Monodehydroascorbate reductase 2 and dehydroascorbate reductase 5 are crucial for a mutualistic interaction between Piriformospora indica and Arabidopsis

Identifying Endogenous Proteins of Perennial Ryegrass (Lolium perenne) with Ex Vivo Antioxidant Activity

Background: During the initial steps of green biorefining aimed at protein recovery, endogenous proteins and enzymes, along with, e.g., phytochemical constituents, are decompartmentalized into a green juice. This creates a highly dynamic environment prone to a plethora of reactions including oxidative protein modification and deterioration. Obtaining a fundamental understanding of the enzymes capable of exerting antioxidant activity ex vivo could help mitigate these reactions for improved product quality. Methods: In this study, we investigated perennial ryegrass (Lolium perenne var. Abosan 1), one of the most widely used turf and forage grasses, as a model system. Using size exclusion chromatography, we fractionated the green juice to investigate in vitro antioxidant properties and coupled this with quantitative bottom-up proteomics, GO-term analysis, and fraction-based enrichment. Results: Our findings revealed that several enzymes, such as superoxide dismutase and peroxiredoxin proteoforms, already known for their involvement in in vivo oxidative protection, are enriched in fractions displaying increased in vitro antioxidant activity, indicating retained activity ex vivo. Moreover, this study provides the most detailed characterization of the L. perenne proteome today and delivers new insights into protein-level partitioning during wet fractionation. Conclusions: Ultimately, this work contributes to a better understanding of the first steps of green biorefining and provides the basis for process optimization.

Adoption of a novel medium for the industrial (3000 L) production of Serendipita indica employing a nutrient limitation strategy using insoluble carbon and phosphate sources

The use of the endophytic fungus Serendipita indica has rapidly increased due to its wide range of host species, ability to foster plant-growth, and ability to confer tolerance to a number of stresses. However, its industrial-scale production is still in its infancy due to its low-biomass yield and prolonged cultivation time. Thus far, Hill-Kafer medium has traditionally been used for S. indica cultivation, resulting in lower yields and excessively long incubation times. Here, we adopted a simple insoluble carbon and phosphate input medium for rapidly generating high biomass. We developed and optimized the SIF1 medium, achieving maximum biomass production (424.5 ± 1.9 g/L), significantly outperforming Hill-Kafer medium. Statistical optimization of SIF1 identified optimal levels (15 g/L oats, 7.5 g/L tricalcium phosphate, 95-hr incubation). Validated results in the laboratory (FUS-10 L: 484.4 ± 4.7), pilot (300 L: 496.5 ± 7 g/L), and industrial (3000L: 492.4 ± 7.1 g/L) bioreactors proved the efficacy of SIF1. Compared to Hill-Kafer (54.8 ± 3.7 g/L), SIF1 showed nine-fold higher biomass productivity and reduced cultivation time by approximately 6 days. Based on our findings, it appears that SF1 will be a highly efficient medium for producing S. indica on an industrial scale and expanding its use.

ONE-SENTENCE SUMMARY

This study presents a rapid industrial production strategy for the beneficial fungus Serendipita indica, providing a scalable solution for wider applications and contributing to global food security and environmental sustainability.

The effect of cadmium on soil and plants, and the influence of Serendipita indica (Piriformospora indica) in mitigating cadmium stress

Due to environmental pollution, the risk of cadmium stress for crops is soaring, so researchers are exploring inexpensive solutions to enhance cultivated crops in contaminated soil. Using microorganisms to reduce cadmium risk has been one of the most effective strategies in recent decades. Serendipita indica (Piriformospora indica) is one of the best endophyte fungi that, in addition to reducing heavy metal stress for crops, can significantly reduce the threat of other abiotic stresses. As part of this research, cadmium in soil has been investigated, as well as its effects on plants' morphophysiological and biochemical characteristics. The present review has also attempted to identify the role of Serendipita indica in improving the growth and performance of crops, as well as its possible effect on reducing the risk of cadmium. The results showed that Serendipita indica enhance the growth and productivity of plants in contaminated environments by improving soil quality, reducing cadmium absorption, improving the activity of antioxidant enzymes and secondary metabolites, raising water and mineral absorption, and altering morphophysiological structures.

Integrated Benefits to Agriculture with Trichoderma and Other Endophytic or Root-Associated Microbes

The use of endophytic microbes is increasing in commercial agriculture. This review will begin with a strain selection. Most strains will not function well, so only a few provide adequate performance. It will also describe the endophyte-plant relationship and the fungi and bacteria involved. Their abilities to alleviate biotic (diseases and pests) and abiotic stresses (drought, salt, and flooding) to remediate pollution and increase photosynthetic capabilities will be described. Their mechanisms of action will be elucidated. These frequently result in increased plant yields. Finally, methods and practices for formulation and commercial use will be described.

Isolation and characterization of a newly discovered plant growth-promoting endophytic fungal strain from the genus Talaromyces

In the Kandi zone of Punjab, India, root and rhizospheric soil samples were collected from the local vegetation near the Shivalik mountain foothills. Fifteen fungal colonies exhibiting distinct cultural morphology on Potato Dextrose Agar (PDA) plates were selected for plant-microbe interaction studies. Among these, the isolate HNB9 was identified as a nonpathogenic root colonizer. Morphological and molecular analyses confirmed HNB9 as Talaromyces albobiverticillius, characterized by the secretion of a red pigment as a secondary metabolite. Plants colonized with T. albobiverticillius HNB9 exhibited enhanced growth, manifesting in increased shoot and root length compared to untreated controls. This study unveiled the first evidence that a species from the Talaromyces genus, specifically T. albobiverticillius, possesses dual capabilities of root colonization and plant growth promotion. Moreover, HNB9 demonstrated the production of plant growth-regulating compounds like Indole Acetic Acid (IAA) and proficient solubilization of crucial nutrients (Phosphorous, Zinc, and Silica) through plate culture methods. This finding represents a significant contribution to the understanding of root-colonizing fungi with plant growth-promoting attributes, challenging the existing knowledge gap within the Talaromyces genus.

