Plant Biopolymers Research Articles

Lignocellulose biodegradation to humic substances in cow manure-straw composting: Characterization of dissolved organic matter and microbial community succession

Composting, a sustainable practice, facilitates the biodegradation of organic waste, notably lignocellulosic biomass, into value-added humic substances. Despite its potential, the application of electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) to characterize dissolved organic matter (DOM) for assessing the changes in maturity during cow manure-straw composting is underexplored. Furthermore, the link between these changes, microbial community succession, and the biochemical pathways of humus formation is seldom investigated. This study leveraged ESI FT-ICR MS and metagenomic analysis to elucidate the molecular changes in DOM, identified key microbes in humus formation, and traced the humus formation pathway during composting. The results highlighted the crucial role of microorganisms such as Thermobifida, Luteimonas, Ascomycota, and Chloroflexi in accelerating the breakdown and transformation of plant biopolymers. Large molecular nitrogen compounds from cow manure-straw were converted into unsaturated, aromatic oxygen compounds, which resemble humic substances in their chemical properties. The ESI FT-ICR MS data revealed that humus formation occurred through a series of reactions, including protein deamination, lignin delignification, and decarbonylation. This research offered new light on strategies to enhance the stabilization and humification of cow manure-straw composting, contributing to more effective composting processes.

Ionically crosslinked Sodium alginate – Galactoxyloglucan hydrogel beads as a controlled release system for sustainable urea delivery

The prolonged usage of chemical fertilizers often causes deleterious effects on the environment, and it remains an alarming issue in agricultural practices. Smart delivery of fertilizers achieved by hydrogels proved their efficiency in reducing risk in action. In this study, we investigated the optimization of urea-encapsulated hydrogel formulations and evaluated their physical and chemical attributes for agricultural applications. The proposed hydrogel formulation consists of ionically crosslinked two promising plant biopolymers (galactoxyloglucan and sodium alginate) which are specifically developed for the controlled release of urea fertilizer. The FT-IR analysis of the hydrogel beads confirmed the presence of biopolymer functional groups and urea. XRD analysis indicated the amorphous nature of the biopolymers. TGA revealed a thermal stability of up to 350°C. SEM images showed the porous structure of the hydrogel beads. To investigate the controlled release of urea, two kinetic models were employed: Korsmeyer-Peppas and Peppas-Sahlin. The results indicated a controlled release mechanism. The hydrogel beads demonstrated excellent water retention properties, maintaining soil moisture for up to 16 days. Additionally, degradability results demonstrated that in the soil environment, the hydrogel beads were degraded completely in 21 days. Therefore, we are confident that the formulated hydrogel bead exhibits eco-friendly and bio-compatible characteristics, which potentially mitigate the risks associated with urea fertilizers.

Arbuscular mycorrhizal symbiosis enhances the accumulation of plant-derived carbon in soil organic carbon by regulating the biosynthesis of plant biopolymers and soil metabolism

Plant-derived carbon (C) is a critical constituent of particulate organic carbon (POC) and plays an essential role in soil organic carbon (SOC) sequestration. Yet, how arbuscular mycorrhizal fungi (AMF) control the contribution of plant-derived C to SOC storage through two processes (biosynthesis of plant biopolymers and soil metabolism) remains poorly understood. Here, we utilized transcriptome analysis to examine the effects of AMF on P. communis roots. Under the AM symbiosis, root morphological growth and tolerance to stress were strengthened, and the biosynthetic pathways of key plant biopolymers (long-chain fatty acids, cutin, suberin, and lignin) contributing to the plant-derived C were enhanced. In the subsequent metabolic processes, AMF increased soil metabolites contributing to plant-derived C (such as syringic acid) and altered soil metabolic pathways, including carbohydrate metabolism. Additionally, C-acquiring soil extracellular enzyme activities were enhanced by AMF, which could affect the stabilization of plant-derived C in soil. The contents of POC (21.71 g kg−1 soil), MAOC (10.75 g kg−1 soil), and TOC (32.47 g kg−1 soil) in soil were significantly increased by AMF. The concentrations of plant-derived C and microbial-derived C were quantified based on biomarker analysis. AMF enhanced the content of plant-derived C in both POC and MAOC fractions. What's more, plant-derived C presented the highest level in the POC fraction under the AMF treatment. This research broadens our understanding of the mechanism through which plant-derived C contributes to the accumulation of POC and SOC induced by AM symbiosis, and evidences the benefits of AMF application in SOC sequestration.

