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Sorghum bicolor is among the most important cereals globally and a staple crop for smallholder farmers in sub-Saharan Africa. Approximately 20% of sorghum yield is lost annually in Africa due to infestation with the root parasitic weed Striga hermonthica. Existing Striga management strategies are not singularly effective and integrated approaches are needed. Here, we demonstrate the functional potential of the soil microbiome to suppress Striga infection in sorghum. We associate this suppression with microbiome-mediated induction of root endodermal suberization and aerenchyma formation and with depletion of haustorium-inducing factors, compounds required for the initial stages of Striga infection. We further identify specific bacterial taxa that trigger the observed Striga-suppressive traits. Collectively, our study describes the importance of the soil microbiome in the early stages of root infection by Striga and pinpoints mechanisms of Striga suppression. These findings open avenues to broaden the effectiveness of integrated Striga management practices.

SUMMARY: The osmotic resistance mechanism has been extensively studied in whole plants or plant tissues. However, little is known about it in embryogenic tissue (ET) which is widely used in plant‐based biotechnological systems. Suberin, a cell wall aliphatic and aromatic heteropolymer, plays a critical role in plant cells against osmosis stress. The suberin regulatory biosynthesis has rarely been studied in gymnosperms. Here, PaMYB11, a subgroup 11 R2R3‐MYB transcription factor, plays a key role in the osmotic resistance of Norway spruce (Picea abies) ETs during cryoprotectant pretreatment. Thus, RNA‐seq, histological, and analytical chemical analyses are performed on the stable transformations of PaMYB11‐OE and PaMYB11‐SRDX in Norway spruce ETs. DAP‐seq, Y1H, and LUC are further combined to explore the PaMYB11 targets. Activation of PaMYB11 is necessary and sufficient for suberin lamellae deposition on Norway spruce embryogenic cell walls, which plays a decisive role in ET survival under osmotic stress. Transcriptome analysis shows that PaMYB11 enhances suberin lamellae monomer synthesis by promoting very long‐chain fatty acid (VLCFA) synthesis. PaPOP, PaADH1, and PaTET8L, the first two (PaADH1 and PaPOP, included) involved in VLCFA synthesis, are proved to be the direct targets of PaMYB11. Our study identified a novel osmotic response directed by PaMYB11 in Norway spruce ET, which provides a new understanding of the resistance mechanism against osmosis in gymnosperms. Significance Statement: In brief, our data suggested that the activation of PaMYB11 enhances SL accumulation by promoting very long‐chain fatty acids synthesis in Picea abies embryogenic tissues. PaADH1, PaPOP and TET8L are direct targets of PaMYB11. However, the correlation between very long‐chain fatty acids synthesis and the expression of PaADH1, PaPOP and TET8L is still unclear. It provides novel insight into the resistance mechanism against osmosis in gymnosperms. [ABSTRACT FROM AUTHOR]

SUMMARY: The essence of wound healing is the accumulation of suberin at wounds, which is formed by suberin polyphenolic (SPP) and suberin polyaliphatic (SPA). The biosynthesis of SPP and SPA monomers is catalyzed by several enzyme classes related to phenylpropanoid metabolism and fatty acid metabolism, respectively. However, how suberin biosynthesis is regulated at the transcriptional level during potato (Solanum tuberosum) tuber wound healing remains largely unknown. Here, 6 target genes and 15 transcription factors related to suberin biosynthesis in tuber wound healing were identified by RNA‐seq technology and qRT‐PCR. Dual luciferase and yeast one‐hybrid assays showed that StMYB168 activated the target genes StPAL, StOMT, and St4CL in phenylpropanoid metabolism. Meanwhile, StMYB24 and StMYB144 activated the target genes StLTP, StLACS, and StCYP in fatty acid metabolism, and StFHT involved in the assembly of SPP and SPA domains in both native and wound periderms. More importantly, virus‐induced gene silencing in S. tuberosum and transient overexpression in Nicotiana benthamiana assays confirmed that StMYB168 regulates the biosynthesis of free phenolic acids, such as ferulic acid. Furthermore, StMYB24/144 regulated the accumulation of suberin monomers, such as ferulates, α, ω‐diacids, and ω‐hydroxy acids. In conclusion, StMYB24, StMYB144, and StMYB168 have an elaborate division of labor in regulating the synthesis of suberin during tuber wound healing. Significance Statement: Three MYBs enhance potato wound suberin synthesis. [ABSTRACT FROM AUTHOR]

Bark, the outermost tissue, plays an important role in protecting trees from damage induced by living organisms and the surrounding environment. Bark differs from the xylem primarily by the presence of suberin in cork cell walls. However, few studies have examined the role of suberin and its interactions with other chemical components in the cork. Consequently, this study aimed to understand the distribution of chemical components, including suberin and lignin, and their respective roles in cork cell walls, using Cerasus jamasakura (Siebold ex Koidz.) H. Ohba. Suberin and lignin were gradually and selectively removed from thin strip specimens. Fourier transform infrared (FTIR) spectroscopy suggested that desuberinization removed both suberin and part of the other matrix substances within a few minutes of treatment, whereas delignification exclusively removed lignin. Further microscopic observation revealed that suberin present was mainly in the secondary wall of cork cells, whereas lignin was present in both the tertiary wall and compound middle lamella. In addition, the cell wall collapse of the cork was only found in desuberinized specimens, whereas delignified specimens only showed monotonic contraction. Taken together, these results suggest that the presence of suberin in the cork contributes to the shape stability of cork cell walls. [ABSTRACT FROM AUTHOR]

All-cellulose composites (ACCs) have been fabricated by using a variety of cellulosic sources, versatile technologies, and are sustainable alternatives for traditional composites. In this study, nonwoven-woven ACC laminates were created from wood-based Spinnova short fibers and Lyocell fabrics via partial dissolution and an NaOH-urea solvent system. The less-known wood-based Spinnova fiber is created for the textile industry, but it also has great potential for the composite industry. To identify the mechanical properties of ACCs--which greatly influence the range of material application--tensile, impact, and flexural tests were conducted. The mechanical properties indicated only moderate properties, which are influenced by high porosity and weak fiber bonding. Despite this, valuable information on the nonwoven-woven structured ACCs was obtained. To improve the ACC laminate's ability to resist moisture, biobased coatings (e.g., commercially available birch bark betulin and suberin acid mixture) were applied on the surface of ACCs and it successfully improved the wetting resistance. The results of contact angle analyses demonstrated that the highest contact angle of 128° was measured for betulin-coated laminates and the best stable hydrophobicity calculated a minute after the beginning of the experiment were observed at 109° for the uncommercial pressurized hot ethanol (PHE) extract of birch bark. [ABSTRACT FROM AUTHOR]

All-cellulose composites (ACCs) have been fabricated by using a variety of cellulosic sources, versatile technologies, and are sustainable alternatives for traditional composites. In this study, nonwoven-woven ACC laminates were created from wood-based Spinnova short fibers and Lyocell fabrics via partial dissolution and an NaOH-urea solvent system. The less-known wood-based Spinnova fiber is created for the textile industry, but it also has great potential for the composite industry. To identify the mechanical properties of ACCs—which greatly influence the range of material application—tensile, impact, and flexural tests were conducted. The mechanical properties indicated only moderate properties, which are influenced by high porosity and weak fiber bonding. Despite this, valuable information on the nonwoven-woven structured ACCs was obtained. To improve the ACC laminate’s ability to resist moisture, bio-based coatings (e.g., commercially available birch bark betulin and suberin acid mixture) were applied on the surface of ACCs and it successfully improved the wetting resistance. The results of contact angle analyses demonstrated that the highest contact angle of 128° was measured for betulin-coated laminates and the best stable hydrophobicity calculated a minute after the beginning of the experiment were observed at 109° for the uncommercial pressurized hot ethanol (PHE) extract of birch bark.

