Pectin Medium Research Articles

Roles of Three FgPel Genes in the Development and Pathogenicity Regulation of Fusarium graminearum.

Fusarium head blight (FHB) is a devastating fungal disease caused by Fusarium graminearum. Pectin lyase, a pectinase, acts on the α-1,4-glycosidic linkage of galacturonic acid primarily by β-elimination. In this study, three pectin lyase genes (FgPel1, 2, 3) in F. graminearum were selected, and deletion mutants (ΔFgPel1, 2, 3) were constructed by homologous recombination for functional characterization. The gene deletions affected the morphology and growth rate of F. graminearum on pectin medium at various concentrations, with the growth rate of ΔFgPel1 being more significant. The growth of ΔFgPel1 colonies slowed at pH 4, with optimal growth at pH 6.5, whereas ΔFgPel2 and ΔFgPel3 exhibited greater inhibition at pH 8. Colony morphology and diameter of the deletion mutants showed no significant differences compared to the wild-type strain PH-1, and there was no effect on conidial production or germination rate. Pathogenicity assays demonstrated that gene deletion significantly reduced the ability of F. graminearum to infest corn silks and wheat ears, and that ΔFgPel2 showed a more pronounced reduction in pathogenicity on wheat spikes. In summary, the pectin lyase genes (FgPel1, 2, 3) are involved in pectin utilization and are influenced by external pH conditions, which attenuate the pathogenicity of F. graminearum without affecting its vegetative growth or asexual spore formation. These findings elucidate the roles of these genes and provide a basis for controlling FHB.

First report of Pseudomonas palleroniana causing potato soft rot in China.

Slimy potato (Solanum tuberosum) tubers with a foul-smelling odor were obtained from a potato field during harvest in Huize county (25.94°N; 103.40°E), Yunnan province, China in August 2021. The incidence of symptomatic potato tubers was approximately 5% while no symptoms were observed on potato stems. To isolate the causal agent, potato tubers were surface-disinfected and infected tissues were mashed in a 15 ml sterile centrifuge tube with 2 ml sterile distilled water. After a series of dilutions, a volume of 200 μl bacterial suspension from each dilution was spread on nutrient agar (NA) medium and incubated at 28 °C for 48 h. Single colonies randomly selected from NA plates were then picked and separately subcultured in nutrient broth (NB) medium. Pure cultures were acquired by successive streaking on NA medium. The colonies with irregular shapes were white and opaque (Fig. S1A). Among all the isolates, strain Q1 exhibited pectinolytic activity on inoculated potato tubers using a pin prick method with an inoculum concentration of 108 CFU/ml while no symptoms appeared for the control group using sterile water (Fig. S1B). However, no obvious pits were observed for strain Q1 when tested on crystal violet pectin (CVP) medium. To further identify the strain Q1, total DNA was extracted using the TaKaRa MiniBEST Bacteria Genomic DNA Extraction Kit. PCR amplification of 16S rDNA of strain Q1 was performed using the universal PCR primer pair 27F/1492R and followed by Sanger sequencing. The BLASTn analysis of the sequence (NCBI accession number ON631256) based on NCBI rRNA/ITS databases revealed 100% query coverage and 99.78% identity to the 16S rDNA sequences of type strain Pseudomonas tolaasii ATCC 33618 and Pseudomonas palleroniana CFBP 4389, respectively. Whole-genome sequencing of strain Q1 was then performed using the Illumina and Nanopore sequencing platform. A single contig (NCBI accession number CP092411) with a length of approx. 6.2 MB was obtained by de novo assembly using Raven (v1.5.1) (Vaser and Šikić 2021) and Pilon (v1.24) (Walker et al. 2014). The completeness and redundancy of this assembly was evaluated by BUSCO (v5.2.2) (Manni et al. 2021), and a score of 100% completeness indicated a high quality of the assembly. The genome sequence of strain Q1 was uploaded to the Type Strain Genome Server (TYGS) for a whole genome-based taxonomic analysis (Meier-Kolthoff and Göker 2019). The distance-based phylogeny revealed that strain Q1 is well clustered together with Pseudomonas palleroniana (Fig. S1C). Furthermore, a digital DNA-DNA hybridization (dDDH) value (86.9%) between strain Q1 and P. palleroniana was above the species boundary (≥70%), indicating that strain Q1 should be classified as P. palleroniana. In addition, P. palleroniana was re-isolated from potato tubers inoculated using a pin prick method with an inoculum concentration of 108 CFU/ml and was identified by morphological similarities and 16s rDNA sequencing described above, thus fulfilling Koch's postulates. Furthermore, aerial stem rot symptoms were observed after 3-5 days post inoculation of strain Q1 with a concentration of 108 CFU/ml on stems of young potato plants using a pin prick method (Fig. S1D). Notably, a couple of Pseudomonas spp. have been reported to cause soft rot in carrot (Godfrey and Marshall 2002) and melon (Zhang et al. 2016). To our knowledge, this is the first report of P. palleroniana causing soft rot on potato tuber in China.

