Secretome Analysis of Thermothelomyces thermophilus LMBC 162 Cultivated with Tamarindus indica Seeds Reveals CAZymes for Degradation of Lignocellulosic Biomass.

The analysis of the secretome allows us to identify the proteins, especially carbohydrate-active enzymes (CAZymes), secreted by different microorganisms cultivated under different conditions. The CAZymes are divided into five classes containing different protein families. Thermothelomyces thermophilus is a thermophilic ascomycete, a source of many glycoside hydrolases and oxidative enzymes that aid in the breakdown of lignocellulosic materials. The secretome analysis of T. thermophilus LMBC 162 cultivated with submerged fermentation using tamarind seeds as a carbon source revealed 79 proteins distributed between the five diverse classes of CAZymes: 5.55% auxiliary activity (AAs); 2.58% carbohydrate esterases (CEs); 20.58% polysaccharide lyases (PLs); and 71.29% glycoside hydrolases (GHs). In the identified GH families, 54.97% are cellulolytic, 16.27% are hemicellulolytic, and 0.05 are classified as other. Furthermore, 48.74% of CAZymes have carbohydrate-binding modules (CBMs). Observing the relative abundance, it is possible to state that only thirteen proteins comprise 92.19% of the identified proteins secreted and are probably the main proteins responsible for the efficient degradation of the bulk of the biomass: cellulose, hemicellulose, and pectin.

Meta-analysis of the responses of tree and herb to elevated CO2 in Brazil.

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, 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 (79% natives and 21% cultivated) and herbs (33% natives and 67% cultivated). 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.

Elevated CO2 increases biomass of Sorghum bicolor green prop roots under drought conditions via soluble sugar accumulation and photosynthetic activity.

Elevated [CO2 ] (E[CO2 ]) mitigates agricultural losses of C4 plants under drought. Although several studies have described the molecular responses of the C4 plant species Sorghum bicolor during drought exposure, few have reported the combined effects of drought and E[CO2 ] (E[CO2 ]/D) on the roots. A previous study showed that, among plant organs, green prop roots (GPRs) under E[CO2 ]/D presented the second highest increase in biomass after leaves compared with ambient [CO2 ]/D. GPRs are photosynthetically active and sensitive to drought. To understand which mechanisms are involved in the increase in biomass of GPRs, we performed transcriptome analyses of GPRs under E[CO2 ]/D. Whole-transcriptome analysis revealed several pathways altered under E[CO2 ]/D, among which photosynthesis was strongly affected. We also used previous metabolome data to support our transcriptome data. Activities associated with photosynthesis and central metabolism increased, as seen by the upregulation of photosynthesis-related genes, a rise in glucose and polyol contents, and increased contents of chlorophyll a and carotenoids. Protein-protein interaction networks revealed that proliferation, biogenesis, and homeostasis categories were enriched and contained mainly upregulated genes. The findings suggest that the previously reported increase in GPR biomass of plants grown under E[CO2 ]/D is mainly attributed to glucose and polyol accumulation, as well as photosynthesis activity and carbon provided by respiratory CO2 refixation. Our findings reveal that an intriguing and complex metabolic process occurs in GPRs under E[CO2 ]/D, showing the crucial role of these organs in plant drought /tolerance.

Carbon allocation of Spirodela polyrhiza under boron toxicity.

Pectic polysaccharides containing apiose, xylose, and uronic acids are excellent candidates for boron fixation. Duckweeds are the fastest-growing angiosperms that can absorb diverse metals and contaminants from water and have high pectin content in their cell walls. Therefore, these plants can be considered excellent boron (B) accumulators. This work aimed to investigate the relationship between B assimilation capacity with apiose content in the cell wall of Spirodela polyrhiza subjected to different boric acid concentrations. Plants were grown for 7 and 10 days in ½ Schenck-Hildebrandt media supplemented with 0 to 56 mg B.L-1, the non-structural and structural carbohydrates, and related genes were evaluated. The results showed that B altered the morphology and carbohydrate composition of this species during plant development. The optimum B concentration (1.8 mg B.L-1) led to the highest relative growth and biomass accumulation, reduced starch, and high pectin and apiose contents, together with increased expression of UDP-apiose/UDP-xylose synthase (AXS) and 1,4-α-galacturonosyltransferase (GAUT). The toxic state (28 and 56 mg B.L-1) increased the hexose contents in the cell wall with a concomitant reduction of pectins, apiose, and growth. The pectin content of S. polyrhiza was strongly associated with its growth capacity and regulation of B content within the cells, which have AXS as an important regulator. These findings suggest that duckweeds are suitable for B remediation, and their biomass can be used for bioenergy production.