Nutrient and mycoremediation of a global menace 'arsenic': exploring the prospects of phosphorus and Serendipita indica-based mitigation strategies in rice and other crops

KEY MESSAGE

Serendipita indica induced metabolic reprogramming in colonized plants complements phosphorus-management in improving their tolerance to arsenic stress on multifaceted biological fronts. Restoration of the anthropic damage done to our environment is inextricably linked to devising strategies that are not only economically sound but are self-renewing and ecologically conscious. The dilemma of heavy metal (HM) dietary ingestion, especially arsenic (As), faced by humans and animals alike, necessitates the exploitation of such technologies and the cultivation of healthy and abundant crops. The remarkable symbiotic alliance between plants and 'mycorrhizas' has evolved across eons, benefiting growth/yield aspects as well as imparting abiotic/biotic stress tolerance. The intricate interdependence of Serendipita indica (S. indica) and rice plant reportedly reduce As accumulation, accentuating the interest of microbiologists, agriculturists, and ecotoxicological scientists apropos of the remediation mechanisms of As in the soil-AMF-rice system. Nutrient management, particularly of phosphorus (P), is also praised for mitigating As phytotoxicity by deterring the uptake of As molecules due to the rhizospheric cationic competition. Taking into consideration the reasonable prospects of success in minimizing As acquisition by rice plants, this review focuses on the physiological, metabolic, and transcriptional alterations underlying S. indica symbiosis, recuperation of As stress together with nutritional management of P by gathering case studies and presenting successful paradigms. Weaving together a volume of literature, we assess the chemical forms of As and related transport pathways, discuss As-P-rice interaction and the significance of fungi in As toxicity mitigation, predominantly the role of mycorrhiza, as well as survey of the multifaceted impacts of S. indica on plants. A potential strategy for simultaneous S. indica + P administration in paddy fields is proposed, followed by future research orientation to expand theoretic comprehension and encourage field-based implementation.

Calcium lignosulfonate modulates physiological and biochemical responses to enhance shoot multiplication in Vanilla planifolia Andrews

Utilisation of calcium lignosulfonate (CaLS) in Vanilla planifolia has been reported to improve shoot multiplication. However, mechanisms responsible for such observation remain unknown. Here, we elucidated the underlying mechanisms of CaLS in promoting shoot multiplication of V. planifolia via comparative proteomics, biochemical assays, and nutrient analysis. The proteome profile of CaLS-treated plants showed enhancement of several important cellular metabolisms such as photosynthesis, protein synthesis, Krebs cycle, glycolysis, gluconeogenesis, and carbohydrate synthesis. Further biochemical analysis recorded that CaLS increased Rubisco activity, hexokinase activity, isocitrate dehydrogenase activity, total carbohydrate content, glutamate synthase activity and total protein content in plant shoot, suggesting the role of CaLS in enhancing shoot growth via upregulation of cellular metabolism. Subsequent nutrient analysis showed that CaLS treatment elevated the contents of several nutrient ions especially calcium and sodium ions. In addition, our study also revealed that CaLS successfully maintained the cellular homeostasis level through the regulation of signalling molecules such as reactive oxygen species and calcium ions. These results demonstrated that the CaLS treatment can enhance shoot multiplication in V. planifolia Andrews by stimulating nutrient uptake, inducing cell metabolism, and regulating cell homeostasis.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01293-w.

Effects of microbial agents on cadmium uptake in Solanum nigrum L. and rhizosphere microbial communities in cadmium-contaminated soil

Solanum nigrum L. (S. nigrum) and microbial agents are often used for the remediation of cadmium (Cd)-contaminated soil; however, no studies to date have examined the efficacy of using various microbial agents for enhancing the remediation efficiency of Cd-contaminated soil by S. nigrum. Here, we conducted greenhouse pot experiments to evaluate the efficacy of applying Bacillus megaterium (BM) along with citric acid (BM + CA), Glomus mosseae (BM + GM), and Piriformospora indica (BM + PI) on the ability of S. nigrum to remediate Cd-contaminated soil. The results showed that BM + GM significantly increased the Cd accumulation of each pot of S. nigrum by 104% compared with the control. Application of microbial agents changed the soil microbial communities. Redundancy analysis showed that the activities of Catalase (CAT) and urease (UE), soil organic matter, available N and total Cd were the main influencing factors. By constructing the microbial co-occurrence networks, the soil microbe was divided into four main Modules. BM + GM and BM + PI significantly increased the relative abundance of Module#1 and Module#3, respectively, when compared with the control. Additionally, Module#1 showed a significant positive correlation with translocation factor (TF), which could be regarded as the key microbial taxa. Further research found that Ascomycota, Glomeromycota, Proteobacteria, and Actinobacteria within Module#1 were also significantly correlated with TF, and these key species enriched in BM + GM. Overall, our findings indicate that the BM + GM treatment was the most effective for the remediation of Cd pollution. This treatment method may further affect the rhizosphere microbial community by affecting soil indicators, which might drive the formation of Module#1, thus greatly enhancing the Cd remediation capacity of S. nigrum.

Root colonization by the endophytic fungus Piriformospora indica shortens the juvenile phase of Piper nigrum L. by fine tuning the floral promotion pathways

Piriformospora indica, the mutualistic biotrophic root colonizing endosymbiotic fungus belonging to the order Sebacinales, offers host plants various benefits and enhances its growth and performance. The effect of colonization of P. indica in Piper nigrum L. cv. Panniyur1 on growth advantages, floral induction and evocation was investigated. Growth and yield benefits are credited to the alteration in the phytohormone levels fine-tuned by plants in response to the fungal colonization and perpetuation. The remarkable upregulation in the phytohormone levels, as estimated by LC- MS/MS and quantified by qRT-PCR, revealed the effectual contribution by the endophyte. qRT-PCR results revealed a significant shift in the expression of putative flowering regulatory genes in the photoperiod induction pathway (FLOWERING LOCUS T, LEAFY, APETALA1, AGAMOUS, SUPPRESSOR OF CONSTANS 1, GIGANTEA, PHYTOCHROMEA, and CRYPTOCHROME1) gibberellin biosynthetic pathway genes (GIBBERELLIN 20-OXIDASE2, GIBBERELLIN 2-OXIDASE, DELLA PROTEIN REPRESSOR OF GA1-3 1) autonomous (FLOWERING LOCUS C, FLOWERING LOCUS VE, FLOWERING LOCUS CA), and age pathway (SQUAMOSA PROMOTER LIKE9, APETALA2). The endophytic colonization had no effect on vernalization (FLOWERING LOCUS C) or biotic stress pathways (SALICYLIC ACID INDUCTION DEFICIENT 2, WRKY family transcription factor 22). The data suggest that P. nigrum responds positively to P. indica colonization, affecting preponement in floral induction as well as evocation, and thereby shortening the juvenile phase of the crop.

Proteomic Profiling and Rhizosphere-Associated Microbial Communities Reveal Adaptive Mechanisms of Dioclea apurensis Kunth in Eastern Amazon's Rehabilitating Minelands

Dioclea apurensis Kunth is native to ferruginous rocky outcrops (known as canga) in the eastern Amazon. Native cangas are considered hotspots of biological diversity and have one of the largest iron ore deposits in the world. There, D. apurensis can grow in post-mining areas where molecular mechanisms and rhizospheric interactions with soil microorganisms are expected to contribute to their establishment in rehabilitating minelands (RM). In this study, we compare the root proteomic profile and rhizosphere-associated bacterial and fungal communities of D. apurensis growing in canga and RM to characterize the main mechanisms that allow the growth and establishment in post-mining areas. The results showed that proteins involved in response to oxidative stress, drought, excess of iron, and phosphorus deficiency showed higher levels in canga and, therefore, helped explain its high establishment rates in RM. Rhizospheric selectivity of microorganisms was more evident in canga. The microbial community structure was mostly different between the two habitats, denoting that despite having its preferences, D. apurensis can associate with beneficial soil microorganisms without specificity. Therefore, its good performance in RM can also be improved or attributed to its ability to cope with beneficial soil-borne microorganisms. Native plants with such adaptations must be used to enhance the rehabilitation process.

