Protect Host Plants Research Articles

Evaluation of antifungal, phosphate solubilisation, and siderophore and chitinase release activities of endophytic fungi from Pistacia vera

Fungal endophytes use different strategies to protect host plants from abiotic and biotic stress. In this study, we isolated endophytic fungi from Pistacia vera and characterised their antifungal activity against Aspergillus flavus, Rhizoctonia solani and Sclerotinia sclerotiorum, and their release of some factors that can alter plant growth capability. Trichoderma harzianum TH 5-1-2, T. harzianum TH 10-2-2 and T. atroviride TA 2-2-1 exhibited the highest growth inhibition percentages in dual culture assays against A. flavus, R. solani and S. sclerotiorum, respectively. Among the fungal endophyte cultures, ethyl acetate extracts of T. harzianum TH 10-2-2, T. harzianum TH 5-1-2 and T. atroviride TA 2-2-1 exhibited the highest growth inhibition of S. sclerotiorum, R. solani and A. flavus, respectively. Phosphate solubilisation was induced by Byssochlamys nivea BN 1-1-1 in culture. Large amounts of siderophore production were observed with Quambalaria cyanescens QC 11-3-2 and Epicoccum nigrum EN1, but Trichoderma spp. also produced siderophore in lower amounts. Trichoderma harzianum TH 5-1-2 produced the highest chitinase activity (2.92 U/mL). In general, among the endophytes isolated, Trichoderma spp. appear to have the most promise for promoting healthy growth of P. vera.

Endophytic fungi as novel sources of biopesticides: the Macaronesian Laurel forest, a case study

Endophytes fungi have been widely bioprospected to find new drugs and drug leads including antimicrobial agents and antifungals. However, an important role in host plant protection has been suggested for their presence and their metabolites. Therefore, nematicidal and insecticidal effects of their metabolites should be expected. In this review, the literature data available on insecicidal and nematicidal compounds identified from fungal endophytes are presented. Additionally we present a recent study on the endophytic biodiversity of a unique paleoflora, the Macaronesian laurel forest, in the light of their role in plant protection.

Symbiosis with systemic fungal endophytes promotes host escape from vector-borne disease.

Plants interact with a myriad of microorganisms that modulate their interactions within the community. A well-described example is the symbiosis between grasses and Epichloë fungal endophytes that protects host plants from herbivores. It is suggested that these symbionts could play a protective role for plants against pathogens through the regulation of their growth and development and/or the induction of host defences. However, other endophyte-mediated ecological mechanisms involved in disease avoidance have been scarcely explored. Here we studied the endophyte impact on plant disease caused by the biotrophic fungus, Claviceps purpurea, under field conditions through (1) changes in the survival of the pathogen´s resistance structure (sclerotia) during overwintering on the soil surface, and (2) effects on insects responsible for the transportation of pathogen spores. This latter mechanism is tested through a visitor exclusion treatment and the measurement of plant volatile cues. We found no significant effects of the endophyte on the survival of sclerotia and thus on disease inocula. However, both pathogen incidence and severity were twofold lower in endophyte-symbiotic plants than in non-symbiotic ones, though when insect visits were prevented this difference disappeared. Endophyte-symbiotic and non-symbiotic plots presented different emission patterns of volatiles suggesting that they can play a role in this protection. We show a novel indirect ecological mechanism by which endophytes can defend host grasses against diseases through negatively interacting with intermediary vectors of the epidemic process.

Diversity and composition of rhizospheric soil and root endogenous bacteria in Panax notoginseng during continuous cropping practices.