SUMMARY: Cytochrome P450 proteins (CYPs) play critical roles in plant development and adaptation to fluctuating environments. Previous reports have shown that CYP86A proteins are involved in the biosynthesis of suberin and cutin in Arabidopsis. However, the functions of these proteins in rice remain obscure. In this study, a rice mutant with incomplete male sterility was identified. Cytological analyses revealed that this mutant was defective in anther development. Cloning of the mutant gene indicated that the responsible mutation was on OsCYP86A9. OsMYB80 is a core transcription factor in the regulation of rice anther development. The expression of OsCYP86A9 was abolished in the anther of osmyb80 mutant. In vivo and in vitro experiments showed that OsMYB80 binds to the MYB‐binding motifs in OsCYP86A9 promoter region and regulates its expression. Furthermore, the oscyp86a9 mutant exhibited an impaired suberin deposition in the root, and was more susceptible to drought stress. Interestingly, genetic and biochemical analyses revealed that OsCYP86A9 expression was regulated in the root by certain MYB transcription factors other than OsMYB80. Moreover, mutations in the MYB genes that regulate OsCYP86A9 expression in the root did not impair the male fertility of the plant. Taken together, these findings revealed the critical roles of OsCYP86A9 in plant development and proposed that OsCYP86A9 functions in anther development and root suberin formation via two distinct tissue‐specific regulatory pathways. Significance Statement: The cytochrome P450 subfamily CYP86A is very important for plant development. However, their functions remain obscure in rice. Here, we reported that OsCYP86A9, a member of CYP86A subfamily, is critical for the development of anther and root suberin, and these functions are determined by two distinct tissue‐specific regulatory pathways. [ABSTRACT FROM AUTHOR]

Background: The periderm is basic for land plants due to its protective role during radial growth, which is achieved by the polymers deposited in the cell walls. In most trees, like holm oak, the first periderm is frequently replaced by subsequent internal periderms yielding a heterogeneous outer bark made of a mixture of periderms and phloem tissues, known as rhytidome. Exceptionally, cork oak forms a persistent or long-lived periderm which results in a homogeneous outer bark of thick phellem cell layers known as cork. Cork oak and holm oak distribution ranges overlap to a great extent, and they often share stands, where they can hybridize and produce offspring showing a rhytidome-type bark. Results: Here we use the outer bark of cork oak, holm oak, and their natural hybrids to analyse the chemical composition, the anatomy and the transcriptome, and further understand the mechanisms underlying periderm development. We also include a unique natural hybrid individual corresponding to a backcross with cork oak that, interestingly, shows a cork-type bark. The inclusion of hybrid samples showing rhytidome-type and cork-type barks is valuable to approach cork and rhytidome development, allowing an accurate identification of candidate genes and processes. The present study underscores that abiotic stress and cell death are enhanced in rhytidome-type barks whereas lipid metabolism and cell cycle are enriched in cork-type barks. Development-related DEGs showing the highest expression, highlight cell division, cell expansion, and cell differentiation as key processes leading to cork or rhytidome-type barks. Conclusion: Transcriptome results, in agreement with anatomical and chemical analyses, show that rhytidome and cork-type barks are active in periderm development, and suberin and lignin deposition. Development and cell wall-related DEGs suggest that cell division and expansion are upregulated in cork-type barks whereas cell differentiation is enhanced in rhytidome-type barks. [ABSTRACT FROM AUTHOR]

The plant cuticle controls non‐stomatal water loss and can serve as a barrier against biotic agents, whereas the heteropolymer suberin and its associated waxes are deposited constitutively at specific cell wall locations. While several transcription factors controlling cuticle formation have been identified, those involved in the transcriptional regulation of suberin biosynthesis remain poorly characterized. The major goal of this study was to further analyse the function of the R2R3‐Myeloblastosis (MYB) transcription factor AtMYB41 in formation of the cuticle, suberin, and suberin‐associated waxes throughout plant development.For functional analysis, the organ‐specific expression pattern of AtMYB41 was analysed and Atmyb41ge alleles were generated using the CRISPR/Cas9 system. These were investigated for root growth and water permeability upon stress. In addition, the fatty acid, wax, cutin, and suberin monomer composition of different organs was evaluated by gas chromatography.The characterization of Atmyb41ge mutants revealed that AtMYB41 negatively regulates the production of cuticular lipids and fatty acid biosynthesis in leaves and seeds, respectively. Remarkably, biochemical analyses indicate that AtMYB41 also positively regulates the formation of cuticular waxes in stems of Arabidopsis thaliana.Overall, these results suggest that the AtMYB41 acts as a negative regulator of cuticle and fatty acid biosynthesis in leaves and seeds, respectively, but also as a positive regulator of wax production in A. thaliana stems. [ABSTRACT FROM AUTHOR]

Global climate change has altered forest productivity across the globe. Although extreme drought and temperature have lowered forest productivity in some regions, increased productivity has been observed in many forests over the last few decades due to increases in atmospheric carbon dioxide, temperature, and nitrogen (N) deposition. These factors can lead to changes in both the quantity and quality of litterfall and root inputs to soil. Additionally, few studies have investigated multifactorial treatments (e.g., detrital changes and N deposition), on soil carbon (C) sequestration. To investigate the long-term compositional changes to soil organic matter (SOM) in response to litter and N inputs, soil samples were collected from the University of Michigan Biological Station (UMBS) Detrital Input and Removal Treatment (DIRT) site after 15 years of experimental treatments. The samples were characterized using elemental analysis, targeted SOM compound analyses, nuclear magnetic resonance spectroscopy and microbial biomass and community composition measurements. The exclusions of C inputs (litter and/or roots) resulted in molecular-level biogeochemical changes, however, the soils at UMBS are seemingly more resistant to losses in soil C compared to other DIRT studies. Although the addition treatments (Double Litter, Double Wood, Double Litter + N, and N) led to increased soil C concentrations at UMBS, we found evidence for enhanced SOM decomposition occurring with litter additions. Notably, the observations made from the concurrent treatment of Double Litter + N demonstrated that the responses of individual treatments are not representative of simultaneous applications. Collectively, these results demonstrate that soil C biogeochemistry is sensitive to fluctuations in C and N deposition and overall, these processes are dictated by site-specific ecological properties. [ABSTRACT FROM AUTHOR]

Background and Aims Internal root aeration is essential for root growth in waterlogged conditions. Aerenchyma provides a path for oxygen to diffuse to the roots. In most wetland species, including rice, a barrier to radial oxygen loss (ROL) allows more of the oxygen to diffuse to the root tip, enabling root growth into anoxic soil. Most dryland crops, including barley, do not form a root ROL barrier. We previously found that abscisic acid (ABA) signalling is involved in the induction of ROL barrier formation in rice during waterlogging. Although rice typically does not form a tight ROL barrier in roots in aerated conditions, an ROL barrier with suberized exodermis was induced by application of exogenous ABA. Therefore, we hypothesized that ABA application could also trigger root ROL barrier formation with hypodermal suberization in barley. Methods Formation of an ROL barrier was examined in roots in different exogenous ABA concentrations and at different time points using cylindrical electrodes and Methylene Blue staining. Additionally, we evaluated root porosity and observed suberin and lignin modification. Suberin, lignin and Casparian strips in the cell walls were observed by histochemical staining. We also evaluated the permeability of the apoplast to a tracer. Key Results Application of ABA induced suberization and ROL barrier formation in the adventitious roots of barley. The hypodermis also formed lignin-containing Casparian strips and a barrier to the infiltration of an apoplastic tracer (periodic acid). However, ABA application did not affect root porosity. Conclusions Our results show that in artificial conditions, barley can induce the formation of ROL and apoplastic barriers in the outer part of roots if ABA is applied exogenously. The difference in ROL barrier inducibility between barley (an upland species) and rice (a wetland species) might be attributable to differences in ABA signalling in roots in response to waterlogging conditions. [ABSTRACT FROM AUTHOR]