Signaling Toward Reactive Oxygen Species-Scavenging Enzymes in Plants

Reactive oxygen species (ROS) are signaling molecules essential for plant responses to abiotic and biotic stimuli as well as for multiple developmental processes. They are produced as byproducts of aerobic metabolism and are affected by adverse environmental conditions. The ROS content is controlled on the side of their production but also by scavenging machinery. Antioxidant enzymes represent a major ROS-scavenging force and are crucial for stress tolerance in plants. Enzymatic antioxidant defense occurs as a series of redox reactions for ROS elimination. Therefore, the deregulation of the antioxidant machinery may lead to the overaccumulation of ROS in plants, with negative consequences both in terms of plant development and resistance to environmental challenges. The transcriptional activation of antioxidant enzymes accompanies the long-term exposure of plants to unfavorable environmental conditions. Fast ROS production requires the immediate mobilization of the antioxidant defense system, which may occur via retrograde signaling, redox-based modifications, and the phosphorylation of ROS detoxifying enzymes. This review aimed to summarize the current knowledge on signaling processes regulating the enzymatic antioxidant capacity of plants.

Piriformospora indica augments arsenic tolerance in rice (Oryza sativa) by immobilizing arsenic in roots and improving iron translocation to shoots

Arsenic (As) toxicity can be a hazardous threat to sustainable agriculture and human health. Piriformospora indica (P. indica), as a beneficial endophytic fungus, is involved in the plant tolerance to stressful conditions. Here, the biochemical and molecular responses of rice plants to As (50 μM) phytotoxicity and P. indica inoculation as well as the role of P. indica in improving rice adaptation to As stress were evaluated. The results showed that As stress reduced chlorophylls content, chlorophyll fluorescence yield (Fv/Fm), electron transport rate (ETR) and growth. However, P. indica restored chlorophyll content and growth. P. indica decreased the contents of methylglyoxal and malondialdehyde by improving the activity of enzymes involved in the glyoxalase pathway and modulating the redox state of the ascorbic acid-glutathione cycle, and consequently, increased the plant tolerance to As toxicity. P. indica, by downregulating Lsi2 expression (involved in As translocation to the shoot) and upregulating PCS1 and PCS2 expression (involved in As sequestration in vacuoles), immobilized As in the roots and reduced damage to photosynthetic organs. P. indica increased iron (Fe) accumulation in the shoot under As toxicity by upregulating the expression of IRO2, YSL2 and FRDL1 genes. The results of the present study augmented our knowledge in using P. indica symbiosis in improving the tolerance of rice plants against As toxicity for sustainable agriculture.

The ameliorative effects of exogenous inoculation of Piriformospora indica on molecular, biochemical and physiological parameters of Artemisia annua L. under arsenic stress condition

Aim of the current study was to investigate the effect of exogenously inoculated root endophytic fungus, Piriformospora indica, on molecular, biochemical, morphological and physiological parameters of Artemisia annua L. treated with different concentrations (0, 50, 100 and 150 μmol/L) of arsenic (As) stress. As was significantly accumulated in the roots than shoots of P. indica-inoculated plants. As accumulation and immobilization in the roots is directly associated with the successful fungal colonization that restricts most of As as compared to the aerial parts. A total of 4.1, 11.2 and 25.6 mg/kg dry weight of As was accumulated in the roots of inoculated plants supplemented with 50, 100 and 150 μmol/L of As, respectively as shown by atomic absorption spectroscopy. P. indica showed significant tolerance in vitro to As toxicity even at high concentration. Furthermore, flavonoids, artemisinin and overall biomass were significantly increased in inoculated-stressed plants. Superoxide dismutase and peroxidase activities were increased 1.6 and 1.2 fold, respectively under 150 μmol/L stress in P. indica-colonized plants. Similar trend was followed by ascorbate peroxidase, catalase and glutathione reductase. Like that, phenolic acid and phenolic compounds showed a significant increase in colonized plants as compared to their respective control/un-colonize stressed plants. The real-time PCR revealed that transcriptional levels of artemisinin biosynthesis genes, isoprenoids, terpenes, flavonoids biosynthetic pathway genes and signal molecules were prominently enhanced in inoculated stressed plants than un-inoculated stressed plants.

The pivotal function of dehydroascorbate reductase in glutathione homeostasis in plants

Under natural conditions, plants are exposed to various abiotic and biotic stresses that trigger rapid changes in the production and removal of reactive oxygen species (ROS) such as hydrogen peroxide (H2O2). The ascorbate-glutathione pathway has been recognized to be a key player in H2O2 metabolism, in which reduced glutathione (GSH) regenerates ascorbate by reducing dehydroascorbate (DHA), either chemically or via DHA reductase (DHAR), an enzyme belonging to the glutathione S-transferase (GST) superfamily. Thus, DHAR has been considered to be important in maintaining the ascorbate pool and its redox state. Although some GSTs and peroxiredoxins may contribute to GSH oxidation, analysis of Arabidopsis dhar mutants has identified the key role of DHAR in coupling H2O2 to GSH oxidation. The reaction of DHAR has been proposed to proceed by a ping-pong mechanism, in which binding of DHA to the free reduced form of the enzyme is followed by binding of GSH. Information from crystal structures has shed light on the formation of sulfenic acid at the catalytic cysteine of DHAR that occurs with the reduction of DHA. In this review, we discuss the molecular properties of DHAR and its importance in coupling the ascorbate and glutathione pools with H2O2 metabolism, together with its functions in plant defense, growth, and development.

Biopriming with Piriformospora indica ameliorates cadmium stress in rice by lowering oxidative stress and cell death in root cells

Piriformospora indica is known for plant growth promotion and abiotic stress alleviation potential in several agricultural crops. However, a systemic analysis is warranted to explore potential application of this important fungus to augment heavy metal tolerance in rice. The present study explores potential of P. indica in ameliorating the effect of cadmium (Cd) stress in rice cultivars N22 and IR64. Seedlings inoculated with P. indica recorded significantly higher root-shoot length and biomass as compared to non-inoculated plants under control and Cd stress, respectively. Moreover, P. indica inoculated stressed roots accumulated more Cd as compared to non-inoculated stressed roots in both the varieties. Interestingly, cell death and reactive oxygen species (ROS) accumulation were significantly lower in the inoculated plant roots as compare with non-inoculated roots under Cd stress. The results emphasized significantly higher accumulation of Cd in fungal spores could reduce ROS accumulation in root cells resulting in lower cell death.

iTRAQ-based proteomic analysis reveals changes in response to sodium nitroprusside treatment in soybean sprouts

In recent years, nitric oxide (NO) has been considered a plant signaling compound involved in antioxidant systems and flavonoid production enhancement. Nevertheless, its mechanism of action, from the perspective of protein expression, remains largely unknown. In this study, isobaric tags for relative and absolute quantitation (iTRAQ) was employed to investigate NO donor sodium nitroprusside treatment-induced proteomic changes in soybean sprouts. Among the 3033 proteins identified, compared with the control, sodium nitroprusside treatment up- and down-regulated 256 proteins. These proteins were involved in antioxidant system pathways, such as the thioredoxin, superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glutathione reductase (GR), glutathione S-transferase (GST), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR) and lipoxygenase (LOX) pathways, including allene oxide synthase and lipoxygenase. In addition, heat shock proteins (HSPs) and flavonoid biosynthetic proteins, such as cinnamate 4-hydroxylase, chalcone isomerase, chalcone synthase, isoflavone synthase and isoflavone reductase, were also modulated in response to sodium nitroprusside treatment.

