How can a cellulose protect a cell

Auxin has also been involved in the protection of stem cell niche from chilling stress-induced PCD in root tissues [ 59 ]. In normal conditions, auxin concentration in root stem cell niche is maximal in the quiescent center QC and follows a local gradient at the root tip.

This auxin distribution allows division of root stem cells and inhibits division of columella stem cell daughters CSCD , which are committed to differentiate. Chilling stress also perturbs the distribution of auxin; low auxin levels contribute to PCD of CSCD, which in turn re-establish an auxin maximum in the stem cell niche to protect root stem cells from division and DNA-damage induced by chilling stress [ 59 ].

These examples and our results show that auxin plays a role in promoting cell survival during specific developmental stages or in response to various external conditions. However, how auxin can inhibit cell death in these cases has not yet been unravelled. In the case of CBI-induced PCD, it is possible that auxin exerts its protective effect directly at the level of the cell wall. Auxin induces the expression of cell wall-wall related genes and stimulates trafficking of vesicles containing new cell wall material [ 60 , 61 ].

Auxin can also regulate a variety of cell wall modifying enzymes including expansins and pectin methylesterase to control cell elongation [ 61 , 62 ]. Regulation of cell elongation by auxin involves changes in the mechanical properties of the cell wall. Auxin can also reduce cell wall stiffness through demethylesterification of the pectin homogalacturonan as observed in the shoot apex of Arabidopsis thaliana prior to organ outgrowth [ 63 ].

Hence, it is possible that auxin-mediated changes in the mechanical properties of the cell wall limit the impact of CBI. We used AFM-based force spectroscopy to evaluate the effect of CBI and auxin on the mechanical properties of the cell wall of Arabidopsis suspension-cultured cells.

This technique is non-destructive and can be used in living cells. This showed that CBI caused a drastic decrease in cell wall stiffness.

This also demonstrated that the induced expression of cell wall genes in response to TA and IXB [ 22 , 26 ] was not sufficient to compensate for changes caused by CBI. Changes induced by treatment with 2,4-D seemed to overcome those induced by TA Fig. Overall, these results indicate that CBI and auxin treatments all reduce cell wall stiffness compared to control cells. Moreover, this data shows that auxin treatment does not enhance cell survival by restoring the cell wall rigidity in CBI-treated cells.

On the other side, the AFM data also suggests that the impacts of auxin treatment on the cell wall rigidity superseded at least partially those induced by CBI. Increased cell wall extensibility by auxin is generally required to stimulate rapid cell elongation. However, we observed that Arabidopsis cell cultures treated with auxin contained a high proportion of cells smaller than control cells Table 1 , indicating that cell elongation was reduced by auxin despite the decreased cell wall stiffness.

While auxin generally stimulates cell elongation, high auxin concentrations are inhibitory in root tissues [ 60 , 64 ]. It is possible that results obtained in dark-grown suspension cell cultures may partly mimic the effect observed in root tissues.

Recently, it was shown that increasing endogenous or exogenous levels of auxin in root tissues induced a transient apoplast alkalinisation that would be responsible for inhibiting root elongation [ 65 ].

As observed in roots, addition of exogenous auxin reduced cell elongation in Arabidopsis suspension cultured-cells Table 1. Similarly, inhibition of cellulose synthesis by TA and IXB also decreased cell elongation in Arabidopsis cells Table 1 and was previously shown to impair root growth in seedlings [ 22 , 25 , 33 ].

Interestingly, a biphasic change in pH was measured after TA treatment of Arabidopsis cell suspensions, with a short acidification period that was followed by a large alkalinisation [ 31 ]. It is possible that changes in pH by auxin and CBI contributed to the inhibition of cell growth observed in this study. Overall, these results demonstrate that decreased cell wall stiffness does not necessarily correlates with stimulation of cell elongation.

Our results indicate that the mode of action of auxin in promoting cell survival in CBI-treated cells is clearly not limited to changes in cell wall mechanical properties. Several other possibilities will need to be explored to fully understand how auxin protects against CBI.

For instance, it was shown that induction of cell wall defects by IXB perturbed the polarized localization of auxin PIN transporters, thus altering polarized auxin transport [ 66 ]. Cellulose synthesis is governed by microtubules, which control the orientation of CSC movement directing the orientation of cellulose microfibrils.

In addition, microtubules appear to control PIN polarity in a cell specific manner [ 67 ]. Therefore, perturbation of cellulose synthesis may compromise microtubule stability, altering PIN localization and inhibiting cell elongation [ 67 ]. Since auxin can itself enhance expression of PIN transporters and re-establish their polarized localization [ 68 , 69 , 70 , 71 ], auxin treatment can potentially restore auxin transport that was perturbed by cell wall defects.