Rhizobacteria and endophytic bacteria play important roles in protecting host plants from infection by phytopathogens, which cause soil-borne diseases and severely impair plant health. Panax notoginseng is negatively affected by continuous cropping and becomes vulnerable to attack by microbial pathogens. In the present study, culture-independent Illumina MiSeq was used to investigate root-endophytic and rhizospheric bacteria in response to continuous cropping of P. notoginseng. Numbers of rhizospheric bacteria decreased with continuous P. notoginseng cropping, while the effects of continuous cropping on endophytic bacteria were not statistically significant. Bacterial diversity was higher in healthy P. notoginseng rhizospheric soils and roots than in those of diseased P. notoginseng. The most dominant phyla detected during continuous cropping were Proteobacteria, Cyanobacteria, Actinobacteria, and Acidobacteria. The genera Pseudomonas, Rhodoplanes, Candidatus Solibacter, and Streptomyces were dominant in P. notoginseng rhizospheric soils and roots. Erwinia, Stenotrophomonas, Pseudomonas, and Sphingobium were specifically detected in relatively high proportions among root-rot rhizospheric bacteria and endogenous root bacteria in plants under continuous cropping, suggesting that they may be the pathogens responsible for the negative effects of continuous cropping on P. notoginseng. Based on canonical correspondence analysis of the bacterial communities that were identified from healthy plants and fallow soils, total phosphorus (P), pH, and organic soil matter exerted the greatest impacts upon bacterial community composition during continuous cropping. In general, continuous cropping practices for P. notoginseng and severe root-rot disease notably affected the community structure and the diversity of rhizospheric and root endophytic bacteria. Our study elucidated the ecological significance of microbial communities in healthy plant maintenance, and our results may inform biological control strategies during the continuous cropping of P. notoginseng.

Screening Arbuscular Mycorrhizal Fungi in Order to Select the Best for Alleviating Wilt Disease Complex of Capsicum

Arbuscular mycorrhizal fungi (AMF) play an important role in protection of host plant from infection by soil-borne plant pathogens. In the present study different AMF were tested for their ability to alleviate wilt disease complex of tomato caused by bacterial pathogen Ralstonia solanacearum, fungal pathogen Phytophthora capsici and root-knot nematode Meloidogyne incognita. Plant growth parameters like plant height, stem girth, biovolume index, root and shoot dry weight, total plant dry weight, disease index and mycorrhizal parameters like per cent root colonization and spore count in the root zone soil were evaluated. In general AMF inoculation increased plant growth parameters. Among 11 AMF screened, Glomus bagyarajii was found to be the best AMF in enhancing plant height, stem girth, total plant dry weight, mycorrhizal root colonization and most importantly exhibited least per cent disease index (50.20 %) as compared to control (82.14 %). The results show the potential of using G. bagyarajii for the biocontrol of wilt disease complex of capsicum.

Spraying of Leaf-Colonizing Bacillus amyloliquefaciens Protects Pepper from Cucumber mosaic virus.

Beneficial plant-associated bacteria protect host plants against pathogens, including viruses. However, leaf-associated (phyllosphere) bacteria have rarely been investigated as potential triggers of plant systemic defense against plant viruses. We found that leaf-colonizing Bacillus amyloliquefaciens strain 5B6 (isolated from a cherry tree leaf) protected Nicotiana benthamiana and pepper plants against Cucumber mosaic virus (CMV). In a field trial, treatment with strain 5B6 significantly reduced the relative contents of CMV coat protein RNA compared with the water control over a 3-year period, as revealed by quantitative reverse-transcription polymerase chain reaction. The expression of Capsicum annuum pathogenesis-related (PR) genes CaPR4, CaPR5, and CaPR10 was upregulated in field-grown pepper plants treated with strain 5B6. In addition, the accumulation of two naturally occurring viruses, Broad bean wilt virus and Pepper mottle virus, was reduced by foliar treatment with strain 5B6, which is similar to the results for benzothiadiazole treatment as a positive control. Taken together, the results suggest that strain 5B6 has strong potential for protecting plants against viruses by increasing defense priming of salicylic acid and jasmonic acid signaling in pepper under field conditions. This is the first report of the protection of a plant against viral diseases by foliar application of leaf-associated bacilli.

Transcriptome analysis of Glomus mosseae/Medicago sativa mycorrhiza on atrazine stress.

