Pectin Methylesterification Research Articles

A Pectin Methylesterase Inhibitor Enhances Resistance to Verticillium Wilt.

Pectins are major components of the primary plant cell wall, which functions as the primary barrier against pathogens. Pectin methylesterases (PMEs) catalyze the demethylesterification of the homogalacturonan domains of pectin in the plant cell wall. Their activity is regulated by PME inhibitors (PMEIs). Here, we provide evidence that the pectin methylesterase-inhibiting protein GhPMEI3 from cotton (Gossypium hirsutum) functions in plant responses to infection by the fungus Verticillium dahliae GhPMEI3 interacts with PMEs and regulates the expression of a specific fungal polygalacturonase (VdPG1). Ectopic expression of GhPMEI3 increased pectin methyl esterification and limited fungal disease in cotton, while also modulating root elongation. Enzymatic analyses revealed that GhPMEI3 efficiently inhibited the activity of cotton GhPME2/GhPME31. Experiments using transgenic Arabidopsis (Arabidopsis thaliana) plants expressing the GhPMEI3 gene under the control of the CaMV 35S promoter revealed that GhPMEI3 inhibits the endogenous PME activity in vitro. Moreover, the enhanced resistance to V. dahliae was associated with altered VdPG1 expression. Virus-induced silencing of GhPMEI3 resulted in increased susceptibility to V. dahliae Further, we investigated the interaction between GhPMEI3 and GhPME2/GhPME31 using inhibition assays and molecular docking simulations. The peculiar structural features of GhPMEI3 were responsible for the formation of a 1:1 stoichiometric complex with GhPME2/GhPME31. Together, these results suggest that GhPMEI3 enhances resistance to Verticillium wilt. Moreover, GhPMEI3-GhPMEs interactions would be needed before drawing the correlation between structure-function and are crucial for plant development against the ever-evolving fungal pathogens.

Interactions between citrus pectin and Zn2+ or Ca2+ and associated in vitro Zn2+ bioaccessibility as affected by degree of methylesterification and blockiness

Insight into the effect of the degree and pattern of methylesterification of citrus pectin on the Ca2+ and Zn2+ adsorption capacity and the associated Zn2+ bioaccessibility was established. Pectins with comparable methylesterification degrees (DM) but different patterns of methylester distribution (blockwise or random) were generated. Blockwise distributions of methylesters were produced through controlled enzymatic means (using carrot pectin methylesterase) while random patterns were obtained through alkaline demethylesterification (using NaOH). The pattern of methylesterification was estimated as the absolute degree of blockiness (DBabs), which is the ratio of non-methylesterified units present in blocks to the total number of galacturonic acid units. Determination and modeling (based on the Langmuir adsorption model) of the adsorption isotherms of these structurally modified pectins for Zn2+ or Ca2+ allowed quantification of their maximum cation binding capacity and interaction energy. Decreasing pectin DM and increasing DBabs were shown to promote the Zn2+ or Ca2+ binding capacity of pectin, with the maximum binding capacity being mainly determined by the DM and interaction energy by DBabs. The influence of cation type was evident, with higher maximum binding capacities and interaction energies exhibited for Zn2+ compared to Ca2+, mainly due to the higher electronegativity of the former. Increased Zn2+ binding to pectin was associated with lower Zn2+ bioaccessibility and no influence of low levels of added Ca2+ was observed. However, enzymes and bile salts added during in vitro simulated digestion were shown to bind substantial amounts of Zn2+ ions.

Changes in the abundance of cell wall apiogalacturonan and xylogalacturonan and conservation of rhamnogalacturonan II structure during the diversification of the Lemnoideae.

