Internode Tissue Research Articles

Potential Roles of the GRF Transcription Factors in Sorghum Internodes during Post-Reproductive Stages.

Growth-regulating factor (GRF) is a plant-specific family of transcription factors crucial for meristem development and plant growth. Sorghum (Sorghum bicolor L. Moench) is a cereal species widely used for food, feed and fuel. While sorghum stems are important biomass components, the regulation of stem development and the carbohydrate composition of the stem tissues remain largely unknown. Here, we identified 11 SbGRF-encoding genes and found the SbGRF expansion driven by whole-genome duplication events. By comparative analyses of GRFs between rice and sorghum, we demonstrated the divergence of whole-genome duplication (WGD)-derived OsGRFs and SbGRFs. A comparison of SbGRFs' expression profiles supports that the WGD-duplicated OsGRFs and SbGRFs experienced distinct evolutionary trajectories, possibly leading to diverged functions. RNA-seq analysis of the internode tissues identified several SbGRFs involved in internode elongation, maturation and cell wall metabolism. We constructed co-expression networks with the RNA-seq data of sorghum internodes. Network analysis discovered that SbGRF1, 5 and 7 could be involved in the down-regulation of the biosynthesis of cell wall components, while SbGRF4, 6, 8 and 9 could be associated with the regulation of cell wall loosening, reassembly and/or starch biosynthesis. In summary, our genome-wide analysis of SbGRFs reveals the distinct evolutionary trajectories of WGD-derived SbGRF pairs. Importantly, expression analyses highlight previously unknown functions of several SbGRFs in internode elongation, maturation and the potential involvement in the metabolism of the cell wall and starch during post-anthesis stages.

Morphological, anatomical, and transcriptomics analysis reveals the regulatory mechanisms of cassava plant height development

BackgroundCassava is one of three major potato crops and the sixth most important food crop globally. Improving yield remains a primary aim in cassava breeding. Notably, plant height significantly impacts the yield and quality of crops; however, the mechanisms underlying cassava plant height development are yet to be elucidated.ResultsIn this study, we investigated the mechanisms responsible for cassava plant height development using phenotypic, anatomical, and transcriptomic analyses. Phenotypic and anatomical analysis revealed that compared to the high-stem cassava cultivar, the dwarf-stem cassava cultivar exhibited a significant reduction in plant height and a notable increase in internode tissue xylem area. Meanwhile, physiological analysis demonstrated that the lignin content of dwarf cassava was significantly higher than that of high cassava. Notably, transcriptome analysis of internode tissues identified several differentially expressed genes involved in cell wall synthesis and expansion, plant hormone signal transduction, phenylpropanoid biosynthesis, and flavonoid biosynthesis between the two cassava cultivars.ConclusionsOur findings suggest that internode tissue cell division, secondary wall lignification, and hormone-related gene expression play important roles in cassava plant height development. Ultimately, this study provides new insights into the mechanisms of plant height morphogenesis in cassava and identifies candidate regulatory genes associated with plant height that can serve as valuable genetic resources for future crop dwarfing breeding.

Deciphering the Molecular Mechanism of the Intermediate Secondary Growth and Internode Elongation of the Castor Bean (Ricinus communis L.) by the Combined Analysis of the Transcriptome and Metabolome.

The length of internodes plays a crucial role in determining the height of the castor plant (Ricinus communis L.). However, the specific mechanisms underlying internode elongation, particularly in the main stem of the castor plant, remain uncertain. To further investigate this, we conducted a study focusing on the internode tissue of the dwarf castor variety 071113, comparing it with the control high-stalk Zhuansihao. Our study included a cytological observation, physiological measurement, transcriptome sequencing, and metabolic determination. Our integrated findings reveal that the dwarf variety 071113 undergoes an earlier lignification development in the main stem and has a more active lignin synthesis pathway during internode intermediate development. In addition, the dwarf variety exhibited lower levels of the plant hormone indole-3-acetic acid (IAA), which had an impact on the development process. Furthermore, we identified specific enzymes and regulators that were enriched in the pathways of the cell cycle, auxin signal transduction, and secondary cell wall synthesis. Using these findings, we developed a model that explained the intermediate secondary growth observed in castor internode elongation and enhanced our comprehension of the dwarfing mechanism of the 071113 variety. This research provides a theoretical groundwork for the future breeding of dwarf castor varieties.