Symbiotic Root-Endophytic Soil Microbes Improve Crop Productivity and Provide Environmental Benefits

Plants should not be regarded as entities unto themselves, but as the visible part of plant-microbe complexes which are best understood as "holobiomes." Some microorganisms when given the opportunity to inhabit plant roots become root symbionts. Such root colonization by symbiotic microbes can raise crop yields by promoting the growth of both shoots and roots, by enhancing uptake, fixation, and/or more efficient use of nutrients, by improving plants' resistance to pests, diseases, and abiotic stresses that include drought, salt, and other environmental conditions, and by enhancing plants' capacity for photosynthesis. We refer plant-microbe associations with these capabilities that have been purposefully established as enhanced plant holobiomes (EPHs). Here, we consider four groups of phylogenetically distinct and distant symbiotic endophytes: (1) Rhizobiaceae bacteria; (2) plant-obligate arbuscular mycorrhizal fungi (AMF); (3) selected endophytic strains of fungi in the genus Trichoderma; and (4) fungi in the Sebicales order, specifically Piriformospora indica. Although these exhibit quite different "lifestyles" when inhabiting plants, all induce beneficial systemic changes in plants' gene expression that are surprisingly similar. For example, all induce gene expression that produces proteins which detoxify reactive oxygen species (ROS). ROS are increased by environmental stresses on plants or by overexcitation of photosynthetic pigments. Gene overexpression results in a cellular environment where ROS levels are controlled and made more compatible with plants' metabolic processes. EPHs also frequently exhibit increased rates of photosynthesis that contribute to greater plant growth and other capabilities. Soil organic matter (SOM) is augmented when plant root growth is increased and roots remain in the soil. The combination of enhanced photosynthesis, increasing sequestration of CO2 from the air, and elevation of SOM removes C from the atmosphere and stores it in the soil. Reductions in global greenhouse gas levels can be accelerated by incentives for carbon farming and carbon cap-and-trade programs that reward such climate-friendly agriculture. The development and spread of EPHs as part of such initiatives has potential both to enhance farm productivity and incomes and to decelerate global warming.

Transcriptional Reprogramming of Arabidopsis thaliana Defence Pathways by the Entomopathogen Beauveria bassiana Correlates With Resistance Against a Fungal Pathogen but Not Against Insects

The entomopathogenic fungus Beauveria bassiana can adopt an endophytic lifestyle by colonising a wide array of plant species. Beauveria-colonised plants can show enhanced resistance against insects and plant pathogens alike. However, little is known about the molecular and physiological mechanisms that govern such interactions. Here, we assessed the effects of two B. bassiana strains (BG11, FRh2) on the growth of Arabidopsis thaliana and its resistance against two herbivore species and a phytopathogen. Plant responses were studied on the transcriptomic and metabolic level using microarrays and by measuring changes in defence-related phytohormones and glucosinolates (GLSs). Root inoculation with B. bassiana BG11 significantly increased plant growth, while FRh2 had no such effect. Both Beauveria strains decreased leaf lesion area caused by the phytopathogen Sclerotinia sclerotiorum but did not affect population growth of the aphid Myzus persicae or the growth of Plutella xylostella caterpillars. Microarray analyses of leaves from endophyte-inoculated A. thaliana provided evidence for transcriptional reprogramming of plant defence pathways, with strain-specific changes in the expression of genes related to pathogenesis, phytoalexin, jasmonic (JA), and salicylic acid (SA) signalling pathways. However, B. bassiana colonisation did not result in higher concentrations of JA and SA or major changes in leaf GLS profiles. We conclude that the endophyte B. bassiana induces plant defence responses and hypothesise that these contribute to enhanced resistance against S. sclerotiorum.

Growth promotion and disease resistance induced in Anthurium colonized by the beneficial root endophyte Piriformospora indica

BACKGROUND

Anthurium andraeanum, an important ornamental flower, has to go through a growth-delaying period after transfer from tissue culture to soil, which requires time and extra costs. Furthermore, during this period, the plantlets are highly susceptible to bacterial infections, which results in impaired development and severe losses. Here, we aimed to address whether application of the endophytic fungus, Piriformospora indica protects the A. andraeanum root system during the critical propagation period, and whether P. indica reduce the mortality rate by stimulating the host's resistance against diseases.

RESULTS

We demonstrate that P. indica shortens the recovery period of Anthurium, promotes growth and confers disease resistance. The beneficial effect of P. indica results in faster elongation of Anthurium roots early in the interaction. P. indica-colonized plants absorb more phosphorus and exhibit higher photosynthesis rates than uncolonized control plants. Moreover, higher activities of stress-related enzymes, of jasmonic acid levels and mRNA levels of jasmonic acid-responsive genes suggest that the fungus prepares the plant to respond more efficiently to potentially upcoming threats, including bacterial wilt.

CONCLUSION

These results suggest that P. indica is a helpful symbiont for promoting Anthurium rooting and development. All our evidences are sufficient to support the disease resistance conferred by P. indica through the plant-fungal symbiosis. Furthermore, it implicates that P. indica has strong potential as bio-fertilizer for utilization in ornamental plant cultivation.

Functional Characterization of a Magnesium Transporter of Root Endophytic Fungus Piriformospora indica

Magnesium (Mg) is a crucial macronutrient required for the regular growth of plants. Here we report the identification, isolation and functional characterization of Mg-transporter PiMgT1 in root endophytic fungus Piriformospora indica. We also report the role of P. indica in the improvement of the Mg nutrition of the plant particularly under Mg deficiency condition. Protein BLAST (BLASTp) for conserved domains analysis showed that PiMgT1 belong to CorA like protein family of bacteria. We have also observed the presence of conserved 'GMN' signature sequence which suggests that PiMgT1 belongs to Mg transporter family. Phylogenetic analysis revealed that PiMgT1 clustered among fungal CorA family members nearer to basidiomycetes. Functionality of PiMgT1 was confirmed by complementation of a yeast magnesium transporter mutant CM66. We have observed that PiMgT1 restored the growth of mutant and showed comparable growth with that of WT. We found statistically significant (p < 0.05) two fold increase in the total intracellular Mg content of mutant complemented with PiMgT1 as compared to the mutant. These observations suggest that PiMgT1 is actively involved in Mg uptake by the fungus and may be helping in the nutritional status of the host plant.

