or triggered by wounding. Agrobacterium-mediated transient expression of ShMYB78 in Nicotiana benthamiana leaves induced the ectopic deposition of suberin and its aliphatic and aromatic monomers. Further, the expression of suberin-related genes was induced by ShMYB78 heterologous expression in Nicotiana benthamiana leaves. ShMYB78 was shown to be a nuclear protein based on its presence in sugarcane internode nuclear protein extracts, and protoplast transactivation assays demonstrated that ShMYB78 activates the promoters of the sugarcane suberin biosynthetic genes β-ketoacyl-CoA synthase (ShKCS20) and caffeic acid-O-methyltransferase (ShCOMT). Our results suggest that ShMYB78 may be involved in the transcriptional regulation of suberin deposition, from fatty acid metabolism to phenylpropanoid biosynthesis, in sugarcane internodes.

Impact of Trichogramma release regimes and combination with mass trapping on sugarcane internode borer (Chilo sacchariphagus indicus) management

Large area study on the impact of six versus ten releases of the biocontrol agent, Trichogramma chilonis , besides large plot assessment of ten releases with and without mass trapping (by pheromone traps) for eco-safe management of the sugarcane internode borer (INB) - Chilo sacchariphagus indicus Kapur were undertaken in Natems Sugar factory area, Koppedu Taluk, Chittoor District, Andhra Pradesh, South India. In 2017-18, a large contiguous sugarcane crop area of 400 hectares received six releases of T. chilonis (as Tricho cards @ 5cc.ha/release) in alternate weeks during 5-7 months age of crop, followed by four additional releases during 8-9 months age (totalling ten releases) in 40 hectares area, besides assigning a no release block of 40 hectares in adjacent area. Harvest-time sampling in each treatment block showed that the INB distribution (per cent canes infested) was 80 % in control (no release) block, while it was 42 and 27 %, respectively, for six and ten releases. The INB intensity (per cent internodes infested) was also more (6.2 %) in control block whereas it was only 3.2 % and 1.5 %, in the two respective release regimes. Based on these results the cost-effectiveness of both the regimes was ascertained. In 2018-19, the impact of ten releases of T. chilonis (@5cc/hectare /release) versus same regime plus mass trapping (@25 pheromone traps/ha) was compared in large plots (each of 2.0 ha) along with an untreated control plot. Harvest-time samples showed that INB distribution was 70.3% in control block, compared to 48.3% in Trichogramma release block versus 19.8% in block combining Trichogramma and mass trapping. The respective INB intensity was 6.04 %, 4.04 % and 2.17 % while the estimated cane yields were 81.0, 86.2 and 92.5 tons/ha, respectively. The cost: benefit ratios for Trichogramma release with and without mass trapping were comparable, so confirming that both are cost-effective alternatives to chemical insecticide use in sugarcane agro-ecosystems.

Integrated mRNA and small RNA sequencing reveals microRNA regulatory network associated with internode elongation in sugarcane (Saccharum officinarum L.)

BackgroundInternode elongation is one of the most important traits in sugarcane because of its relation to crop productivity. Understanding the microRNA (miRNA) and mRNA expression profiles related to sugarcane internode elongation would help develop molecular improvement strategies but they are not yet well-investigated. To identify genes and miRNAs involved in internode elongation, the cDNA and small RNA libraries from the pre-elongation stage (EI), early elongation stage (EII) and rapid elongation stage (EIII) were sequenced and their expression were studied.ResultsBased on the sequencing results, 499,495,518 reads and 80,745 unigenes were identified from stem internodes of sugarcane. The comparisons of EI vs. EII, EI vs. EIII, and EII vs. EIII identified 493, 5035 and 3041 differentially expressed genes, respectively. Further analysis revealed that the differentially expressed genes were enriched in the GO terms oxidoreductase activity and tetrapyrrole binding. KEGG pathway annotation showed significant enrichment in “zeatin biosynthesis”, “nitrogen metabolism” and “plant hormone signal transduction”, which might be participating in internode elongation. miRNA identification showed 241 known miRNAs and 245 novel candidate miRNAs. By pairwise comparison, 11, 42 and 26 differentially expressed miRNAs were identified from EI and EII, EI and EIII, and EII and EIII comparisons, respectively. The target prediction revealed that the genes involved in “zeatin biosynthesis”, “nitrogen metabolism” and “plant hormone signal transduction” pathways are targets of the miRNAs. We found that the known miRNAs miR2592-y, miR1520-x, miR390-x, miR5658-x, miR6169-x and miR8154-x were likely regulators of genes with internode elongation in sugarcane.ConclusionsThe results of this study provided a global view of mRNA and miRNA regulation during sugarcane internode elongation. A genetic network of miRNA-mRNA was identified with miRNA-mediated gene expression as a mechanism in sugarcane internode elongation. Such evidence will be valuable for further investigations of the molecular regulatory mechanisms underpinning sugarcane growth and development.

