Search

The overexpression of the soybean GmEXPA1 gene reduces plant susceptibility to M. incognita by the increase of root lignification. Plant expansins are enzymes that act in a pH-dependent manner in the plant cell wall loosening and are associated with improved tolerance or resistance to abiotic or biotic stresses. Plant-parasitic nematodes (PPN) can alter the expression profile of several expansin genes in infected root cells. Studies have shown that overexpression or downregulation of particular expansin genes can reduce plant susceptibility to PPNs. Root-knot nematodes (RKN) are obligate sedentary endoparasites of the genus Meloidogyne spp. of which M. incognita is one of the most reported species. Herein, using a transcriptome dataset and real-time PCR assays were identified an expansin A gene (GmEXPA1; Glyma.02G109100) that is upregulated in the soybean nematode-resistant genotype PI595099 compared to the susceptible cultivar BRS133 during plant parasitism by M. incognita. To understand the role of the GmEXPA1 gene during the interaction between soybean plant and M. incognita were generated stable A. thaliana and N. tabacum transgenic lines. Remarkably, both A. thaliana and N. tabacum transgenic lines overexpressing the GmEXPA1 gene showed reduced susceptibility to M. incognita. Furthermore, plant growth, biomass accumulation, and seed yield were not affected in these transgenic lines. Interestingly, significant upregulation of the NtACC oxidase and NtEFE26 genes, involved in ethylene biosynthesis, and NtCCR and Nt4CL genes, involved in lignin biosynthesis, was observed in roots of the N. tabacum transgenic lines, which also showed higher lignin content. These data suggested a possible link between GmEXPA1 gene expression and increased lignification of the root cell wall. Therefore, these data support that engineering of the GmEXPA1 gene in soybean offers a powerful biotechnology tool to assist in RKN management.

The CO2 concentration has increased in the atmosphere due to fossil fuel consumption, deforestation, and land-use changes. Brazil represents one of the primary sources of food on the planet and is also the world's largest tropical rainforest, which is one of the hot spots of biodiversity in the world. In this work, a meta-analysis was conducted to compare several CO2 Brazilian experiments displaying the diversity of plant responses according to life habits, such as trees and herbs. We found that trees and herbs display different responses. The young trees tend to allocate carbon - from increased photosynthetic rates and lower respiration in the dark - to organ development, increasing leaves, roots, and stem biomasses. In addition, more starch is accumulated in the young trees, denoting a fine control of carbon metabolism through carbohydrate storage. Herbs increased drastically in water use efficiency, controlled by stomatal conductance, with more soluble sugars, probably with a transient accumulation of carbon primarily stored in seeds as a response to elevated CO2.

The overexpression of the GmGlb1-1 gene reduces plant susceptibility to Meloidogyne incognita. Non-symbiotic globin class #1 (Glb1) genes are expressed in different plant organs, have a high affinity for oxygen, and are related to nitric oxide (NO) turnover. Previous studies showed that soybean Glb1 genes are upregulated in soybean plants under flooding conditions. Herein, the GmGlb1-1 gene was identified in soybean as being upregulated in the nematode-resistant genotype PI595099 compared to the nematode-susceptible cultivar BRS133 during plant parasitism by Meloidogyne incognita. The Arabidopsis thaliana and Nicotiana tabacum transgenic lines overexpressing the GmGlb1-1 gene showed reduced susceptibility to M. incognita. Consistently, gall morphology data indicated that pJ2 nematodes that infected the transgenic lines showed developmental alterations and delayed parasitism progress. Although no significant changes in biomass and seed yield were detected, the transgenic lines showed an elongated, etiolation-like growth under well-irrigation, and also developed more axillary roots under flooding conditions. In addition, transgenic lines showed upregulation of some important genes involved in plant defense response to oxidative stress. In agreement, higher hydrogen peroxide accumulation and reduced activity of reactive oxygen species (ROS) detoxification enzymes were also observed in these transgenic lines. Thus, based on our data and previous studies, it was hypothesized that constitutive overexpression of the GmGlb1-1 gene can interfere in the dynamics of ROS production and NO scavenging, enhancing the acquired systemic acclimation to biotic and abiotic stresses, and improving the cellular homeostasis. Therefore, these collective data suggest that ectopic or nematode-induced overexpression, or enhanced expression of the GmGlb1-1 gene using CRISPR/dCas9 offers great potential for application in commercial soybean cultivars aiming to reduce plant susceptibility to M. incognita.

Economic interest in sugarcane bagasse has significantly increased in recent years due to the worldwide demand for sustainable energy production. The use of sugarcane bagasse for holocellulase production has been a strategy for bioconversion of lignocellulosic residues into second-generation ethanol. The fungi secrete to the culture medium a cocktail of enzymes necessary to convert biomass into nutrients. Thus, this study aimed to analyze the production profile of holocellulases from Aspergillus and Humicola species, Trichoderma reesei RP698, and Mycothermus thermophilus grown in sugarcane bagasse, culm of energy cane, and culm of sugarcane SP80-3280. The capacity of the enzymatic pools in the hydrolysis of cell walls of these sugarcane varieties was also verified. M. thermophilus was the best producer of endoglucanase, cellobiohydrolase, β-glucosidase, xylanase, β-xylosidase, xyloglucanase, arabinanase, arabinofuranosidase, mannanase, and acetyl xylan esterase. T. reesei RP698 also produced and secreted a wide range of holocellulases to the medium. The saccharification of sugarcane bagasse, energy cane, and sugarcane SP80-3280 by the enzymatic cocktails obtained from M. thermophilus released 0.87 ± 0.05 mg.mL−1, 0.88 ± 0.07 mg.mL−1, and 1.10 ± 0.08 mg.mL−1 of reducing sugars, respectively. However, the application of T. reesei RP698 extracts showed a release of 0.85 ± 0.03 mg.mL−1, 0.40 ± 0.03 mg.mL−1, and 0.83 ± 0.03 mg.mL−1 of reducing sugars. Therefore, T. reesei RP698 and M. thermophilus showed to be good holocellulase producers, and their crude extracts presented a great capacity for the hydrolysis of the different kinds of sugarcane residues.