Restoration of PIN localization may stabilize their association with CSCs, which could in turn partially restore cell wall integrity by resuming cell wall synthesis. This hypothesis could also explain why the auxin-mediated decrease in cell wall stiffness seemed to override that induced by CBI. Microtubules appear to work together with actin filaments to maintain auxin fluxes and establish auxin maxima.

Therefore, changes in the configuration of the actin cytoskeleton may also play a role in the auxin-mediated protection against CBI. The induction of cell wall defects by IXB can stimulate actin bundling [ 43 ] which is an early and essential event in PCD [ 72 ]. Auxin treatment can restore normal actin configuration [ 73 , 74 ]. It was shown by Chang et al. The protective effect of auxin would rely on modifications of the level of actin organization and its interaction with the plasma membrane [ 75 ].

Hence, it is possible that auxin prevents cell death induced by CBI by restoring a normal actin configuration that in turn would stabilize the plasma membrane - cell wall - cytoskeleton continuum. For both CBIs, initiation of cell death depended on an increase in cytosolic calcium originating from external and internal sources, which shows that calcium is involved at an early step in the signaling cascade leading to CBI-induced PCD.

These findings support work by others who showed that specific development- or defense-related PCDs can be inhibited by auxin. Auxin may also protect cells from CBI-induced cell death by inducing changes in the cell wall composition and organization to compensate for reduced cellulose synthesis. Further investigation will be required to evaluate these possibilities. Arabidopsis thaliana accession Landsberg erecta cell suspension cultures were graciously provided by Dr.

All chemicals were purchased from Sigma Aldrich unless otherwise indicated. Thaxtomin A TA was prepared as described before [ 30 ]. The same volume of methanol less than 0. These chemicals were added at the final concentration indicated in each experiment. Calcium inhibitors ruthenium red RR and lanthanum chloride LaCl 3 were diluted in water and filtered. Cell death was assessed using trypan blue staining as described before [ 30 ]. For each condition, at least cells in groups of were counted.

Each experiment was repeated at least three times. Cell dimensions were determined using Fiji software [ 37 ] by measuring the length of cells per condition from three independent experiments. AFM analysis was conducted in contact mode as described before [ 41 ]. MLCT cantilevers A with a nominal spring constant of 0. For this cantilever we typically obtain a spring constant ranging from 0.

All studies were carried at room temperature. We used 3 to 4 cells per experiment. Each experiment was repeated 3 times. Statistical analysis was performed with GraphPad Prism 7. For cell death assay and measurements, cells were counted in groups of and the mean was calculated from 3 to 15 replicates. Cosgrove DJ. Growth of the plant cell wall. Nat Rev Mol Cell Biol. Keegstra K. Plant cell walls. Plant Physiol. Plant cell wall extensibility: connecting plant cell growth with cell wall structure, mechanics, and the action of wall-modifying enzymes.

J Exp Bot. Diffuse growth of plant cell walls. The cell biology of cellulose synthesis. Annu Rev Plant Biol. Cellulose biosynthesis inhibitors - a multifunctional toolbox. Highly methyl esterified seeds is a pectin methyl esterase involved in embryo development.

Curr Biol. Pectin biosynthesis is critical for cell wall integrity and immunity in Arabidopsis thaliana. Plant Cell. Three pectin methylesterase inhibitors protect cell wall integrity for Arabidopsis immunity to Botrytis.

Brabham C, Debolt S. Chemical genetics to examine cellulose biosynthesis. Front Plant Sci. Interaction between pathogenic streptomycetes and plants: the role of thaxtomins. Plant-Microbe Interactions: Research Signpost; — Google Scholar. Potato common scab: a review of the causal pathogens, management practices, varietal resistance screening methods, and host resistance. Am J Potato Res. Article Google Scholar. Correlation of phytotoxin production with pathogenicity of Streptomyces scabies isolates from scab infected potato tubers.

Am Potato J. Thaxtomin biosynthesis: the path to plant pathogenicity in the genus Streptomyces. Antonie Van Leeuwenhoek. An Arabidopsis mutant resistant to thaxtomin a, a cellulose synthesis inhibitor from Streptomyces species. Chemistry of phytotoxins associated with Streptomyces scabies , the causal organism of potato common scab.