A putative cyclin, SiPHO80 from root endophytic fungus Serendipita indica regulates phosphate homeostasis, salinity and heavy metal toxicity tolerance

Serendipita indica previously known as Piriformospora indica is an arbuscular mycorrhizal fungi (AMF) like endophytic fungus which can be cultivated axenically and colonizes an array of plants, thereby promoting their growth and confers biotic and abiotic stress tolerance to the colonized host plant. It efficiently sequestrates heavy metals and defends host plant against heavy metal-induced toxicity. In the present study, SiPHO80, a homologue of S. cerevisiae PHO80 was isolated from S. indica and functionally characterized in S. cerevisiae. SiPHO80 has conserved 'cyclin box' domain and closely related to negative regulator cyclin of the wood decaying fungi. In S. indica, its expression gets upregulated in phosphate-rich media. The regulation of Pi homeostasis which was disrupted in S. cerevisiae Δpho80 grown under high Pi condition was restored upon complementation with SiPHO80. Also, the expression of SiPHO80 in Δpho80 mutant restored osmotolerance and heavy metal tolerance. This is the first report of a cyclin which is involved in Pi homeostasis, salt tolerance, heavy metal toxicity tolerance in any plant growth promoting endophytic fungi.

Piriformospora indica, an excellent system for heavy metal sequestration and amelioration of oxidative stress and DNA damage in Cassia angustifolia Vahl under copper stress

Present investigation reveals copper induced phytotoxicity, oxidative stress and DNA damage in Cassia angustifolia Vahl and its amelioration by employing a symbiotic fungus, Piriformospora indica. Seeds were germinated on Knop's medium containing five Cu levels (0, 1, 10, 50, 100 and 200 mg L^-1), with and without P. indica. Colonization with P. indica significantly (P < 0.05) ameliorated Cu induced oxidative stress. However, maximum amelioration was observed at 50 mg L^-1 Cu with P. indica. Atomic absorption spectroscopy revealed that P. indica colonization significantly inhibited Cu accumulation in shoots. Maximum decline in Cu accumulation in shoots was observed at 50 mg L^-1 (27.27%) with P. indica over Cu alone. Besides, P. indica colonized seedlings stored 16.86% higher Cu in roots as compared to Cu alone at 200 mg L^-1. Similarly, maximum proline accumulation increased up to 19.32% over Cu alone at 50 mg L^-1 Cu with P. indica. Significant elevation in antioxidant enzyme levels of superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase and glutathione reductase was seen with P. indica. Contrary to increase in antioxidant level, toxic parameters such as lipid peroxidation and hydrogen peroxide decreased significantly with P. indica. Maximum decline in lipid peroxidation (13.76%) and hydrogen peroxide (18.58%) was observed at 50 mg L^-1 with P. indica over Cu alone. P. indica significantly reduced DNA damage as well as changed the protein profile in C. angustifolia seedlings. Thus, P. indica proved to be an excellent system to alleviate Cu induced oxidative stress and might be useful as a phytostabilization tool.

Plant growth-promoting endophyte Piriformospora indica alleviates salinity stress in Medicago truncatula

Piriformospora indica, a cultivable root endophytic fungus, induces growth promotion as well as biotic stress resistance and tolerance to abiotic stress in a broad range of host plants. In this study, the potential protection for M Medicago truncatula plants from salinity stress by P. indica was explored. The improved plant growth under severe saline condition was exhibited in P. indica-colonized lines. Moreover, the antioxidant enzymes activities and hyphae density in roots were increased by the endophyte under high salt concentration. Conversely, reduced malondialdehyde (MDA) activity, Na⁺ content and relative electrolyte conductivity (REC) were observed in P. indica colonized plants. Especially, osmoprotectant proline accumulated and the expression of Delta 1-Pyrroline-5-carboxylate synthetase gene (P5CS2) was induced. The defense related genes PR1 and PR10 and the transcription factors MtAlfin1-like and C2H2-type zinc finger protein MtZfp-c2h2 were induced by P. indica colonization as well. Further work indicated that salinity resistance was increased in overexpressing P5CS2, MtAlfin1-like and MtZfp-c2h2 transgenic M. truncatula plants. Interestingly, our data showed that the transcription factors MtAlfin1-like and MtZfp-c2h2 were positively contributed to P. indica colonization. These results demonstrate that tolerance to salinity stress was conferred by P. indica in M. truncatula via accumulation of osmoprotectant, stimulating antioxidant enzymes and the expression of defense-related genes. This work revealed the potential application of P. indica's as a plant growth-promoting fungus for the target improvement either in crop protection or in the salinized soil improvement indirectly.

Metabolomic compounds identified in Piriformospora indica-colonized Chinese cabbage roots delineate symbiotic functions of the interaction

Root colonization by endophytic fungus Piriformospora indica facilitating growth/development and stress tolerance has been demonstrated in various host plants. However, global metabolomic studies are rare. By using high-throughput gas-chromatography-based mass spectrometry, 549 metabolites of 1,126 total compounds observed were identified in colonized and uncolonized Chinese cabbage roots, and hyphae of P. indica. The analyses demonstrate that the host metabolomic compounds and metabolite pathways are globally reprogrammed after symbiosis with P. indica. Especially, γ-amino butyrate (GABA), oxylipin-family compounds, poly-saturated fatty acids, and auxin and its intermediates were highly induced and de novo synthesized in colonized roots. Conversely, nicotinic acid (niacin) and dimethylallylpyrophosphate were strongly decreased. In vivo assays with exogenously applied compounds confirmed that GABA primes plant immunity toward pathogen attack and enhances high salinity and temperature tolerance. Moreover, generation of reactive oxygen/nitrogen species stimulated by nicotinic acid is repressed by P. indica, and causes the feasibility of symbiotic interaction. This global metabolomic analysis and the identification of symbiosis-specific metabolites may help to understand how P. indica confers benefits to the host plant.

Metabolomic compounds identified in Piriformospora indica-colonized Chinese cabbage roots delineate symbiotic functions of the interaction

Root colonization by endophytic fungus Piriformospora indica facilitating growth/development and stress tolerance has been demonstrated in various host plants. However, global metabolomic studies are rare. By using high-throughput gas-chromatography-based mass spectrometry, 549 metabolites of 1,126 total compounds observed were identified in colonized and uncolonized Chinese cabbage roots, and hyphae of P. indica. The analyses demonstrate that the host metabolomic compounds and metabolite pathways are globally reprogrammed after symbiosis with P. indica. Especially, γ-amino butyrate (GABA), oxylipin-family compounds, poly-saturated fatty acids, and auxin and its intermediates were highly induced and de novo synthesized in colonized roots. Conversely, nicotinic acid (niacin) and dimethylallylpyrophosphate were strongly decreased. In vivo assays with exogenously applied compounds confirmed that GABA primes plant immunity toward pathogen attack and enhances high salinity and temperature tolerance. Moreover, generation of reactive oxygen/nitrogen species stimulated by nicotinic acid is repressed by P. indica, and causes the feasibility of symbiotic interaction. This global metabolomic analysis and the identification of symbiosis-specific metabolites may help to understand how P. indica confers benefits to the host plant.