Trichoderma longibrachiatum and thermothelomyces thermophilus co-culture: improvement the saccharification profile of different sugarcane bagasse varieties.

OBJECTIVES: The aim of the present work was to perform the co-culture between Trichoderma longibrachiatum LMBC 172, a mesophilic fungus, with Thermothelomyces thermophilus LMBC 162, a thermophilic fungus, by submerged fermentation in a bioreactor. RESULTS: There was an increase in protein production, reaching the value of 35.60 ± 3.76 µg/ml at 72 h. An increase in the amount of proteins of 27.5% in relation to the isolated cultivation of T. longibrachiatum and 19.7% in comparison when T. thermophilus was isolated and cultivated. After that, the saccharification profile of three varieties of sugarcane (sugarcane in natura, culms of sugarcane SP80-3280, and culms of Energy cane) submitted in two pretreatments (autohydrolysis and chemical) was performed. The (e) chemical pretreatment was the better in generating of fermentable sugars from sugarcane bagasse and culms of Energy cane, while with the autohydrolysis pretreatment was obtained the better values to culms of SP80-3280 sugarcane. The sugars found were glucose, xylose, arabinose, and cellobiose. CONCLUSION: These results suggest that the co-culture between these microorganisms has the potential to produce an enzymatic cocktail with high performance in the hydrolysis of materials from the sugar-alcohol industry.

Glycomic profiling identifies key-structural differences in three arabinoxylan fractions from sugarcane culms.

Sugarcane is an important food and bioenergy crop, and although the residual biomass is potentially available for biorefinery and biofuels production the complex plant cell wall matrix requires pretreatment prior to enzymatic hydrolysis. Arabinoxylans require multiple enzymes for xylose backbone and saccharide side-branch hydrolysis to release xylooligosaccharides and pentoses. The effect of arabinoxylan structure on xylooligosaccharide release by combinations of up to five xylanolytic enzymes was studied using three arabinoxylan fractions extracted from sugarcane culms by sodium chlorite, DMSO and alkaline treatments. Reducing sugar release and LC-MS detection with chemometric analysis identified different xylooligosaccharide profiles between extracts following enzyme treatments. The position and degree of side-branch decorations are determinants of enzyme activity and xylooligosaccharide diversity with the alkaline and post­sodium chlorite extracts as the most accessible and most recalcitrant, respectively, indicating acetyl substituents as a major recalcitrance factor. The complex xylooligosaccharide profile with the DMSO extract suggests regions with different levels of branching. Chemometric analysis identified GH10 xylanase hydrolysis products that act as substrates for other enzymes, such as α-glucuronidase. The strategy reported here can identify specific enzyme combinations to overcome barriers for biomass processing such as pretreatment selection, recalcitrance to enzyme digestion and optimization of reducing sugar release.

Xylose isomerase from Piromyces sp. E2 is a promiscuous enzyme with epimerase activity.