The diversification of the Lemnoideae was accompanied by a reduction in the abundance of cell wall apiogalacturonan and an increase in xylogalacturonan whereas rhamnogalacturonan II structure and cross-linking are conserved. The subfamily Lemnoideae is comprised of five genera and 38 species of small, fast-growing aquatic monocots. Lemna minor and Spirodela polyrhiza belong to this subfamily and have primary cell walls that contain large amounts of apiogalacturonan and thus are distinct from the primary walls of most other flowering plants. However, the pectins in the cell walls of other members of the Lemnoideae have not been investigated. Here, we show that apiogalacturonan decreased substantially as the Lemnoideae diversified since Wolffiella and Wolffia walls contain between 63 and 88% less apiose than Spirodela, Landoltia, and Lemna walls. In Wolffia, the most derived genus, xylogalacturonan is far more abundant than apiogalacturonan, whereas in Wolffiella pectic polysaccharides have a high arabinose content, which may arise from arabinan sidechains of RG I. The apiose-containing pectin rhamnogalacturonan II (RG-II) exists in Lemnoideae walls as a borate cross-linked dimer and has a glycosyl sequence similar to RG-II from terrestrial plants. Nevertheless, species-dependent variations in the extent of methyl-etherification of RG-II sidechain A and arabinosylation of sidechain B are discernible. Immunocytochemical studies revealed that pectin methyl-esterification is higher in developing daughter frond walls than in mother frond walls, indicating that methyl-esterification is associated with expanding cells. Our data support the notion that a functional cell wall requires conservation of RG-II structure and cross-linking but can accommodate structural changes in other pectins. The Lemnoideae provide a model system to study the mechanisms by which wall structure and composition has changed in closely related plants with similar growth habits.

Cell Wall Localization of Two DUF642 Proteins, BIIDXI and TEEBE, during Meloidogyne incognita Early Inoculation.

The root-knot nematode Meloidogyne incognita infects a variety of plants, including Arabidopsis thaliana. During migration, root-knot nematodes secrete different proteins to modify cell walls, which include pectolytic enzymes. However, the contribution of host cell wall proteins has not been described during this process. The function of two DUF642 cell wall proteins, BIIDXI (BDX, At4g32460) and TEEBE (TEB, At2g41800), in plant development could be related to the regulation of pectin methyl esterification status in the cell walls of different tissues. Accordingly, the expression of these two genes is up-regulated by auxin. BDX and TEB were highly induced during early M. incognita inoculation. Moreover, cell wall localization of the proteins was also induced. The cell wall localization of BDX and TEB DUF642 proteins during M. incognita early inoculation suggested that these two proteins could be involved in the regulation of the degree of pectin methylation during cell separation.

Degree of pectin methyl esterification in endosperm cell walls is involved in embryo bending in Arabidopsis thaliana

The endosperm is a transitory structure involved in proper embryo elongation. The cell walls of mature seed endosperm are generally composed of a uniform distribution of cellulose, unesterified homogalacturonans, and arabinans. Recent studies suggest that changes in cell wall properties during endosperm development could be related to embryo growth. The degree of methyl esterification of homogalacturonans may be involved in this endosperm tissue remodelling. The relevance of the degree of homogalacturonan methyl esterification during seed development was determined by immunohistochemical analyses using a panel of probes with specificity for homogalaturonans with different degrees of methyl esterification. Low-esterified and un-esterified homogalacturonans were abundant in endosperm cells during embryo bending and were also detected in mature embryos. BIDXII (BDX) could be involved in seed development, because bdx-1 mutants had misshapen embryos. The methyl esterification pattern described for WT seeds was different during bdx-1 seed development; un-esterified homogalacturonans were scarcely present in the cell walls of endosperm in bending embryos and mature seeds. Our results suggested that the degree of methyl esterification of homogalacturonans in the endosperm cell wall may be involved in proper embryo development.

Pectic enzymes as potential enhancers of ascorbic acid production through the D-galacturonate pathway in Solanaceae

The increase of L-Ascorbic Acid (AsA) content in tomato (Solanum lycopersicum) is a common goal in breeding programs due to its beneficial effect on human health. To shed light into the regulation of fruit AsA content, we exploited a Solanum pennellii introgression line (IL12-4-SL) harbouring one quantitative trait locus that increases the content of total AsA in the fruit. Biochemical and transcriptomic analyses were carried out in fruits of IL12-4-SL in comparison with the cultivated line M82 at different stages of ripening. AsA content was studied in relation with pectin methylesterase (PME) activity and the degree of pectin methylesterification (DME). Our results indicated that the increase of AsA content in IL12-4-SL fruits was related with pectin de-methylesterification/degradation. Specific PME, polygalacturonase (PG) and UDP-D-glucuronic-acid-4-epimerase (UGlcAE) isoforms were proposed as components of the D-galacturonate pathway leading to AsA biosynthesis. The relationship between AsA content and PME activity was also exploited in PMEI tobacco plants expressing a specific PME inhibitor (PMEI). Here we report that tobacco PMEI plants, altered in PME activity and degree of pectin methylesterification, showed a reduction in low methylesterified pectic domains and exhibited a reduced AsA content. Overall, our results provide novel biochemical and genetic traits for increasing antioxidant content by marker-assisted selection in the Solanaceae family.