Bark extracts are sustainable sources of biopolymers and hold great promise for replacing fossil fuel-based polymers, for example, in wood-based composites. In addition to primary and secondary metabolites, tree bark also contains suberin, which plays a major role in protecting the tree from environmental conditions. Suberin is a natural aliphatic-aromatic cross-linked polyester present in the cell walls of both normal and damaged external tissues, the main component of which are long-chain aliphatic acids. Its main role as a plant ingredient is to protect against microbiological factors and water loss. One of the most important suberin monomers are suberin fatty acids, known for their hydrophobic and barrier properties. Therefore, due to the diverse chemical composition of suberin, it is an attractive alternative to hydrocarbon-based materials. Although its potential is recognized, it is not widely used in biocomposites technology, including wood-based composites and the polymer industry. The article will discuss the current knowledge about the potential of suberin and its components in biocomposites technology, which will include surface finishes, composite adhesives and polymer blends. [ABSTRACT FROM AUTHOR]

Lipid polymers such as cutin and suberin strengthen the diffusion barrier properties of the cell wall in specific cell types and are essential for water relations, mineral nutrition, and stress protection in plants. Land plant-specific glycerol-3-phosphate acyltransferases (GPATs) of different clades are central players in cutin and suberin monomer biosynthesis. Here, we show that the GPAT4/6/8 clade in Arabidopsis thaliana, which is known to mediate cutin formation, is also required for developmentally regulated root suberization, in addition to the established roles of GPAT5/7 in suberization. The GPAT5/7 clade is mainly required for abscisic acid-regulated suberization. In addition, the GPAT5/7 clade is crucial for the formation of the typical lamellated suberin ultrastructure observed by transmission electron microscopy, as distinct amorphous globular polyester structures were deposited in the apoplast of the gpat5 gpat7 double mutant, in contrast to the thinner but still lamellated suberin deposition in the gpat4 gpat6 gpat8 triple mutant. Site-directed mutagenesis revealed that the intrinsic phosphatase activity of GPAT4, GPAT6, and GPAT8, which leads to monoacylglycerol biosynthesis, contributes to suberin formation. GPAT5/7 lack an active phosphatase domain and the amorphous globular polyester structure observed in the gpat5 gpat7 double mutant was partially reverted by treatment with a phosphatase inhibitor or the expression of phosphatase-dead variants of GPAT4/6/8. Thus, GPATs that lack an active phosphatase domain synthetize lysophosphatidic acids that might play a role in the formation of the lamellated structure of suberin. GPATs with active and nonactive phosphatase domains appear to have nonredundant functions and must cooperate to achieve the efficient biosynthesis of correctly structured suberin. [ABSTRACT FROM AUTHOR]

The bark of Pinus radiata offers an underutilized source of high-value renewable chemicals such as extractable polyphenols and lipophilic compounds (waxes and suberin). Here, the depolymerization and extraction of suberin from P. radiata bark and its repolymerization to form novel polyesters are reported. Three different strategies were evaluated for repolymerization of the suberin monomers, with starting materials and products characterized using chemical and thermal analysis techniques. The inclusion of comonomer (1,12-dodecanediol) to provide stoichiometric balance improved the conversion, product yield, solubility and increased molecular weight. Enzymatic polymerization conditions gave the highest yield, while the highest molecular weight was achieved using titanium butoxide, demonstrating that polymerization conditions could be varied to target desired product properties. Products were hydrophobic, as shown by contact angles, ϴ ≥ 90° after 30 s. This work highlights opportunities for utilizing suberin to add value to a P. radiata bark biorefinery concept. Potential future applications include its use as a starting material for novel bio-based polymers that can serve as water-repellent surfaces and coatings, replacing established products derived from fossil resources. [ABSTRACT FROM AUTHOR]

Rainfall and land-use interactions drive temporal shifts in suspended sediment sources, yet the magnitude of such changes remains poorly understood due to the lack of land-use specific source tracers. We investigated α,ω-dicarboxylic fatty acid root-specific biomarkers, as diagnostic tracers for apportioning sources of time-integrated suspended sediment samples collected from a grassland dominated agricultural catchment in the southwest of England during the wet winter period. Applying fatty acids-specific stable carbon isotope analysis and a Bayesian isotope mixing model, we show that stream banks contributed most of the sediment in the early winter, i.e. October–December, while winter cereal-dominated arable land contributed more than half of the sediment during the late winter, i.e. January–March. The dominant sediment source shifted in conjunction with a period of prolonged consecutive rainfall days in the later period suggesting that intervention required to mitigate soil erosion and sediment delivery should adapt to changing rainfall patterns. Our novel findings demonstrate that isotopic signatures of α,ω-dicarboxylic fatty acids are promising tracers for understanding the resistance of agricultural soils to water erosion and quantifying the interactive effects of extreme rainfall and land use on catchment sediment source dynamics. [ABSTRACT FROM AUTHOR]

The utilization of polyols derived from renewable sources presents an opportunity to enhance the sustainability of rigid polyurethane (PUR) foams, thereby contributing to the advancement of a circular bioeconomy. This study explores the development of PUR rigid foams exclusively using polyols sourced from second-generation renewable biomass feedstocks, specifically depolymerized birch bark suberin (suberinic acids) and tall oil fatty acids. The polyols achieved a total renewable material content as high as 74%, with a suberinic acid content of 37%. Response surface modeling was employed to determine the optimal bio-polyol, blowing agents, and catalyst content, hence, optimizing the bio-based foam formulations. In addition, response surface modeling was applied to rigid PUR foam formulations based on commercially available petroleum-based polyols for comparison. The results, including apparent density (~40–44 kg/m3), closed cell content (~95%), compression strength (>0.2 MPa, parallel to the foaming direction), and thermal conductivity (~0.019 W/(m·K)), demonstrated that the suberinic acids-based rigid PUR foam exhibited competitive qualities in comparison to petroleum-based polyols. Remarkably, the bio-based rigid PUR foams comprised up to 29% renewable materials. These findings highlight the potential of suberinic acid-tall oil polyols as effective candidates for developing rigid PUR foams, offering promising solutions for sustainable insulation applications. [ABSTRACT FROM AUTHOR]

The runner reed (Phragmites japonica) is the dominant species on riverbanks, whereas the common reed (Phragmites australis) thrives in continuously flooded areas. Here, we aimed to identify the key root anatomical traits that determine the different adaptative responses of the two Phragmites species to water-deficit and low-oxygen conditions. Growth measurements revealed that P. japonica tolerated high osmotic conditions, whereas P. australis preferred low-oxygen conditions. Root anatomical analysis revealed that the ratios of the cortex to stele area and aerenchyma (gas space) to cortex area in both species increased under low-oxygen conditions. However, a higher ratio of cortex to stele area in P. australis resulted in a higher ratio of aerenchyma to stele, which includes xylem vessels that are essential for water and nutrient uptakes. In contrast, a lower ratio of cortex to stele area in P. japonica could be advantageous for efficient water uptake under high-osmotic conditions. In addition to the ratio of root tissue areas, rigid outer apoplastic barriers composed of a suberised exodermis may contribute to the adaptation of P. japonica and P. australis to water-deficit and low-oxygen conditions, respectively. Our results suggested that root anatomical plasticity is essential for plants to adapt and respond to different soil moisture levels. [ABSTRACT FROM AUTHOR]