Exploring Lignin Biosynthesis Genes in Rice: Evolution, Function, and Expression.

Lignin is nature's second most abundant vascular plant biopolymer, playing significant roles in mechanical support, water transport, and stress responses. This study identified 90 lignin biosynthesis genes in rice based on phylogeny and motif constitution, and they belong to PAL, C4H, 4CL, HCT, C3H, CCoAOMT, CCR, F5H, COMT, and CAD families. Duplication events contributed largely to the expansion of these gene families, such as PAL, CCoAOMT, CCR, and CAD families, mainly attributed to tandem and segmental duplication. Microarray data of 33 tissue samples covering the entire life cycle of rice suggested fairly high PAL, HCT, C3H, CCoAOMT, CCR, COMT, and CAD gene expressions and rather variable C4H, 4CL, and F5H expressions. Some members of lignin-related genes (OsCCRL11, OsHCT1/2/5, OsCCoAOMT1/3/5, OsCOMT, OsC3H, OsCAD2, and OsPAL1/6) were expressed in all tissues examined. The expression patterns of lignin-related genes can be divided into two major groups with eight subgroups, each showing a distinct co-expression in tissues representing typically primary and secondary cell wall constitutions. Some lignin-related genes were strongly co-expressed in tissues typical of secondary cell walls. Combined HPLC analysis showed increased lignin monomer (H, G, and S) contents from young to old growth stages in five genotypes. Based on 90 genes' microarray data, 27 genes were selected for qRT-PCR gene expression analysis. Four genes (OsPAL9, OsCAD8C, OsCCR8, and OsCOMTL4) were significantly negatively correlated with lignin monomers. Furthermore, eleven genes were co-expressed in certain genotypes during secondary growth stages. Among them, six genes (OsC3H, OsCAD2, OsCCR2, OsCOMT, OsPAL2, and OsPAL8) were overlapped with microarray gene expressions, highlighting their importance in lignin biosynthesis.

Neem (Azadirachta indica) seed extract formulation for managing anthracnose and gray mold diseases in strawberry

Anthracnose caused by Colletotrichum nymphaeae and gray mold caused by Botrytis cinerea are the most epidemic fungal diseases causing significantly losses in strawberry plantings. The objective of the study is to determine the antifungal activity of neem (Azadirachta indica A. Juss.) seed extracts and preparing new formulated antifungal agent. Plant extracts including alcoholic, aqueous and oil were extracted from neem seeds and used in concentrations of 1000, 2000, 4000, 8000 and 10,000 µl/l to control the vegetative mycelial growth of pathogens. The results showed that alcoholic extract had highest antifungal effect and used for the formulation. The concentration of 10,000 microliters of alcoholic extract showed 91.6 % inhibition of gray mold disease, while it inhibited 80.66 % in anthracnose disease and a significant difference was observed between them. For encapsulation of alcoholic neem extract with plant biopolymers with new changes, the separation method of water-miscible solvent through precipitation with salt was used. The results showed that the best effect of the formulation was observed at a dose of four per thousand. Inhibition at this concentration as the best option in terms of controlling gray mold and anthracnose disease was 86.3 % and 79.38 %, respectively, and they were placed in the same statistical group (d). This formulation is designed to determine the minimum concentration threshold and reduce the consumption of alcoholic extract. Based on the results, the use of formulated alcoholic extract of neem seed as an alternative to chemical fungicides can help control anthracnose and gray mold in strawberries.