Pectin methylesterases contribute the pathogenic differences between races 1 and 4 of Fusarium oxysporum f. sp. cubense

Plant cell walls, which are mainly composed of pectin, play important roles in plant defence responses to pathogens. Pectin is synthesised in a highly esterified form and then de-esterified by pectin methylesterases (PMEs). Because of this, PMEs are directly involved in plant defence. However, the molecular mechanisms of their interactions with pectins remain unclear. In this study, we compared the expression level and enzyme activities of PMEs in a banana Cavendish cultivar (Musa AAA ‘Brazilian’) inoculated with Fusarium oxysporum f. sp. cubense pathogenic races 1 (Foc1) and 4 (Foc4). We further examined the spatial distribution of PMEs and five individual homogalacturonans (HGs) with different degree of pectin methylesterification (DM). Results suggested that the banana roots infected with Foc1 showed lower PME activity than those infected with Foc4, which was consisted with observed higher level of pectin DM. The level of HGs crosslinked with Ca2+ was significantly higher in roots infected with Foc1 compared with those infected with Foc4. Therefore, banana exhibited significantly different responses to Foc1 and Foc4 infection, and these results suggest differences in PME activities, DM of pectin and Ca2+-bridged HG production. These differences could have resulted in observed differences in virulence between Foc1 and Foc4.

The influence of sweet pepper pectin structural characteristics on cytokine secretion by THP-1 macrophages

Pectins can modulate the biological responses interacting directly with immune cells. The observed responses can strongly be affected by polysaccharide structural features. We analyzed the intrinsic activation capacity of native and modified sweet pepper pectin on cytokine secretion by THP-1 macrophages as well as compare their effects in the presence of lipopolysaccharide. Modified pectin was obtained by partial acid hydrolysis which promoted the removal of side chains as well as the reduction of molecular weight and the degree of methyl esterification of native pectin. The results showed that both fractions had no effect on THP-1 viability. Native pectin at 300μg/mL increased TNF-α, IL-1β and IL-10 cytokine secretion by THP-1 macrophages. However, in the presence of lipopolysaccharide, it can attenuate the inflammatory response by reducing the production of the pro-inflammatory cytokines TNF-α and IL-1β and increasing the anti-inflammatory cytokine IL-10, as well as decreasing the TNF-α/IL-10 and IL-1β/IL-10 ratios. The structural modifications caused by acid hydrolysis affected the intrinsic activation capacity of native pectin to modulate the cytokines secretion. These results indicate that degree of methyl esterification, molecular weight and presence of side chains are important structural features of pectins involved in the modulation of cytokine secretion by THP-1 macrophages.

Cell wall pectin methyl-esterification and organic acids of root tips involve in aluminum tolerance in Camellia sinensis

Tea plant (Camellia sinensis (O.) Kuntze) can survive from high levels of aluminum (Al) in strongly acidic soils. However, the mechanism driving its tolerance to Al, the predominant factor limiting plant growth in acid condition, is still not fully understood. Here, two-year-old rooted cuttings of C. sinensis cultivar ‘Longjingchangye’ were used for Al resistance experiments. We found that the tea plants grew better in the presence of 0.4 mM Al than those grew under lower concentration of Al treatments (0 and 0.1 mM) as well as higher levels treatment (2 and 4 mM), confirming that appropriate Al increased tea plant growth. Hematoxylin staining assay showed that the apical region was the main accumulator in tea plant root. Subsequently, immunolocalization of pectins in the root tip cell wall showed a rise in low-methyl-ester pectin levels and a reduction of high-methyl-ester pectin content with the increasing Al concentration of treatments. Furthermore, we observed the increased expressions of C. sinensis pectin methylesterase (CsPME) genes along with the increasing de-esterified pectin levels during response to Al treatments. Additionally, the levels of organic acids increased steadily after treatment with 0.1, 0.4 or 2 mM Al, while they dropped after treatment with 4 mM Al. The organic acids secretion from root followed a similar trend. Similarly, a gradual increase in malate dehydrogenase (MDH), citrate synthase (CS) and glycolate oxidase (GO) enzyme activities and relevant metabolic genes expression were detected after the treatment of 0.1, 0.4 or 2 mM Al, while a sharp decrease was resulted from treatment with 4 mM Al. These results confirm that both pectin methylesterases and organic acids contribute to Al tolerance in C. sinensis.