Lignocellulosic biomass is an abundant renewable feedstock, rich in polysaccharides that are covalently linked with lignin. In this study, biomass composition of nine forage grasses revealed the role of lignin in biomass recalcitrance. We determined the profiles of cell wall-bound phenolics, lignin, monosaccharides, enzymatic saccharification, and the chemical fingerprints using Fourier transform infrared (FTIR) and Raman spectroscopies. Coastcross and Tifton 85, both bermuda grass cultivars, showed lower lignin content and higher saccharification at 2 h and 72 h of enzymatic hydrolysis, supporting their use as valuable sources of carbohydrates for ethanol production. Principal component analysis (PCA) of thirteen different cell wall traits revealed that lignin was a hierarchical factor in reduced saccharification of forage grasses. As such, lignin content could be used as a marker for the selection of grass cultivars for genetic engineering programs for improved sustainable biofuel production.

Purpose Large parts of the Amazon rainforest grow on weathered soils depleted in phosphorus and rock-derived cations. We tested the hypothesis that in this ecosystem, fine roots stimulate decomposition and nutrient release from leaf litter biochemically by releasing enzymes, and by exuding labile carbon stimulating microbial decomposers. Methods We monitored leaf litter decomposition in a Central Amazon tropical rainforest, where fine roots were either present or excluded, over 188 days and added labile carbon substrates (glucose and citric acid) in a fully factorial design. We tracked litter mass loss, remaining carbon, nitrogen, phosphorus and cation concentrations, extracellular enzyme activity and microbial carbon and nutrient concentrations. Results Fine root presence did not affect litter mass loss but significantly increased the loss of phosphorus and cations from leaf litter. In the presence of fine roots, acid phosphatase activity was 43.2% higher, while neither microbial stoichiometry, nor extracellular enzyme activities targeting carbon- and nitrogen-containing compounds changed. Glucose additions increased phosphorus loss from litter when fine roots were present, and enhanced phosphatase activity in root exclusions. Citric acid additions reduced litter mass loss, microbial biomass nitrogen and phosphorus, regardless of fine root presence or exclusion. Conclusions We conclude that plant roots release significant amounts of acid phosphatases into the litter layer and mobilize phosphorus without affecting litter mass loss. Our results further indicate that added labile carbon inputs (i.e. glucose) can stimulate acid phosphatase production by microbial decomposers, highlighting the potential importance of plant-microbial feedbacks in tropical forest ecosystems.

Duckweeds are fast-growing aquatic plants suitable for bioenergy due to fermentable-rich biomass with low lignin. The duckweed sub-families Lemnoideae and Wolffioideae are also distinguished by the distribution of two pectin classes (apiogalacturonan and xylogalacturonan), which seem to be related to their growing capacity and the starch content. The plant cell wall is built from pathways of nucleotide sugars syntheses that culminate in cell wall synthesis and deposition. Therefore, understanding these pathways through mapping the genes involved and their expression would be important to develop tools to improve bioenergy production. Here we used the available information of NDP-sugar metabolism to search for orthologous genes involved in the synthesis of cell wall polysaccharides in Spirodela polyrhiza . We detected 190 genes and mapped them onto the plant chromosomes . The genes were roughly arranged in groups according to their category: "Starch and sucrose metabolism," "Pectins," "Hemicelluloses," and "Cellulose." We followed the expression of thirty-eight of the orthologues’ transcripts – the higher expression being starch ( SBE ), pectin ( GAUT1, MUR, USP , and GER ), and mannan ( CSLA ) syntheses - corroborating the chemical composition of S. polyrhiza cell wall . We further investigated the carbohydrate metabolism pathways and discussed the implications of altering the NDP pathways for bioenergy and biorefinery. We conclude that S. polyrhiza displays suitable features for future genetic transformations leading to the adaptation of its cell wall for biofuels. However, such strategies will have to consider the trade-offs between fermentation and ethanol production benefits and the potential adverse effects of genetic transformation on plant growth and development.

Sugarcane is the base of a successful agroindustrial system in several tropical and subtropical regions of the world. This industry is evolving towards diversification of its product portfolio and valorization of the vast amounts of lignocellulosic feedstocks: bagasse and straw. These trends make the sugarcane industry a learning ground for the utilization of agricultural residues and herbaceous biomass for bioenergy and biorefining. The presence of inorganics in sugarcane bagasse and straw, constitutive of the plant as well as originated from contamination, impacts several of the current and potential uses of the biomass. Although many studies refer broadly to terms like “inorganics”, “ash”, “silica”, “sand” or “mineral impurity”, there is a lack of a coherent and nuanced presentation of the inorganics of bagasse and straw: what they are, how variable they can be, and how they can impact different processes and products in biorefineries. This review article aims at filling this gap. Bagasse and straw inorganics are discussed considering their agroindustrial context and how they can impact processes such as combustion, pyrolysis, production of cellulosic ethanol and biomaterials. Prospects for valorization of the biomass inorganics are also discussed, beyond nutrient recycling. In the vision of this review, inorganics are not a marginal concern for biorefineries, as the percentage of inorganic content in biomass may seem to suggest. On the contrary, proper understanding and management of inorganics is key for the design of processes for advanced biorefineries.