Quantitative morphological transformation of vascular bundles in the culm of moso bamboo (Phyllostachys pubescens).

Vascular bundles of bamboo are determinants for mechanical properties of bamboo material and for physiological properties of living bamboo. The morphology of vascular bundles reflecting mechanical and physiological functions differs not only within internode tissue but also among different internodes in the culm. Although the distribution of vascular bundle fibers has received much attention, quantitative evaluation of the morphological transformation of vascular bundles associated with spatial distribution patterns has been limited. In this study deep learning models were used to determine quantitative changes in the distribution and morphology of vascular bundles in the culms of moso bamboo (Phyllostachys pubescens). A precise model for extracting vascular bundles from cross-sectional images was constructed using the U-Net model. Analyses of extracted vascular bundles from different internodes showed significant changes in vascular bundle distribution and morphology among internodes. Vascular bundles in lower internodes showed outer relative position and larger area than those in upper internodes. Aspect ratio and eccentricity indicate that vascular bundles in internodes near the base have more elliptical morphology, with a long axis in the radial direction. The variational autoencoder model using extracted vascular bundles enabled simulation of the morphological transformation of vascular bundles along with radial direction. These deep learning models enabled highly accurate quantification of vascular bundle morphologies, and will contribute to a further understanding of bamboo development as well as evaluation of the mechanical and physiological properties of bamboo.

Close relationship between potassium accumulation in internodes and translocation of non-structural carbohydrate to grains in rice cultivars with different yields

Potassium (K) is an important macronutrient together with nitrogen and phosphorous. Potassium mostly accumulates in the internodes of rice plants during ripening stage. Since internodes are responsible for translocation of carbohydrates to the grains during ripening, the involvement of internode K in grain yield has been suggested, however, the precise mechanism remains unclear. This study aims to examine the relationship between rice grain yield in different cultivars and the dynamics of K and non-structural carbohydrates (NSC) in the internodes during the ripening period. Field experiments were conducted to investigate the differences in the dynamics of K and NSCs in internodes from heading to maturation in 10 cultivars with different yields and three mutants with different grain numbers. To reveal the localization of K in internode tissues, we conducted laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis. During the early ripening period from heading to 14 days after heading (14 DAH), the decrease in NSC contents in lower internodes was higher in the high-yielding indica cultivars than in japonica cultivars. In the late ripening period from 14 DAH to maturing, re-accumulation of NSC in lower internodes was higher in the japonica than in the indica. In contrast, the increase in K contents in the internodes was larger in the indica than in the japonica throughout the ripening stage. In the internodes of low-yielding whole crop silage (WCS) cultivar, the NSC contents were maintained at high levels during ripening, while K contents were consistently low. Similar results were observed in the mutant with low grain numbers. The mutant had lower K contents and higher NSC contents than the wild type (WT). Correlation analysis of different cultivars indicated that the change in K content in whole internodes from heading to maturing was negatively correlated with the change in NSC content. LA-ICP-MS analysis of internode tissues of the indica cultivar revealed that K accumulated more in the parenchyma cells than in large vascular bundles. These results suggest that K accumulation in the internodes is positively correlated with NSC translocation from internodes to grains, which could be through indirect effect of K accumulation in parenchyma on enhancement of long distance transport of NSC from internodes to the grains. This study provides new insights into the mechanism underlying the role of K in grain filling, which would help improving usage of K fertilizer for optimum plant growth and yields.