Sucrose content, lignocellulose accumulation and in vitro digestibility of sugarcane internodes depicted in relation to internode maturation stage and Saccharum genotypes

Sugarcane hybrids acquired several characteristics through plant breeding, including high sucrose and lignocellulose production. Recently, biomass-based industries designed to produce high-value chemicals and fuels from whole plant biomass encouraged new breeding efforts to develop plants with high sucrose yields and low lignocellulose recalcitrance. The present study utilized four experimental sugarcane hybrids to evaluate the dynamics of sucrose and lignocellulose accumulation, lignocellulose composition, and enzymatic digestibility during internode development. During the internode maturation stages, the sucrose content increased while the lignocellulose fraction presented an increased lignin and decreased glucan content. Enzymatic digestibility and lignin content of the lignocellulose fraction displayed an inversely related pattern, and the first internode was two-fold more digestible than mature internodes, indicating that digestibility decreases significantly with internode maturation and tissue lignification. Some sugarcane hybrids (H89 and H58) combined desirable phenotype characteristics (high sucrose yield and low lignocellulose recalcitrance) that were not detected in H140 and H321. Proper molecular markers discriminating these samples will help to further design breeding steps to produce sugarcane modern hybrids combining high sucrose yields and low lignocellulose recalcitrance.

Erianthus arundinaceus as a trap crop for the sugarcane stem borer Chilo sacchariphagus: Field validation and disease risk assessment

The sugarcane internode spotted stem borer Chilo sacchariphagus (Bojer, 1856) (Lepidoptera: Crambidae) is a major pest of sugarcane. In a previous work carried out in Reunion, we showed that Erianthus arundinaceus (Retz.) Jeswiet (Poales: Poaceae), accession 28NG7, can be used as trap crop to control C. sacchariphagus. The aim of this study was to determine the efficiency of using E. arundinaceus 28NG7 as a trap crop to control C. sacchariphagus in commercial field conditions and to assess the susceptibility of E. arundinaceus 28NG7 to the three main sugarcane diseases in Reunion: smut, leaf-scald and gumming.Our results confirmed that E. arundinaceus 28NG7 effectively reduced C. sacchariphagus damage on sugarcane in large fields. The E. arundinaceus 28NG7 perimeter trap considerably reduced the mean number of bored internodes in the adjacent sugarcane fields, by a factor ranging from 2.8 to 4.4. Using on-station trials, we also showed that E. arundinaceus 28NG7 is tolerant or resistant to the three sugarcane diseases and is, therefore, unlikely to act as a disease reservoir and source of inoculum for contaminating sugarcane. The first step to encourage the use of E. arundinaceus 28NG7 borders in commercial fields described here was also successful in terms of growers’ adoption. All ten growers involved in the experiment spontaneously increased the area of sugarcane protected by E. arundinaceus 28NG7 borders on their farm.

Effects of Exogenous GA3 and DPC Treatments on Levels of Endogenous Hormone and Expression of Key Gibberellin Biosynthesis Pathway Genes During Stem Elongation in Sugarcane