Xyloglucans are highly substituted and recalcitrant polysaccharides found in the primary cell walls of vascular plants, acting as a barrier against pathogens. Here, we reveal that the diverse and economically relevant Xanthomonas bacteria are endowed with a xyloglucan depolymerization machinery that is linked to pathogenesis. Using the citrus canker pathogen as a model organism, we show that this system encompasses distinctive glycoside hydrolases, a modular xyloglucan acetylesterase and specific membrane transporters, demonstrating that plant-associated bacteria employ distinct molecular strategies from commensal gut bacteria to cope with xyloglucans. Notably, the sugars released by this system elicit the expression of several key virulence factors, including the type III secretion system, a membrane-embedded apparatus to deliver effector proteins into the host cells. Together, these findings shed light on the molecular mechanisms underpinning the intricate enzymatic machinery of Xanthomonas to depolymerize xyloglucans and uncover a role for this system in signaling pathways driving pathogenesis., Xyloglucans are polysaccharides found in plant cell walls. Here, the authors describe the xyloglucan depolymerization machinery of phytopathogenic Xanthomonas bacteria, and show that sugars released by this system induce the expression of key virulence factors driving pathogenesis.

Cellulosic ethanol is an alternative for increasing the amount of bioethanol production in the world. In Brazil, sugarcane leads the bioethanol production, and to improve its yield, besides bagasse, sugarcane straw is a possible feedstock. However, the process that leads to cell wall disassembly under field conditions is unknown, and understanding how this happens can improve sugarcane biorefinery and soil quality. In the present work, we aimed at studying how sugarcane straw is degraded in the field after 3, 6, 9, and 12 months. Non-structural and structural carbohydrates, lignin content, ash, and cellulose crystallinity were analyzed. The cell wall composition was determined by cell wall fractionation and determination of monosaccharide composition. Non-structural carbohydrates degraded quickly during the first 3 months in the field. Pectins and lignin remained in the plant waste for up to 12 months, while the hemicelluloses and cellulose decreased 7.4 and 12.4%, respectively. Changes in monosaccharide compositions indicated solubilization of arabinoxylan (xylose and arabinose) and β-glucans (β-1,3 1,4 glucan; after 3 months) followed by degradation of cellulose (after 6 months). Despite cellulose reduction, the xylose:glucose ratio increased, suggesting that glucose is consumed faster than xylose. The degradation and solubilization of the cell wall polysaccharides concomitantly increased the level of compounds related to recalcitrance, which led to a reduction in saccharification and an increase in minerals and ash contents. Cellulose crystallinity changed little, with evidence of silica at the latter stages, indicating mineralization of the material. Our data suggest that for better soil mineralization, sugarcane straw must stay in the field for over 1 year. Alternatively, for bioenergy purposes, straw should be used in less than 3 months.

Duckweeds are the smallest free-floating flowering aquatic plants. Their biotechnological applications include their use as food, bioenergy, and environmental sustainability, as they can help clean polluted water. The high growth capacity and their chemical properties make them suitable for human health applications. Here we evaluated the ethanolic extracts from five species of duckweeds by HPLC-DAD/MS-MS for chemical characterization. Sixteen compounds were identified and quantified, in which three were chlorogenic acid derivatives and eleven apigenin and luteolin derivatives. We describe for the first time the presence in duckweeds of 5-O-(E)-caffeoylquinic acid (1), 3-O-(E)-coumaroylquinic acid (2), luteolin-7-O-glucoside-C-glucoside (3), 4-O-(E)-coumaroylquinic acid (4), luteolin-6-C-glucoside-8-C-rhamnoside (5), and luteolin-8-C-glucoside-6-C-rhamnoside (6). The flavonoids diversity showed a significant content of luteolin and its derivatives, except for Landoltia punctata that had significant apigenin content. Flavones identified in duckweeds were mostly C-glycosides, which can benefit human diets, and its abundance seems to be related to the higher antioxidant and anticancer capacities of Wolffiella caudata, Wolffia borealis, and Landoltia punctata. Our findings reinforce the idea that duckweeds could be valuable additives to the human diet, and their potential should be further explored.

Small RNAs comprise three families of noncoding regulatory RNAs that control gene expression by blocking mRNA translation or leading to mRNA cleavage. Such post‐transcriptional negative regulation is relevant for both plant development and environmental adaptations. An important biotechnological application of miRNA identification is the discovery of regulators and effectors of cell wall degradation, which can improve/facilitate hydrolysis of cell wall polymers for second‐generation bioethanol production. The recent characterization of plant innate cell wall modifications occurring during root aerenchyma development triggered by ethylene led to the possibility of prospection for mechanisms of cell wall disassembly in sugarcane. By using next‐generation sequencing, 39 miRNAs were identified in root segments along the process of aerenchyma development. Among them, 31 miRNAs were unknown to the sugarcane miRBase repository but previously identified as produced by its relative Sorghum bicolor. Key putative targets related to signal transduction, carbohydrate metabolic process, and cell wall organization or biogenesis were among the most representative gene categories targeted by miRNA. They belong to the subclasses of genes associated with the four modules of cell wall modification in sugarcane roots: cell expansion, cell separation, hemicellulose, and cellulose hydrolysis. Thirteen miRNAs possibly related to ethylene perception and signaling were also identified. Our findings suggest that miRNAs may be involved in the regulation of cell wall degradation during aerenchyma formation. This work also points out to potential molecular tools for sugarcane improvement in the context of second‐generation biofuels.