Very long-chain fatty acids (VLCFAs) are precursors for the synthesis of membrane lipids, cuticular waxes, suberins, and storage oils in plants. 3-Ketoacyl CoA synthase (KCS) catalyzes the condensation of C2 units from malonyl-CoA to acyl-CoA, the first rate-limiting step in VLCFA synthesis. In this study, we revealed that Arabidopsis KCS17 catalyzes the elongation of C22–C24 VLCFAs required for synthesizing seed coat suberin. Histochemical analysis of Arabidopsis plants expressing GUS (β-glucuronidase) under the control of the KCS17 promoter revealed predominant GUS expression in seed coats, petals, stigma, and developing pollen. The expression of KCS17:eYFP (enhanced yellow fluorescent protein) driven by the KCS17 promoter was observed in the outer integument1 of Arabidopsis seed coats. The KCS17:eYFP signal was detected in the endoplasmic reticulum of tobacco epidermal cells. The levels of C22 VLCFAs and their derivatives, primary alcohols, α,ω-alkane diols, ω-hydroxy fatty acids, and α,ω-dicarboxylic acids increased by ~2-fold, but those of C24 VLCFAs, ω-hydroxy fatty acids, and α,ω-dicarboxylic acids were reduced by half in kcs17-1 and kcs17-2 seed coats relative to the wild type (WT). The seed coat of kcs17 displayed decreased autofluorescence under UV and increased permeability to tetrazolium salt compared with the WT. Seed germination and seedling establishment of kcs17 were more delayed by salt and osmotic stress treatments than the WT. KCS17 formed homo- and hetero-interactions with KCR1, PAS2, and ECR, but not with PAS1. Therefore, KCS17-mediated VLCFA synthesis is required for suberin layer formation in Arabidopsis seed coats. [ABSTRACT FROM AUTHOR]

Floods and droughts are becoming more frequent as a result of climate change and it is imperative to find ways to enhance the resilience of staple crops to abiotic stresses. This is crucial to sustain food production during unfavourable conditions. Here, we analyse the current knowledge about suberised and lignified outer apoplastic barriers, focusing on the functional roles of the barrier to radial O2 loss formed as a response to soil flooding and we discuss whether this trait also provides resilience to multiple abiotic stresses. The barrier is composed of suberin and lignin depositions in the exodermal and/or sclerenchyma cell walls. In addition to the important role during soil flooding, the barrier can also restrict radial water loss, prevent phytotoxin intrusion, salt intrusion and the main components of the barrier can impede invasion of pathogens in the root. However, more research is needed to fully unravel the induction pathway of the outer apoplastic barriers and to address potential trade-offs such as reduced nutrient or water uptake. Nevertheless, we suggest that the outer apoplastic barriers might act as a jack of all trades providing tolerance to multiple abiotic and/or biotic stressors. [ABSTRACT FROM AUTHOR]

This paper comprehensively discusses the pathways of heavy metals into the plant root epidermis, the short-range transport pathway through the horizontal transport of coplanar and plasmodesmata, and the long-range transport pathway through the xylem and phloem for loading and unloading. The transport of heavy metal ions by the coplanar pathway is slow, while the transport of heavy metal ions by the extra plastid pathway has low resistance to migration and high rate. Cell wall adsorption and resolution are en-dogenous factors affecting the transport of heavy metal ions into the root xylem via the cytoplasmic ectodomain pathway, but the development of the Casparian strip and suberin in the root cortex, which constitute the ectodomain barrier, can block the ectodomain pathway of heavy metal ion migration to the xylem. Plant transpiration and root pressure provide the driving force for the long-distance transport of heavy metal ions in the xylem and are related to the transpiration rate of plants. The mechanism of plant detoxification and tolerance to heavy metals is mainly induced by the production of metallothionein, the formation of phytoch-elating pep tides (PCs) in stressed plants and the regionalization of heavy metals by vesicles. [ABSTRACT FROM AUTHOR]

Research was carried out on the isolation of betulin and suberin from the debarking waste of the Arkhangelsk Pulp and Paper Mill pulpwood, ground on an abrasive crusher. Betulin was extracted from various fractions of technical bark with 86% ethanol under exposure to microwave electromagnetic field (EMF) (microwave extraction). Suberin was isolated from the extracted bark by hydrolysis with an aqueous KOH solution under microwave heating conditions as well. The maximum yields of betulin and suberin were achieved when using coarse bark fractions (3–4.5 mm), which were essentially crushed birch bark. The resulting products were identified by IR and NMR spectroscopy and by gas chromatography combined with mass spectrometry (GC/MS). The contents of the components in the bark extracts were determined by HPLC analysis. The extractives were dominated by triterpenoid betulinol (70–72%), with betulinic acid, lupeol, and erythrodiol being present less abundantly. Fatty, dibasic carboxylic acids, and hydroxy acids, dominated by 2-hydroxydecanedioic (2-hydroxysebacic) acid, were identified among the suberin monomers. The content of ferulic acid, a natural antioxidant, was determined in the product from different fractions of the bark (from 2.65 to 11.27 g/kg). The suberin obtained from fine bark fractions differs in the composition from that obtained from coarse fractions. Ribofuranose and xylose were detected in the product obtained from the 1–2 mm bark fraction but were absent in that from the 2–3 mm fraction; lanosterol was present in the suberin from fine fraction of the bark, and cycloartenol, in that from coarse fraction. [ABSTRACT FROM AUTHOR]

Mangrove plants demonstrate an impressive ability to tolerate environmental pollutants, but excessive levels of cadmium (Cd) can impede their growth. Few studies have focused on the effects of apoplast barriers on heavy metal tolerance in mangrove plants. To investigate the uptake and tolerance of Cd in mangrove plants, two distinct mangrove species, Avicennia marina and Rhizophora stylosa, are characterized by unique apoplast barriers. The results showed that both mangrove plants exhibited the highest concentration of Cd2+ in roots, followed by stems and leaves. The Cd2+ concentrations in all organs of R. stylosa consistently exhibited lower levels than those of A. marina. In addition, R. stylosa displayed a reduced concentration of apparent PTS and a smaller percentage of bypass flow when compared to A. marina. The root anatomical characteristics indicated that Cd treatment significantly enhanced endodermal suberization in both A. marina and R. stylosa roots, and R. stylosa exhibited a higher degree of suberization. The transcriptomic analysis of R. stylosa and A. marina roots under Cd stress revealed 23 candidate genes involved in suberin biosynthesis and 8 candidate genes associated with suberin regulation. This study has confirmed that suberized apoplastic barriers play a crucial role in preventing Cd from entering mangrove roots. [ABSTRACT FROM AUTHOR]

Premise: Leaf subepidermal secretory cavities are a notable trait in Myrtaceae, but their formation is still controversial because of the lack of consensus on their ontogeny among authors. Knowledge about the compounds present in these cavities has grown over the last few years, demonstrating that terpenoid‐rich oils are not their unique content. These two points are the focus of this study on the ontogeny, structure, and contents of secretory cavities in neotropical Myrtaceae. Methods: We used histochemical tests and Raman analysis to verify the basic chemical composition of the cavity contents of nine species. We studied the ontogeny of glands in one species, comparing aldehyde‐fixed tissues and fresh sections mounted in an inert medium. Results: We observed schizogenous development and appearance of the secretory cavities and found that sample processing may induce cell breakdown, which can be misinterpreted as lysigeny. The content of these cavities contains putative terpenes, resins, carbonyl groups, and flavonoids. Conclusions: Our findings support the hypothesis that the lysigenous appearance of the oil glands is a technical artifact. These tissue distortions must be considered when interpreting the development of this type of secretory structure. Moreover, the basic analyses of chemical constituents show for the first time that the glands of neotropical Myrtaceae are potential reservoirs of some compounds such as flavonoids previously reported as novelties for a few other myrtaceous species. Because some of them are non‐lipid compounds, the idea that the glands are just oil repositories is no longer applicable. [ABSTRACT FROM AUTHOR]

Fire hazard is a constant risk in everyday life with the use of combustibles such as polymeric materials, wood, and fabrics, to name a few. Halogenated compounds have been widely used as efficient flame-retardants, often being applied as coatings or impregnations. With growing environmental concerns and regional bans on the use of halogenated flame-retardant compounds, bio-based alternatives are garnering significant research interest. Naturally occurring materials such as eggshells, DNA, and certain proteins have developed a self-defense mechanism against fire over millions of years of evolution. Cork, a naturally occurring biological tissue in outer bark, is of interest as it is often used as a heat shield and moisture repellent, specifically in spacecraft. A deeper look into the chemical structure of cork indicates the presence of suberin, a bio-polyester group that makes up as much as 40% of its chemical composition. These bio-polyester groups play a key role as a protective barrier between the plant and the surrounding external environment. Thus, the role of suberin in plants could be mimicked for the design of biobased flame-retardant materials.