Elucidation of lignin and polysaccharide linkages in wheat straw by 2H/13C isotopic tracer

To elucidate chemical linkages between lignin and polysaccharides, the aqueous mixed solutions of coniferin-[α-13C], syringin-[α-13C], D-glucose-[6-2H], and phenylalanine ammonia-lyase inhibitor were injected into a living wheat stalk. Internode tissues with high abundance of 2H-13C were collected. The milled wood lignin, lignin-carbohydrate complex (LCC), and residual LCC (R-LCC) with enrichment of 2H-13C were isolated. The 13C and 2H abundances showed that the lignin and polysaccharides of internode tissues were labeled by 13C and 2H, respectively. Analysis with carbon-13 nuclear magnetic resonance (13C-NMR) showed that ketal and benzyl ether bonds were formed between α-C of lignin and carbohydrates. The R-LCC and LCC were further treated with enzymes to obtain enzymatic degraded R-LCC (ED-R-LCC) and enzymatic degraded LCC (ED-LCC). 13C-NMR spectra of ED-LCC showed that the α-C of lignin side chain was combined with 6-C of carbohydrates by ether, ester, and ketal linkages. 1H-NMR differential spectra of ED-LCCs revealed an LC linkage of benzyl ether bond. Glucan-lignin (En-R-GL) and xylan-lignin (En-R-XL) complexes were separated from ED-R-LCC by ionic liquid. A part of lignin α-C was linked to cellulose 6-C by benzyl ether and α-ketal linkages. 13C-NMR spectra of En-R-XL showed there were α-benzyl ether and α-ketal bonds between lignin and xylan.

Integrated genomic and transcriptomic analysis reveals genes associated with plant height of foxtail millet

Foxtail millet (Setaria italica) is an important C4 model crop; however, due to its high-density planting and high stature, lodging at the filling stage resulted in a serious reduction in yield and quality. Therefore, it is imperative to identify and deploy the genes controlling foxtail millet plant height. In this study, we used a semi-dwarf line 263A and an elite high-stalk breeding variety, Chuang 29 to construct an F2 population to identify dwarf genes. We performed transcriptome analysis (RNA-seq) using internode tissues sampled at three jointing stages of 263A and Chuang 29, as well as bulk segregant analysis (BSA) on their F2 population. A total of 8918 differentially expressed genes (DEGs) were obtained from RNA-seq analysis, and GO analysis showed that DEGs were enriched in functions such as “gibberellin metabolic process” and “oxidoreductase activity”, which have previously been shown to be associated with plant height. A total 593 mutated genes were screened by BSA-seq method. One hundred and seventy-six out of the 593 mutated genes showed differential expression levels between the two parental lines, and seven genes not only showed differential expression in two or three internode tissues but also showed high genomic variation in coding regions, which indicated they play a crucial role in plant height determination. Among them, we found a gibberellin biosynthesis related GA20 oxidase gene (Seita.5G404900), which had a single-base deletion at the third exon, leading to the frameshift mutation at 263A. Cleaved amplified polymorphic sequence assay and association analysis proved the single-base deletion in Seita.5G404900 co-segregated with dwarf phenotype in two independent F2 populations planted in entirely different environments. Taken together, the candidate genes identified in this study will help to elucidate the genetic basis of foxtail millet plant height, and the molecular marker will be useful for marker-assisted dwarf breeding.

Targeted suppression of gibberellin biosynthetic genes ZmGA20ox3 and ZmGA20ox5 produces a short stature maize ideotype.

SummaryMaize is one of the world’s most widely cultivated crops. As future demands for maize will continue to rise, fields will face ever more frequent and extreme weather patterns that directly affect crop productivity. Development of environmentally resilient crops with improved standability in the field, like wheat and rice, was enabled by shifting the architecture of plants to a short stature ideotype. However, such architectural change has not been implemented in maize due to the unique interactions between gibberellin (GA) and floral morphology which limited the use of the same type of mutations as in rice and wheat. Here, we report the development of a short stature maize ideotype in commercial hybrid germplasm, which was generated by targeted suppression of the biosynthetic pathway for GA. To accomplish this, we utilized a dominant, miRNA‐based construct expressed in a hemizygous state to selectively reduce expression of the ZmGA20ox3 and ZmGA20ox5 genes that control GA biosynthesis primarily in vegetative tissues. Suppression of both genes resulted in the reduction of GA levels leading to inhibition of cell elongation in internodal tissues, which reduced plant height. Expression of the miRNA did not alter GA levels in reproductive tissues, and thus, the reproductive potential of the plants remained unchanged. As a result, we developed a dominant, short‐stature maize ideotype that is conducive for the commercial production of hybrid maize. We expect that the new maize ideotype would enable more efficient and more sustainable maize farming for a growing world population.