Internode elongation determines plant height, which in turn affects the cane yield in sugarcane. This study aimed to explore the mechanisms of sugarcane internode elongation regulation by plant growth regulators, gibberellic acid (GA3) and its inhibitor 1, 1-dimethylpiperidinium chloride (DPC, also called mepiquat chloride). We sprayed GA3 or DPC on the leaves at the early shoot elongation stage with water as the control. The contents of endogenous hormones and the expression of GA20 ox1, GID1, and GAI in sugarcane leaves were measured at days 3, 6, 12, and 24 after treatment. It was found that the height of sugarcane plants treated with GA3 showed a significant increase compared to the control, whereas an opposite trend was observed in the DPC-treated plants. Compared to the control, the content of gibberellins (GAs) in leaves was increased significantly, while the indole acetic acid (IAA) content showed an initial increase, then a decline, and eventually remained stable in the GA3-treated plants. The contents of cytokinins (CTK), abscisic acid (ABA), and ethylene (ETH) in leaves exhibited a significant downward trend in the GA3-treated plants compared to the control. In the DCP-treated plants, however, the levels of ABA and ETH in leaves were significantly increased, IAA and GAs significantly decreased, and CTK showed a trend of an initial decline followed by an increase. After GA3 treatment, the gene expression levels of GA20 ox1 and GID1 in sugarcane increased first then decreased, whereas the gene expression level of GAI first decreased and then stabilized. After DPC treatment, the expression of GA20 ox1 in sugarcane showed an initial decrease followed by an increase, while the expression of GID1 decreased gradually and then stabilized, and the expression of GAI showed a trend of an initial increase followed by stabilization. The results of the present study indicate that exogenous GA3 treatment stimulated the internode elongation in sugarcane mainly by increasing the endogenous levels of GAs, decreasing the levels of ABA and ETH, and regulating the expression of GA20 ox1, GID1 and GAI genes; the DPC treatment mainly increased the contents of ABA and ETH and reduced the contents of GAs and IAA, thereby inhibiting the expression of GID1, promoting the expression of GAI, and ultimately inhibiting the internode elongation in sugarcane.

The FBH family of bHLH transcription factors controls ACC synthase expression in sugarcane.

Ethylene is a phytohormone involved in the regulation of several aspects of plant development and in responses to biotic and abiotic stress. The effects of exogenous application of ethylene to sugarcane plants are well characterized as growth inhibition of immature internodes and stimulation of sucrose accumulation. However, the molecular network underlying the control of ethylene biosynthesis in sugarcane remains largely unknown. The chemical reaction catalyzed by 1-aminocyclopropane-1-carboxylic acid synthase (ACS) is an important rate-limiting step that regulates ethylene production in plants. In this work, using a yeast one-hybrid approach, we identified three basic helix-loop-helix (bHLH) transcription factors, homologs of Arabidopsis FBH (FLOWERING BHLH), that bind to the promoter of ScACS2 (Sugarcane ACS2), a sugarcane type 3 ACS isozyme gene. Protein-protein interaction assays showed that sugarcane FBH1 (ScFBH1), ScFBH2, and ScFBH3 form homo- and heterodimers in the nucleus. Gene expression analysis revealed that ScFBHs and ScACS2 transcripts are more abundant in maturing internodes during afternoon and night. In addition, Arabidopsis functional analysis demonstrated that FBH controls ethylene production by regulating transcript levels of ACS7, a homolog of ScACS2. These results indicate that ScFBHs transcriptionally regulate ethylene biosynthesis in maturing internodes of sugarcane.

Identification, classification and transcriptional profiles of dirigent domain-containing proteins in sugarcane.

Dirigent (DIR) proteins, encoded by DIR genes, are referred to as "dirigent" because they direct the outcome of the coupling of the monolignol coniferyl alcohol into (+) or (-) pinoresinol, the first intermediates in the enantiocomplementary pathways for lignan biosynthesis. DIR domain-containing or DIR-like proteins are, thus, termed for not having a clear characterization. A transcriptome- and genome-wide survey of DIR domain-containing proteins in sugarcane was carried out, in addition to phylogenetic, physicochemical and transcriptional analyses. A total of 120 non-redundant sequences containing the DIR domain were identified and classified into 64 groups according to phylogenetic and sequence alignment analyses. In silico analysis of transcript abundance showed that these sequences are expressed at low levels in leaves and genes in the same phylogenetic clade have similar expression patterns. Expression analysis of ShDIR1-like transcripts in the culm internodes of sugarcane demonstrates their abundance in mature internodes, their induction by nitrogen fertilization and their predominant expression in cells that have a lignified secondary cell wall, such as vascular bundles of young internodes and parenchymal cells of the pith of mature internodes. Due to the lack of information about the functional role of DIR in plants, a possible relationship is discussed between the ShDIR1-like transcriptional profile and cell wall development in parenchyma cells of sugarcane culm, which typically accumulates large amounts of sucrose. The number of genes encoding the DIR domain-containing proteins in sugarcane is intriguing and is an indication per se that these proteins may have an important metabolic role and thus deserve to be better studied.