Background: Russeting is a major problem in many fruit crops. Russeting is caused by environmental factors such as wounding or moisture exposure of the fruit surface. Despite extensive research, the molecular sequence that triggers russet initiation remains unclear. Here, we present high-resolution transcriptomic data by controlled russet induction at very early stages of fruit development. During Phase I, a patch of the fruit surface is exposed to surface moisture. For Phase II, moisture exposure is terminated, and the formerly exposed surface remains dry. We targeted differentially expressed transcripts as soon as 24 h after russet induction. Results: During moisture exposure (Phase I) of 'Pinova' apple, transcripts associated with the cell cycle, cell wall, and cuticle synthesis (SHN3) decrease, while those related to abiotic stress increase. NAC35 and MYB17 were the earliest induced genes during Phase I. They are therefore linked to the initial processes of cuticle microcracking. After moisture removal (Phase II), the expression of genes related to meristematic activity increased (WOX4 within 24 h, MYB84 within 48 h). Genes related to lignin synthesis (MYB52) and suberin synthesis (MYB93, WRKY56) were upregulated within 3 d after moisture removal. WOX4 and AP2B3 are the earliest differentially expressed genes induced in Phase II. They are therefore linked to early events in periderm formation. The expression profiles were consistent between two different seasons and mirrored differences in russet susceptibility in a comparison of cultivars. Furthermore, expression profiles during Phase II of moisture induction were largely identical to those following wounding. Conclusions: The combination of a unique controlled russet induction technique with high-resolution transcriptomic data allowed for the very first time to analyse the formation of cuticular microcracks and periderm in apple fruit immediately after the onset of triggering factors. This data provides valuable insights into the spatial-temporal dynamics of russeting, including the synthesis of cuticles, dedifferentiation of cells, and impregnation of cell walls with suberin and lignin. [ABSTRACT FROM AUTHOR]

Measurements of oxygen isotope enrichment of leaf water above source water (Δ18OLW) can improve our understanding of the interaction between leaf anatomy and physiology on leaf water transport. Models have been developed to predict Δ18OLW such as the string‐of‐lakes model, which describes the mixing of leaf water pools, and the Péclet effect model, which incorporates transpiration rate and the mixing length between unenriched xylem and enriched mesophyll water in the mesophyll (Lm) or veins (Lv). Here we compare measurements and models of Δ18OLW on two cell wall composition mutants grown under two light intensities and relative humidities to evaluate cell wall properties on leaf water transport. In maize (Zea mays), the compromised ultrastructure of the suberin lamellae in the bundle sheath of the ALIPHATIC SUBERIN FERULOYL TRANSFERASE mutant (Zmasft) reduced barriers to apoplastic water movement, resulting in higher E and, potentially, Lv and, consequently, lower Δ18OLW. The difference in Δ18OLW in cellulose synthase‐like F6 (CslF6) mutants and wild‐type of rice (Oryza sativa) grown under two light intensities co‐varied with stomatal density. These results show that cell wall composition and stomatal density influence Δ18OLW and that stable isotopes can facilitate the development of a physiologically and anatomically explicit water transport model. Summary statement: The greater apoplastic permeability in maize (Zea mays) mutants that had a compromised ultrastructure of the suberin lamellae in the bundle sheath led to higher transpiration rates and lower isotopic mixing length than wildtype, resulting in lower oxygen isotope enrichment of leaf water (Péclet effect). In rice (Oryza sativa) wild type and mutants with no mixed linkage glucan in the cell wall, oxygen isotope enrichment in leaf water in response to growth light intensity co‐varied with stomatal density, showing that differences in stomatal density modulate oxygen isotopic enrichment in leaf water. [ABSTRACT FROM AUTHOR]

Exocarp color is a commercially essential quality for pear which can be divided into two types: green and russet. The occurrence of russet color is associated with deficiencies and defects in the cuticular and epidermal layers, which affect the structure of the cell wall and the deposition of suberin. Until now, the genetic basics triggering this trait have not been well understood, and limited genes have been identified for the trait. To figure out the gene controlling the trait of exocarp color, we perform a comprehensive genome-wide association study, and we describe the candidate genes. One gene encoding the ABCG protein has been verified to be associated with the trait, using an integrative analysis of the metabolomic and transcriptomic data. This review covers a variety of omics resources, which provide a valuable resource for identifying gene-controlled traits of interest. The findings in this study help to elucidate the genetic components responsible for the trait of exocarp color in pear, and the implications of these findings for future pear breeding are evaluated. [ABSTRACT FROM AUTHOR]

Taurus flowering ash (Fraxinus ornus subsp. cilicica) is an endemic tree species in Turkey. The bark of the species was characterized for summative chemical composition, the monomeric composition of polysaccharides, phenolic content, in vitro and ex vivo antioxidant properties of hydrophilic extracts, the composition of lipophilic extractives and suberin, and thermal degradation. The bark has an elevated ash content (17%), primarily composed of calcium, and a noteworthy extractive content (38.9%), predominantly of hydrophilic compounds. The antioxidant activity of the bark extracts is moderate, with an IC50 value of 40 μg/mL and an EC50 value of 230 μg/mL by DPPH and TBARS methods. The lipophilic extractives principally contain fatty acids and diterpenoids. The suberin content is low (1%) and composed primarily of ω-hydroxy acids with 9,10,18 trihydroxyoctadecanoic acid as the major suberin monomer. The lignin content is low (9.8%), and polysaccharides represent 33%. The ignition temperature of the bark is 190 °C, the burnout temperature is 653 °C, and the activation energy in combustion is 29 kJ mol−1. A biorefinery concept was developed considering the bark's chemical and thermal characteristics to convert approximately 90% of the bark mass into valuable chemicals, extracts, functional materials, and additives. [ABSTRACT FROM AUTHOR]