Xylose isomerase catalyzes the isomerization of D-xylose to D-xylulose with promiscuous activity for other saccharides including D-glucose, D-allose, and L-arabinose. The xylose isomerase from the fungus Piromyces sp. E2 (PirE2_XI) is used to engineer xylose usage by the fermenting yeast Saccharomyces cerevisiae, but its biochemical characterization is poorly understood with divergent catalytic parameters reported. We have measured the kinetic parameters of the PirE2_XI and analyzed its thermostability and pH-dependence towards different substrates. The PirE2_XI shows promiscuous activity towards D-xylose, D-glucose, D-ribose and L-arabinose with variable effects depending on different divalent ions and epimerizes D-xylose at C3 to produce D-ribulose in a substrate/product dependent ratio. The enzyme follows Michaelis-Menten kinetics for the substrates used and although KM values for D-xylose are comparable at 30 and 60 °C, the kcat/KM is three-fold greater at 60 °C. The purified PirE2_XI shows maximal activity at 65 °C in the pH range of 6.5-7.5 and is a thermostable enzyme, maintaining full activity over 48 h at 30 °C or 12 h at 60 °C. This is the first report demonstrating epimerase activity of the PirE2_XI and its ability to isomerize D-ribose and L-arabinose, and provides a comprehensive in vitro study of substrate specificity, effect of metal ions and temperature on enzyme activity and these findings advance the knowledge of the mechanism of action of this enzyme.

Overexpression of the GmEXPA1 gene reduces plant susceptibility to Meloidogyne incognita.

KEY MESSAGE: 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.

Immobilization and Application of the Recombinant Xylanase GH10 of Malbranchea pulchella in the Production of Xylooligosaccharides from Hydrothermal Liquor of the Eucalyptus (Eucalyptus grandis) Wood Chips.

Xylooligosaccharides (XOS) are widely used in the food industry as prebiotic components. XOS with high purity are required for practical prebiotic function and other biological benefits, such as antioxidant and inflammatory properties. In this work, we immobilized the recombinant endo-1,4-ß-xylanase of Malbranchea pulchella (MpXyn10) in various chemical supports and evaluated its potential to produce xylooligosaccharides (XOS) from hydrothermal liquor of eucalyptus wood chips. Values >90% of immobilization yields were achieved from amino-activated supports for 120 min. The highest recovery values were found on Purolite (142%) and MANAE-MpXyn10 (137%) derivatives, which maintained more than 90% residual activity for 24 h at 70 °C, while the free-MpXyn10 maintained only 11%. In addition, active MpXyn10 derivatives were stable in the range of pH 4.0−6.0 and the presence of the furfural and HMF compounds. MpXyn10 derivatives were tested to produce XOS from xylan of various sources. Maximum values were observed for birchwood xylan at 8.6 mg mL−1 and wheat arabinoxylan at 8.9 mg mL−1, using Purolite-MpXyn10. Its derivative was also successfully applied in the hydrolysis of soluble xylan present in hydrothermal liquor, with 0.9 mg mL−1 of XOS after 3 h at 50 °C. This derivative maintained more than 80% XOS yield after six cycles of the assay. The results obtained provide a basis for the application of immobilized MpXyn10 to produce XOS with high purity and other high-value-added products in the lignocellulosic biorefinery field.

Overexpression of a soybean Globin (GmGlb1-1) gene reduces plant susceptibility to Meloidogyne incognita.

MAIN CONCLUSION: 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.

Bioinformatic analyses to uncover genes involved in trehalose metabolism in the polyploid sugarcane.

Trehalose-6-phosphate (T6P) is an intermediate of trehalose biosynthesis that plays an essential role in plant metabolism and development. Here, we comprehensively analyzed sequences from enzymes of trehalose metabolism in sugarcane, one of the main crops used for bioenergy production. We identified protein domains, phylogeny, and in silico expression levels for all classes of enzymes. However, post-translational modifications and residues involved in catalysis and substrate binding were analyzed only in trehalose-6-phosphate synthase (TPS) sequences. We retrieved 71 putative full-length TPS, 93 trehalose-6-phosphate phosphatase (TPP), and 3 trehalase (TRE) of sugarcane, showing all their conserved domains, respectively. Putative TPS (Classes I and II) and TPP sugarcane sequences were categorized into well-known groups reported in the literature. We measured the expression levels of the sequences from one sugarcane leaf transcriptomic dataset. Furthermore, TPS Class I has specific N-glycosylation sites inserted in conserved motifs and carries catalytic and binding residues in its TPS domain. Some of these residues are mutated in TPS Class II members, which implies loss of enzyme activity. Our approach retrieved many homo(eo)logous sequences for genes involved in trehalose metabolism, paving the way to discover the role of T6P signaling in sugarcane.