Duckweeds are the smallest free-floating aquatic monocots. They have a unique cell wall containing pectin polymers named apiogalacturonan and xylogalacturonan. Knowing that the cell wall composition is essential for duckweeds as a bioenergy feedstock, notably ethanol production, this work reports the five duckweed species’ (Spirodela polyrhiza, Landoltia punctata, Lemna gibba, Wolffiella caudata, and Wolffia borealis) composition and saccharification potential. Nonstructural carbohydrates were, on average, 42% of the dry weight. The cell wall comprises 20.1% pectin and glucomannan, 35.2% hemicelluloses, 30% cellulose, and 5% lignin, and the fermentable sugars in duckweed walls are glucose, galactose, and xylose. Together, these monosaccharides constitute 51.4% of the cell wall. Duckweeds displayed low recalcitrance to hydrolysis, probably due to the low lignin and cellulose contents. Furthermore, the saccharification of the duckweeds was higher than sugarcane, a primary bioethanol feedstock. Results indicate that duckweed biomass displays a high potential as a feedstock for bioethanol production.

This work investigates the thermal degradation of leaves from the Amazon Rainforest litter, which is currently unknown. It formulates innovative thermal degradation equations useful for numerical simulation of wildfires in this biome. Furthermore, this work quantifies for the first time structural and non-structural components of litter leaves, which translates into an improved representation of the thermal degradation process. The main output of this work is the reaction mechanism with six parallel independent reactions for soluble sugars, pectin, hemicellulose, cellulose, lignin, and other organic compounds, which represent the thermal degradation of the litter leaves. The average composition of the Amazonian litter leaves is soluble sugars 22.9%, pectin 9.0%, hemicellulose 18.3%, cellulose 9.1%, lignin 21.2%, and inorganic plus other organic compounds 19.5%.

Meta-analysis synthesizes individual research results on the same subject and provides information that indicates bottlenecks in research. Due to the massive production of data, integrative analyzes are necessary, presenting more consistent views of biological phenomena. Broad themes such as plants’ response to climate change have been the subject of meta-analyses since 1996, as there is a global concern about the effect of elevated CO\(_{2}\) on plants and forests. We propose using meta-analysis to compile existing data, including studies related to the effects of high CO\(_{2}\) on Brazilian biomes’ vegetation. For that, we found 36 articles on the theme after a systematic review. Physiological parameters such as photosynthesis, leaf area, and non-structural carbohydrates are essential to understand the plant’s responses to elevated CO\(_{2}\) using meta-analysis. However, these parameters are not present in a considerable portion of the literature, decreasing the statistical power of meta-analytical strategies. The meta-analysis of plants’ biological responses is usually performed with several species, although there are also studies with single species. The use of many species increases the variance of the effects, highlighting the need for multilevel modeling to consider the dependence among data on the same species. We discuss how to carry out studies considering the variables needed in future meta-analyses to contribute to better data integration relevant to national reports. In this way, we expect that meta-analytical strategies could be essential for national decision-making and complement global analyses such as those made by the IPCC.

Background and aims Aerenchyma develops in different plant organs and leads to the formation of intercellular spaces that can be used by the plant to transport volatile substances. Little is known about the role of cell walls in this process, although the mechanism of aerenchyma formation is known to involve programmed cell death and some cell wall modifications. We assessed the role that cell wall-related mechanisms might play in the formation of aerenchyma in sugarcane roots. Methods Sections of roots (5 cm) were subjected to microtomography analysis. These roots were divided into 1-cm segments and subjected to cell wall fractionation. We performed analyses of monosaccharides, oligosaccharides and lignin and glycome profiling. Sections were visualized by immunofluorescence and immunogold labelling using selected monoclonal antibodies against polysaccharide epitopes according to the glycome profiles. Key results During aerenchyma formation, gas spaces occupied up to 40 % of the cortex cross-section within the first 5 cm of the root. As some of the cortex cells underwent dissolution of the middle lamellae, leading to cell separation, cell expansion took place along with cell death. Mixed-linkage β-glucan was degraded along with some homogalacturonan and galactan, culminating in the formation of cell wall composites made of xyloglucan, arabinoxylans, cellulose and possibly lignin. Conclusion The composites formed seem to play a role in the physical-chemical properties of the gas chambers, providing mechanical resistance to forces acting upon the root and at the same time decreasing permeability to gases.

Background and AimsCell wall disassembly occurs naturally in plants by the action of several glycosyl-hydrolases during different developmental processes such as lysigenous and constitutive aerenchyma formation in sugarcane roots. Wall degradation has been reported in aerenchyma development in different species, but little is known about the action of glycosyl-hydrolases in this process.MethodsIn this work, gene expression, protein levels and enzymatic activity of cell wall hydrolases were assessed. Since aerenchyma formation is constitutive in sugarcane roots, they were assessed in segments corresponding to the first 5 cm from the root tip where aerenchyma develops.Key ResultsOur results indicate that the wall degradation starts with a partial attack on pectins (by acetyl esterases, endopolygalacturonases, β-galactosidases and α-arabinofuranosidases) followed by the action of β-glucan-/callose-hydrolysing enzymes. At the same time, there are modifications in arabinoxylan (by α-arabinofuranosidases), xyloglucan (by XTH), xyloglucan–cellulose interactions (by expansins) and partial hydrolysis of cellulose. Saccharification revealed that access to the cell wall varies among segments, consistent with an increase in recalcitrance and composite formation during aerenchyma development.ConclusionOur findings corroborate the hypothesis that hydrolases are synchronically synthesized, leading to cell wall modifications that are modulated by the fine structure of cell wall polymers during aerenchyma formation in the cortex of sugarcane roots.