Antitumor Effects of Carrier-Free Functionalized Lignin Materials on Human Hepatocellular Carcinoma (HepG2) Cells.

Lignin, as an abundant aromatic biopolymer in plants, has great potential for medical applications due to its active sites, antioxidant activity, low biotoxicity, and good biocompatibility. In this work, a simple and ecofriendly approach for lignin fractionation and modification was developed to improve the antitumor activity of lignin. The lignin fraction KL-3 obtained by the lignin gradient acid precipitation at pH = 9-13 showed good cytotoxicity. Furthermore, the cell-feeding lignin after additional structural modifications such as demethylation (DKL-3), sulfonation (SL-3), and demethylsulfonation (DSKL-3) could exhibit higher glutathione responsiveness in the tumor microenvironment, resulting in reactive oxygen species accumulation and mitochondrial damage and eventually leading to apoptosis in HepG2 cells with minimal damage to normal cells. The IC50 values for KL-3, SL-3, and DSKL-3 were 0.71, 0.57, and 0.41 mg/mL, respectively, which were superior to those of other biomass extractives or unmodified lignin. Importantly, in vivo experiments conducted in nude mouse models demonstrated good biosafety and effective tumor destruction. This work provides a promising example of constructing carrier-free functionalized lignin antitumor materials with different structures for inhibiting the growth of human hepatocellular carcinoma (HepG2) cells, which is expected to improve cancer therapy outcomes.

Short-Term Effect of Biopolymer-Based Coatings on Surface Hardness and Color of Limestone Exposed to Tropical Outdoor Conditions

It has previously been shown that epilithic bacterial biopolymers used as coatings influenced the physical properties (surface hardness and color change) at different levels and decreased the surface disaggregation of experimental limestone when evaluated at the laboratory level. A short-term study (30 days) was conducted to evaluate the performance under natural conditions of limestone blocks exposed to tropical conditions of a selected bacterial biopolymer (TM1B-488, after the producing bacterium) and a previously unreported Mayan plant biopolymer known as “Escobilla”, Sida rhombifolia (Malvaceae) used in conservation procedures. Surface hardness (Leeb units) and color (L*a*b* coordinates) were measured and statistically tested for two types of limestone blocks (sound and deteriorated limestone). Both biopolymers increased surface hardness, decreased surface disaggregation, and did not alter color. Escobilla polymer is a carbohydrate-rich biopolymer characterized by tangential filtration, global chemical composition, and monosaccharide composition of hydrolyzed polymer. These results indicate that biopolymers of a heteropolysaccharide nature are constituted by some anionic charge residues that could contribute to surface stabilization and consolidation, but compatibility with traditional building materials (mortars) and longer time of exposure (a year) are necessary to fully assess their applicability in the restoration of architectural heritage.

Isomolar series methodology in sensory analysis of fish culinary products for HEALTHY-CAFE

The object of research is the technology of fish products for HELTHY-CAFE with regulated histamine content for the development of health food diets for the population. One of the most problematic places in the technology of food products from raw materials of aquatic origin is microbiological spoilage and, as a result, the formation and accumulation of HisA, which in a certain amount causes a toxic effect. In the course of the study, the methods of isomolar series, sensory analysis, and the study of quality indicators were used. The methodology chosen in the work allows to determine the optimal ratio of hydrocolloids in the system for maximum complexation with histamine in the technology of fish culinary products in gelatin fillings with a harmonious sensory profile and adjustable histamine content. The obtained results of the conducted research allow to state that the proposed method of determining the optimal ratio of sodium alginate and low-esterified pectin substances contributes to the development of a gelatinous filling for fish culinary products in order to ensure the harmonious flavor of ready-made fish dishes and contributes to the expansion of the range of fish products for HELTHY-CAFE with functional and preventive properties. This is due to the fact that taking into account the modern trends in nutrition regarding the safety, functionality, palatability, and attractiveness of fish food products made it possible, based on the method of isomolar series and sensory analysis, to scientifically substantiate the optimal ratio of plant biopolymers, to form requirements for the texture of gelatin filling in fish technology culinary products. On the basis of previous experimental studies, it was shown that the accumulation of histamine occurs more actively in sea fish, which made it possible to substantiate the choice of raw materials for the production of fish culinary products. Taking into account the main global trends in the development of aquaculture, it is proposed to use crucian carp as a raw material, as the main object of aquaculture in Ukraine. The low activity of the peptide hydrolase complex of the muscle tissue of the carp, compared to sea fish, contributes to the formation of a harmonious aromatic profile of fish culinary products, which corresponds to consumer expectations, and the use of natural hydrocolloids of vegetable origin to form a gelatinous structure provides functional properties to the food product and allows controlling the histamine content.