Cellulose and lignin profiling in seven, economically important bamboo species of India by anatomical, biochemical, FTIR spectroscopy and thermogravimetric analysis

Bamboos, a group of non-timber grasses, offers a great promise for the ligno-cellulosic biomass industry due to their very fast growth resulting rapid accumulation of lignocellulose biomasses, high fibre contents, low maintenance cost and existence of a diverse genetic pool. Despite, not voluminous and significant studies aimed to investigate the anatomy and biochemistry related to the cellulose and lignin synthesis in bamboos. Particularly, there remains a big knowledge gap on the variations of cellulose and lignin contents that exists at the germplasm level. Therefore, this study aimed to analyse chemical composition of ligno-cellulosic biomasses obtained from internode tissues of seven, abundantly available bamboo species of India (Bambusa balcooa, B. tulda, B. bambos, B. nutans, B. striata, Dendrocalamus giganteus, and D. strictus) by performing Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) Spectroscopy and Thermogravimetric analysis (TGA). Four anatomical parameters were used to predict ‘superior’ bamboo species/genotypes with respect to high cellulose vs. low lignin content. Particularly integrated density (ID) of Fast green and Phloroglucinol stains were correlated to the biochemical estimates of cellulose and lignin conducted on 63 samples. Hence the study concludes that stain ID can be used for quick screening of bamboo germplasms having desired ligno-cellulose contents. On the basis of multiple parameters analysed, B. bambos emerged as a reference bamboo for future ligno-cellulose research.

Genetic manipulation of trehalose-6-phosphate synthase results in changes in the soluble sugar profile in transgenic sugarcane stems.

Trehalose is a non‐reducing disaccharide widely distributed in nature. The trehalose biosynthetic intermediate, trehalose 6‐phosphate (Tre6P) is an essential regulatory and signaling molecule involved in both regulation of carbon metabolism and photosynthesis. To investigate the effect of altered trehalose synthesis on sucrose accumulation in sugarcane (Saccharum spp. hybrid), we independently overexpressed the Escherichia coli otsA (trehalose‐6‐phosphate synthase; TPS) and otsB (trehalose‐6‐phosphate phosphatase; TPP) genes and additionally partially silenced native TPS expression. In mature cane, sucrose levels in the otsA transgenic plants were lowered, whereas sucrose levels in the otsB transgenic plants were increased. Partial silencing of TPS expression in sugarcane transformed with a TPS‐targeted microRNA recombinant construct was confirmed in leaf and mature internode tissue of transgenic plants. Most of the silencing transgenic lines accumulated trehalose at lower levels than the wild‐type (WT) plants. The immature stalk tissue of these transgenic lines had lower levels of glucose and fructose, whereas the mature internode tissue had lower sucrose and glucose levels, when compared with the WT. Furthermore, various minor metabolites and sugars were detected in the sugarcane plants, which mostly decreased as the stalk tissue of the cane matured. The results demonstrate that manipulation of Tre6P/trehalose metabolism has the potential to modify the profile of soluble sugars accumulated in sugarcane stems.

Friction coefficient calibration of corn stalk particle mixtures using Plackett-Burman design and response surface methodology