Aerenchyma formation in sugarcane roots is controlled by an ethylene-related RAV transcription factor. It binds to the promoter of an endogalacturonase and apparently controls cell separation., The development of lysigenous aerenchyma starts with cell expansion and degradation of pectin from the middle lamella, leading to cell wall modification, and culminating with cell separation. Here we report that nutritional starvation of sugarcane induced gene expression along sections of the first 5 cm of the root and between treatments. We selected two candidate genes: a RAV transcription factor, from the ethylene response factors superfamily, and an endopolygalacturonase (EPG), a glycosyl hydrolase related to homogalacturonan hydrolysis from the middle lamella. epg1 and rav1 transcriptional patterns suggest they are essential genes at the initial steps of pectin degradation during aerenchyma development in sugarcane. Due to the high complexity of the sugarcane genome, rav1 and epg1 were sequenced from 17 bacterial artificial chromosome clones containing hom(e)ologous genomic regions, and the sequences were compared with those of Sorghum bicolor. We used one hom(e)olog sequence from each gene for transactivation assays in tobacco. rav1 was shown to bind to the epg1 promoter, repressing β-glucuronidase activity. RAV repression upon epg1 transcription is the first reported link between ethylene regulation and pectin hydrolysis during aerenchyma formation. Our findings may help to elucidate cell wall degradation in sugarcane and therefore contribute to second-generation bioethanol production.

Soybean plants of the variety 'MG/BR Conquista' were grown in open top chambers, simulating elevated CO2 concentration ([CO2]) and high temperature under the following treatments: 1) ambient [CO2] and ambient temperature (Amb); 2) elevated [CO2] (eCO2) and ambient temperature (Elev); 3) ambient [CO2] and high temperature (Amb/Temp); 4) elevated CO2 and high temperature (Elev/Temp). The aim was to evaluate responses to elevated [CO2] and high temperature, with focus on plant development and seed yield, and composition. Elev stimulated grain yield and Amb/Temp had opposite effect. Several biochemical parameters were affected by Amb/Temp, most of them reversed by simultaneous application of Elev. The oil obtained with Elev/Temp had lower degree of unsaturation. A network of relationships among biochemical parameters of grains at three developmental stages revealed that Amb/Temp and Elev/Temp affect significantly both carbohydrate and lipid metabolisms. No significant difference was obtained comparing networks corresponding to Amb and Elev/Temp.

Cell walls are biologically encoded nanocomposites of interwoven polymers—polysaccharides (pectins, cellulose, and hemicelluloses), proteins and lignin—that surround plant cells. These polymers are the targets of bioenergy research because their hydrolysis is needed to release free sugars to produce bioethanol. We already know what covalent crosslinks are within polysaccharides of the walls of key bioenergy grasses (e.g., sugarcane, maize, and miscanthus), so that we can choose most of the enzymes necessary to break them. However, besides covalent linkages, the way these polymers are assembled through weak linkages in plant cell walls holds another important barrier for production of bioethanol. Such chemical forces within the walls include hydrogen bonds between cellullose molecules and within microfibrils, between cellulose and hemicelluloses and, the interaction of pectins with divalent ions. This chapter reviews how those interactions act as barriers to biomass pretreatment and hydrolysis, thus affecting the improvement of bioethanol production from sugarcane.

Aerosols emitted from biomass burning in South American tropical forests have been a concern in the last decades. On August 19th, 2019 darkened precipitation was observed over the metropolitan area of Sao Paulo (MASP), in an unprecedented event termed “black rain”, after intense biomass burning episodes in the South American hinterland. Satellite imagery, back trajectory analyses, and meteorological reports showed air masses transporting thick plumes of biomass burning aerosols originated in part from the Amazon Basin and Bolivia. Rainwater samples were collected in different sites of the metropolitan area, during and after the “black rain” event, and both physically and chemically characterized to assess the possible influence of biomass burning aerosols in the event. The collected samples in the “black rain” event presented high turbidity (above 70 NTU), and biomass burning organic tracers (levoglucosan, mannosan, and galactosan) were observed in higher concentrations in the “black rain” samples than in control ones (e.g. average levoglucosan of 0.33 μg mL−1, compared to 0.02 μg mL−1 after the event), with deposition fluxes more than three times higher during the event (1.04 mg m−2 and 0.31 mg m−2, respectively). The detection of glucose, xylose, and mannose, after hydrolysis of the solid material present in the “black rain” samples, strongly suggested the presence of plant cell wall material derived from the partial combustion of wood and grass matter. Total polycyclic aromatic hydrocarbons (PAHs) concentrations were, in general, higher during the event than in post-event control samples collected in the MASP (on average, almost 15 times higher than after the event), with a higher deposition flux (5.1 and 2.7 mg m−2, respectively). Overall, there are strong pieces of evidence that the long-range transport of smoke produced in South American forest fires was connected to the precipitation of darkened rainwater over the Metropolitan Area of Sao Paulo.

The architecture, composition, and chemical properties of wood cell walls have a direct influence on the process that occurs prior to fermentation in second-generation biofuel production. The understanding of the construction patterns of cell wall types is the key to the new era of second-generation biofuels. Eucalyptus species are great candidates for this purpose since these species are among the fastest growing hardwood trees in the world and they have been improved for biomass production. We applied the glycome profiling and other combined techniques to study xylem cell walls of three economically important species (Eucalyptus globulus, Eucalyptus grandis, and Eucalyptus urophylla). Glycome profiling analyses revealed that species differ in the same key aspects of cell wall polymer linkages, with E. globulus and E. urophylla presenting contrasting phenotypes, and E. grandis with intermediate characteristics. E. urophylla is known for high recalcitrance, that is probably determined by the strong associations between lignin and cell wall polymers, and also lignin content. On the other hand, E. globulus cell wall polymers are loosely linked, so its cell wall can be easily deconstructed. We have shown in this work that the composition of cell walls differs in quantity and quality among the Eucalyptus species and such variations in composition influence the process of lignocellulosic feedstock assessment. However, the greatest influence relies on the amount and type of associations between cell wall polymers. A high yield of cellulose, from any biomass source, directly depends on the cell wall architecture.