Mechanical regulation of organ asymmetry in leaves.

How appendages, such as plant leaves or animal limbs, develop asymmetric shapes remains a fundamental question in biology. Although ongoing research has revealed the genetic regulation of organ pattern formation, how gene activity ultimately directs organ shape remains unclear. Here, we show that leaf dorsoventral (adaxial-abaxial) polarity signals lead to mechanical heterogeneity of the cell wall, related to the methyl-esterification of cell-wall pectins in tomato and Arabidopsis. Numerical simulations predicate that mechanical heterogeneity is sufficient to produce the asymmetry seen in planar leaves. Experimental tests that alter pectin methyl-esterification, and therefore cell wall mechanical properties, support this model and lead to polar changes in gene expression, suggesting the existence of a feedback mechanism for mechanical signals in morphogenesis. Thus, mechanical heterogeneity within tissue may underlie organ shape asymmetry.

Insertional calcaneal tendinopathy: Results of treatment with the Speedbridge® system

Metallic ions were quantified and mapped at the tissue and the cell scales in two texture and phenolic content contrasted cider apples by atomic absorption spectroscopy, ion chromatography and synchrotron cryo X-ray fluorescence imaging. Metallic ions content and gradient distribution from the cuticle to the inner tissue significantly varied between years of harvest (1–294 % of differences between years). The content of non-esterified uronic acid in the cell wall pectin was also measured (3.1 and 4.9 mol kg−1 of dry weight fruit) and found higher than the total metallic ions in the two varieties (0.22 and 0.27 mol kg−1 of dry weight fruit). Calcium content and cell wall pectin methyl-esterification were not determinants distinguishing firm from soft apples. The results are discussed with regard to the co-location of metallic ions with the phenolic compounds which questions their role in oxidative mechanisms during fruit development and processing, affecting particularly the colour and taste of fruit products.

How the Depletion in Mineral Major Elements Affects Grapevine (Vitis vinifera L.) Primary Cell Wall.

The noteworthy fine remodeling that plant cell walls (CWs) undergo to adapt to developmental, physiological and environmental cues and the observation that its composition and dynamics differ between species represents an opportunity to couple crop species agronomic studies with research on CW modifications. Vitis vinifera is one of the most important crops from an economic point-of-view due to the high value of the fruit, predominantly for winemaking. The availability of some information related to this species’ CWs allows researching its responses to imposed conditions that affect the plant’s development. Mineral deficiency, in particular nitrogen, phosphorus, potassium and sulfur, strongly affects plant metabolism, reducing both growth and crop yield. Despite the importance of mineral nutrition in development, its influence on CW synthesis and modifications is still insufficiently documented. Addressing this knowledge gap, V. vinifera experimental models were used to study CW responses to imposed mineral depletion in unorganized (callus) and organized (shoots) tissues. The discussion of the obtained results is the main focus of this review. Callus and shoots submitted to mineral restriction are impaired in specific CW components, predominantly cellulose. Reorganization on structure and deposition of several other polymers, in particular the degree and pattern of pectin methyl-esterification and the amount of xyloglucan (XyG), arabinan and extensin, is also observed. In view of recently proposed CW models that consider biomechanical hotspots and direct linkages between pectins and XyG/cellulose, the outcome of these modifications in explaining maintenance of CW integrity through compensatory stiffening can be debated. Nutrient stresses do not affect evenly all tissues with undifferentiated callus tissues showing more pronounced responses, followed by shoot mature internodes, and then newly formed internodes. The impact of nitrogen depletion leads to more noticeable responses, supporting this nutrient’s primary role in plant development and metabolism. The consequential compensatory mechanisms highlight the pivotal role of CW in rearranging under environmental stresses.