Pectin induced transcriptome of a Rhizoctonia solani strain causing sheath blight disease in rice reveals insights on key genes and RNAi machinery for development of pathogen derived resistance.

RNAi mediated silencing of pectin degrading enzyme of R. solani gives a high level of resistance against sheath blight disease of rice. Rice sheath blight disease caused by Rhizoctonia solani Kuhn (telemorph; Thanatephorus cucumeris) is one of the most devastating fungal diseases which cause severe loss to rice grain production. In the absence of resistant cultivars, the disease is currently managed through fungicides which add to environmental pollution. To explore the potential of utilizing RNA interference (RNAi)-mediated resistance against sheath blight disease, we identified genes encoding proteins and enzymes involved in the RNAi pathway in this fungal pathogen. The RNAi target genes were deciphered by RNAseq analysis of a highly virulent strain of the R. solani grown in pectin medium. Additionally, pectin metabolism associated genes of R. solani were analyzed through transcriptome sequencing of infected rice tissues obtained from six diverse rice cultivars. One of the key candidate gene AG1IA_04727 encoding polygalacturonase (PG), which was observed to be significantly upregulated during infection, was targeted through RNAi to develop disease resistance. Stable expression of PG-RNAi construct in rice showed efficient silencing of AG1IA_04727 and suppression of sheath blight disease. This study highlights important information about the existence of RNAi machinery and key genes of R. solani which can be targeted through RNAi to develop pathogen-derived resistance, thus opening an alternative strategy for developing sheath blight-resistant rice cultivars.

HESPERIDIN HYDROGEL FORMULATION USING PECTIN-CHITOSAN POLYMER COMBINATION

Objective: Hesperidin is flavonoid glycosides that proven to have therapeutic activity to any desease, one of them is colon disease; but, its low solubility (< 100 mg/L) makes small absosption inside the body so it needs delivery system that could deliver hesperidin to the therapy target. The objective of this research is to get optimum formula from hydrogel with polimer pectin-chitosan combination that can control in vitro hesperidin release.Method: Optimum hydrogel formula determination using Design Expert 7.0.0 with factorial method design, resulted in formula plans with pectin-chitosan consentration comparison of (P3% : C1%), (P3% : C2%), (P5% : C1%), (P5% : C2%) respectively.Result: Optimum formula with pectin : chitosan concentration comparison (5% : 1%) has entrapment efficiency about 96.658%; k(/hour) swelling index at pH 5.0, 6.8, and 7.4, about 34.917, 15.766, and 8.146 respectively; drug release at pH 5.0, 6.8, and a medium contained 2% mouse’s caecum about 0.461, 20.116, and 52.955% respectively; and the mucoadhesive strength about 0.184 N/cm2.Conclusion: The combination of pectin-chitosan polymer in hydrogel muchoadhesive matrix can control hesperidin in vitro release with the drug release value at the highest concentration of pectin in medium contained 2% mouse’s saecum that could release drug about 56%. Hesperidin hydrogel release mechanism follows Higuchi kinetic.