Piriformospora indica Reprograms Gene Expression in Arabidopsis Phosphate Metabolism Mutants But Does Not Compensate for Phosphate Limitation

Piriformospora indica is an endophytic fungus of Sebacinaceae which colonizes the roots of many plant species and confers benefits to the hosts. We demonstrate that approximately 75% of the genes, which respond to P. indica in Arabidopsis roots, differ among seedlings grown on normal phosphate (Pi) or Pi limitation conditions, and among wild-type and the wrky6 mutant impaired in the regulation of the Pi metabolism. Mapman analyses suggest that the fungus activates different signaling, transport, metabolic and developmental programs in the roots of wild-type and wrky6 seedlings under normal and low Pi conditions. Under low Pi, P. indica promotes growth and Pi uptake of wild-type seedlings, and the stimulatory effects are identical for mutants impaired in the PHOSPHATE TRANSPORTERS1;1, -1;2 and -1;4. The data suggest that the fungus does not stimulate Pi uptake, but adapts the expression profiles to Pi limitation in Pi metabolism mutants.

Elevation of secondary metabolites synthesis in Brassica campestris ssp. chinensis L. via exogenous inoculation of Piriformospora indica with appropriate fertilizer

This work evaluated the impact of exogenous soil inoculation of beneficial fungal strain Piriformospora indica on phytochemical changes and the related genes expression of Chinese cabbage (Brassica campestris ssp. chinensis L.) by greenhouse pot experiments. High performance liquid chromatography (HPLC) affirmed that among the different combinations of fungal and organic fertilizer treatments, the phenolic acids and flavonoids were considerably enriched in organic fertilizer and fungi (OP) followed by organic fertilizer, biochar, fungi (OBP) treated plants. The antiradical activity was higher in OP (61.29%) followed by P (60%) and organic fertilizer (OF) (53.84%) inoculated plants which positively correlated with chlorophyll, carotenoids and flavonoids level (P<0.05). Furthermore, results showed that the exogenous application of P. indica significantly (P<0.05) enhanced plant growth, as well as stimulating the activation of chlorophyll, carotenoids and other antioxidant related pathways. The RT-qPCR analysis indicated that key FLS gene triggering the synthesis of kaemferol was up-regulated by the inoculation of P. indica. In conclusion, the results revealed that organic fertilizer and P. indica (OP) is the most appropriate combination for improving phytochemical and antiradical properties in Pakchoi.

Dynamic expression analysis of early response genes induced by potato virus Y in PVY-resistant Nicotiana tabacum

KEY MESSAGE

Dynamic transcriptional changes of the host early responses genes were detected in PVY-resistant tobacco varieties infected with Potato virus Y; PVY resistance is a complex process that needs series of stress responses. Potato virus Y (PVY) causes a severe viral disease in cultivated crops, especially in Solanum plants. To understand the molecular basis of plant responses to the PVY stress, suppression subtractive hybridization (SSH) and microarray approaches were combined to identify the potentially important or novel genes that were involved in early stages (12 h, 1, 2, 3, 5, 8 days) of tobacco response to PVY infection. Dynamic changes of the host plant early responses to PVY infection on a transcriptional level were detected. In total, 167 different expressed ESTs were identified. The majority of genes involved in the metabolic process were found to be down-regulated at 12 h and 1 day, and then up-regulated at least one later period. Genes related to signaling and transcriptions were almost up-regulated at 12 h, 1 or 2 days, while stress response genes were almost up-regulated at a later stage. Genes involved in transcription, transport, cell wall, and several stress responses were found to have changed expression during the PVY infection stage, and numbers of these genes have not been previously reported to be associated with tobacco PVY infection. The diversity expression of these genes indicated that PVY resistance is a complex process that needs a series of stress responses. To resist the PVY infection, the tobacco plant has numerous active and silent responses.

A Chinese cabbage (Brassica campetris subsp. Chinensis) τ-type glutathione-S-transferase stimulates Arabidopsis development and primes against abiotic and biotic stress

The beneficial root-colonizing fungus Piriformospora indica stimulates root development of Chinese cabbage (Brassica campestris subsp. Chinensis) and this is accompanied by the up-regulation of a τ-class glutathione (GSH)-S-transferase gene (BcGSTU) (Lee et al. 2011) in the roots. BcGSTU expression is further promoted by osmotic (salt and PEG) and heat stress. Ectopic expression of BcGSTU in Arabidopsis under the control of the 35S promoter results in the promotion of root and shoot growth as well as better performance of the plants under abiotic (150 mM NaCl, PEG, 42 °C) and biotic (Alternaria brassicae infection) stresses. Higher levels of glutathione, auxin and stress-related (salicylic and jasmonic acid) phytohormones as well as changes in the gene expression profile result in better performance of the BcGSTU expressors upon exposure to stress. Simultaneously the plants are primed against upcoming stresses. We propose that BcGSTU is a target of P. indica in Chinese cabbage roots because the enzyme participates in balancing growth and stress responses, depending on the equilibrium of the symbiotic interaction. A comparable function of BcGST in transgenic Arabidopsis makes the enzyme a valuable tool for agricultural applications.

Arabidopsis dehydroascorbate reductase 1 and 2 modulate redox states of ascorbate-glutathione cycle in the cytosol in response to photooxidative stress

Ascorbate and glutathione are indispensable cellular redox buffers and allow plants to acclimate stressful conditions. Arabidopsis contains three functional dehydroascorbate reductases (DHAR1-3), which catalyzes the conversion of dehydroascorbate into its reduced form using glutathione as a reductant. We herein attempted to elucidate the physiological role in DHAR1 and DHAR2 in stress responses. The total DHAR activities in DHAR knockout Arabidopsis plants, dhar1 and dhar2, were 22 and 92%, respectively, that in wild-type leaves. Under high light (HL), the levels of total ascorbate and dehydroascorbate were only reduced and increased, respectively, in dhar1. The oxidation of glutathione under HL was significantly inhibited in both dhar1 and dhar2, while glutathione contents were only enhanced in dhar1. The dhar1 showed stronger visible symptoms than the dhar2 under photooxidative stress conditions. Our results demonstrated a pivotal role of DHAR1 in the modulation of cellular redox states under photooxidative stress.