Polysaccharide compositions of collenchyma cell walls from celery (Apium graveolens L.) petioles

BackgroundCollenchyma serves as a mechanical support tissue for many herbaceous plants. Previous work based on solid-state NMR and immunomicroscopy suggested collenchyma cell walls (CWs) may have similar polysaccharide compositions to those commonly found in eudicotyledon parenchyma walls, but no detailed chemical analysis was available. In this study, compositions and structures of cell wall polysaccharides of peripheral collenchyma from celery petioles were investigated.ResultsThis is the first detailed investigation of the cell wall composition of collenchyma from any plant. Celery petioles were found to elongate throughout their length during early growth, but as they matured elongation was increasingly confined to the upper region, until elongation ceased. Mature, fully elongated, petioles were divided into three equal segments, upper, middle and lower, and peripheral collenchyma strands isolated from each. Cell walls (CWs) were prepared from the strands, which also yielded a HEPES buffer soluble fraction. The CWs were sequentially extracted with CDTA, Na2CO3, 1 M KOH and 4 M KOH. Monosaccharide compositions of the CWs showed that pectin was the most abundant polysaccharide [with homogalacturonan (HG) more abundant than rhamnogalacturonan I (RG-I) and rhamnogalacturonan II (RG-II)], followed by cellulose, and other polysaccharides, mainly xyloglucans, with smaller amounts of heteroxylans and heteromannans. CWs from different segments had similar compositions, but those from the upper segments had slightly more pectin than those from the lower two segments. Further, the pectin in the CWs of the upper segment had a higher degree of methyl esterification than the other segments. In addition to the anticipated water-soluble pectins, the HEPES-soluble fractions surprisingly contained large amounts of heteroxylans. The CDTA and Na2CO3 fractions were rich in HG and RG-I, the 1 M KOH fraction had abundant heteroxylans, the 4 M KOH fraction was rich in xyloglucan and heteromannans, and cellulose was predominant in the final residue. The structures of the xyloglucans, heteroxylans and heteromannans were deduced from the linkage analysis and were similar to those present in most eudicotyledon parenchyma CWs. Cross polarization with magic angle spinning (CP/MAS) NMR spectroscopy showed no apparent difference in the rigid and semi-rigid polysaccharides in the CWs of the three segments. Single-pulse excitation with magic-angle spinning (SPE/MAS) NMR spectroscopy, which detects highly mobile polysaccharides, showed the presence of arabinan, the detailed structure of which varied among the cell walls from the three segments.ConclusionsCelery collenchyma CWs have similar polysaccharide compositions to most eudicotyledon parenchyma CWs. However, celery collenchyma CWs have much higher XG content than celery parenchyma CWs. The degree of methyl esterification of pectin and the structures of the arabinan side chains of RG-I show some variation in the collenchyma CWs from the different segments. Unexpectedly, the HEPES-soluble fraction contained a large amount of heteroxylans.

Cell separation in kiwifruit without development of a specialised detachment zone

BackgroundUnlike in abscission or dehiscence, fruit of kiwifruit Actinidia eriantha develop the ability for peel detachment when they are ripe and soft in the absence of a morphologically identifiable abscission zone. Two closely-related genotypes with contrasting detachment behaviour have been identified. The ‘good-peeling’ genotype has detachment with clean debonding of cells, and a peel tissue that does not tear. The ‘poor-peeling’ genotype has poor detachability, with cells that rupture upon debonding, and peel tissue that fragments easily.ResultsStructural studies indicated that peel detachability in both genotypes occurred in the outer pericarp beneath the hypodermis. Immunolabelling showed differences in methylesterification of pectin, where the interface of labelling coincided with the location of detachment in the good-peeling genotype, whereas in the poor-peeling genotype, no such interface existed. This zone of difference in methylesterification was enhanced by differential cell wall changes between the peel and outer pericarp tissue. Although both genotypes expressed two polygalacturonase genes, no enzyme activity was detected in the good-peeling genotype, suggesting limited pectin breakdown, keeping cell walls strong without tearing or fragmentation of the peel and flesh upon detachment. Differences in location and amounts of wall-stiffening galactan in the peel of the good-peeling genotype possibly contributed to this phenotype. Hemicellulose-acting transglycosylases were more active in the good-peeling genotype, suggesting an influence on peel flexibility by remodelling their substrates during development of detachability. High xyloglucanase activity in the peel of the good-peeling genotype may contribute by having a strengthening effect on the cellulose-xyloglucan network.ConclusionsIn fruit of A. eriantha, peel detachability is due to the establishment of a zone of discontinuity created by differential cell wall changes in peel and outer pericarp tissues that lead to changes in mechanical properties of the peel. During ripening, the peel becomes flexible and the cells continue to adhere strongly to each other, preventing breakage, whereas the underlying outer pericarp loses cell wall strength as softening proceeds. Together these results reveal a novel and interesting mechanism for enabling cell separation.

Boron Supply Enhances Aluminum Tolerance in Root Border Cells of Pea (Pisum sativum) by Interacting with Cell Wall Pectins.