Necrotizing Activity of Verticillium dahliae and Fusarium oxysporum f. sp. vasinfectum Endopolygalacturonases in Cotton.

Polygalacturonase (PG), which digests the pectin of plant cell walls, contributes to pathogenicity of fungi in plants. To explore the role of PG in pathogenicity of the fungal cotton pathogens Verticillium dahliae and Fusarium oxysporum f. sp. vasinfectum, VDPG1 and FOVPG1 were cloned and their expression in different cotton (Gossypium hirsutum) cultivars and media was analyzed. VDPG1 and FOVPG1 were strongly upregulated during infection. Purified VDPG1 and FOVPG1 play important roles in the symptom development of both resistant and susceptible cotton. Moreover, after inoculation with purified PGs, the hydroxyproline content of the cell walls increased in cotton seedlings, with resistant cultivar seedlings showing significantly higher hydroxyproline content than seedlings of the susceptible cultivar. PG gene expression analysis in different media showed that both PG genes were induced in pectin medium but not in glucose medium. This study highlighted the role of VDPG1 and FOVPG1 in pathogenicity and virulence, which were detected in fungus-inoculated cotton, suggesting that PGs play an important role in the pathogenicity of V. dahliae and F. oxysporum f. sp. vasinfectum.

Polygalacturonase production by AR2 pectinolytic bacteria through submerged fermentation of raja nangka banana peel (Musa paradisiaca var. formatypica) with variation of carbon source and pectin

Polygalacturonase (EC 3.1.2.15) catalyzes the hydrolysis of α-1,4-glycosidic bonds on galacturonic acid. Polygalacturonase can be produced from AR2 pectinolytic bacteria isolated from orange peel and vegetable waste. Commonly cost production of enzymes were high. However, with the advancement of technology, enzymes can now be manufactured at a low cost. Production of enzymes in low cost media with agro-industrial waste is interesting. Raja nangka banana peel is agro-industrial waste that is uneconomic. Therefore, this material can be used as a pectin source in polygalacturonase production. Polygalacturonase was produced by AR2 pectinolytic bacteria with the addition of various carbon sources (1% glucose, 1% galactose, 1% lactose) and variation of pectin concentrations (5%; 7.5%; 10%). This study used submerged fermentation with a cultivation temperature of 55°C and an agitation speed of 144 rpm for a 48-h incubation time. The results showed that variation of carbon sources and pectin concentrations affected the production of polygalacturonase. After 48 h fermentation, the results showed that the number of cells of samples ranged from 8.3 to 9.445 log cells/mL; the used pectin of samples ranged from 87.170-93.745%; and the polygalacturonase activity of samples ranged from 0.030 to 0.151 U/mL. The highest polygalacturonase activity was obtained by production of polygalacturonase on 1% glucose and 10% pectin medium.

Polygalacturonase gene pgxB in Aspergillus niger is a virulence factor in apple fruit.

Aspergillus niger, a saprophytic fungus, is widely distributed in soil, air and cereals, and can cause postharvest diseases in fruit. Polygalacturonase (PG) is one of the main enzymes in fungal pathogens to degrade plant cell wall. To evaluate whether the deletion of an exo-polygalacturonase gene pgxB would influence fungal pathogenicity to fruit, pgxB gene was deleted in Aspergillus niger MA 70.15 (wild type) via homologous recombination. The ΔpgxB mutant showed similar growth behavior compared with the wild type. Pectin medium induced significant higher expression of all pectinase genes in both wild type and ΔpgxB in comparison to potato dextrose agar medium. However, the ΔpgxB mutant was less virulent on apple fruits as the necrosis diameter caused by ΔpgxB mutant was significantly smaller than that of wild type. Results of quantitive-PCR showed that, in the process of infection in apple fruit, gene expressions of polygalacturonase genes pgaI, pgaII, pgaA, pgaC, pgaD and pgaE were enhanced in ΔpgxB mutant in comparison to wild type. These results prove that, despite the increased gene expression of other polygalacturonase genes in ΔpgxB mutant, the lack of pgxB gene significantly reduced the virulence of A. niger on apple fruit, suggesting that pgxB plays an important role in the infection process on the apple fruit.