Arbuscular mycorrhizal fungi (AMF) protect host plants against diverse biotic and abiotic stresses, and promote biodegradation of various contaminants. In this study effect of Glomus mosseae/Medicago sativa mycorrhiza on atrazine degradation was investigated. It was observed that the atrazine degradation rates with any addition level in mycorrhizal treatments were all significantly higher than those in non- mycorrhizal treatments. When atrazine was applied at 20 mg kg−1, the removal efficiency was up to 74.65%. Therefore, G. mosseae can be considered as ideal inhabitants of technical installations to facilitate phytoremediation. Furthermore, a total of 10.4 Gb was used for de novo transcriptome assembly, resulting in a comprehensive data set for the identification of genes corresponding to atrazine stress in the AM association. After comparative analysis with edgeR, a total of 2,060 differential expressed genes were identified, including 570 up-regulated genes and 1490 down-regulated genes. After excluding ‘function unknown’ and ‘general function predictions only’ genes, 172 up-regulated genes were obtained. The differentially expressed genes in AM association with and without atrazine stress were associated with molecular processes/other proteins, zinc finger protein, intracellular/extracellular enzymes, structural proteins, anti-stress/anti-disease protein, electron transport-related protein, and plant growth associated protein. Our results not only prove AMF has important ecological significance on atrazine degradation but also provide evidence for the molecular mechanisms of atrazine degradation by AMF.

Plant Genotype Influences Mycorrhiza Benefits and Susceptibility to a Soil Pathogen

Abstract This study examines the role mycorrhizae may play in protecting host plants from a soil fungal pathogen. Asexual propagules of three Allium vineale genotypes were grown in the presence and absence of mycorrhizae and the pathogen, Sclerotium cepivorum (white rot), with some plants encountering the mycorrhizal fungi first and others encountering the pathogen first. A significant three-way interaction indicates plant genotypes vary in response to the combined effects of mycorrhizae and the pathogen, with the A. vineale genotype most resistant to the pathogen deriving the least growth benefit from mycorrhizae and the genotype most susceptible to the pathogen receiving the highest relative growth benefit from mycorrhizae, despite there being no difference in the level of mycorrhizal colonization among the plant genotypes. No evidence was found that the presence of mycorrhizae reduced the impact of the pathogen for the most susceptible plant genotype (B). These findings support the hypothesis the prima...

Chromium immobilization by extraradical mycelium of arbuscular mycorrhiza contributes to plant chromium tolerance

Arbuscular mycorrhizal (AM) fungi, as important plant mutualists, can protect host plants against environmental stresses, including heavy metal contaminations. It is generally accepted that improvement of plant P nutrition by AM symbiosis plays an important role in plant tolerance to heavy metals. In the present study, we tested if exogenous P amendment to the chromium (Cr) contaminated soil could match the positive effects of AM symbiosis on plant Cr tolerance for the highly mycorrhizal dependent plant—dandelion (Taraxacum platypecidum Diels.). Experimental results showed that P addition could not enhance plant growth as well as AM symbiosis did. AM fungi could immobilize Cr in mycorrhizal roots besides enhancing plant P acquisition. Cr distribution pattern in principal roots as revealed by synchrotron radiation micro-focused X-ray fluorescence (SR μ-XRF) analysis supported the stabilization of Cr in mycorrrihzal roots. Furthermore, by using a three-compartment cultivation system, we demonstrated that extraradical mycelium (ERM) could take up and transport Cr to mycorrhizal roots, but restrained Cr translocation from roots to shoots, and thus contributed to Cr immobilization in roots and relieved Cr phytotoxicity.

Bioelicitors Induce Association of Defence Enzymes with Cell Walls of Lycopersicum esculentum

AbstractCell walls of plants are complex structures impregnated with various proteins having wide array of functions. In this study, twenty‐eight proteins isolated from tomato cell walls were subjected to MALDI‐TOF MS followed by mass peak analysis using ORIGIN 6 software. The mass peaks subjected to MASCOT and ProFound databases for peptide mass fingerprinting led to the identification of 9 protein domains. These proteins were further classified according to their functions. Fruit extracts of A. indica could elicit induction, localization and functioning of peroxidase (POX) and polyphenol oxidase (PPO) and their isoenzymes in cell walls of Lycopersicum esculentum (tomato) against Pseudomonas syringae pv. tomato. The results revealed the possible involvement of cell wall‐bound proteins in defence of plants against the invading pathogens. A number of novel isoenzymes of both POX and PPO were found to be located in the cell walls of the plants treated with neem extract. Neem extract can induce accumulation and binding of isoenzymes to cell walls. These isoenzymes could possibly protect host plants against the invading pathogens.