Stress promotes Arabidopsis - Piriformospora indica interaction

The endophytic fungus Piriformospora indica colonizes Arabidopsis thaliana roots and promotes plant performance, growth and resistance/tolerance against abiotic and biotic stress. Here we demonstrate that the benefits for the plant increase when the two partners are co-cultivated under stress (limited access to nutrient, exposure to heavy metals and salt, light and osmotic stress, pathogen infection). Moreover, physical contact between P. indica and Arabidopsis roots is necessary for optimal growth promotion, and chemical communication cannot replace the physical contact. Lower nutrient availability down-regulates and higher nutrient availability up-regulates the plant defense system including the expression of pathogenesis-related genes in roots. High light, osmotic and salt stresses support the beneficial interaction between the plant and the fungus. P. indica reduces stomata closure and H2O2 production after Alternaria brassicae infection in leaves and suppresses the defense-related accumulation of the phytohormone jasmonic acid. Thus, shifting the growth conditions toward a stress promotes the mutualistic interaction, while optimal supply with nutrients or low stress diminishes the benefits for the plant in the symbiosis.

Reactive Oxygen Species Generation-Scavenging and Signaling during Plant-Arbuscular Mycorrhizal and Piriformospora indica Interaction under Stress Condition

A defined balance between the generation and scavenging of reactive oxygen species (ROS) is essential to utilize ROS as an adaptive defense response of plants under biotic and abiotic stress conditions. Moreover, ROS are not only a major determinant of stress response but also act as signaling molecule that regulates various cellular processes including plant-microbe interaction. In particular, rhizosphere constitutes the biologically dynamic zone for plant-microbe interactions which forms a mutual link leading to reciprocal signaling in both the partners. Among plant-microbe interactions, symbiotic associations of arbuscular mycorrhizal fungi (AMF) and arbuscular mycorrhizal-like fungus especially Piriformospora indica with plants are well known to improve plant growth by alleviating the stress-impacts and consequently enhance the plant fitness. AMF and P. indica colonization mainly enhances ROS-metabolism, maintains ROS-homeostasis, and thereby averts higher ROS-level accrued inhibition in plant cellular processes and plant growth and survival under stressful environments. This article summarizes the major outcomes of the recent reports on the ROS-generation, scavenging and signaling in biotic-abiotic stressed plants with AMF and P. indica colonization. Overall, a detailed exploration of ROS-signature kinetics during plant-AMF/P. indica interaction can help in designing innovative strategies for improving plant health and productivity under stress conditions.

Piriformospora indica confers cadmium tolerance in Nicotiana tabacum

Piriformospora indica, a root-colonizing endophytic fungus of Sebacinales, promotes plant growth and confers resistance against biotic and abiotic stresses. In order to confirm the influence of P. indica on growth, proline, malondialdehyde (MDA), chlorophyll, and cadmium (Cd) amounts in Nicotiana tabacum under Cd stress, hydroponics, pot and field trials were conducted. The results showed that P. indica can store Cd in plant roots and reduce leaf Cd content, reduce the concentration of MDA, and increase the proline and chlorophyll content and the activities of catalase, peroxidase, and superoxide dismutase under hydroponic Cd stress. RT-PCR analysis showed that the relative expression level of genes Gsh2, TaPCS1, oas1, GPX, and Hsp70 in colonized plants was 4.3, 1.4, 2.9, 1.7, and 6.9 fold higher than in un-colonized plants respectively. Cd exposure significantly reduced un-colonized plants' agronomic traits compared to P. indica-colonized ones. Our results suggested that P. indica can sequester Cd in roots, so that much less cadmium was transported to leaves, and the increased concentrations of antioxidant enzymes, pigments and proline contents, as well as the higher expression of stress-related phytochelatin biosynthesis genes in P. indica-inoculated plants, may also serve to protect N. tabacum plants against oxidative damage, enhancing Cd tolerance.

Role of Trichoderma harzianum in mitigating NaCl stress in Indian mustard (Brassica juncea L) through antioxidative defense system

Salinity stress affected crop production of more than 20% of irrigated land globally. In the present study the effect of different concentrations of NaCl (0, 100, and 200 mM) on growth, physio-biochemical attributes, antioxidant enzymes, oil content, etc. in Brassica juncea and the protective role of Trichoderma harzianum (TH) was investigated. Salinity stress deteriorates growth, physio-biochemical attributes, that ultimately leads to decreased biomass yield in mustard seedlings. Higher concentration of NaCl (200 mM) decreased the plant height by 33.7%, root length by 29.7% and plant dry weight (DW) by 34.5%. On the other hand, supplementation of TH to NaCl treated mustard seedlings showed elevation by 13.8, 11.8, and 16.7% in shoot, root length and plant DW respectively as compared to plants treated with NaCl (200 mM) alone. Oil content was drastically affected by NaCl treatment; however, TH added plants showed enhanced oil percentage from 19.4 to 23.4% in the present study. NaCl also degenerate the pigment content and the maximum drop of 52.0% was recorded in Chl. 'a'. Enhanced pigment content was observed by the application of TH to NaCl treated plants. Proline content showed increase by NaCl stress and maximum accumulation of 59.12% was recorded at 200 mM NaCl. Further enhancement to 70.37% in proline content was recorded by supplementation of TH. NaCl stress (200 mM) affirms the increase in H2O2 by 69.5% and MDA by 36.5%, but reduction in the accumulation is recorded by addition of TH to mustard seedlings. 200 mM NaCl elevated SOD, POD, APX, GR, GST, GPX, GSH, and GSSG in the present study. Further enhancement was observed by the application of TH to the NaCl fed seedlings. NaCl stress suppresses the uptake of important elements in both roots and shoots, however, addition of TH restored the elemental uptake in the present study. Mustard seedlings treated with NaCl and TH showed restricted Na uptake as compared to seedlings treated with NaCl alone. In conclusion, TH proved to be very beneficial in imparting resistance to the mustard plants against NaCl stress through improved uptake of essential elements, modulation of osmolytes and antioxidants.

Oxidative stress induced expression of monodehydroascorbate reductase gene in Eleusine coracana

Abiotic stresses constitute a serious threats to the world food security as they cause significant economic losses in terms of reduction in crop productivity and also greatly limit the geographical locations where crops can be grown. Exposure to abiotic stress causes over-production of reactive oxygen species, leading to oxidative stress in plants. Induction of oxidative stress is primarily responsible for a variety of detrimental changes in the cellular physiology. However, plants have evolved intricate anti-oxidative defence machinery, for their survival under stress. Plant defence strategies for stress tolerance rely on the expression of anti-oxidative genes required for scavenging the toxic reactive oxygen species. Monodehydroascorbate reductase is one of the key anti-oxidant enzyme responsible for scavenging reactive oxygen species. In the present study, efforts have been made to understand the role of monodehydroascorbate reductase in finger millet under different abiotic stresses (drought, salt and UV radiation). The study establishes a differential link between mdar gene expression and enzyme activity under oxidative stress that is validated under different types of imposed stresses. Alteration in correlation between gene expression and enzyme activities under varying magnitude of oxidative stress is elucidated.

