Plant protein inhibitors of cell wall degrading enzymes

Plant cell walls, which consist mainly of polysaccharides (i.e. cellulose, hemicelluloses and pectins), play an important role in defending plants against pathogens. Most phytopathogenic microorganisms secrete an array of cell wall degrading enzymes (CWDEs) capable of depolymerizing the polysaccharides in the plant host wall. In response, plants have evolved a diverse battery of defence responses including protein inhibitors of these enzymes. These include inhibitors of pectin degrading enzymes such as polygalacturonases, pectinmethyl esterases and pectin lyases, and hemicellulose degrading enzymes such as endoxylanases and xyloglucan endoglucanases. The discovery of these plant inhibitors and the recent resolution of their three-dimensional structures, free or in complex with their target enzymes, provide new lines of evidence regarding their function and evolution in plant-pathogen interactions.     

Cell elongation and metabolic turnover of the cell wall as affected by auxin and cell wall degrading enzymes

A cell wall fraction (pectic substances) of oat coleoptile segmentsfed with ¹⁴C-glucose contained more radioactivity under theeffect of auxin than did the control. When labeled segmentswere grown for 6 hr in auxin or glucanase solution the labelin the hemicellulose fraction decreased as growth increased.ß-1,3-Glucanase prepared from the culture of a fungus,Sclerotinia libertiana, induces elongation of segments of thepea stem and the oat coleoptile. Traces of cellulase and pectinmethylesterase contaminating the enzyme preparation are notresponsible for the stimulatory effect. Cellulase seemed tobe rather inhibitory and pectin methylesterase showed only aslight effect on coleoptile elongation. A possible relationshipbetween the metabolic turnover of hemicellulosic polysaccharideand cell wall extension is suggested. (Received February 5, 1968; )     

Regenerated cell wall of carrot protoplasts isolated from suspension-cultured cells

Protoplasts of Daucus carota L. cultured in a synthetic liquid medium resumed cell division after about 4 days of cultivation. During this lag period, nucleic acid and protein showed only slight increases but the protoplasts commenced cell-wall regeneration soon after the removal of lytic enzymes. The originally spherical protoplasts became ellipsoidal before they underwent division. Radioactive glucose and myo-inositol were readily utilized by the protoplasts. Most of the radioactivity, however, appeared in extracellular polysaccharides and only a small portion was deposited in the regenerated wall. The sugar composition of new cell wall, as studies by chemical analysis and incorporation of labelled precursors, was shown to be considerably different from that of normal cell wall.     

Heterogeneity and cell type-specific localization of a cell wall glycoprotein from carrot suspension cells

EP1, an extracellular protein from carrot (Daucus carota) cell suspensions, has been partially characterized by means of an antiserum and a cDNA clone. In both embryo and suspension cultures different molecular mass EP1 proteins were detected, some of which (31, 32, 52, and 54 kilodaltons) were bound to the cell wall and released into the medium, whereas others (49, 60, and 62 kilodaltons) were more firmly bound to the cell wall and could be extracted with a salt solution. Immunoprecipitation of in vitro translation products revealed a single primary translation product of 45 kilodaltons, suggesting that EP1 heterogeneity is due to differential posttranslational modification. In seedlings organ-specific modification of EP1 proteins was observed, a phenomenon which did not persist in suspension cultures initiated from different seedling organs. In culture EP1 proteins were only found to be associated with vacuolated, nonembryogenic cells, and on these cells they were localized in loosely attached, pectin-containing cell wall material. Purified 52/54 kilodaltons EP1 proteins did not alleviate the inhibitory effect of the glycosylation inhibitor tunicamycin on somatic embryogenesis.     

Arsenal of plant cell wall degrading enzymes reflects host preference among plant pathogenic fungi

Background  

The discovery and development of novel plant cell wall degrading enzymes is a key step towards more efficient depolymerization of polysaccharides to fermentable sugars for the production of liquid transportation biofuels and other bioproducts. The industrial fungus Trichoderma reesei is known to be highly cellulolytic and is a major industrial microbial source for commercial cellulases, xylanases and other cell wall degrading enzymes. However, enzyme-prospecting research continues to identify opportunities to enhance the activity of T. reesei enzyme preparations by supplementing with enzymatic diversity from other microbes. The goal of this study was to evaluate the enzymatic potential of a broad range of plant pathogenic and non-pathogenic fungi for their ability to degrade plant biomass and isolated polysaccharides.     

AepA of Pectobacterium is not involved in the regulation of extracellular plant cell wall degrading enzymes production

Plant cell wall degrading enzymes (PCWDE) are the major virulence determinants in phytopathogenic Pectobacterium, and their production is controlled by many regulatory factors. In this study, we focus on the role of the AepA protein, which was previously described to be a global regulator of PCWDE production in Pectobacterium carotovorum (Murata et al. in Mol Plant Microbe Interact 4:239–246, 1991). Our results show that neither inactivation nor overexpression of aepA affects PCWDE production in either Pectobacterium atrosepticum SCRI1043 or Pectobacterium carotovorum subsp. carotovorum SCC3193. The previously published observation based on the overexpression of aepA could be explained by the presence of the adjacent regulatory rsmB gene in the constructs used. Our database searches indicated that AepA belongs to the YtcJ subfamily of amidohydrolases. YtcJ-like amidohydrolases are present in bacteria, archaea, plants and some fungi. Although AepA has 28% identity with the formamide deformylase NfdA in Arthrobacter pascens F164, AepA was unable to catalyze the degradation of NdfA-specific N-substituted formamides. We conclude that AepA is a putative aminohydrolase not involved in regulation of PCWDE production.     