Effects of 1-aminocyclopropane-1-carboxylate (ACC) deaminase-overproducing Sinorhizobium meliloti on plant growth and copper tolerance of Medicago lupulina

Rhizobia typically produce a lower level of ACC deaminase compared with free-living plant growth-promoting bacteria. While the endogenous rhizobial ACC deaminase is important in legume nodulation, it is not sufficient to protect host plants against environmental stresses. The main goal of this study was to assess the effects of a genetically engineered Sinorhizobium meliloti strain overproducing ACC deaminase, and its symbiotic performance in Medicago lupulina under copper stress conditions. The engineered strain was transformed with an exogenous acdS gene by triparental conjugation. A plant growth assay was conducted to assess its plant growth promotion ability under copper stress conditions. The expressions of antioxidant genes in these plants were analyzed using quantitative real-time PCR. Plants nodulated with the engineered strain showed a greater dry weight, a decreased ethylene level in roots, a higher total copper uptake but a lower level of copper translocation to aerial parts, as compared with the plants nodulated with the wild-type strain under copper stress conditions. These results were positively correlated with higher expression of antioxidant genes in the roots of these plants exposed to severe copper stress. The engineered strain could improve plant growth as well as copper tolerance of M. lupulina, and enhance the antioxidant defense system.

Structural Analyses of AC4 Protein of Sri Lankan Cassava Mosaic Virus

RNA silencing is one of the important phenomenon in plant defense mechanism, it actively protect host plants against viral infections. Existing viruses must have developed counter defense strategies to survive this arms race. Such counter defense strategy is the viral silencing suppressor (VSRs) which have been reported to directly interfere with the various steps leading to the interference of viral RNAs. Most identified VSRs are multifunctional, besides being RNA-silencing suppressors, they often perform essential roles by functioning as coat proteins, helper components for viral transmission, replicases and movement proteins, proteases or transcriptional regulators. One such identified VSR is AC4 of Sri Lankan cassava mosaic virus strain. Trivial knowledge about the structure –function relationship of this VSR leads to this work, where we focus on the structure generation by modelling to identify the mode of interactions with the various effector molecules of the silencing pathways. Structural analyses have been performed to screen interacting residues. Results indicate conserved structural features which signify propensity of functional interactions and further shows that this VSR can be a potent tool for the analysis of RNA silencing mechanisms and the relationships between different silencing pathways and VSRs.

MB1533 is a Defensin-Like Antimicrobial Peptide from the Intracellular Meristem Endophyte of Scots Pine Methylobacterium extorquens DSM13060

Endophytes induce plant growth and protect host plants against abiotic and biotic stresses, such phytopathogenic bacteria and fungi. Here we explored the genome of plant growth-promoting, intracellular endophyte Methylobacterium extorquens DSM13060, isolated from bud meristems of Pinus sylvestris L., for antimicrobial peptides. A defensinlike antimicrobial peptide MB1533 was identified using computational and prediction models from the genome sequence. MB1533 was produced in Escherichia coli with a molecular weight of 6160.26 Da. The antimicrobial activity was tested against several strains of bacteria and yeasts, and the peptide had activity against the grampositive Staphylococcus aureus and Bacillus subtilis at 128 μg/ml. The potency of the peptide can be improved further by rational-design-techniques. MB1533 is the first defensin-like peptide identified from Methylobacterium genus and from bacterial endophytes, in general.

Structural Analyses of AC4 Protein of Sri Lankan Cassava Mosaic Virus

RNA silencing is one of the important phenomenon in plant defense mechanism, it actively protect host plants against viral infections. Existing viruses must have developed counter defense strategies to survive this arms race. Such counter defense strategy is the viral silencing suppressor (VSRs) which have been reported to directly interfere with the various steps leading to the interference of viral RNAs. Most identified VSRs are multifunctional, besides being RNA-silencing suppressors, they often perform essential roles by functioning as coat proteins, helper components for viral transmission, replicases and movement proteins, proteases or transcriptional regulators. One such identified VSR is AC4 of Sri Lankan cassava mosaic virus strain. Trivial knowledge about the structure –function relationship of this VSR leads to this work, where we focus on the structure generation by modelling to identify the mode of interactions with the various effector molecules of the silencing pathways. Structural analyses have been performed to screen interacting residues. Results indicate conserved structural features which signify propensity of functional interactions and further shows that this VSR can be a potent tool for the analysis of RNA silencing mechanisms and the relationships between different silencing pathways and VSRs.