The accuracy of the particle parameter settings directly affects the reliability of the simulation results. The discrete element method used a repose angle test to address incorrect particle parameter settings when throwing straw particles thrown by a chaff cutter. The tests calibrated the static and rolling friction coefficients using the repose angle of a mixture of maize stalk internodal tissue, pith, and nodal tissue particles as response indicators. Physical tests measured particle materiality parameters and contact parameters to provide data for the simulation tests. A Plackett-Burman design was performed to test the significance of the parameters to be calibrated. The results show that the static friction coefficient of Rind-Node, the rolling friction coefficient of Rind-Rind, the rolling friction coefficient of Pith-Pith, and the rolling friction coefficient of Pith-Iron have a significant effect on the repose angle. The purpose of the steepest ascent test is to narrow down the optimization range of the parameters. The central composite design was used to determine the DEM parameters' levels and quantify their effects. The central composite design test modeled a second-order polynomial regression equation for the repose angle and significance parameters. The physical test values were used as the target values for the optimization solution to obtain a calibrated and better combination of simulation parameters. The two-sample heteroskedasticity t-test showed no significant difference between the simulated and experimental values. The maximum relative error was 1.75%, the mean relative error was only 0.29%, verifying the reliability and authenticity of the simulation test. These parameters provide a basis for future work, such as the design of a corn stalk processing machine and the discrete-element study on the motion of corn stalk particles inside such machines.

Reduced apoplastic barriers in tissues of shoot-proximal rhizomes of Oryza coarctata are associated with Na+ sequestration.

Oryza coarctata is the only wild rice species with significant salinity tolerance. The present work examines the role of the substantial rhizomatous tissues of O. coarctata in conferring salinity tolerance. Transition to an erect phenotype (shoot emergence) from prostrate growth of rhizome tissues is characterized by marked lignification and suberization of supporting sclerenchymatous tissue, epidermis, and bundle sheath cells in aerial shoot-proximal nodes and internodes in O. coarctata. With salinity, however, aerial shoot-proximal internodal tissues show reductions in lignification and suberization, most probably related to re-direction of carbon flux towards synthesis of the osmporotectant proline. Concurrent with hypolignification and reduced suberization, the aerial rhizomatous biomass of O. coarctata appears to have evolved mechanisms to store Na+ in these specific tissues under salinity. This was confirmed by histochemical staining, quantitative real-time reverse transcription-PCR expression patterns of genes involved in lignification/suberization, Na+ and K+ contents of internodal tissues, as well as non-invasive microelectrode ion flux measurements of NaCl-induced net Na+, K+, and H+ flux profiles of aerial nodes were determined. In O. coarctata, aerial proximal internodes appear to act as 'traffic controllers', sending required amounts of Na+ and K+ into developing leaves for osmotic adjustment and turgor-driven growth, while more deeply positioned internodes assume a Na+ buffering/storage role.

An aptamer highly specific to cellulose enables the analysis of the association of cellulose with matrix cell wall polymers in vitro and in muro.

The current toolbox of cell wall-directed molecular probes has been pivotal for advancing basic and application-oriented plant carbohydrate research; however, it still exhibits limitations regarding target diversity and specificity. Scarcity of probes targeting intramolecular associations between cell wall polymers particularly hinders our understanding of the cell wall microstructure and affects the development of effective means for its efficient deconstruction for bioconversion. Here we report a detailed characterization of a cellulose-binding DNA aptamer CELAPT MINI using a combination of various in vitro biochemical, biophysical, and molecular biology techniques. Our results show evidence for its high specificity towards long non-substituted β-(1-4)-glucan chains in both crystalline and amorphous forms. Fluorescent conjugates of CELAPT MINI are applicable as in situ cellulose probes and are well suited for various microscopy techniques, including super-resolution imaging. Compatibility of fluorescent CELAPT MINI variants with immunodetection of cell wall matrix polymers enabled them simultaneously to resolve the fibrillar organization of complex cellulose-enriched pulp material and to quantify the level of cellulose masking by xyloglucan and xylan. Using enzymatically, chemically, or genetically modulated Brachypodium internode sections we showed the diversity in cell wall packing among various cell types and even cell wall microdomains. We showed that xylan is the most prominent, but not the only, cellulose-masking agent in Brachypodium internode tissues. These results collectively highlight the hitherto unexplored potential to expand the cell wall probing toolbox with highly specific and versatile in vitro generated polynucleotide probes.