Selective xyloglucan oligosaccharide hydrolysis by a GH31 α-xylosidase from Escherichia coli.

Xyloglucan is ubiquitous in the cell walls of land plants and is also an essential storage polymer in seeds of many species. We studied the hydrolysis of the non-reducing end xylosyl residue of xyloglucan oligosaccharides (XGOs) by the Escherichia coli α-xylosidase (YicI). Electrospray Ionization Tandem Mass Spectrometry (ESI-MS/MS) and ion fragmentation analysis together with high performance anion exchange chromatography with pulsed amperometric detection revealed that YicI preferentially removes the xylosyl residue from the glycosyl residue of non-galactosylated oligosaccharides. The YicI shows decreasing activity against the galactosylated oligosaccharides XXXG>XXLG≥XLXG. Studies of the XGOs interaction with active site residues by molecular dynamics simulations suggested that hydrogen bond interactions between the D49 and galactosylated oligosaccharides play an important role in enzyme-XGO interactions. This was confirmed by site-directed mutagenesis, where the D49A mutant affected catalytic efficiency against galactosylated XGOs. Our findings advance xyloglucan disassembly models and highlight the importance of YicI for biotechnology applications.

Biochemical composition of the pericarp cell wall of popcorn inbred lines with different popping expansion.

The popping expansion is a characteristic that is positively related with the quality of popcorn. A positive correlation between the volume of expansion and the thickness of the pericarp, and between the proportion of the opaque/shiny endosperm and the grain weight and volume, were postulated. However, there are no reports in the literature that address the importance of cell wall components in the popping expansion. Here, we investigate the biochemical composition of the pericarp cell walls of three inbred lines of popcorn with different popping expansion. Inbred lines GP12 (expansion volume >40 mL g-1), P11 (expansion volume 30 mL g-1) and P16 (expansion volume 14 mL g-1) were used for the analysis and quantification of monosaccharides by HPAEC-PAD, and ferulic and p-coumaric acids and lignin by HPLC. Our hypothesis is that the biochemical composition of the pericarp cell walls may be related to greater or lesser popping expansion. Our data suggest that the lignin content and composition contribute to popping expansion. The highest concentration of lignin (129.74 µg mg-1; 12.97%) was detected in the pericarp cell wall of the GP12 inbred line with extremely high popping expansion, and the lowest concentration (113.52 µg mg-1; 11.35%) was observed in the P16 inbred line with low popping expansion. These findings may contribute to indicating the quantitative trait locus for breeding programs and to developing other methods to improve the popping expansion of popcorn.

Bioinformatic analyses to uncover genes involved in trehalose metabolism in the polyploid sugarcane

Trehalose-6-phosphate (T6P) is an intermediate of trehalose biosynthesis that plays an essential role in plant metabolism and development. Here, we comprehensively analyzed sequences from enzymes of trehalose metabolism in sugarcane, one of the main crops used for bioenergy production. We identified protein domains, phylogeny, and in silico expression levels for all classes of enzymes. However, post-translational modifications and residues involved in catalysis and substrate binding were analyzed only in trehalose-6-phosphate synthase (TPS) sequences. We retrieved 71 putative full-length TPS, 93 trehalose-6-phosphate phosphatase (TPP), and 3 trehalase (TRE) of sugarcane, showing all their conserved domains, respectively. Putative TPS (Classes I and II) and TPP sugarcane sequences were categorized into well-known groups reported in the literature. We measured the expression levels of the sequences from one sugarcane leaf transcriptomic dataset. Furthermore, TPS Class I has specific N-glycosylation sites inserted in conserved motifs and carries catalytic and binding residues in its TPS domain. Some of these residues are mutated in TPS Class II members, which implies loss of enzyme activity. Our approach retrieved many homo(eo)logous sequences for genes involved in trehalose metabolism, paving the way to discover the role of T6P signaling in sugarcane.

The Effect of Sugarcane Straw Aging in the Field on Cell Wall Composition.

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 ß-glucans (ß-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.