In Vitro Fermentation of Xylooligosaccharides Produced from Miscanthus × giganteus by Human Fecal Microbiota.

Purified xylooligosaccharides from Miscanthus × giganteus (M×G XOS) were used in an in vitro fermentation experiment inoculated with human fecal microbiota. A commercial XOS product and pectin were used as controls. Decreases in pH by 2.3, 2.4, and 2.0 units and production of short-chain fatty acids (SCFA; acetic acid, 7764.2, 6664.1, and 6387.9 μmol/g; propionic acid, 1006.7, 1089.5, and 661.5 μmol/g; and butyric acid, 955.5, 1252.9, and 917.7 μmol/g) were observed in M×G XOS, commercial XOS, and pectin medium after 12 h of fermentation, respectively. Titers of Bifidobacterium spp., Lactobacillus spp., and Escherichia coli increased when fed all three substrates as monitored by qPCR. There was no significant trend for Clostridium perfringens. During fermentation, M×G XOS was statistically equivalent in performance to the commercial XOS sample as measured by culture acidification and growth of health-promoting bacteria and resulted in the highest SCFA production among the three substrates.

Extracellular Xylanolytic and Pectinolytic Hydrolase Production by Aspergillus flavus Isolates Contributes to Crop Invasion.

Several atoxigenic Aspergillus flavus isolates, including some being used as biocontrol agents, and one toxigenic isolate were surveyed for the ability to produce extracellular xylanolytic and pectinolytic hydrolases. All of the tested isolates displayed good production of endoxylanases when grown on a medium utilizing larch xylan as a sole carbon substrate. Four of the tested isolates produced reasonably high levels of esterase activity, while the atoxigenic biocontrol agent NRRL 21882 isolate esterase level was significantly lower than the others. Atoxigenic A. flavus isolates 19, 22, K49, AF36 (the latter two are biocontrol agents) and toxigenic AF13 produced copious levels of pectinolytic activity when grown on a pectin medium. The pectinolytic activity levels of the atoxigenic A. flavus 17 and NRRL 21882 isolates were significantly lower than the other tested isolates. In addition, A. flavus isolates that displayed high levels of pectinolytic activity in the plate assay produced high levels of endopolygalacturonase (pectinase) P2c, as ascertained by isoelectric focusing electrophoresis. Isolate NRRL 21882 displayed low levels of both pectinase P2c and pectin methyl esterase. A. flavus appears capable of producing these hydrolytic enzymes irrespective of aflatoxin production. This ability of atoxigenic isolates to produce xylanolytic and pectinolytic hydrolases mimics that of toxigenic isolates and, therefore, contributes to the ability of atoxigenic isolates to occupy the same niche as A. flavus toxigenic isolates.

Cellulolytic and Pectinolytic Enzymes of Some Selected Heat Resistant Fungi

Ten heat resistant fungi, Arthrinium sp., Aspergillus cejpii, A. nidulans, A. spinosus, Byssochlamys nivea, Hamigera avellanea, Talaromyces trachyspermus, T. barcinensis, T. ucrainicus, and Trichoderma asperellum were tested on their ability to produce cellulolytic and pectinolytic enzymes. Except for B. nivea and A. cejpii, all species secreted cellulolytic enzymes in the used cup plate assay. All isolates produced considerable levels of pectinolytic enzymes, when investigated on a liquid pectin medium. The appearance of unexpected blue color in the pectin medium for some species was discussed, but further investigation is required to elucidate this phenomenon.