Transcriptomic exploration of a high sucrose mutant in comparison with the low sucrose mother genotype in sugarcane during sugar accumulating stage

AbstractSugarcane (Saccharum spp. hybrid) is a noteworthy crop in the world for sugar and bioenergy production. In the present study, transcriptomic analysis was steered for a high sucrose mutant Guixuan B9 (GXB9) and the low sucrose mother genotype B9 of sugarcane during sugar accumulating stage. A total of 112,170 unigenes were obtained, and 106,026 (94.52%) were annotated by using the available public databases nonredundant, Gene ontology, COG, Kyoto Encyclopedia of Genes and Genomes, Swiss‐Prot, and Pfam. Functional assignment analysis of unigenes exhibited that they were active in a diversity of metabolic pathways. The vital unigenes for sucrose metabolism and accumulation were relatively characterized in the immature internodes (int. 5, 6) and maturing internodes (int. 13, 14) of GXB9 in comparison with B9. The differentially expressed unigenes (DEGs) encoding sucrose phosphate synthase (SPS, EC2.4.1.14), sucrose synthase (SuSy, EC2.4.1.13), and invertase (EC3.2.1.26), which are the vital enzymes functioning in the biosynthesis and splitting of sucrose, in the internodal tissues were revealed by using Illumina Hiseq 2000 platform, and verified by quantitative reverse transcription‐polymerase chain reaction analysis. The DEGs encoding SPS proteins SPS1, SPS2, SPS4, and SPS5 were upregulated in the maturing internodes of GXB9 compared with B9. The DEGs encoding SuSy proteins were majorly upregulated in the immature internodes of GXB9, and those encoding the enzymes involved in trehalose synthesis were downregulated in GXB9 compared with B9. The results in this study have revealed the opportunities for future sugarcane improvement by concentrating on the DEGs linked to sucrose metabolic pathways by applying omics technologies.

A microscopic study on scattering in tissue section of Alternanthera philoxeroides under polarized light

Like any other biological tissue, plant tissue also exhibits optical properties like refraction, transmission, absorption, coloration, scattering and so on. Several studies have been conducted using different parts of plants such as leaves, seedlings, roots, stems and so on, and their optical properties have been analyzed to study plant physiology, influence of environmental cues on plant metabolism, light propagation through plant parts and the like. Thus, it is essential to study in detail the optical properties of several plant parts to determine their structural relationship. In this backdrop, an experimental study was conducted to observe and analyze the optical properties of node and inter-nodal tissue cross-sections of the plant Alternanthera philoxeroides under a polarizing microscope constructed and standardized in the laboratory. The observed optical properties of the microscopic tissue sections have been then studied to determine a significant structural relationship between nodal and inter-nodal tissue arrangement patterns as a whole. Tissue sections that have undergone a sort of biological perturbation like loss of water (dried in air for 15 min) have also been studied to study the change in the pattern of tissue optical property when compared with that of normal plant-tissue cross-sections under a polarizing microscope. This type of biological perturbation was chosen for the study because water plays an important role in maintenance of the normal physiological processes in plants and most other forms of life.

New insight into the rapid growth of the Mikania micrantha stem based on DIA proteomic and RNA-Seq analysis

Mikania micrantha is one of the world's most invasive plants, which causes severe damage to natural ecosystems and agroforestry systems due to its rapid stem growth. This work investigated the proteomic and transcriptomic profiles of M. micrantha in different stem tissues (pre-internode, post-internode, and internode), as well as in adventitious roots and primary roots with the final goal of elucidating differentially expressed genes and proteins responsible for the rapid growth of stem. The objective was approached by using DIA-based proteomic and RNA-Seq technologies. More than seven giga-transcriptome clean reads were sequenced, and 5196 protein species were identified. Differentially expressed genes identified in all stem tissues were significantly enriched in photosynthesis and carbon fixation, suggesting that the stem possesses a strong photosynthetic capacity in order to maintain the energy supply for this species. Analysis of differentially expressed proteins showed that proteins related to photosystem I/II and the cytochrome b6/f complex, such as D1, D2, and cp43, were also highly accumulated in the adventitious roots, corroborating the transcriptome analysis results. These results provided basic proteomic and transcriptional expression information about the M. micrantha stem and adventitious root, thereby improving our understanding of the molecular mechanism underlying rapid growth in this species. SignificanceThis is the first study to investigate the proteomic and transcriptomic profiles of Mikania micrantha, a highly invasive plant, in different stem tissues (pre-internode, post-internode, and internode), as well as in adventitious and primary roots, using the latest DIA-based (data-independent acquisition mode) proteomic and RNA-Seq technologies. A comprehensive study was carried out, and differentially expressed genes and differentially expressed proteins identified in the pre-internode, post-internode, and internode tissues were significantly enriched during photosynthesis and carbon fixation, suggesting that the M. micrantha stem possesses a strong photosynthetic capacity that allows the plant to maintain a high energy supply. Enriched plant hormone signal transduction pathway analysis revealed an interaction between auxin and other phytohormones involved in adventitious root development. The study provided basic data on the molecular mechanism of M. micrantha vegetative propagation and the rapid growth of its stem. The novel scientific content of this study successfully builds upon the limited information currently available on the subject, therefore warranting publication.