Aluminum (Al) toxicity is the primary factor limiting crop growth in acidic soils. Boron (B) alleviates Al toxicity in plants, which is mainly considered to be due to the formation of Rhamnogalacturonan II-B (RGII-B) complexes, which helps to stabilize the cytoskeleton. It is unclear yet whether this is due to the increasing of net negative charges and/or further mechanisms. Kinetics of Al accumulation and adsorption were investigated using entire cells, cell wall and pectin of root border cells (RBCs) of pea (Pisum sativum), to reveal the mechanism of B in interacting with alkali-soluble and chelator-soluble pectin for an increased Al tolerance in RBCs. The results show that B could rescue RBCs from Al-induced cell death by accumulating more Al in the cell wall, predominately in alkali-soluble pectin. Boron also promotes Al3+ adsorption and inhibits Al3+ desorption from alkali-soluble pectin. Thus, more Al3+ is immobilized within the alkali-soluble pectin fraction and less in the chelator-soluble pectin, rendering Al3+ less mobile. Boron induces an increase of RG-II (KDO,2-keto-3-deoxyoctonic acid) content for forming more borate-RGII complexes, and the decrease of pectin methyl-esterification, thus creates more negative charges to immobilize Al3+ in cell wall pectin. The study provides evidence that abundant B supply enhances the immobilization of Al in alkali-soluble pectin, thus most likely reducing the entry of Al3+ into the symplast from the surroundings.

PECTIN METHYLESTERASE34 Contributes to Heat Tolerance through Its Role in Promoting Stomatal Movement.

Pectin, a major component of the primary cell wall, is synthesized in the Golgi apparatus and exported to the cell wall in a highly methylesterified form, then is partially demethylesterified by pectin methylesterases (PMEs; EC 3.1.1.11). PME activity on the status of pectin methylesterification profoundly affects the properties of pectin and, thereby, is critical for plant development and the plant defense response, although the roles of PMEs under heat stress (HS) are poorly understood. Functional genome annotation predicts that at least 66 potential PME genes are contained in Arabidopsis (Arabidopsis thaliana). Thermotolerance assays of PME gene T-DNA insertion lines revealed two null mutant alleles of PME34 (At3g49220) that both consistently showed reduced thermotolerance. Nevertheless, their impairment was independently associated with the expression of HS-responsive genes. It was also observed that PME34 transcription was induced by abscisic acid and highly expressed in guard cells. We showed that the PME34 mutation has a defect in the control of stomatal movement and greatly altered PME and polygalacturonase (EC 3.2.1.15) activity, resulting in a heat-sensitive phenotype. PME34 has a role in the regulation of transpiration through the control of the stomatal aperture due to its cell wall-modifying enzyme activity during the HS response. Hence, PME34 is required for regulating guard cell wall flexibility to mediate the heat response in Arabidopsis.

LEUNIG_HOMOLOG transcriptional co-repressor mediates aluminium sensitivity through PECTIN METHYLESTERASE46-modulated root cell wall pectin methylesterification in Arabidopsis.

A major factor determining aluminium (Al) sensitivity in higher plants is the binding of Al to root cell walls. The Al binding capacity of cell walls is closely linked to the extent of pectin methylesterification, as the presence of methyl groups attached to the pectin backbone reduces the net negative charge of this polymer and hence limits Al binding. Despite recent progress in understanding the molecular basis of Al resistance in a wide range of plants, it is not well understood how the methylation status of pectin is mediated in response to Al stress. Here we show in Arabidopsis that mutants lacking the gene LEUNIG_HOMOLOG (LUH), a member of the Groucho-like family of transcriptional co-repressor, are less sensitive to Al-mediated repression of root growth. This phenotype is correlated with increased levels of methylated pectin in the cell walls of luh roots as well as altered expression of cell wall-related genes. Among the LUH-repressed genes, PECTIN METHYLESTERASE46 (PME46) was identified as reducing Al binding to cell walls and hence alleviating Al-induced root growth inhibition by decreasing PME enzyme activity. seuss-like2 (slk2) mutants responded to Al in a similar way as luh mutants suggesting that a LUH-SLK2 complex represses the expression of PME46. The data are integrated into a model in which it is proposed that PME46 is a major inhibitor of pectin methylesterase activity within root cell walls.