Arbuscular mycorrhizal symbiosis can mitigate the negative effects of night warming on physiological traits of Medicago truncatula L

Elevated night temperature, one of the main climate warming scenarios, can have profound effects on plant growth and metabolism. However, little attention has been paid to the potential role of mycorrhizal associations in plant responses to night warming, although it is well known that symbiotic fungi can protect host plants against various environmental stresses. In the present study, physiological traits of Medicago truncatula L. in association with the arbuscular mycorrhizal (AM) fungus Rhizophagus irregularis were investigated under simulated night warming. A constant increase in night temperature of 1.53°C significantly reduced plant shoot and root biomass, flower and seed number, leaf sugar concentration, and shoot Zn and root P concentrations. However, the AM association essentially mitigated these negative effects of night warming by improving plant growth, especially through increased root biomass, root to shoot ratio, and shoot Zn and root P concentrations. A significant interaction was observed between R. irregularis inoculation and night warming in influencing both root sucrose concentration and expression of sucrose synthase (SusS) genes, suggesting that AM symbiosis and increased night temperature jointly regulated plant sugar metabolism. Night warming stimulated AM fungal colonization but did not influence arbuscule abundance, symbiosis-related plant or fungal gene expression, or growth of extraradical mycelium, indicating little effect of night warming on the development or functioning of AM symbiosis. These findings highlight the importance of mycorrhizal symbiosis in assisting plant resilience to climate warming.

Diverse and bioactive endophytic Aspergilli inhabit Cupressaceae plant family.

Aspergilli are filamentous, cosmopolitan and ubiquitous fungi which have significant impact on human, animal and plant welfare worldwide. Due to their extraordinary metabolic diversity, Aspergillus species are used in biotechnology for the production of a vast array of biomolecules. However, little is known about Aspergillus species that are able to adapt an endophytic lifestyle in Cupressaceae plant family and are capable of producing cytotoxic, antifungal and antibacterial metabolites. In this work, we report a possible ecological niche for pathogenic fungi such as Aspergillus fumigatus and Aspergillus flavus. Indeed, our findings indicate that A. fumigatus, A. flavus, Aspergillus niger var. niger and A. niger var. awamori adapt an endophytic lifestyle inside the Cupressaceous plants including Cupressus arizonica, Cupressus sempervirens var. fastigiata, Cupressus semipervirens var. cereiformis, and Thuja orientalis. In addition, we found that extracts of endophytic Aspergilli showed significant growth inhibition and cytotoxicity against the model fungus Pyricularia oryzae and bacteria such as Bacillus sp., Erwinia amylovora and Pseudomonas syringae. These endophytic Aspergilli also showed in vitro antifungal effects on the cypress fungal phytopathogens including Diplodia seriata, Phaeobotryon cupressi and Spencermartinsia viticola. In conclusion, our findings clearly support the endophytic association of Aspergilli with Cupressaceae plants and their possible role in protection of host plants against biotic stresses. Observed bioactivities of such endophytic Aspergilli may represent a significant potential for bioindustry and biocontrol applications.

Evaluation of arbuscular mycorrhizal fungi capacity to alleviate abiotic stress of olive (Olea europaea L.) plants at different transplant conditions.

The capacity of roots to sense soil physicochemical parameters plays an essential role in maintaining plant nutritional and developmental functions under abiotic stress. These conditions generate reactive oxygen species (ROS) in plant tissues causing oxidation of proteins and lipids among others. Some plants have developed adaptive mechanisms to counteract such adverse conditions such as symbiotic association with arbuscular mycorrhizal fungi (AMF). AMF enhance plant growth and improve transplant survival by protecting host plants against environmental stresses. The aim of this study was to evaluate the alleviation of transplanting stress by two strains of Rhizophagus irregularis (GC2 and GA5) in olive. Our results show that olive plants have an additional energetic expense in growth due to an adaptative response to the growing stage and to the mycorrhizal colonization at the first transplant. However, at the second transplant the coinoculation improves olive plant growth and protects against oxidative stress followed by the GA5-inoculation. In conclusion, a combination of two AMF strains at the beginning of olive propagation produces vigorous plants successfully protected in field cultivation even with an additional cost at the beginning of growth.