Stage-specific events in tomato graft formation and the regulatory effects of auxin and cytokinin

Grafting is widely used worldwide because of its obvious advantages, especially in solanaceous vegetable crops. However, the molecular mechanisms underlying graft formation are unknown. In this study, internode tissues from above and below the graft junction were harvested, and we performed weighted gene co-expression network analysis (WGCNA) to describe the temporal and spatial transcriptional dynamics that occur during graft formation in tomato. The wounding stress response involved in JA, ETH, and oxylipins mainly occurred at 1 h after grafting (HAG). From 3 to 12 HAG, the biological processes of snRNA and snoRNA modification and the gibberellin-mediated signaling pathway functioned both above and below the graft junction. However, auxin transport and signaling, DNA replication, and xylem and phloem pattern formation were restricted to the scion, whereas the cytokinin-activated signaling pathway and the cellular response to sucrose starvation was restricted to the rootstock. At 24−72 HAG, cell division occurred above the graft junction, and photosynthesis-related pathways were activated below the graft junction. The levels of auxin and cytokinin reached their maxima above and below the graft junction at 12 HAG, respectively. Exogenous application of certain concentrations of IAA and 6-BA will promote xylem and phloem transport capacity. The current work has analyzed the stage-specific events and hub genes during the developmental progression of tomato grafting. We found that auxin and cytokinin levels respond to grafting, above and below the graft junction, respectively, to promote the formation of xylem and phloem patterning. In addition, the accumulation of auxin above the graft junction induced cells to prepare for mitosis and promoted the formation of callus. In short, our work provides an important reference for theoretical research and production application of tomato grafting in the future.

Variation in sugarcane biomass composition and enzymatic saccharification of leaves, internodes and roots

BackgroundThe composition of biomass determines its suitability for different applications within a biorefinery system. The proportion of the major biomass fractions (sugar, cellulose, hemicellulose and lignin) may vary in different sugarcane genotypes and growth environments and different parts of the plant. This study investigated the composition of mature and immature internodes, roots and mature leaves of sugarcane.ResultsInternodes were found to have a significantly larger alcohol-soluble component than leaves and roots. The primary difference between the immature and mature internodes was the ratio of soluble sugars. In mature tissues, sucrose content was significantly higher, whereas in immature internodal tissues there was lower sucrose and heightened concentrations of reducing sugars. Carbon (C) partitioning in leaf tissues was characterised by low levels of soluble components and high “other” and cell wall fractions. Root tissue had low ratios of soluble fractions relative to their cell wall contents, indicating a lack of storage of soluble carbon. There was no significant difference in the ratio of the major cell wall fractions between the major organ types. Characterisation of individual non-cellulosic monomers indicated leaf and root tissues had significantly higher arabinose and galactose fractions. Significantly larger proportions of syringyl lignin compounds and the hydroxycinnamic compound, p-coumaric acid were observed in mature internodal tissues compared to the other tissue types. Tissue-specific differences in composition were shown to greatly affect the recalcitrance of the cell wall to enzymatic saccharification.ConclusionsOverall, this study displayed clear evidence of the differential partitioning of C throughout the sugarcane plant in specific organs. These organ-specific differences have major implications in their utility as a bioproduct feedstock. For example, the inclusion of trash (leaves) with the culms (internodes) may alter processing efficiency.