STRUCTURE AND BIOMEDICAL PROPERTIES OF LIGNINS (REVIEW)

The proposed literature review is in line with current trends in the development of nature-like technologies and is devoted to the analysis of the chemical structure and the search for new ways to use lignins for biomedical applications. Lignins are unique biopolymers of plant origin, the structural organization of which is multivariate and largely depends on the biological species of the plant. Fundamental structural and chemical studies are increasingly clarifying our understanding of the macromolecules structure of this key plant biopolymer, and the study of various taxonomic origins lignins shows to what extent evolution and natural variability have led to a complication of the chemical structure of macromolecules, including through the inclusion of "unconventional" phenolic monomers. This suggests that lignins contain much more structural units than the three monolignol variants described in lignin chemistry textbooks. As a result, as the analysis of the literature data shows, the very definition of lignin continues to expand and refine. Currently, there is a dramatic increase in interest in lignin-based materials, mainly due to their diverse beneficial properties, such as biodegradability, reactivity, biocompatibility, low toxicity and a wide range of biological activity. One of the main objectives of this article is to identify and discuss the mechanisms of biological action of lignins on living organisms to assess the biomedical potential and substantiate the possibility of their use as innovative drugs of antioxidant, radioprotective and geroprotective action. Finding new ways to use lignins is necessary to meet the challenges of maintaining health and improving the quality and duration of people's lives.

Uncovering a phylogenetic signal in plant biopolymer chemistry: a comparison of sporopollenin isolation approaches for use in palynological research

AbstractSporomorphs (pollen and spores) are a mainstay of research into past vegetation, and increasingly sporomorph chemistry is being used as a palaeoecological tool. To make extant sporomorphs directly comparable to fossil specimens, fresh material is processed to remove labile compounds and isolate the sporopollenin wall. A range of processing approaches are currently in use, but the chemistries produced by these different techniques have not yet been compared across a range of taxa. It is therefore not clear how they compare in terms of efficiently isolating sporopollenin without changing its chemical structure, and what impact they have on relative chemical similarities and differences among taxa (i.e. whether more closely related species will always appear chemically more similar, regardless of how they have been processed). Here, we test this by applying five different processing approaches to sporomorphs from 15 taxa from across the vascular plant phylogeny. We show that each approach has its own idiosyncrasies in terms of impacts on sporomorph chemistry. For the most part a common pattern of among‐taxon chemical variability is uncovered, and a phylogenetic signal within sporopollenin chemistry is supported. Working with spectral derivatives generally increases agreement among the different processing approaches, but decreases the strength of the phylogenetic signal. No one processing approach is ideal, and the choice of which to use is likely to depend on the goal of the study, the type and quantity of material being processed, and the laboratory facilities available for processing.