External nitrogen input affects pre- and post-harvest cell wall composition but not the enzymatic saccharification of wheat straw

Wheat is one of the most important crops for food and feed and its straw is a potential feedstock for biorefinery purposes. Nitrogen (N) is an essential input factor in wheat agriculture but no information is available on how it affects straw composition during maturation and at harvest. To investigate this, we conducted a large scale field experiment in which wheat plants were cultivated at three levels of externally applied N. The plants were harvested at different stages of maturation, spanning green straw at heading (ear emergence) to fully yellow straw at final maturity. Defined parts of the straw were analyzed for cell wall characteristics relevant for further biomass processing. The straw N concentration corroborated with the level of N input, but the yield of straw biomass was not largely affected. High N treatment modified cell wall composition, namely increased abundance of arabinogalactan proteins (AGPs) and lignin in the mature straw. A general decrease in pectin methylesterification as well as in ferulate linkages was also observed. Importantly, no significant changes in crystalline cellulose and silicon concentration or in saccharification efficiency were observed among the different N treatments. Nitrogen fertilization partially alters the cell wall composition in wheat straw but is not a limiting factor in wheat biomass refinery.

Three Pectin Methylesterase Inhibitors Protect Cell Wall Integrity for Arabidopsis Immunity to Botrytis.

Infection by necrotrophs is a complex process that starts with the breakdown of the cell wall (CW) matrix initiated by CW-degrading enzymes and results in an extensive tissue maceration. Plants exploit induced defense mechanisms based on biochemical modification of the CW components to protect themselves from enzymatic degradation. The pectin matrix is the main CW target of Botrytis cinerea, and pectin methylesterification status is strongly altered in response to infection. The methylesterification of pectin is controlled mainly by pectin methylesterases (PMEs), whose activity is posttranscriptionally regulated by endogenous protein inhibitors (PMEIs). Here, AtPMEI10, AtPMEI11, and AtPMEI12 are identified as functional PMEIs induced in Arabidopsis (Arabidopsis thaliana) during B. cinerea infection. AtPMEI expression is strictly regulated by jasmonic acid and ethylene signaling, while only AtPMEI11 expression is controlled by PME-related damage-associated molecular patterns, such as oligogalacturonides and methanol. The decrease of pectin methylesterification during infection is higher and the immunity to B. cinerea is compromised in pmei10, pmei11, and pmei12 mutants with respect to the control plants. A higher stimulation of the fungal oxalic acid biosynthetic pathway also can contribute to the higher susceptibility of pmei mutants. The lack of PMEI expression does not affect hemicellulose strengthening, callose deposition, and the synthesis of structural defense proteins, proposed as CW-remodeling mechanisms exploited by Arabidopsis to resist CW degradation upon B. cinerea infection. We show that PME activity and pectin methylesterification are dynamically modulated by PMEIs during B. cinerea infection. Our findings point to AtPMEI10, AtPMEI11, and AtPMEI12 as mediators of CW integrity maintenance in plant immunity.

Cell wall biochemical alterations during Agrobacterium-mediated expression of haemagglutinin-based influenza virus-like vaccine particles in tobacco.

SummaryInfluenza virus‐like particles (VLPs) have been shown to induce a safe and potent immune response through both humoral and cellular responses. They represent promising novel influenza vaccines. Plant‐based biotechnology allows for the large‐scale production of VLPs of biopharmaceutical interest using different model organisms, including Nicotiana benthamiana plants. Through this platform, influenza VLPs bud from the plasma membrane and accumulate between the membrane and the plant cell wall. To design and optimize efficient production processes, a better understanding of the plant cell wall composition of infiltrated tobacco leaves is a major interest for the plant biotechnology industry. In this study, we have investigated the alteration of the biochemical composition of the cell walls of N. benthamiana leaves subjected to abiotic and biotic stresses induced by the Agrobacterium‐mediated transient transformation and the resulting high expression levels of influenza VLPs. Results show that abiotic stress due to vacuum infiltration without Agrobacterium did not induce any detectable modification of the leaf cell wall when compared to non infiltrated leaves. In contrast, various chemical changes of the leaf cell wall were observed post‐Agrobacterium infiltration. Indeed, Agrobacterium infection induced deposition of callose and lignin, modified the pectin methylesterification and increased both arabinosylation of RG‐I side chains and the expression of arabinogalactan proteins. Moreover, these modifications were slightly greater in plants expressing haemagglutinin‐based VLP than in plants infiltrated with the Agrobacterium strain containing only the p19 suppressor of silencing.