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.

First Report of Fusarium sacchari That Causes Sugarcane Wilt Disease in China

China is the world’s third-largest sugar producer after India and Brazil, with sugarcane plants accounting for 90% of total sugar production in China. Susceptible sugarcane cultivars were vulnerable to severe damage by wilt, which in China has caused yield losses of about 10.0%. During a disease survey in a nationwide test of sugarcane varieties in different regions in August 2019, 5-month-old plants of the sugarcane hybrid variety Zhongzhe1 (ZZ1) grown in Beihai (109°06′52″E, 21°28′37″N) of Guangxi Zhuang Autonomous Region were found to exhibit dried internodal tissue, yellowed leaves, and hollow stalks consistent with wilt. A total of 18 sugarcane stalk samples affected by symptomatic wilt were collected from Beihai. Symptomatic internal stalk tissues were dissected into 0.5 × 0.5-cm pieces that were surface sterilized with 0.1% HgCl₂ for 45 s, followed by 70% ethanol for 60 s, and rinsed three times with sterile water. Around 5 to 10 pieces were placed on potato dextrose agar (PDA) and incubated at 28°C for 2 to 3 days. Growing hyphal tips were picked and transferred to fresh PDA plates to purify fungal isolates and maintained on PDA and carnation leaf-piece agar (CLA) for observing conidia and conidial fructification. A total of six fungal strains were isolated from the 18 symptomatic stalk samples (Ho and Ko 1997). These isolates produced abundant white mycelia on the PDA medium for 3 days. The macroconidia typically had three to five septa and were slightly falcate, relatively slender, and had thin walls. The microconidia were slim, oval, and primarily nonseptate. The microconidia grown on CLA had an oval shape that was similar to Fusarium sacchari (Leslie and Summerell 2006), which had no long chains and produced false heads from mono- and polyphialides. Genomic DNA from the six single-spore cultured isolates was extracted, amplified, and sequenced using two specific primer pairs of the translation elongation factor TEF1-α (EF1/EF2, 0.6 kb) and the second-largest subunit of RNA polymerase II, RPB2 (5f2/7cr and 7cf/11ar, 1.8 kb) (O’Donnell et al. 2013). All 12 sequences were submitted to GenBank (MN894584 to MN894595) and had over 99% homology to F. sacchari with 657/657 for TEF1-α (MK152503) and 1,700/1,706 for RPB2 (MK829741) through pairwise alignment against the Fusarium MLST database. A phylogenetic tree on the TEF1-α and RPB2 gene sequences was constructed by neighbor-joining methods with the reference sequences from other Fusarium species, including F. sacchari, F. mangiferae, F. fujikuroi, F. proliferatum, F. thapsinum, and F. verticillioides. Sequence alignment confirmed that the six isolates belonged to F. sacchari. A pathogenicity test was conducted on 5-month-old cultivar ZZ1. Stalk inoculation was achieved through a borehole made at the third internode from the top visible dewlap of the plant using a 5-mm-diameter hole punch (Viswanathan et al. 2011). A mycelial plug of the three strains isolated from wilt-affected plants (GX-BH01, GX-BH02, and GX-BH03) was placed in the borehole and sealed with Parafilm. A plug of the sterile medium was used as a control. All pathogenicity assays were repeated three times. The inoculated plants were placed in a growth chamber at 25 to 28°C with a 12-h day/12-h night photoperiod. After 30 days, the canes inoculated with the fungal isolates exhibited tissue discoloration and hollow stalks that were similar to those observed in field-grown sugarcane, whereas the control plants had no symptoms. The reisolated fungi were identified as F. sacchari based on morphological, cultural, and molecular characteristics. Our results confirmed that F. sacchari is the causative pathogen of sugarcane wilt, and this is the first report of this pathogen in China. This report has epidemiological significance for the planning of suitable management practices to prevent wilt disease in China.