The Components and Activities of Flax-Degumming Enzymes Produced by <i>Bacillus licheniformis</i> HDYM-03

Bacillus licheniformis HDYM-03 was isolated from flax-retting water. In this research, the production of flax-degumming enzymes by this strain was investigated in four medium, whose sole carbon source was beef extract peptone (BP), pectin (PEC), konjac powder (KGM) and carboxymethylcellulose sodium (CMC), respectively. In PEC medium, the production of pectinase (455.06 U/mL) and polygalacturonase (540.32 U/mL) is higher than that in other medium. In KGM medium, the mannanase reach the highest activity 193.33 U/mL. The production of xylanase and cellulase is extremely lower and could be ignored in all of the four medium. The results show that the production of flax-degumming enzymes by this strain could be significantly induced by flax colloid. B.licheniformis HDYM-03 suggest an applicable potential in flax-retting industry.

Carbon, nitrogen and pH regulate the production and activity of a polygalacturonase isozyme produced by Penicillium expansum

The influence of carbon, nitrogen and pH on polygalacturonase (PG) activity produced by Penicillium expansum were investigated. P. expansum mycelial growth was greatest on lyophilized lyophilised fruit tissue and the highest PG activity occurred in apple pectin medium. Nitrogen source influenced PG activity and was highest with ammonia while the greatest mycelial mass was supported by glutamate or glutamine. PG activity and mycelial mass peaked 5 five days after inoculation as polyuronide content decreased and the pH and ammonium levels increased in apple pectin medium. A single active PG isozyme with an isoelectric point of ∼7.6 was produced in apple pectin medium and a partial cDNA clone was obtained that was most homologous to the pggII gene from Penicillium. griseoroseum. The results from this study indicate that P. expansum can modulate the activity of PG in response to nutrient sources and ambient pH through signalling pathways that modulate nutrient acquisition, uptake and metabolism.

Characterization of hemicellulases from thermophilic fungi

The thermophilic fungi Thermomyces lanuginosus, Malbranchea cinnamomea, Myceliophthora fergusii and the thermotolerant Aspergillus terreus were cultivated on various carbon sources, and hemicellulolytic and cellulolytic enzyme profiles were evaluated. All fungi could grow on locust bean galactomannan (LBG), Solka floc, wheat bran and pectin, except T. lanuginosus, which failed to utilize LBG for growth. Different levels of cellulase and hemicellulase activities were produced by these fungal strains. Depending on the carbon source, variable ratios of thermostable hydrolytic enzymes were obtained, which may be useful in various applications. All strains were found to secrete xylanolytic and mannanolytic enzymes. Generally, LBG was the most efficient carbon source to induce mannanase activities, although T. lanuginosus was able to produce mannanase only on wheat bran as a carbon source. Xylanolytic activities were usually highest on wheat bran medium, but in contrast to other investigated fungi, xylanase production by M. fergusii was enhanced on pectin medium. Preliminary thermostability screening indicated that among the investigated species, thermotolerant glycosidases can be found. Some of the accessory activities, including the α-arabinosidase activity, were surprisingly high. The capability of the produced enzymes to improve the hydrolysis of lignocellulosic pretreated substrate was evaluated and revealed potential for these enzymes.

Isolating Tomato Rhizobacteria Using Root Exuding Pectin

Pectin is the major secretions of tomato rhizosphere.Four different kinds of pectin media(PM nutrient medium,PA medium with only a single pectin carbon source,oligotrophic medium YPP with pectin,and oligotrophic medium YPG without pectin) were applied to compare the ability in isolating tomato rhizosphere bacteria by plate technique and denaturing gradient gel electrophoresis(DGGE).The results showed that PA medium isolated up to 42 types of soil bacteria;YPP medium isolated the highest numbers of colonies among the four media,and lower types of bacteria than that by PA medium;YPG medium isolated lower quantities and species of bacteria than those by YPP medium.Clustering analysis also revealed that PA medium with pectin as the nutrition could isolate more bacteria than other media,and the bacteria community isolated by PA medium was most similar to that in natural environment.Therefore,adding pectin from tomato rhizosphere into the culture medium could increase the separative capacity of the medium.