The phytoremediation of soil contaminated with petroleum depends on the association of plants with rhizosphere bacteria capable of promoting plant growth and destroying petroleum hydrocarbonates. In the present work, we studied the effects of "Lenoil" biological product containing bacteria Pseudomonas turukhanskensis IB 1.1, capable of destroying petroleum hydrocarbons on Secale cereale L plants, which previously proved to be resistant to the weak oil pollution of gray forest soil and to the composition of microorganisms in their rhizosphere. The composition of microorganisms in the rhizosphere of rye roots was studied, morphometric parameters of shoots and roots of rye plants were estimated, and hormone concentration was immunoassayed under conditions of 4% petroleum pollution of the soil. Addition of petroleum to the soil increased the content of oligonitrophilic (by 24%) and hydrocarbon-oxidizing (by 33%) microorganisms; however, the content of cellulolytic (by 12.5 times) microorganisms in the rhizosphere decreased. The use of Lenoil led to a further increase in the number of cellulolytic (by 5.6 times) and hydrocarbon-oxidizing (by 3.8 times) microorganisms and a decrease in the number of oligonitrophilic (by 22.7%) microorganisms in the rhizosphere. Under petroleum pollution, the content of auxins (IAA), zeatin riboside, zeatin nucleotide, and zeatin decreased, while the content of abscisic acid (ABA) increased in the shoots of rye plants. Lenoil treatment led to an eight-fold increase in the IAA content in the roots and a decrease in the ABA content in the aerial part and in the roots. It was shown for the first time that the treatment of petroleum-contaminated soil with "Lenoil" increased root mass due to the development of lateral roots, concurrent with high root IAA content. Petroleum pollution increased the deposition of lignin and suberin in the roots, which strengthened the apoplastic barrier and, thus, reduced the infiltration of toxic components. The deposition of suberin and lignin decreased under "Lenoil" treatment, indicating a decrease in the concentration of toxic petroleum components in the soil degraded by the bacteria. Thus, the biological preparation reduced the growth-inhibiting effect of petroleum on rye plants by increasing the content of growth-stimulating phytohormones (IAA and cytokinins) and reducing the content of ABA, justifying the importance of further study of relevant hormones for the improvement of phytoremediation. [ABSTRACT FROM AUTHOR]

Cuticular wax, cutin and suberin polyesters covering the surface of some fleshy fruit are tightly associated with skin color and appearance. β-Ketoacyl-CoA synthase (KCS) is a rate-limiting enzyme participating in the synthesis of very-long-chain fatty acids (VLCFAs), the essential precursors of cuticular waxes and aliphatic monomers of suberin. However, information on the KCS gene family in pear genome and the specific members involved in pear fruit skin formation remain unclear. In the present study, we performed an investigation of the composition and amount of cuticular waxes, cutin and aliphatic suberin in skins of four sand pear varieties with distinct colors (russet, semi-russet, and green) and demonstrated that the metabolic shifts of cuticular waxes and suberin leading to the significant differences of sand pear skin color. A genome-wide identification of KCS genes from the pear genome was conducted and 35 KCS coding genes were characterized and analyzed. Expression profile analysis revealed that the KCS genes had diverse expression patterns among different pear skins and the transcript abundance of PbrKCS15, PbrKCS19, PbrKCS24, and PbrKCS28 were consistent with the accumulation of cuticular waxes and suberin in fruit skin respectively. Subcellular localization analysis demonstrated that PbrKCS15, PbrKCS19, PbrKCS24 and PbrKCS28 located on the endoplasmic reticulum (ER). Further, transient over-expression of PbrKCS15, PbrKCS19, and PbrKCS24 in pear fruit skins significantly increased cuticular wax accumulation, whereas PbrKCS28 notably induced suberin deposition. In conclusion, pear fruit skin color and appearance are controlled in a coordinated way by the deposition of the cuticular waxes and suberin. PbrKCS15, PbrKCS19, and PbrKCS24 are involved in cuticular wax biosynthesis, and PbrKCS28 is involved in suberin biosynthesis, which play essential roles in pear fruit skin formation. Moreover, this work provides a foundation for further understanding the functions of KCS genes in pear. Key message: Thirty-five KCS genes were identified and analyzed in pear and functional characterization of PbrKCS15, PbrKCS19, PbrKCS24, and PbrKCS28 in cuticular wax and suberin synthesis and pear fruit skin formation. [ABSTRACT FROM AUTHOR]

Parinari curatellifolia is an important evergreen tree from the Miombo woodland of south-central and eastern Africa. The bark is corky, suggesting an increased protection against the ecosystem high temperatures and drought conditions as well as against wild fires. The cork in the bark rhytidome of P. curatellifolia was analyzed here for the first time with a focus on chemical and cellular features. P. curatellifolia cork has the cellular characteristics of cork tissues, with typical honeycomb structure in the tangential section and a brick-wall layer in the transverse and radial sections, without intercellular voids. Chemically P. curatellifolia cork has 8.4 % extractives, 33.9 % suberin, 31.9 % lignin and 25.2 % polysaccharides of the cork. The hemicelluloses are mostly xylans, with a substantial proportion of arabinose and galactose. Suberin showed a proportion of long chain lipids to glycerol (LCLip:Gly, mass ratio) of 8.5, and the long chain monomeric composition included a similar proportion of α,ω-diacids and ω-hydroxy acids (35.4 % and 31.5 % of long chain monomers) with a substantial proportion of monoacids (19.4 % of long chain monomers). Lignin is a guaiacyl-syringyl lignin with S/G of 0.32 and H:G:S of 1:14.1:4.5. The rhytidome composition and the cellular and chemical features of its cork are in line with environment-targeted protective features namely as a transpiration and insulation barrier, and as an increased fire protection.

Developing polyols from biomass sources contributes to a more circular economy by replacing petroleum-based polyols in the vast production of polyurethanes (PUR). One such potential biomass source could be leftover birch bark from which suberinic acids (SA) can be obtained. The purpose of this study was to identify the best synthesis routes for novel SA-based polyols, obtain rigid PUR foams, and evaluate their competitiveness and potential suitability as thermal insulation material. Novel polyols were synthesized from depolymerized SA by esterification with various functionality and molecular weight alcohols in several molar ratios. The moisture content, hydroxyl and acid values, and apparent viscosity were tested. Free-rise rigid PUR foams from the most suitable SA-based polyol and tall oil-based polyol were successfully prepared, reaching ~20 wt.% total renewable material content in the foam. The obtained rigid PUR foams' morphological, mechanical, and thermal properties were investigated and compared to present foam materials, including commercial foams. The apparent density (~33 kg/m3), as well as the closed cell content (~94%), compression strength (0.25 MPa, parallel to the foaming direction), and thermal conductivity (~0.019 W/(m·K)), approved the competitiveness and potential ability of SA-based rigid PUR foam production as thermal insulation material. [ABSTRACT FROM AUTHOR]

Growth- and health-promoting bacteria can boost crop productivity in a sustainable way. Pseudomonas simiae WCS417 is such a bacterium that efficiently colonizes roots, modifies the architecture of the root system to increase its size, and induces systemic resistance to make plants more resistant to pests and pathogens. Our previous work suggested that WCS417-induced phenotypes are controlled by root cell-type-specific mechanisms. However, it remains unclear how WCS417 affects these mechanisms. In this study, we transcriptionally profiled five Arabidopsis thaliana root cell types following WCS417 colonization. We found that the cortex and endodermis have the most differentially expressed genes, even though they are not in direct contact with this epiphytic bacterium. Many of these genes are associated with reduced cell wall biogenesis, and mutant analysis suggests that this downregulation facilitates WCS417-driven root architectural changes. Furthermore, we observed elevated expression of suberin biosynthesis genes and increased deposition of suberin in the endodermis of WCS417-colonized roots. Using an endodermal barrier mutant, we showed the importance of endodermal barrier integrity for optimal plant-beneficial bacterium association. Comparison of the transcriptome profiles in the two epidermal cell types that are in direct contact with WCS417—trichoblasts that form root hairs and atrichoblasts that do not—implies a difference in potential for defense gene activation. While both cell types respond to WCS417, trichoblasts displayed both higher basal and WCS417-dependent activation of defense-related genes compared with atrichoblasts. This suggests that root hairs may activate root immunity, a hypothesis that is supported by differential immune responses in root hair mutants. Taken together, these results highlight the strength of cell-type-specific transcriptional profiling to uncover "masked" biological mechanisms underlying beneficial plant-microbe associations. This study investigates how the epiphytic plant-beneficial bacterium Pseudomonas simiae WCS417 affects different root cell types of Arabidopsis thaliana using cell-type-specific transcriptomics. Bioinformatic analysis and further experimental validation demonstrate that WCS417 alters cell wall biogenesis and suberin deposition inside the root, potentially facilitating root development and bacterial colonization. Furthermore, this study reveals a role of root hairs in immune activation. [ABSTRACT FROM AUTHOR]