Xyloglucan processing machinery in Xanthomonas pathogens and its role in the transcriptional activation of virulence factors.

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.

Increased Malbranchea pulchella ß-glucosidase production and its application in agroindustrial residue hydrolysis: A research based on experimental designs.

ß-Glucosidases are a limiting factor in the conversion of cellulose to glucose for the subsequent ethanol production. Here, ß-glucosidase production by Malbranchea pulchella was optimized using Composite Central Designs and Response Surface Methodologies from a medium designed. The coefficient of determination (R2 ) was 0.9960, F-value was very high, and the lack of fit was found to be non-significant. This indicates a statistic valid and predictive result. M. pulchella enzymatic extract was successfully tested as an enzymatic cocktail in a mixture design using sugarcane bagasse, soybean hull and barley bagasse. We proved that the optimization of the ß-glucosidase production and the application in hydrolysis using unexpansive biomass and agricultural wastes can be accomplished by means of statistical methodologies. The strategy presented here can be useful for the improvement of enzyme production and the hydrolysis process, arising as an alternative for bioeconomy.

Prospection of Fungal Lignocellulolytic Enzymes Produced from Jatoba (Hymenaea courbaril) and Tamarind (Tamarindus indica) Seeds: Scaling for Bioreactor and Saccharification Profile of Sugarcane Bagasse.

The lignocellulosic biomass comprises three main components: cellulose, hemicellulose, and lignin. Degradation and conversion of these three components are attractive to biotechnology. This study aimed to prospect fungal lignocellulolytic enzymes with potential industrial applications, produced through a temporal analysis using Hymenaea courbaril and Tamarindus indica seeds as carbon sources. α-L-arabinofuranosidase, acetyl xylan esterase, endo-1,5-α-L-arabinanase, ß-D-galactosidase, ß-D-glucosidase, ß-glucanase, ß-D-xylosidase, cellobiohydrolase, endoglucanase, lichenase, mannanase, polygalacturonase, endo-1,4-ß-xylanase, and xyloglucanase activities were determined. The enzymes were produced for eight filamentous fungi: Aspergillus fumigatus, Trametes hirsuta, Lasiodiplodia sp., two strains of Trichoderma longibrachiatum, Neocosmospora perseae, Fusarium sp. and Thermothelomyces thermophilus. The best producers concerning enzymatic activity were T. thermophilus and T. longibrachiatum. The optimal conditions for enzyme production were the media supplemented with tamarind seeds, under agitation, for 72 h. This analysis was essential to demonstrate that cultivation conditions, static and under agitation, exert strong influences on the production of several enzymes produced by different fungi. The kind of sugarcane, pretreatment used, microorganisms, and carbon sources proved limiting sugar profile factors.

Xyloglucan processing machinery in Xanthomonas pathogens and its role in the transcriptional activation of virulence factors

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.

Global tree-ring analysis reveals rapid decrease in tropical tree longevity with temperature.

Forests are the largest terrestrial biomass pool, with over half of this biomass stored in the highly productive tropical lowland forests. The future evolution of forest biomass depends critically on the response of tree longevity and growth rates to future climate. We present an analysis of the variation in tree longevity and growth rate using tree-ring data of 3,343 populations and 438 tree species and assess how climate controls growth and tree longevity across world biomes. Tropical trees grow, on average, two times faster compared to trees from temperate and boreal biomes and live significantly shorter, on average (186 ± 138 y compared to 322 ± 201 y outside the tropics). At the global scale, growth rates and longevity covary strongly with temperature. Within the warm tropical lowlands, where broadleaf species dominate the vegetation, we find consistent decreases in tree longevity with increasing aridity, as well as a pronounced reduction in longevity above mean annual temperatures of 25.4 °C. These independent effects of temperature and water availability on tree longevity in the tropics are consistent with theoretical predictions of increases in evaporative demands at the leaf level under a warmer and drier climate and could explain observed increases in tree mortality in tropical forests, including the Amazon, and shifts in forest composition in western Africa. Our results suggest that conditions supporting only lower tree longevity in the tropical lowlands are likely to expand under future drier and especially warmer climates.