J Agric Food Chem. Induction of common scab symptoms in aseptically cultured potato tubers by the vivotoxin, thaxtomin. The cellobiose sensor CebR is the gatekeeper of Streptomyces scabies pathogenicity. Pathogenicity of Streptomyces scabies mutants altered in thaxtomin a production. The txtAB genes of the plant pathogen Streptomyces acidiscabies encode a peptide synthetase required for phytotoxin thaxtomin a production and pathogenicity.

Mol Microbiol. Thaxtomin a affects CESA-complex density, expression of cell wall genes, cell wall composition, and causes ectopic lignification in Arabidopsis thaliana seedlings. Reduced cellulose synthesis invokes lignification and defense responses in Arabidopsis thaliana. Plant J. The Arabidopsis mutant cev1 links cell wall signaling to jasmonate and ethylene responses.

Cell wall integrity controls root elongation via a general 1-aminocyclopropanecarboxylic acid-dependent, ethylene-independent pathway. Duval I, Beaudoin N.

Transcriptional profiling in response to inhibition of cellulose synthesis by thaxtomin a and isoxaben in Arabidopsis thaliana suspension cells. Plant Cell Rep. Resistance against herbicide isoxaben and cellulose deficiency caused by distinct mutations in same cellulose synthase isoform CESA6.

Modifications of cellulose synthase confer resistance to isoxaben and thiazolidinone herbicides in Arabidopsis Ixr1 mutants. Enhanced resistance to the cellulose biosynthetic inhibitors, thaxtomin a and isoxaben in Arabidopsis thaliana mutants, also provides specific co-resistance to the auxin transport inhibitor, 1-NPA.

BMC Plant Biol. Thaxtomin a induces programmed cell death in Arabidopsis thaliana suspension-cultured cells. Auxin-induced resistance to common scab disease of potato linked to inhibition of thaxtomin a toxicity. Plant Dis. Plant cell growth and ion flux responses to the streptomycete phytotoxin thaxtomin a: calcium and hydrogen flux patterns revealed by the non-invasive MIFE technique.

Plant Cell Physiol. In this study, the researchers used a coarse-grained computer model at the level of the polymers that make up the cell wall — the strings of cellulose and other sugar molecules that are linked together in long chains.

Instead of modeling individual atoms, the researchers represented cellulose microfibers and other components with chains of beads that behave like sticky springs, in order to replicate these components' physical properties.

The team specifically modeled layers of an onion cell wall so that they could compare their modeled values of mechanical characteristics to experiments they conducted with actual onion skins. New research by Penn State biologists models the plant cell wall and reveal's the molecular basis for its unique ability to expand without weakening or breaking. Credit: Penn State. The researchers determined that individual cellulose fibers align with and stick to each other, forming a network of bundles.

In this study, we clarified the roles of the various components in the plant cell wall and provide a quantitative framework for interpreting experiments used in plant research.

The insights from this study may be particularly useful in future work investigating how plants regulate their cell wall properties, which impacts the speed and the direction of their growth. Afterwards, microfibril is linked with xyloglucans XyG and pectic polysaccharides to form the cell wall complex network. Matrix polysaccharides not only cross-link microfibrils but also prevent the self association of new microfibrils into larger aggregates. XyG interacts with the formed microfibrils in the surface and also may be trapped inside them [ 36 ].

It has been observed that in primary walls, microfibrils linked to xyloglucan are smaller in diameter less chain per fiber than those in secondary walls. Besides, the binding between XyG and cellulose is known to weaken cellulose networks but increase their expansibility.

The XyG is bound differently to three cellulose microfibrils domains. The first is available to endoglucanases, the second has to be solubilized by concentrated alkali and a third XyG is neither enzyme accessible nor chemical [ 36 ].

According to this, the type of hydrolysis used to obtain the fractions of polysaccharides oligosaccharides in some assays results in products of different degree of polymerization, which is related to some specific biological functions in the cell.

In contrast to cellulose, pectic polysaccharides are synthesized in the Golgi apparatus of the plant cell, and then are secreted to the apoplastic space through vesicular compartment. Polysaccharides are transported from cis-face to trans-face of the Golgi where they are sorted and packaged into vesicles of the trans-Golgi network for transport to the plasma membrane. The movement of the vesicles containing the polymers is presumably along actin filaments that have myosin motors.

It is no clear, how the synthesis of the pectin polysaccharides is initiated or whether lipid or protein donors are involved. The possible modification of the pectic glycosyl residues may be esterification, O -mehtylation, acetylation and feruloylation by feruloyltransferases in some Chemopodiaceae species [ 16 ].