Fire hazard is a constant risk in everyday life with the use of combustibles such as polymeric materials, wood, and fabrics, to name a few. Halogenated compounds have been widely used as efficient flameretardants, often being applied as coatings or impregnations. With growing environmental concerns and regional bans on the use of halogenated flame-retardant compounds, bio-based alternatives are garnering significant research interest. Naturally occurring materials such as eggshells, DNA, and certain proteins have developed a self-defense mechanism against fire over millions of years of evolution. Cork, a naturally occurring biological tissue in outer bark, is of interest as it is often used as a heat shield and moisture repellent, specifically in spacecraft. A deeper look into the chemical structure of cork indicates the presence of suberin, a bio-polyester group that makes up as much as 40% of its chemical composition. These bio-polyester groups play a key role as a protective barrier between the plant and the surrounding external environment. Thus, the role of suberin in plants could be mimicked for the design of biobased flame-retardant materials. [ABSTRACT FROM AUTHOR]

Histological stains are useful tools for characterizing cell shape, arrangement and the material they are made from. Stains can be used individually or simultaneously to mark different cell structures or polymers within the same cells, and to visualize them in different colors. Histological stains can be combined with genetically-encoded fluorescent proteins, which are useful for understanding of plant development. To visualize suberin lamellae by fluorescent microscopy, we improved a histological staining procedure with the dyes Fluorol Yellow 088 and aniline blue. In the complex plant organs such as roots, suberin lamellae are deposited deep within the root on the endodermal cell wall. Our procedure yields reliable and detailed images that can be used to determine the suberin pattern in root cells. The main advantage of this protocol is its efficiency, the detailed visualization of suberin localization it generates in the root, and the possibility of returning to the confocal images to analyze and re-evaluate data if necessary.

The utilization of polyols derived from renewable sources presents an opportunity to enhance the sustainability of rigid polyurethane (PUR) foams, thereby contributing to the advancement of a circular bioeconomy. This study explores the development of PUR rigid foams exclusively using polyols sourced from second-generation renewable biomass feedstocks, specifically depolymerized birch bark suberin (suberinic acids) and tall oil fatty acids. The polyols achieved a total renewable material content as high as 74%, with a suberinic acid content of 37%. Response surface modeling was employed to determine the optimal bio-polyol, blowing agents, and catalyst content, hence, optimizing the bio-based foam formulations. In addition, response surface modeling was applied to rigid PUR foam formulations based on commercially available petroleum-based polyols for comparison. The results, including apparent density (~40–44 kg/m3), closed cell content (~95%), compression strength (>0.2 MPa, parallel to the foaming direction), and thermal conductivity (~0.019 W/(m·K)), demonstrated that the suberinic acids-based rigid PUR foam exhibited competitive qualities in comparison to petroleum-based polyols. Remarkably, the bio-based rigid PUR foams comprised up to 29% renewable materials. These findings highlight the potential of suberinic acid-tall oil polyols as effective candidates for developing rigid PUR foams, offering promising solutions for sustainable insulation applications.

Summary: The root barrier to radial O2 loss (ROL) is a key root trait preventing O2 loss from roots to anoxic soils, thereby enabling root growth into anoxic, flooded soils.We hypothesized that the ROL barrier can also prevent intrusion of hydrogen sulphide (H2S), a potent phytotoxin in flooded soils. Using H2S‐ and O2‐sensitive microsensors, we measured the apparent permeance to H2S of rice roots, tested whether restricted H2S intrusion reduced its adverse effects on root respiration, and whether H2S could induce the formation of a ROL barrier.The ROL barrier reduced apparent permeance to H2S by almost 99%, greatly restricting H2S intrusion. The ROL barrier acted as a shield towards H2S; O2 consumption in roots with a ROL barrier remained unaffected at high H2S concentration (500 μM), compared to a 67% decline in roots without a barrier. Importantly, low H2S concentrations induced the formation of a ROL barrier.In conclusion, the ROL barrier plays a key role in protecting against H2S intrusion, and H2S can act as an environmental signalling molecule for the induction of the barrier. This study demonstrates the multiple functions of the suberized/lignified outer part of the rice root beyond that of restricting ROL. [ABSTRACT FROM AUTHOR]

Key message: This compilation is focused on the role of cork oak periderm, a protective layer with unique physical and chemical traits for the cork industry, highlighting the recent periderm-specific genomic resources available. Cork oak is a unique species with the ability to produce a continuous and renewable cork throughout its lifespan. Periderm is a protective tissue composed of the phellem, phellogen, and phelloderm that replaces the epidermis. Phellem or "cork", the outermost layer, is produced by the original phellogen, a secondary meristem originated from the dedifferentiation of mature parenchyma cells. The formation and differentiation of periderm have been widely studied demonstrating the importance of fatty acid biosynthesis, phenylpropanoid, and metabolism of suberin, a complex glycerol-based polymer and the principal component of phellem. The contributions of several areas reveal new clues concerning the molecular mechanisms behind periderm differentiation. However, the whole process is still poorly understood. In this review, we compile information regarding the cellular structure and molecular basis, including the regulatory network of periderm formation and differentiation, focusing on the cork oak. The cork quality and its genetic and epigenetic mechanisms are also explored, highlighting the importance of molecular regulation in such economically important species. An increased understanding of the all periderm differentiation process may serve as a basis for future studies on functional genomics with an impact on fundamental science and on the forest industry for the production of high-quality cork. [ABSTRACT FROM AUTHOR]

Summary: Seeds slowly accumulate damage during storage, which ultimately results in germination failure. The seed coat protects the embryo from the external environment, and its composition is critical for seed longevity. Flavonols accumulate in the outer integument. The link between flavonol composition and outer integument development has not been explored.Genetic, molecular and ultrastructural assays on loss‐of‐function mutants of the flavonoid biosynthesis pathway were used to study the effect of altered flavonoid composition on seed coat development and seed longevity.Controlled deterioration assays indicate that loss of function of the flavonoid 3′ hydroxylase gene TT7 dramatically affects seed longevity and seed coat development. Outer integument differentiation is compromised from 9 d after pollination in tt7 developing seeds, resulting in a defective suberin layer and incomplete degradation of seed coat starch. These distinctive phenotypes are not shared by other mutants showing abnormal flavonoid composition. Genetic analysis indicates that overaccumulation of kaempferol‐3‐rhamnoside is mainly responsible for the observed phenotypes. Expression profiling suggests that multiple cellular processes are altered in the tt7 mutant.Overaccumulation of kaempferol‐3‐rhamnoside in the seed coat compromises normal seed coat development. This observation positions TRANSPARENT TESTA 7 and the UGT78D1 glycosyltransferase, catalysing flavonol 3‐O‐rhamnosylation, as essential players in the modulation of seed longevity. [ABSTRACT FROM AUTHOR]

In this study, an analysis of the influence of extractives, suberin and lignocellulosic components on the pyrolysis decomposition and fire reaction mechanisms of a cork oak powder from Quercus suber L. is presented. The summative chemical composition of cork powder was determined. Suberin was the main component at 40% of the total weight, followed by 24% of lignin, 19% of polysaccharides and 14% of extractives. The absorbance peaks of cork and its individual components were further analyzed by means of ATR-FTIR spectrometry. Thermogravimetric analysis (TGA) showed that the removal of extractives from cork slightly increased the thermal stability between 200 °C and 300 °C and led to the formation of a more thermally stable residue at the end of the cork decomposition. Moreover, by removing suberin, a shift of the onset decomposition temperature to a lower temperature was noticed, indicating that suberin plays a major role in enhancing the thermal stability of cork. Furthermore, non-polar extractives showed the highest flammability with a peak of heat release rate (pHRR) of 365 W/g analyzed by means of micro-scale combustion calorimetry (MCC). Above 300 °C, the heat release rate (HRR) of suberin was lower than that of polysaccharides or lignin. However, below that temperature it released more flammable gases with a pHRR of 180 W/g, without significant charring ability, contrary to the mentioned components that showed lower HRR due to their prominent condensed mode of action that slowed down the mass and heat transfer processes during the combustion process. [ABSTRACT FROM AUTHOR]