The ThPG1 Endopolygalacturonase Is Required for the Trichoderma harzianum–Plant Beneficial Interaction

Considering the complexity of the in vivo interactions established by a mycoparasitic biocontrol agent at the plant rhizosphere, proteomic, genomic, and transcriptomic approaches were used to study a novel Trichoderma gene coding for a plant cell wall (PCW)-degrading enzyme. A proteome analysis, using a three-component (Trichoderma spp.-tomato plantlets-pathogen) system, allowed us to identify a differentially expressed Trichoderma harzianum endopolygalacturonase (endoPG). Spot 0303 remarkably increased only in the presence of the soilborne pathogens Rhizoctonia solani and Pythium ultimum, and corresponded to an expressed sequence tag from a T. harzianum T34 cDNA library that was constructed in the presence of PCW polymers and used to isolate the Thpg1 gene. Compared with the wild-type strain, Thpg1-silenced transformants showed lower PG activity, less growth on pectin medium, and reduced capability to colonize tomato roots. These results were combined with microarray comparative data from the transcriptome of Arabidopsis plants inoculated with the wild type or a Thpg1-silenced transformant (ePG5). The endoPG-encoding gene was found to be required for active root colonization and plant defense induction by T. harzianum T34. In vivo assays showed that Botrytis cinerea leaf necrotic lesions were slightly smaller in plants colonized by ePG5, although no statistically significant differences were observed.

Effect of rubber petiole cell walls and virulence of strains on secretion of pectic enzymes by <i>Pytophthora meadii</i>

The characteristics of the pectic enzyme polygalacturonase (PG) of Phytophthora meadii isolates from petioles of rubber (Hevea brasiliensis) genotypes were compared in relation to (i) aggressiveness (virulence) in infecting detached petioles of a susceptible rubber genotype (PB86) or (ii) in relation to the availability of purified rubber petiole cell walls (obtained from a Phytophthora-resistant clone, RRIC100) in the growth medium, as the sole carbon source. The four most highly aggressive isolates produced PG forms varying within mw 48-60 kDa, while, the highly aggressive MAD86 isolate produced two PG forms of mw 48 and 70 kDa. Moderately or weakly aggressive isolates produced PG forms within the range of 62-66 kDa. With rubber petiole cell walls in the growth medium, the four most highly aggressive isolates produced PG forms of mw 42-62 kDa, while, MAD86 produced a much smaller PG form of 21 kDa. Weak or moderately aggressive isolates produced similar PG forms in both cell wall and pectin media. Quite smaller PG molecules produced in rubber cell wall medium could be due to elicitor molecular fragments bound to rubber cell walls, which may induce P. meadii to secret specific PG forms via signal transduction pathway. None of the isolates produced pectin lyase (PL) in any growth medium. Neither PG nor PL activity was detected in P. meadii-infected petioles. Key Words: Cell wall degrading enzymes, resistance, Hevea brasiliensis, leaf disease doi: 10.4038/cjsbs.v36i2.485 Cey. J. Sci. (Bio. Sci.) 36 (2): 108-114, 2007

Utilization of Nutritional Compounds and Sclerotial Development of <i>Sclerotium Rolfsii</i> Isolated From <i>Elaeis Guineensis</i> and <i>Xanthosoma Mafaffa</i> in Ghana