Bio-intensive management of internode borer (Chilo sacchariphagus indicus Kapur) and stalk borer (Chilo auricilius Dudgeon)

parasitoid, Trichogramma chilonis, larval parasitiod, Cotesia flavipes and pupal parasitoid, Tetrastichus howardi against sugarcane internode and stalk borer in RBD with a plot size of 72sq.m. The incidence of internode borer ranged from 2.34 to 4.91% in treated plot as compared to control (7.87%) in August, however during October incidence ranged from 2.14 to 6.86%.At harvest, minimum incidence of internode borer (5.62%) was observed in T. chilonis followed by C. flavipes (7.52%) released plots. The released parasitoids are more active in the field for its parasitisation and multiplication which result a reduction in the incidence of INB in released plots where as beyond October the prevailing low temperature, appeared to be non-conductive for its mating and field parasitisation. The incidence of stalk borer during August and October was low (1.03- 5.54%). At harvest minimum incidence (5.55%) was observed in C. flavipes followed by T. howardi release plots (10.92%) as against 17.24% in control. Removal of dry leaves and late shoots was observed to reduce the damage by migratory borer larvae in August and October. The results indicates that parasitoids (egg, larva and pupal) play a significant role in the management of INB and SB to check the spread and lowering the incidence of this pests. It is suggested that a working of these parasitoids can be exploited in programmes for management of sugarcane stalk and internode borer.

Tissue-specific distribution of hemicelluloses in six different sugarcane hybrids as related to cell wall recalcitrance.

BackgroundGrasses are lignocellulosic materials useful to supply the billion-tons annual requirement for renewable resources that aim to produce transportation fuels and a variety of chemicals. However, the polysaccharides contained in grass cell walls are built in a recalcitrant composite. Deconstruction of these cell walls is still a challenge for the energy-efficient and economically viable transformation of lignocellulosic materials. The varied tissue-specific distribution of cell wall components adds complexity to the origins of cell wall recalcitrance in grasses. This complexity usually led to empirically developed pretreatment processes to overcome recalcitrance. A further complication is that efficient pretreatment procedures generally treat the less recalcitrant tissues more than necessary, which results in the generation of undesirable biomass degradation products.ResultsSix different sugarcane hybrids were used as model grasses to evaluate the tissue-specific distribution of hemicelluloses and the role of these components in cell wall recalcitrance. Acetylated glucuronoarabinoxylan (GAX) occurs in all tissues. Mixed-linkage glucan (MLG) was relevant in the innermost regions of the sugarcane internodes (up to 15.4 % w/w), especially in the low-lignin content hybrids. Immunofluorescence microscopy showed that xylans predominated in vascular bundles, whereas MLG occurred mostly in the parenchyma cell walls from the pith region of the hybrids with low-lignin content. Evaluation of the digestibility of sugarcane polysaccharides by commercial enzymes indicated that the cell wall recalcitrance varied considerably along the internode regions and in the sugarcane hybrids. Pith regions of the hybrids with high MLG and low-lignin contents reached up to 85 % cellulose conversion after 72 h of hydrolysis, without any pretreatment.ConclusionsThe collective characteristics of the internode regions were related to the varied recalcitrance found in the samples. Components such as lignin and GAX were critical for the increased recalcitrance, but low cellulose crystallinity index, high MLG contents, and highly substituted GAX contributed to the generation of a less recalcitrant material.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0513-2) contains supplementary material, which is available to authorized users.

Anatomic and Ultrastructural Characteristics of Different Regions of Sugar Cane Internodes Which Affect Their Response to Alkaline-Sulfite Pretreatment and Material Recalcitrance

Sugar cane internodes have great morphological heterogeneity and different cell types that respond in varied ways to pretreatment processes. At the outermost region of the internode there are epithelial cells and a ring of cortical cells. Toward the central part of the internode there are a number of vascular bundles surrounded by parenchyma cells. The innermost regions are richer in parenchyma cells. The sugar cane internode regions were evaluated according to their response to alkaline-sulfite pretreatment and the consequences for material recalcitrance. The experimental data set included 4 sugar cane hybrids dissected into 3 different internode regions that were pretreated for 5 different reaction times, totaling 60 samples. Cellular ultraviolet microspectrophotometric evaluation of the samples suggested that in the thin cell walls (parenchyma and vessels) the hydroxycinnamic acids were accessible to the pretreatment reagents, whereas in the thicker fiber cell walls lignin and hydroxycinnamic acids wer...