A novel substitution pattern in glucuronoarabinoxylans from woody bamboos

(1 → 4)-β-D-Xylans are the second most abundant plant biopolymers on Earth after cellulose. Although their structures have been extensively studied, and industrial applications have been found for them and their derivatives, they are still investigated due to the diversity of their structures and uses. In this work, hemicellulose fractions obtained previously with 1 M KOH from two species of woody bamboos, Phyllostachys aurea and Guadua chacoensis, were purified, and the structures of the glucuronoarabinoxylans (GAX) were studied by chemical and spectroscopic methods. In both cases, major amounts of α-L-arabinofuranose residues were linked to C3 of the xylose units of the backbone, and also α-D-glucuronic acid residues and their 4-O-methyl-derivatives were detected in minor quantities, linked to C2 of some xylose residues. Methylation analysis of the carboxyl-reduced derivative from GAX from P. aurea indicated the presence of terminal and 5-linked arabinofuranose units. NMR spectroscopy showed the presence of disaccharidic side chains of 5-O-α-l-arabinofuranosyl-L-arabinofuranose for the GAX from P. aurea, while for those of G. chacoensis, only single side chains were found. To the best of our knowledge, this disaccharide was not found before as side chain of xylans.

Advances Toward Sustainable Lignin-based Gel for Energy Storage and Smart Sensing

Polymers obtained from biomass are promising alternatives to petro-based polymers owing to their low cost, biocompatibility, and biodegradability. Lignin, a complex aromatic polymer containing several functional hydrophilic and active groups including hydroxyls, carbonyls, and methoxyls, is the second most abundant biopolymer in plants. In particular, sustainable lignin-based gels are emerging as an appealing material platform for developing energy- and sensing-related applications owing to their attractive and tailorable physiochemical properties. This study describes the preparation strategies of lignin-based gels according to previously reported methods, with significant attention on the diverse performance of lignin-derived gel materials. Additionally, a detailed review of lignin-based gels utilized as an important resource in diverse fields is provided. Finally, a future vision on challenges and their possible solutions is presented.

Intrinsic growth rate and cellobiohydrolase activity underlie the phylogenetic signal to fungal decomposer succession

During litter decay, different fungal decomposer genera reach their highest relative abundance at different times. We tested the long-standinghypothesis that this “peak decay stage” of fungi is related to the activity of their fungal extracellular enzymes that break down various plant biopolymers and related as well to the growth rate of fungi. Using 50 decomposer fungal species, spanning a range of peak decay stages, we measured (1) the activity of four polysaccharidases and two oxidases generated by each species, and (2) fungal species’ growth rates. We found that the activity of cellobiohydrolase and growth rate were negatively correlated with peak time point for filamentous fungi; fungi peaking early had greatest cellobiohydrolase activity and fastest growth. No relationships were found between peak decay stage and enzymes or growth for yeasts. These data suggest growth and resource use are important factors shaping succession during decay by the main fungal decomposers, but as-yetuninvestigated traits may explain the remainder of the variation in succession.

Global Distribution of Carbohydrate Utilization Potential in the Prokaryotic Tree of Life.

Microorganisms dominate all ecosystems on Earth and play a key role in the turnover of organic matter. By producing enzymes, they degrade complex carbohydrates, facilitating the recycling of nutrients and controlling the carbon cycle. Despite their importance, our knowledge regarding microbial carbohydrate utilization has been limited to genome-sequenced taxa and thus heavily biased to specific groups and environments. Here, we used the Genomes from Earth's Microbiomes (GEM) catalog to describe the carbohydrate utilization potential in >7000 bacterial and archaeal taxa originating from a range of terrestrial, marine and host-associated habitats. We show that the production of carbohydrate-active enzymes (CAZymes) is phylogenetically conserved and varies significantly among microbial phyla. High numbers of carbohydrate-active enzymes were recorded in phyla known for their versatile use of carbohydrates, such as Firmicutes, Fibrobacterota, and Armatimonadota, but also phyla without cultured representatives whose carbohydrate utilization potential was so far unknown, such as KSB1, Hydrogenedentota, Sumerlaeota, and UBP3. Carbohydrate utilization potential reflected the specificity of various habitats: the richest complements of CAZymes were observed in MAGs of plant microbiomes, indicating the structural complexity of plant biopolymers. IMPORTANCE This study expanded our knowledge of the phylogenetic distribution of carbohydrate-active enzymes across prokaryotic tree of life, including new phyla where the carbohydrate-active enzymes composition have not been described until now and demonstrated the potential for carbohydrate utilization of numerous yet uncultured phyla. Profiles of carbohydrate-active enzymes are largely habitat-specific and reflect local carbohydrate availability by selecting taxa with appropriate complements of these enzymes. This information should aid in the prediction of functions in microbiomes of known taxonomic composition and helps to identify key components of habitat-specific carbohydrate pools. In addition, these findings have a high relevance for the understanding of carbohydrate utilization and carbon cycling in the environment, the process that is closely link to the carbon storage potential of Earth habitats and the production of greenhouse gasses.