Sclerotium rolfsii is a facultative soil parasite of economic importance causing disease of several economic crop plants. Bacterial and fungal parasites are themselves an assemblage of strains differing genetically and liable to variation. The possible effect of external nutrients on different S. rolfsii strains in Ghana has not been studied. In this study the utilization of twelve different nutritional compounds and sclerotia formation by five strains of Sclerotium rolfsii, SrXLL, SrXA1, SrXA2, SrEL1 and SrEL2 was investigated. In broth media with different carbon compounds - fructose, glucose, maltose, starch and sucrose - and with different nitrogen compounds - Ammonium chloride, Ammonium nitrate, Asparagine, Peptone and Sodium nitrate - a clearly discernible order of ability to utilize the two groups of compounds was noticed. The order of the strains in descending order of efficiency was SrEL2 > SrEL1 > SrXLL > SrXA1 > SrXA2. Among the carbon compounds the least utilized was starch. The best carbon compound varied with the strains. Peptone was universally a good nitrogen source. Over a concentration range of 0.5 to 2.0%, the greatest amount of pectolytic enzymes was produced in pectin media (20.0 per minute). Filtrates of strains SrXLL, SrXA1 and SrEL2 showed greater pectolytic enzymes activity than those of strains SrXA2 and SrEL1. But strains SrXA1 and SrXA2 showed greater ability to break down cellulose than the other three strains. In all the media studied the pH of the culture filtrate decreased to acidic levels at the end of incubation period. Journal of the Ghana Science Association Vol. 10 (2) 2008: pp. 116-128

Overexpression of a Gene Encoding a Catabolite Repression Element in Alternaria citri Causes Severe Symptoms of Black Rot in Citrus Fruit

ABSTRACT A gene (AcCreA) encoding a catabolite repression element (CreA) with (two zinc fingers of the Cys(2)His(2) type was isolated from the postharvest fungal pathogen Alternaria citri. The AcCreA overexpression mutant AcOEC2 of A. citri showed normal growth on pectin medium and on segments of peel or the juice sac area from citrus fruit. Production of endopolygalacturonase, an essential virulence factor of this pathogen, was similar in AcOEC2 and the wild type in pectin-containing media. However, addition of glucose to the medium showed that carbon catabolite repression of endopolygalacturonase gene (Acpg1) expression, as well as endopolygalacturonase production, was lost in AcOEC2. The wild-type strain of A. citri causes rot mainly in the central axis of citrus fruit without development of rotting in the juice sac area; however, AcOEC2 caused severe black rot symptoms in both the central axis and juice sac areas. These results indicate that AcCreA-mediated catabolite repression controls the virulence or infection of this pathogen, and that the wild-type A. citri does not cause symptoms in the juice sac area due to carbon catabolite repression by sugars in the juice of the juice sac area.

Overexpression of citrus polygalacturonase-inhibiting protein in citrus black rot pathogen Alternaria citri

The rough lemon (Citrus jambhiri) gene encoding polygalacturonase-inhibiting protein (RlemPGIPA) was overexpressed in the pathogenic fungus Alternaria citri. The overexpression mutant AcOPI6 retained the ability to utilize pectin as a sole carbon source, and the overexpression of polygalacturonase-inhibiting protein did not have any effect on the growth of AcOPI6 in potato dextrose and pectin medium. The pathogenicity of AcOPI6 to cause a black rot symptom in citrus fruits was also unchanged. Polygalacturonase-inhibiting protein was secreted together with endopolygalacturonase into culture filtrates of AcOPI6, and oligogalacturonides were digested from polygalacturonic acid by both proteins in the culture filtrates. The reaction mixture containing oligogalacturonides possessed activity for induction of defense-related gene, RlemLOX, in rough lemon leaves.

The life style of Aureobasidium pullulans and the multiple forms of its polygalacturonase

The life style of Aureobasidium pullulans on pectin medium and its production of extracellular polygalacturonases are closely related. Polygalacturonases with random action pattern (EC 3.2.1.15) were formed in the first phases of cultivation, whereas exopolygalacturonases (EC 3.2.1.67) with terminal action pattern on pectin were produced during the whole growth of this yeast-like fungus. The production and inactivation of individual enzyme forms during cultivation were strongly dependent on the pH value of the pectin medium. Various kinds of stress can support the prolongation of the phase of endo-acting enzyme production, as well as the increase of their activity.