To complete the biosynthesis of polysaccharides, it is necessary the assembly of the transported elements to form the functional matrix. This event involves both enzymatic and non-enzymatic mechanisms in the apoplast [ 37 ]. The physicochemical properties existing in the wall are dependent on the hydrophobic and hydrophilic domains given by the water and solutes.

The hydrophobic domain is formed by the link of cellulose microfibrils to the hydrogen bonds that lead the exclusion of water from the interacting chains. The hydrophobic interactions may also be controlled by enzymes that diminish the branching of the xyloglucan linked to cellulose microfibrils such as xylosidases and glucanases [ 38 ].

Meanwhile, the hydrophilic domain of the wall is given by pectin polymers. Together, both domains contribute to the protoplast matrix medium leading the rearrangement of some polymers as the homogalacturonan. Linear homogalacturonans are synthesized in a highly methyl-esterified form in the Golgi and transported to the wall in membrane vesicles to be desesterified by wall localized pectin methylesterases.

The conversion of the HG from the methylesterified form to the negatively charged form has been associated with the decrease of growth [ 39 ]. The glycosiltransferases and hydrolases are enzymes localized in the Golgi apparatus and work together to produce the xyloglucan precursors.

Some changes take place after the synthesis of hemicelulloses in the Golgi. It has been shown that a specific apoplastic glycosidases are responsible for the trimming of new xyloglycan chains and this determines the heterogeneity of the polymer in the cell wall [ 6 ].

Hydrolases are likely to play an important role in determining hemicelluloses structures in the cell wall, and are coexpressed with polysaccharide biosynthetic enzymes. For detailed information about the cell wall related enzymes see [ 4 , 6 , 10 , 16 , 40 ].

In the last decades many biochemical approaches have enabled the identification and characterization of the structure of cell wall polymers and the enzymes involved in their biosynthesis. Beside classical molecular analyses, the development of Arabidopsis thaliana mutants has been a breakthrough to reveal specific functions of certain components of the wall. The advances in the determination of the structures of polymers through microscopy provide one of the best views of the organization and structure allowing the development of different plant cell wall models.

Immunolocalization studies also have shown the location of some polysaccharides within the cell wall and in the apoplastic region. For instance, low methyl-esterified HGs are located in the middle lamella at the cell corners and around air spaces, whereas high methyl-esterified HGs are present throughout the cell wall [ 20 ]. Therefore, non-destructive methodologies such as NMR have been key techniques for elucidating the topology, dynamic and tridimensional arrangement of some cell structures, contributing to the cell wall knowledge.

Exhaustive studies on the structure and function of the plant cell wall have led to the discovery of biologically active molecules derived from its polymeric carbohydrate components. These molecules are found in nature and can be released by acid, basic or enzymatic hydrolysis of the primary cell wall polysaccharides.

Due to the complex combination of carbohydrate polymers in the cell wall of plants, there are variations among the physicochemical structure of hydrolyzed fragments, which exerts striking differences on activity and specificity to regulate some physiological processes in plants.

These plant oligosaccharides with regulatory properties were called oligosaccharins and have been extensively studied by the workgroup of Albersheim since the mids reviewed in [ 41 ]. Among the oligosaccharins derived from plants, the most active and therefore the most studied are those derived from pectins and hemicelluloses, whose main regulatory functions depend on the degree of polymerization, chemical composition and structure, and can be divided in two broad categories: activation of plant defense mechanisms and plant growth and development.

In order to exert their regulatory properties, oigosaccharins must be first recognized by specific plant cell receptors which may be lectin-type proteins capable of transmitting the signal into the cell [ 42 ]. Even when the complete recognition mechanisms and signaling pathway for plant-derived oligosaccharins is far from being fully understood, protein receptors that recognize these molecules have been characterized in the model plant Arabidopsis thaliana [ 43 - 44 ] and its believed the downstream processes may occur via MAP kinases activity [ 45 ] For review about the detailed perception mechanisms of oligosaccharines by plants, see [ 46 ].

Even when the most abundant component of pectins is the galacturonic acid, partial depolymerization of the pectic polysaccharides generates fragments that may or not contain other residues such as rhamnose, galactose, arabinose, xylose, glucose and mannose [ 20 ].

This combination confers variability to the structure, and thereby to the biological activity of the oligosaccharins. The oligosaccharins derived from homogalacturonan are called oligogalacturonides OGAs , which are linear oligomers of galacturonic acid, where some residues may be methyl-esterified or acetylated. OGAs are elicitors of defense responses in plants, triggering the synthesis and accumulation of phytoalexins antimicrobial compounds and other molecular indicators of the activation of defensive patterns, such as the induction of pathogenesis related proteins and genes related to the hypersensitive reaction [ 47 ].