Highlight Phytopathogens can co-opt plant primary metabolism to enhance pathogenesis and pathogen nutrition. In witches’ broom disease of cacao, sensing and modulation of compartmentalized carbon availability can also temporally regulate disease development., Witches’ broom disease (WBD) of cacao differs from other typical hemibiotrophic plant diseases by its unusually long biotrophic phase. Plant carbon sources have been proposed to regulate WBD developmental transitions; however, nothing is known about their availability at the plant–fungus interface, the apoplastic fluid of cacao. Data are provided supporting a role for the dynamics of soluble carbon in the apoplastic fluid in prompting the end of the biotrophic phase of infection. Carbon depletion and the consequent fungal sensing of starvation were identified as key signalling factors at the apoplast. MpNEP2, a fungal effector of host necrosis, was found to be up-regulated in an autophagic-like response to carbon starvation in vitro. In addition, the in vivo artificial manipulation of carbon availability in the apoplastic fluid considerably modulated both its expression and plant necrosis rate. Strikingly, infected cacao tissues accumulated intracellular hexoses, and showed stunted photosynthesis and the up-regulation of senescence markers immediately prior to the transition to the necrotrophic phase. These opposite findings of carbon depletion and accumulation in different host cell compartments are discussed within the frame of WBD development. A model is suggested to explain phase transition as a synergic outcome of fungal-related factors released upon sensing of extracellular carbon starvation, and an early senescence of infected tissues probably triggered by intracellular sugar accumulation.

For hundreds of years, sugarcane has been a main source of sugar, used as a sweetener, and alcohol, fermented from the plant juice. The high cost of petroleum towards the end of the twentieth century stimulated the development of new fermentation technologies for producing economically viable bioethanol from sugarcane as an alternative to importing petroleum. More recently, awareness of the effects of greenhouse gas emissions due to the global climate changes propelled bioethanol as a viable renewable fuel. Consequently, sugarcane gained importance as a bioenergy feedstock. However, the lack of knowledge about sugarcane physiology, notably on aspects of photosynthesis and source–sink relationship, has slowed the advance of this expanding bioenergy-producing system. Besides the changes in source–sink relationship, another option to increase bioethanol production even more would be to use a greater fraction of the total biomass of plants, i.e., not only the soluble sugars but also the sugars present in the cell wall fractions. Here, we review the history of sugarcane as a bioenergy crop and discuss some of the relevant routes that could be adopted in the near future to make sugarcane an even better feedstock for producing biofuels.

A resistência das paredes celulares vegetais à hidrólise enzimática é um dos grandes gargalos tecnológicos para a obtenção do etanol celulósico. Acredita-se que as modificações nas paredes celulares em processos como a mobilização de reservas, formação de aerênquima, amadurecimento de frutos e senescência, por exemplo, envolvam a ativação de módulos funcionais que culminam em alterações nas paredes celulares. Estes módulos são: 1) recepção de um sinal para início do processo; 2) Morte Celular Programada (PCD); 3) separação celular; 4) expansão celular; 5) hidrólise de hemiceluloses e 6) hidrólise de celulose. No caso da formação de aerênquimas lisígenos o processo que se inicia com a PCD e é seguido pela liberação de glicosil hidrolases que atuam a na degradação e/ou modificação da parede celular, formando espaços de ar no córtex radicular. A formação de aerênquima nas raízes de cana de açúcar é constitutiva e pouco se sabe sobre os mecanismos de modificação que ocorrem na parede celular durante este processo. Este estudo buscou compreender os padrões de variação expressão gênica, proteínas e de atividades enzimáticas associados à formação do aerênquima em raízes de cana de açúcar, com ênfase no papel das hidrolases de parede celular e em algumas proteínas relacionadas à PCD. Foram utilizados 5 segmentos de raízes de 1 cm cada, a partir do ápice radicular. No material coletado observou-se a formação gradual de aerênquima. Foram realizadas análises transcricional, proteômica e atividade enzimática das glicosil hidrolases e outras proteínas que atuam na modificação da parede celular, os quais foram identificados e quantificados ao longo da formação do aerênquima. As glicosil hidrolases pertencentes às famílias Cazy GH1, GH3, GH17, GH18 bem como expansinas, celulose sintase, lacase, calreticulina, calmodulina e proteínas relacionadas a degradação de pectinas, foram encontradas ao longo dos segmentos, principalmente após o segmento 2. De acordo com a atividade transcricional e dados da proteômica, sugere-se que os polissacarídeos seriam atacados por enzimas nos estágios iniciais da formação do aerênquima (seg 2 e 3). O ataque ocorre principalmente sobre as pectinas e o β-glucano. Contudo, os dados apontam para a deposição de xiloglucano, xilanos e celulose (após seg 3), que formam um compósito ao redor dos espaços de ar. Isto sugere que parte dos polissacarídeos das paredes não sejam degradados ao longo do processo, embora enzimas específicas detectadas possam atuar na modificação dos mesmos, como verificado para algumas pectinases e membros de GH17. Além disso, nos pré-tratamentos com água foi possível observar que há maior sacarificação da parede nos seg. 1 e 2. Contudo quando retira-se a maior parte das pectinas e hemiceluloses após pré-tratamento com NaOH, a sacarificação é maior nos segmentos 2, 3 e 4, devido ao maior acesso e a maior quantidade de celulose. As glicosil hidrolases encontradas neste trabalho sugerem que estas atacam a parede de um específico conjunto de células do córtex que dá origem ao aerênquima. Já no fim do processo, quando há lise celular, algumas paredes de células remanescentes são recalcitrante à hidrólise, provavelmente devido a sua arquitetura e composição. Este trabalho traz informações para o desenvolvimento de futuras tecnologias para a produção do etanol do etanol celulósico de cana-de-açúcar The resistance of plant cell walls to enzymatic hydrolysis is one of the main bottlenecks of the development of technology of production of cellulosic ethanol. It is believed that the modifications in cell walls related to processes of storage mobilization, aerenchyma formation, fruit ripening and senescence, for instance, involve the activation of functional moduli that culminate in alterations of cell walls. These moduli are: 1) signal perception to start the process; 2) Programmed Cell Death (PCD); 3) cell separation; 4) cell expansion; 5) hydrolysis of hemicelluloses and 6) hydrolysis of cellulose. In the case of the formation of lysigenous aerenchyma, the process starts with PCD and is followed by the release of glycosil hydrolases that act on the degradation and/or cell wall modifications, forming air spaces in the cortex of the root. The formation of aerenchyma in the roots of sugarcane is a constitutive phenomenon and little is known about the mechanisms of modification that occur in cell walls during its development. Thus, the present study focused on the visualization of the patterns of variation of gene expression, proteins and enzyme activities associated to the formation of aerenchyma in roots of sugarcane in order to understand the role of the cell wall hydrolases and some proteins related to PCD in cell wall modifications along the process. Five root segments of 1cm each, starting from root apex, were used. A gradual centripetal formation of aerenchyma was recorded in the cortex of developing roots. Analyses of the transcriptional, proteomic and enzyme activity profiles during the process revealed that several enzymes act on cell wall modifications. The glycosil hydrolases belonging to the Cazy families GH1. GH3, GH17, GH18, as well as expansins, cellulose synthase, laccase, calreticulin, calmodulin and other proteins related to pectin degradation have been found along the segments, mainly after segment 2. According to the data on transcriptomics and proteomics, it is suggested that enzymes attack polysaccharides during the initial stages of aerenchyma formation (seg. 2 and 3). The attack of the enzymes occurs mainly on pectins and β-glucan. Conversely, the data point out to the deposition (or maintenance) of xyloglucan, xylan and cellulose (after seg. 3), which form a composite that surrounds the air spaces. This suggests that part of the polysaccharides present in cell walls are not degraded during the process, although specific enzymes have been detected that could act on polysaccharide mobilization, such as the GH17 family. Further, under pretreatment with water, it has been observed that cell wall saccharification was higher at segments 1 and 2. On the other hand, when most of the pectins and hemicelluloses are retrieved by pretreatment with NaOH, saccharification is higher of segments 2, 3 and 4, probably due to the higher access to the wall and also to the higher proportion of cellulose. The profiles related to the glycosil hydrolases found in this work, suggest that these enzymes attack the cell wall. Initially, they are probably kept within a group of cells that will originate the aerenchyma. At the end of the process, when there is cell lysis, the remaining walls of some cells are recalcitrant to hydrolysis probably due to changes in their architecture and composition. Our findings bring promising information that could be used in the future to improve efficiency of hydrolysis for cellulosic ethanol production from sugarcane