Microwave-Assisted Lignin Extraction-Utilizing Deep Eutectic Solvents to Their Full Potential.

The current research intended to investigate the suitability of different choline-chloride-based deep eutectic solvents for their role in microwave lignin extraction. Lignin, a widely spread biopolymer in plants and woody structures, is a valuable replacement for fossil-fuel-based materials. While some promising applications have been trialled already, the extraction of this material from its matrix still causes problems. Here, we highlight an efficient and fast method to extract lignin from untreated larch bark with deep eutectic solvents in a standard domestic microwave. We developed a straightforward, green methodology, which can be used on various reaction scales, with materials available to many researchers. Lignin was extracted within only 30 min of microwave irradiation in yields of up to 96%. Compared to traditional deep eutectic extraction by conventional heating, the reaction time was cut by 87% and the energy costs were reduced by 93.5%. The hydrogen bond donors were exchanged and different types, namely acid-based, hydroxyl-based and amide-based donor systems, were evaluated for their suitability concerning microwave lignin extraction. This study presents a novel approach towards energy-efficient and green lignin valorisation, without the inherent need for costly equipment.

Galloylated proanthocyanidins in dentin matrix exhibit biocompatibility and induce differentiation in dental stem cells.

Grape seed extract contains a complex mixture of proanthocyanidins (PACs), a plant biopolymer used as a biomaterial to improve reparative and preventive dental therapies. Co-polymerization of PACs with type I collagen mechanically reinforces the dentin extracellular matrix. This study assessed the biocompatibility of PACs from grape seed extract on dental pulp stem cells (DPSCs) in a model simulating leaching through dentin to the pulp cavity. The aim was to determine the type of PACs (galloylated vs. non-galloylated) within grape seed extract that are most compatible with dental pulp tissue. Human demineralized dentin was treated with selectively-enriched dimeric PACs prepared from grape seed extract using liquid-liquid chromatography. DPSCs were cultured within a 2D matrix and exposed to PAC-treated dentin extracellular matrix. Cell proliferation was measured using the MTS assay and expression of odontoblastic genes was analyzed by qRT-PCR. Categorization of PACs leaching from dentin was performed using HPLC-MS. Enriched dimeric fractions containing galloylated PACs increased the expression of certain odontoblastic genes in DPSCs, including Runt-related transcription factor 2 (RUNX2), vascular endothelial growth factor (VEGF), bone morphogenetic protein 2 (BMP2), basic fibroblast growth factor (FGF2), dentin sialophosphoprotein (DSPP) and collagen, type I, alpha 1 (COLI). Galloylated dimeric PACs also exhibited minor effects on DPSC proliferation, resulting in a decrease compared to control after five days of treatment. The non-galloylated dimer fraction had no effect on these genes or on DPSC proliferation. Galloylated PACs are biocompatible with DPSCs and may exert a beneficial effect on cells within dental pulp tissue. The observed increase in odontoblastic genes induced by galloylated PACs together with a decrease in DPSC proliferation is suggestive of a shift toward cell differentiation. This data supports the use of dimeric PACs as a safe biomaterial, with galloylated dimeric PACs exhibiting potential benefits to odontoblasts supporting dentin regeneration.