Plasmalemma patch clamp experiments in plant root cells: procedure for fast isolation of protoplasts with minimal exposure to cell wall degrading enzymes

Summary A convenient and rapid isolation procedure for root cell protoplasts suitable for patch clamp experiments, was developed for root cells of tomato (Lycopersicon esculentum) andPlantago species, grown on hydroculture. The procedure is based on a minimal exposure of cells to cell wall degrading enzyme mixtures. After an incubation period of 30 min in a cell wall degrading enzyme mixture all free floating cells were discarded. Subsequently the root material was rinsed and a second group of cells, still present inside the tissue, was freed by application of mechanical pressure. The newly released protoplasts were filtered and collected on the glass bottom of a patch clamp dish. The bathing medium was rinsed extensively removing cellulose fibrils and protoplasts not attached to the glass. Removal of these cellulose fibrils significantly improved the seal success ratio. The isolated protoplasts were suitable for patch clamp experiments in the cell-attached patch, the whole cell and the isolated patch configuration.Abbreviations BSA bovine serum albumin - BTP bis-tris propane - CAP cell-attached patch - OOP outside out patch - PEG polyethylene glycol - WC whole cell     

Callus culture as substrate for the production of specific cell wall degrading enzymes for derived protoplast isolation

Callus culture of spruce (Picea excelsa LINK) appears to be a suitable substrate for the fungusTrichoderma reesei to produce an efficient extracellular lytic system for protoplast isolation. In comparison with Onozuka R-10 cellulase, a yield of protoplasts from the spruce callus 2·5 higher was obtained. Another testea commercial cellulase DK was less efficient. The addition of Macerozyme R–10 significantly enhanced release of protoplasts within all tested enzyme preparations. No difference in the viability of protoplasts has been observed.     

Screening for microorganism with cell wall lytic activity to produce protoplast-forming enzymes

Several different bacteria and fungi capable of degrading yeast cell walls were isolated in the course of a screening programme. One Streptomyces and one Acremonium strain were found to degrade yeast cell walls extremely well. Both isolates produced enzymes in liquid culture that could be used for protoplasting of Sporobolomyces salmonicolor (DSM 70851) and Rhodotorula rubra (DSM 70403). This fact is quite remarkable as, so far, S. salmonicolor could not be protoplasted by commercially available enzymes. Correspondence to: W. Kaul     

Selection of a Streptomyces strain able to produce cell wall degrading enzymes and active against Sclerotinia sclerotiorum

Control of plant pathogen Sclerotinia sclerotiorum is an ongoing challenge because of its wide host range and the persistence of its sclerotia in soil. Fungicides are the most commonly used method to control this fungus but these can have ecotoxicity impacts. Chitinolytic Streptomyces strains isolated from Brazilian tropical soils were capable of inhibiting S. sclerotiorum growth in vitro, offering new possibilities for integrated pest management and biocontrol, with a new approach to dealing with an old problem. Strain Streptomyces sp. 80 was capable of irreversibly inhibiting fungal growth. Compared to other strains, its crude enzymes had the highest chitinolytic levels when measured at 25°C and strongly inhibited sclerotia from S. sclerotiorum. It produced four hydrolytic enzymes involved in fungal cell wall degradation when cultured in presence of the fungal mycelium. The best production, obtained after three days, was 0.75 U/ml for exochitinase, 0.9 U/ml for endochitinase, 0.16 U/ml for glucanase, and 1.78 U/ml for peptidase. Zymogram analysis confirmed two hydrolytic bands of chitinolytic activity with apparent molecular masses of 45.8 and 206.8 kDa. One glucanase activity with an apparent molecular mass of 55 kDa was also recorded, as well as seven bands of peptidase activity with apparent molecular masses ranging from 15.5 to 108.4 kDa. Differential interference contrast microscopy also showed alterations of hyphal morphology after co-culture. Streptomyces sp. 80 seems to be promising as a biocontrol agent against S. sclerotiorum, contributing to the development of new methods for controlling plant diseases and reducing the negative impact of using fungicides.     