Carbon emissions related to human activities have been significantly contributing to the elevation of atmospheric [CO2] and temperature. More recently, carbon emissions have greatly accelerated, thus much stronger effects on crops are expected. Here, we revise literature data concerning the physiological effects of CO2 enrichment and temperature rise on crop species. We discuss the main advantages and limitations of the most used CO2-enrichment technologies, the Open-Top Chambers (OTCs) and the Free-Air Carbon Enrichment (FACE). Within the conditions expected for the next few years, the physiological responses of crops suggest that they will grow faster, with slight changes in development, such as flowering and fruiting, depending on the species. There is growing evidence suggesting that C3 crops are likely to produce more harvestable products and that both C3 and C4 crops are likely to use less water with rising atmospheric [CO2] in the absence of stressful conditions. However, the beneficial direct impact of elevated [CO2] on crop yield can be offset by other effects of climate change, such as elevated temperatures and altered patterns of precipitation. Changes in food quality in a warmer, high-CO2 world are to be expected, e.g., decreased protein and mineral nutrient concentrations, as well as altered lipid composition. We point out that studies related to changes in crop yield and food quality as a consequence of global climatic changes should be priority areas for further studies, particularly because they will be increasingly associated with food security.

Although the cross-talk between auxin and ethylene has been described during plant development, the role played by auxin upon gene expression during aerenchyma formation is poorly understood. Root aerenchyma formation results from the opening of gas spaces in the cortex. It is part of a developmental program (constitutive) or due to ethylene treatment or abiotic stress (induced) such as flooding and nutrient starvation. This process relies on programmed cell death and cell wall modifications. Here we followed development of aerenchyma formation in sugarcane along 5 cm from the root apex. As a constitutive process, the aerenchyma formation was observed in the cortex from the 3rd cm onwards. This occurred despite 1-methylcyclepropene (1-MCP) treatment, an inhibitor of ethylene perception. However, this process occurred while ethylene (and auxin) levels decreased. Within the aerenchyma formation zone, the concentration of ethylene is lower in comparison to the concentration in maize. Besides, the ratio between both hormones (ethylene and auxin) was around 1:1. These pieces of evidence suggest that ethylene sensitivity and ethylene-auxin balance may play a role in the formation of aerenchyma. Furthermore, the transcriptional analysis showed that genes related to cell expansion are up-regulated due to 1-MCP treatment. Our results help explaining the regulation of the formation constitutive aerenchyma in sugarcane.