Biological Functions and Applications of Antimicrobial Peptides.

Despite antimicrobial resistance, which is attributed to the misuse of broad-spectrum antibiotics, antibiotics can indiscriminately kill pathogenic and beneficial microorganisms. These events disrupt the delicate microbial balance in both humans and animals, leading to secondary infections and other negative effects. Antimicrobial peptides (AMPs) are functional natural biopolymers in plants and animals. Due to their excellent antimicrobial activities and absence of microbial resistance, AMPs have attracted enormous research attention. We reviewed the antibacterial, antifungal, antiviral, antiparasitic, as well as antitumor properties of AMPs and research progress on AMPs. In addition, we highlighted various recommendations and potential research areas for their progress and challenges in practical applications.

Extracellular vesiculo-tubular structures associated with suberin deposition in plant cell walls

Suberin is a fundamental plant biopolymer, found in protective tissues, such as seed coats, exodermis and endodermis of roots. Suberin is deposited in most suberizing cells in the form of lamellae just outside of the plasma membrane, below the primary cell wall. How monomeric suberin precursors, thought to be synthesized at the endoplasmic reticulum, are transported outside of the cell, for polymerization into suberin lamellae has remained obscure. Using electron-microscopy, we observed large numbers of extracellular vesiculo-tubular structures (EVs) to accumulate specifically in suberizing cells, in both chemically and cryo-fixed samples. EV presence correlates perfectly with root suberization and we could block suberin deposition and vesicle accumulation by affecting early, as well as late steps in the secretory pathway. Whereas many previous reports have described EVs in the context of biotic interactions, our results suggest a developmental role for extracellular vesicles in the formation of a major cell wall polymer.

Composition and functioning of the soil microbiome in the highest altitudes of the Italian Alps and potential effects of climate change

As the European Alps are experiencing a strong climate warming, this study analyzed the soil microbiome at different altitudes and among different vegetation types at the Stelvio Pass (Italian Alps), aiming to (i) characterize the composition and functional potential of the microbiome of soils and their gene expression during the peak vegetative stage; (ii) explore the potential short-term (using open-top chambers) and long-term (space-for-time substitutions) effects of increasing temperature on the alpine soil microbiome. We found that the functional potential of the soil microbiome and its expression differed among vegetation types. Microbial α-diversity increased along the altitudinal gradient. At lower altitude, shrubland had the highest proportion of fungi, which was correlated with higher amounts of CAZymes, specific for degrading fungal biomass and recalcitrant plant biopolymers. Subalpine upward vegetation shift could lead a possible loss of species of alpine soils. Shrub encroachment may accelerate higher recalcitrant C decomposition and reduce total ecosystem C storage, increasing the efflux of CO2 to the atmosphere with a positive feedback to warming. A total of 5 years of warming had no effect on the composition and functioning of microbial communities, indicating that longer-term warming experiments are needed to investigate the effects of temperature increases on the soil microbiome.

Coalescence and directed anisotropic growth of starch granule initials in subdomains of Arabidopsis thaliana chloroplasts

Living cells orchestrate enzyme activities to produce myriads of biopolymers but cell-biological understanding of such processes is scarce. Starch, a plant biopolymer forming discrete, semi-crystalline granules within plastids, plays a central role in glucose storage, which is fundamental to life. Combining complementary imaging techniques and Arabidopsis genetics we reveal that, in chloroplasts, multiple starch granules initiate in stromal pockets between thylakoid membranes. These initials coalesce, then grow anisotropically to form lenticular granules. The major starch polymer, amylopectin, is synthesized at the granule surface, while the minor amylose component is deposited internally. The non-enzymatic domain of STARCH SYNTHASE 4, which controls the protein’s localization, is required for anisotropic growth. These results present us with a conceptual framework for understanding the biosynthesis of this key nutrient.