As a wall polymer, suberin has a multifaceted role in plant development and stress responses. It is deposited between the plasma membrane and the primary cell wall in specialized tissues such as root exodermis, endodermis, phellem, and seed coats. It is formed de novo in response to stresses such as wounding, salt injury, drought, and pathogen attack and is a complex polyester mainly consisting of fatty acids, glycerol, and minor amounts of ferulic acid that are associated to a lignin-like polymer predominantly composed of ferulates. Metabolomic and transcriptomic studies have revealed that cell wall lignification precedes suberin deposition. The ferulic acid esterified to ω-hydroxy fatty acids, synthetized by the feruloyl transferase FHT (or ASFT), presumably plays a role in coupling both polymers, although the precise mechanism is not understood. Here, we use the promoter of tomato suberin feruloyl transferase (FHT/ASFT) fused to GUS (β-glucuronidase) to demonstrate that ferulate deposition agrees with the site of promoter FHT activation by using a combination of histochemical staining and UV microscopy. Hence, FHT promoter activation and alkali UV microscopy can be used to identify the precise localization of early suberizing cells rich in ferulic acid and can additionally be used as an efficient marker of early suberization events during plant development and stress responses. This line can be used in the future as a tool to identify emerging suberization sites via ferulate deposition in tomato plants, which may contribute to germplasm screening in varietal improvement programs. [ABSTRACT FROM AUTHOR]

Summary: Wood is the most important repository of assimilated carbon in the biosphere, in the form of large polymers (cellulose, hemicelluloses including glucuronoxylan, and lignin) that interactively form a composite, together with soluble extractives including phenolic and aliphatic compounds. Molecular interactions among these compounds are not fully understood.We have targeted the expression of a fungal α‐glucuronidase to the wood cell wall of aspen (Populus tremula L. × tremuloides Michx.) and Arabidopsis (Arabidopsis thaliana (L.) Heynh), to decrease contents of the 4‐O‐methyl glucuronopyranose acid (mGlcA) substituent of xylan, to elucidate mGlcA's functions.The enzyme affected the content of aliphatic insoluble cell wall components having composition similar to suberin, which required mGlcA for binding to cell walls. Such suberin‐like compounds have been previously identified in decayed wood, but here, we show their presence in healthy wood of both hardwood and softwood species. By contrast, γ‐ester bonds between mGlcA and lignin were insensitive to cell wall‐localized α‐glucuronidase, supporting the intracellular formation of these bonds.These findings challenge the current view of the wood cell wall composition and reveal a novel function of mGlcA substituent of xylan in fastening of suberin‐like compounds to cell wall. They also suggest an intracellular initiation of lignin–carbohydrate complex assembly. See also the Commentary on this article by Oliveira, 238: 8–10. [ABSTRACT FROM AUTHOR]

Main Conclusion: PpyMYB144 directly activates the promoter of PpyCYP86B1, promotes the synthesis of α, ω-diacids, and involves in pear fruit skin russeting. Russeting is an economically important surface disorder in pear (Pyrus pyrifolia) fruit. Previous research has demonstrated that suberin is the pivotal chemical component contributing to pear fruit skin russeting, and fruit bagging treatment effectively reduces the amount of suberin of fruits, and thereby reduces the russeting phenotype. However, the mechanisms of pear fruit skin russeting remain largely unclear, particularly the transcriptional regulation. Here, we dissected suberin concentration and composition of pear fruits along fruit development and confirmed that α, ω-diacids are the predominant constituents in russeted pear fruit skins. Two cytochrome P450 monooxygenase (CYP) family genes (PpyCYP86A1 and PpyCYP86B1) and nine MYB genes were isolated from pear fruit. Expressions of PpyCYP86A1, PpyCYP86B1, and five MYB genes (PpyMYB34, PpyMYB138, PpyMYB138-like, PpyMYB139, and PpyMYB144) were up-regulated during fruit russeting and showed significant correlations with the changes of α, ω-diacids. In addition, dual-luciferase assays indicated that PpyMYB144 could trans-activate the promoter of PpyCYP86B1, and the activation was abolished by motif mutagenesis of AC element on the PpyCYP86B1 promoter. Further, Agrobacterium-mediated transient expression of PpyCYP86B1 and PpyMYB144 in pear fruits induced the deposition of aliphatic suberin. Thus, PpyMYB144 is a novel direct activator of PpyCYP86B1 and contributes to pear fruit skin russeting. [ABSTRACT FROM AUTHOR]

The intensive use of groundwater in agriculture under the current climate conditions leads to acceleration of soil salinization. Given that almond is a salt-sensitive crop, selection of salt-tolerant rootstocks can help maintain productivity under salinity stress. Selection for tolerant rootstocks at an early growth stage can reduce the investment of time and resources. However, salinity-sensitive markers and salinity tolerance mechanisms of almond species to assist this selection process are largely unknown. We established a microscopy-based approach to investigate mechanisms of stress tolerance in and identified cellular, root anatomical, and molecular traits associated with rootstocks exhibiting salt tolerance. We characterized three almond rootstocks: Empyrean-1 (E1), Controller-5 (C5), and Krymsk-86 (K86). Based on cellular and molecular evidence, our results show that E1 has a higher capacity for salt exclusion by a combination of upregulating ion transporter expression and enhanced deposition of suberin and lignin in the root apoplastic barriers, exodermis, and endodermis, in response to salt stress. Expression analyses revealed differential regulation of cation transporters, stress signaling, and biopolymer synthesis genes in the different rootstocks. This foundational study reveals the mechanisms of salinity tolerance in almond rootstocks from cellular and structural perspectives across a root developmental gradient and provides insights for future screens targeting stress response.

Introduction: Apple russeting is mainly due to the accumulation of suberin in the cell wall in response to defects and damages in the cuticle layer. Over the last decades, massive efforts have been done to better understand the complex interplay between pathways involved in the suberization process in model plants. However, the regulation mechanisms which orchestrate this complex process are still under investigation. Our previous studies highlighted a number of transcription factor candidates from the Myeloblastosis (MYB) transcription factor family which might regulate suberization in russeted or suberized apple fruit skin. Among these, we identified MdMYB68, which was co-expressed with number of well-known key suberin biosynthesis genes. Method: To validate the MdMYB68 function, we conducted an heterologous transient expression in Nicotiana benthamiana combined with whole gene expression profiling analysis (RNA-Seq), quantification of lipids and cell wall monosaccharides, and microscopy. Results: MdMYB68 overexpression is able to trigger the expression of the whole suberin biosynthesis pathway. The lipid content analysis confirmed that MdMYB68 regulates the deposition of suberin in cell walls. Furthermore, we also investigated the alteration of the non-lipid cell wall components and showed that MdMYB68 triggers a massive modification of hemicelluloses and pectins. These results were finally supported by the microscopy. Discussion: Once again, we demonstrated that the heterologous transient expression in N. benthamiana coupled with RNA-seq is a powerful and efficient tool to investigate the function of suberin related transcription factors. Here, we suggest MdMYB68 as a new regulator of the aliphatic and aromatic suberin deposition in apple fruit, and further describe, for the first time, rearrangements occurring in the carbohydrate cell wall matrix, preparing this suberin deposition. [ABSTRACT FROM AUTHOR]