Ecological and Mechanistic Insights Into the Direct and Indirect Antimicrobial Properties of Bacillus subtilis Lipopeptides on Plant Pathogens

Members of the genus Bacillus produce a wide variety of antimicrobial compounds. Cyclic lipopeptides (CLP) produced by Bacillus subtilis strains have been shown to protect host plants from a numbers of pathogens. The representative families of these CLP (surfactins, fengycins, and iturins) share a polypeptide ring linked to a lipid tail of varying length. CLP provide plant protection through a variety of unique mechanisms. Members of the surfactin and fengycin families elicit induced systemic resistance in certain host plants, and they also function by directly affecting the biological membranes of bacterial and fungal pathogens, mainly resulting in membrane pore formation. Specific pore forming mechanisms differ between CLP families, causing differential activities. CLP also may aid in enhanced B. subtilis colonization of the plant environment in addition to potentially preventing the adhesion of competitive microorganisms. Several recent studies have highlighted the control of plant pathogens by CLP-producing B. subtilis strains. Strong ecological advantages through multifaceted activities of CLP provide these strains with immense promise in controlling pathogens in a variety of plant ecosystems.

Host Plant Resistance of Cool-Season (C3) Turfgrasses to Above- and Belowground Feeding by <I>Tipula paludosa</I> (Diptera: Tipulidae)

Feeding on above- and belowground plant tissues by Tipula paludosa Meigen during the period of rapid growth from second to forth instars is highly damaging to cool-season (C3) turfgrasses. It may be possible to reduce this damage by identifying grass genotypes that increase host plant protection. This study examined the impacts of plant genotype, endophyte infection, and plant ontogeny on host plant and insect responses during whole-plant feeding by T. paludosa. A series of no-choice greenhouse trials were conducted with third instar crane flies to determine 1) host plant tolerance in terms of reductions to above- and belowground plant biomass, 2) antixenosis resistance impacting insect behavior (emigration), and 3) antibiosis resistance impacting insect growth. Results showed that insect infestation level was the primary factor influencing plant biomass reductions. Belowground tissues were more tolerant to feeding than were aboveground tissues, with tall fescues, Festuca arundinacea Schreber, being most resistant to aboveground biomass reduction. Host plant associations with intercellular fungal endophytes (E+) decreased insect weight gain and decreased insect movement, but did not increase host plant tolerance. Plant ontogeny affected this response with insect weight gain significantly decreased on young (28 d) growth E+ grasses but not on old (90 d) growth E+ grasses, however. Host plant genotype and plant ontogeny can have significant impacts to host plant tolerance and insect physiology for T. paludosa larva. Furthermore, plant-endophyte associations have apparent sublethal effects that impact insect fitness and may further enhance host plant protection.

The polyamine spermine protects Arabidopsis from heat stress-induced damage by increasing expression of heat shock-related genes

It is known that the polyamine (PA) biosynthetic pathway is modulated at the transcriptional level during abiotic stresses. Here we studied the expression of PA biosynthetic pathway genes upon exposure to heat shock (HS) in Arabidopsis and showed that the spermine (Spm) synthase gene (SPMS) and S-adenosylmethionine decarboxylase 2 gene are induced at the earliest stage, followed by the induction of the arginine decarboxylase 2 gene. Correspondingly, Spm content increased linearly upon HS, and putrescine (Put) and spermidine (Spd) content also increased but not thermospermine (T-Spm) content. Exogenously applied Spm had a potential to protect Arabidopsis plants from HS-induced damage. Such protection was also observed to the same extent with T-Spm and by Spd to a lesser extent but not by Put. Then we tested whether altered endogenous Spm content affects sensitivity to HS using both transgenic plants overexpressing SPMS and a Spm deficient (spms) mutant plant. The result revealed that the higher the Spm content the higher the thermotolerance. Even in the spms plant, representative genes encoding heat shock proteins (HSPs) and heat shock transcription factors were upregulated upon HS, while the expression of such genes was increased in a positively correlated manner with Spm content. Furthermore four kinds of HSPs (HSP101, HSP90, HSP70 and HSP17.6) were detected proportionally with the levels of their respective transcripts upon HS. We propose that Spm increases the HS response at transcriptional and translational levels and protects host plants from HS-induced damage.