OGA-induced defense response patterns are summarized in Table 1. OGAs trigger the rapid accumulation of reactive oxygen species ROS in plants, which is necessary for the deposition of callose, polysaccharide produced in response to wounding and pathogen infection.

Furthermore, ROS are signaling molecules of several intracellular events. Therefore it was proposed ROS were involved in the OGA-induced resistance against fungal pathogens in three different ways: 1 directly exerting a cytotoxic effect to the invading pathogen, 2 inducing callose deposition for reinforcing the plant cell wall, and 3 mediating the signals leading to the expression of defense related genes and defensive metabolites [ 48 ].

Nevertheless, recent findings in Arabidopsis thaliana showed that the defensive gene activation was not directly correlated to the accumulation of hydrogen peroxide, and that OGA-induced resistance against the fungal pathogen Botrytis cinerea was independent of both the oxidative burst and callose deposition [ 49 ].

Plants treated with OGAs exhibit an enhanced resistance to pathogen infections. In grapevine Vitis vinifera L. Some genes related to the formation of phytoalexins from the phenylpropanoid pathway were expressed rapidly and transient, various chitinase isoforms were expressed rapidly but their induction was more sustained, and some inhibitors of fungal hydrolytic enzymes were up-regulated later.

The degree of acetylation and methylation of OGAs has been less addressed but emerging research showed the influence of these functional group substituents on plant defense responses. The effect of the degree of acetylation of OGAs on the elicitation of defenses in wheat Triticum aestivum L.

It was found both acetylated and unacetylated OGAs induced accumulation of hydrogen peroxide at the site of fungal penetration, through activation of oxalate oxidase, which is also related to the enhanced peroxidase activity.

Besides, the induction of lipoxigenase activity demonstrated the stimulation of the octadecanoid pathaway. Moreover, transgenic strawberries Fragaria vesca L. Table 1 shows that OGAs modulate diverse growth and developmental processes in plants. Calcium ions are very important second messengers in plants and its level in intracellular compartments is determinant for the kind of physiological response.

OGAs regulate morphogenesis in plant tissues in a process associated with the action of auxins, which are growth-regulating phytohormones.

Particularly, OGAs and auxins appear to play an antagonist role; since OGAs inhibit the expression of some auxin-inducible genes steps downstream of the auxin perception [ 58 ]. In this sense, root differentiation induced by OGAs was studied in Arabidopsis thaliana seedlings, where treatments decreased trichoblasts length but increased the number and length of root hairs [ 59 ]. Similar results were found in maize Zea mays L. The growth inhibitory activity exerted by OGAs seems to be caused by 1 inhibition of cell elongation; since cell division in the primary root meristem is not altered [ 59 ] and 2 inactivation of a kinase enzyme implicated in the TOR signaling pathway, which integrates nutrient and growth factor signals in eukaryotic cells [ 60 ].

Interestingly, the structure and stimulating activity of a rhamnogalacturonan I-derived oligosaccharide RG-IO isolated from flowers of Nerium indicum Mill. The structural features of the oligomer consisted in a rhamnogalacturonan backbone with several branches O -4 linked to L-rhamnose residues. To determine the structure of the branches the oligomer was partialy hidrolized and analyzed by mass spectrometry ESI-MS.

Furthermore, RG-IO stimulated in vitro the production of nitric oxide in macrophage cells. Removal of some side chains from RG-IO reduced nitric oxide production, pointing out the relevance of the branches for its biological activity. Xyloglucan is the main hemicellulosic component of the plant cell wall.

Biological effects of xyloglucan derivatives are related to the intrinsic physiological function of polymeric xyloglucan in plant cells, comprising the control of extensibility and mechanics of the cell wall and cell expansion.

Most research in this field highlights their regulatory activity on cell growth and elongation, which relies in the molecular size, distribution, and levels of substituted xylosyl units with galactosyl and fucosyl residues [ 63 ]. It has been observed active xyloglucan oligomers XGOs accelerate cell elongation in peeled stem segments of Pisum sativum [ 64 ], and in suspension-cultured cells of Nicotiana tabacum , expansion led to cell division [ 65 ].

On the contrary, treatments with polymeric xyloglucan suppressed cell elongation [ 64 - 65 ], indicating that molecular size is a determinant factor of response specificity. In wheat immature embryos a xyloglucan-derived pentasaccharide induced rhizogenesis and stimulated the formation of callus and meristematic zones [ 66 ].