Conforme previsões do último relatório do IPCC (Intergovernmental Panel of Climatic Change) em 2007, até meados deste século haverá um aumento na concentração de CO2 na atmosfera podendo chegar a 720 μmol mol-1. Consequentemente haverá uma elevação da temperatura de até +3 °C, o que ocorrerá em conjunto com mudanças no padrão de precipitação. O mesmo relatório sugere que isto poderá acarretar uma substituição gradual da floresta tropical por vegetação similar a uma savana na parte oriental da Amazônia, porém nada é conclusivo. Diante dessas possibilidades, pergunta-se - Como as espécies de árvores que compõem as regiões de alagamento da Amazônia irão responder às alterações climáticas por vir? Apesar dessas previsões serem pessimistas, o alagamento ainda ocorrerá por vários anos na Amazônia e é de grande importância compreender os efeitos do alagamento sobre as respostas fisiológicas das plantas num contexto das mudanças climáticas. Os principais efeitos sobre a sinalização metabólica e hormonal durante o alagamento são revisados e os possíveis efeitos que as mudanças climáticas poderão ter sobre as plantas amazônicas são discutidos. As informações existentes sugerem que sob alagamento, as plantas tendem a mobilizar reservas para suprir a demanda de carbono necessário para a manutenção do metabolismo sob o estresse da falta de oxigênio. Até certo limite, com o aumento da concentração de CO2, as plantas tendem a fazer mais fotossíntese e a produzir mais biomassa, que poderão aumentar ainda mais com um acréscimo de temperatura de até 3 °C. Alternativamente, com o alagamento, há uma diminuição geral do potencial de crescimento e é possível que quando em condições de CO2 e temperatura elevados os efeitos positivo e negativo se somem. Com isso, as respostas fisiológicas poderão ser amenizadas ou, ainda, promover maior crescimento para a maioria das espécies de regiões alagáveis até o meio do século. Porém, quando a temperatura e o CO2 atingirem valores acima dos ótimos para a maioria das plantas, estas possivelmente diminuirão a atividade fisiológica. According to the last report of IPCC (Intergovernmental Panel of Climatic Change, 2007) an increase in atmospheric CO2 concentration to ca. 0.072% is predicted to occur until the middle of this century. As a result, a tandem elevation of temperature of ca. +3 °C and a decrease in precipitation are to be expected. It has also been suggested that this scenario may lead to a gradual substitution of the tropical forest for savanna-like vegetation in Eastern parts of the Amazon. Within this perspective, a worth question is how the tree species that make up the Amazonian floodplains will respond to the global climatic change? Although predictions have been quite pessimistic, flooding of part of the Amazon will continue to occur for several years and it is important to understand its synergistic effects within the scenario of climate change. In this work, features related to plant metabolism and hormonal signaling during flooding is revised, and the possible effects that the climatic changes might have on plants from the Amazon are discussed. The information available in the literature suggests that under flooding, plants tend to mobilize storage compounds to supply carbon demand needed for maintenance metabolism under the effect of stress caused by the lack of oxygen. In contrast, under elevated CO2 concentration, plants tend to increase photosynthesis and biomass. With an increase of about 3 °C these parameters may increase even more. Alternatively, with flooding, there is a general decrease in growth potential and it is possible that while favorable conditions of elevated CO2 and temperature prevail, the positive effects may be counterbalanced by the negative effects of flooding. Thus, the physiological responses might be imperceptible or promote further growth up to the middle of the 21st Century for most species that occur in the floodplains. However, if temperature and CO2 levels surpass the threshold of optimal conditions for most plants, a decrease in physiological activity is to be expected.

Photosynthesis and growth are dependent on environmental conditions and plant developmental stages. However, it is still not clear how the environment and development influence the diurnal dynamics of nonstructural carbohydrates production and how they affect growth. This is particularly the case of C4 plants such as sugarcane (Saccharum spp.). Aiming to understand the dynamics of leaf gas exchange and nonstructural carbohydrates accumulation in different organs during diurnal cycles across the developmental stages, we evaluated these parameters in sugarcane plants in a 12-month field experiment. Our results show that during the first 3 months of development, light and vapour pressure deficit (VPD) were the primary drivers of photosynthesis, stomatal conductance and growth. After 6 months, in addition to light and VPD, drought, carbohydrate accumulation and the mechanisms possibly associated with water status maintenance were also likely to play a role in gas exchange and growth regulation. Carbohydrates vary throughout the day in all organs until Month 9, consistent with their use for growth during the night. At 12 months, sucrose is accumulated in all organs and starch had accumulated in leaves without any diurnal variation. Understanding of how photosynthesis and the dynamics of carbohydrates are controlled might lead to strategies that could increase sugarcane’s biomass production.

Key message The Amazonian treeSenna reticulatashowed an increase in photosynthesis and starch content under elevated [CO2] that led an increment in biomass after 90 days. Elevated [CO2] was also capable of reducing the negative effect of waterlogging.

Cell wall hydrolysis is one of the key processes needed for development of the technology for second-generation (2G) bioethanol production. Thus, finding and characterizing enzymes that can deal with the complexity of the walls has been the main focus of research. As a result, data on pretreatments of many kinds and performances of enzyme cocktails containing glycosyl hydrolases from microorganisms are becoming quickly available. Here we propose that the efficiency of the 2G process could be increased even further by acquiring control of mechanisms that plants themselves use to degrade their own walls, so that wall loosening provoked by such processes would decrease the energy demand for pretreatments and facilitate hydrolysis. The examined in this chapter are plant-microorganism interaction, cell wall storage mobilization, fruit ripening, abscission, and aerenchyma formation. These systems are seen as having in common the use of modules that are coupled sequentially in order to lead to cell wall modification, including hydrolysis, for performance of different biological functions. These modules are (1) target cells perception of a message from the hormonal balance, (2) cell separation, (3) cell expansion, (4) programmed cell death, (5) hemicellulose-cellulose relaxation/hydrolysis and (6) cellulose hydrolysis. We propose that the use of synthetic biology to transform bioenergy feedstocks could be a route to increase the efficiency of 2G processes.