Production of fungal cell wall degrading enzymes by a biocontrol strain of Bacillus subtilis AF 1

Fungal cell wall degrading chitinases and glucanases attained significance in agriculture, medicine, and environment management. The present study was conducted to describe the optimum conditions required for the production of beta-1,4-N-acetyl glucosaminidase (NAGase) and beta-1,3-glucanase by a biocontrol strain of Bacillus subtilis AF 1. B. subtilis AF 1 was grown in minimal medium with colloidal chitin (3.0%) and yeast extract (0.3% YE ) and incubated at pH 7.0 and 30 degrees C on constant shaker at 180 rpm for 6 days produced highest amounts of NAGase. Presence of 0.5 mM of phenyl methyl sulfonyl fluoride (PMSF) and 0.04% of Tween 20 further improved the enzyme production. B. subtilis AF 1 grown in minimal medium with laminarin (1%) and yeast extract (0.3%) for 3 days produced maximum amount of beta-1,3-glucanase. These conditions can be further scaled-up for large-scale production of NAGase and beta-1,3-glucanase by B. subtilis AF 1.     

The Rcs phosphorelay modulates the expression of plant cell wall degrading enzymes and virulence in Pectobacterium carotovorum ssp. carotovorum

Production of plant cell wall degrading enzymes, the major virulence factors of soft-rot Pectobacterium species, is controlled by many regulatory factors. Pectobacterium carotovorum ssp. carotovorum SCC3193 encodes an Rcs phosphorelay system that involves two sensor kinases, RcsC(Pcc) and RcsD(Pcc), and a response regulator RcsB(Pcc) as key components of this system, and an additional small lipoprotein RcsF(Pcc). This study indicates that inactivation of rcsC(Pcc), rcsD(Pcc) and rcsB(Pcc) enhances production of virulence factors with the highest effect detected for rcsB(Pcc). Interestingly, mutation of rcsF(Pcc) has no effect on virulence factors synthesis. These results suggest that in SCC3193 a parallel phosphorylation mechanism may activate the RcsB(Pcc) response regulator, which acts as a repressor suppressing the plant cell wall degrading enzyme production. Enhanced production of virulence factors in Rcs mutants is more pronounced when bacteria are growing in the absence of plant signal components.     

Influence of cell wall degrading enzymes on colonization of N2 fixing bacterium,Azorhizobium caulinodans in rice

In rice, nodule like structures were formed by inoculation of A. caulinodans combined with growth regulators and enzymes. Among the treatments, combination of cell wall degrading enzyme mixture and NAA with A. caulinodans induced more number of paranodules in rice. Total nitrogen content also increased in treated plants compared to uninoculated control.     

Pieiotropic effect of two cell wall mutants on the activity of some cell wall enzymes in the yeast Saccharomyces cerevisiae.

Summary The two mutants (abs) and (wal) affecting the cell morphology of yeast lead also to higher in vivo activities of the cell wall enzymes acid phosphatase. invertase and melibiase.The investigations were supported by a fellowship from the Max Kade Foundation New York.     

Levels of cell wall enzymes in endospores and vegetative cells of Bacillus subtilis

Vegetative bacilli and refractile endospores of Bacillus subtilis 168 were disrupted by homogenization with glass beads and fractionated by differential centrifugation. Most of the protein of endospores was particulate, whereas for bacilli most was soluble. Alanine racemase activity was sixfold higher in extract of endospores than in extract of bacilli and was particulate, whereas the enzyme from bacilli was soluble. The specific activities of seven other enzymes involved in peptidoglycan and teichoic acid biosynthesis were higher in extracts of bacilli than in those of endospores. The results suggest that restoration of activities of these seven enzymes to vegetative levels occurs during germination and outgrowth.     

Chronic desipramine treatment increases activity of noradrenergic postsynaptic cells

Chronic administration of tricyclic antidepressant drugs has been shown to exert multiple influences on various mechanisms of noradrenergic nervous systems. To determine the overall effect of these influences, this study examined the effect of long-term desipramine administration on the firing rate of noradrenergic postsynaptic neurons, specifically, those in the rat hippocampus that were inhibited by the nucleus locus coeruleus. Daily injections for 3 weeks of 5 or 10 mg/kg desipramine resulted in a 32% or 49% increase, respectively, of hippocampal cell activity, suggesting that long-term desipramine treatment is antagonistic to noradrenergic functions.     

Expression of the JIM8 cell wall epitope in carrot somatic embryogenesis

Certain single cells in carrot (Daucus carota L.) suspension cultures react with the monoclonal antibody JIM8, and it has been proposed that these cells represent a transitional stage in somatic embryo formation. Shortly after isolation of the single cells by sieving, up to 80% of the cells react with JIM8. Within 4 d, JIM8 labelling becomes restricted to 1% of the single cells. To obtain evidence for the proposed correlation between expression of the JIM8 cell wall epitope and somatic embryo formation the developmental fate of carrot single cells labelled with JIM8 was determined by cell tracking. The results, obtained by recording 43 000 cells, show that only few JIM8-labelled cells give rise to embryos, and most somatic embryos develop from cells devoid of the JIM8 cell wall epitope. We therefore conclude that the presence of the JIM8 cell wall epitope does not coincide with the ability of single suspension cells to form embryos.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - AGP arabino galactan protein - B5-0 Gamborg's B5 medium - B5-0.2 Gamborg's B5 medium supplemented with 0.2 M 2,4-D - FITC fluoresceïn isothiocyanate - PBS phosphate-buffered saline