High REDOX RESPONSIVE TRANSCRIPTION FACTOR1 Levels Result in Accumulation of Reactive Oxygen Species in Arabidopsis thaliana Shoots and Roots

Redox Responsive Transcription Factor1 (RRTF1) in Arabidopsis is rapidly and transiently upregulated by H2O2, as well as biotic- and abiotic-induced redox signals. RRTF1 is highly conserved in angiosperms, but its physiological role remains elusive. Here we show that inactivation of RRTF1 restricts and overexpression promotes reactive oxygen species (ROS) accumulation in response to stress. Transgenic lines overexpressing RRTF1 are impaired in root and shoot development, light sensitive, and susceptible to Alternaria brassicae infection. These symptoms are diminished by the beneficial root endophyte Piriformospora indica, which reduces ROS accumulation locally in roots and systemically in shoots, and by antioxidants and ROS inhibitors that scavenge ROS. More than 800 genes were detected in mature leaves and seedlings of transgenic lines overexpressing RRTF1; ∼ 40% of them have stress-, redox-, ROS-regulated-, ROS-scavenging-, defense-, cell death- and senescence-related functions. Bioinformatic analyses and in vitro DNA binding assays demonstrate that RRTF1 binds to GCC-box-like sequences in the promoter of RRTF1-responsive genes. Upregulation of RRTF1 by stress stimuli and H2O2 requires WRKY18/40/60. RRTF1 is co-regulated with the phylogenetically related RAP2.6, which contains a GCC-box-like sequence in its promoter, but transgenic lines overexpressing RAP2.6 do not accumulate higher ROS levels. RRTF1 also stimulates systemic ROS accumulation in distal non-stressed leaves. We conclude that the elevated levels of the highly conserved RRTF1 induce ROS accumulation in response to ROS and ROS-producing abiotic and biotic stress signals.

An ecological role of fungal endophytes to ameliorate plants under biotic stress

It is our consensus that plants survive and flourish in stressed ecosystems because of endosymbiotic organisms that have co-evolved and were essential for their adaptation to changing environments. Some of these microbial components are noncultivable and vertically transmitted from generation to generation. They represent a vast reservoir of heritable DNA that can enhance plant performance in changing environments and add genetic flexibility to adaptation of long-lived plants. If such endophytes can be identified that not only persist in progeny of novel hosts, but can confer benefits in mechanized, agricultural systems, they would be increasingly important in agricultural production and lead to a rapid and economical method of providing novel germplasms of native and crop plants. In the present review, authors advocate the deployment of fungal diversity and its role to overcome the biotic stress in plants. Endophytic fungal association with plants helps it to protect from various pathogen and pests and adapt to survive in harsh biotic and abiotic stress condition.

The interaction of Arabidopsis with Piriformospora indica shifts from initial transient stress induced by fungus-released chemical mediators to a mutualistic interaction after physical contact of the two symbionts

BACKGROUND

Piriformospora indica, an endophytic fungus of Sebacinales, colonizes the roots of many plant species including Arabidopsis thaliana. The symbiotic interaction promotes plant performance, growth and resistance/tolerance against abiotic and biotic stress.

RESULTS

We demonstrate that exudated compounds from the fungus activate stress and defense responses in the Arabidopsis roots and shoots before the two partners are in physical contact. They induce stomata closure, stimulate reactive oxygen species (ROS) production, stress-related phytohormone accumulation and activate defense and stress genes in the roots and/or shoots. Once a physical contact is established, the stomata re-open, ROS and phytohormone levels decline, and the number and expression level of defense/stress-related genes decreases.

CONCLUSIONS

We propose that exudated compounds from P. indica induce stress and defense responses in the host. Root colonization results in the down-regulation of defense responses and the activation of genes involved in promoting plant growth, metabolism and performance.

Mutualism-parasitism paradigm synthesized from results of root-endophyte models

Plant tissues host a variety of fungi. One important group is the dark septate endophytes (DSEs) that colonize plant roots and form characteristic intracellular structures - melanized hyphae and microsclerotia. The DSE associations are common and frequently observed in various biomes and plant taxa. Reviews suggest that the proportion of plant species colonized by DSE equal that colonized by AM and microscopic studies show that the proportion of the root system colonized by fungi DSE can equal, or even exceed, the colonization by AM fungi. Despite the high frequency and suspected ecological importance, the effects of DSE colonization on plant growth and performance have remained unclear. Here, we draw from over a decade of experimentation with the obscure DSE symbiosis and synthesize across large bodies of published and unpublished data from Arabidopsis thaliana and Allium porrum model systems as well as from experiments that use native plants to better resolve the host responses to DSE colonization. The data indicate similar distribution of host responses in model and native plant studies, validating the use of model plants for tractable dissection of DSE symbioses. The available data also permit empirical testing of the environmental modulation of host responses to DSE colonization and refining the "mutualism-parasitism-continuum" paradigm for DSE symbioses. These data highlight the context dependency of the DSE symbioses: not only plant species but also ecotypes vary in their responses to populations of conspecific DSE fungi - environmental conditions further shift the host responses similar to those predicted based on the mutualism-parasitism-continuum paradigm. The model systems provide several established avenues of inquiry that permit more detailed molecular and functional dissection of fungal endophyte symbioses, identifying thus likely mechanisms that may underlie the observed host responses to endophyte colonization.

Spatial dissection of the Arabidopsis thaliana transcriptional response to downy mildew using Fluorescence Activated Cell Sorting

Changes in gene expression form a crucial part of the plant response to infection. In the last decade, whole-leaf expression profiling has played a valuable role in identifying genes and processes that contribute to the interactions between the model plant Arabidopsis thaliana and a diverse range of pathogens. However, with some pathogens such as downy mildew caused by the biotrophic oomycete pathogen Hyaloperonospora arabidopsidis (Hpa), whole-leaf profiling may fail to capture the complete Arabidopsis response encompassing responses of non-infected as well as infected cells within the leaf. Highly localized expression changes that occur in infected cells may be diluted by the comparative abundance of non-infected cells. Furthermore, local and systemic Hpa responses of a differing nature may become conflated. To address this we applied the technique of Fluorescence Activated Cell Sorting (FACS), typically used for analyzing plant abiotic responses, to the study of plant-pathogen interactions. We isolated haustoriated (Hpa-proximal) and non-haustoriated (Hpa-distal) cells from infected seedling samples using FACS, and measured global gene expression. When compared with an uninfected control, 278 transcripts were identified as significantly differentially expressed, the vast majority of which were differentially expressed specifically in Hpa-proximal cells. By comparing our data to previous, whole organ studies, we discovered many highly locally regulated genes that can be implicated as novel in the Hpa response, and that were uncovered for the first time using our sensitive FACS technique.

A class-information-based penalized matrix decomposition for identifying plants core genes responding to abiotic stresses

In terms of making genes expression data more interpretable and comprehensible, there exists a significant superiority on sparse methods. Many sparse methods, such as penalized matrix decomposition (PMD) and sparse principal component analysis (SPCA), have been applied to extract plants core genes. Supervised algorithms, especially the support vector machine-recursive feature elimination (SVM-RFE) method, always have good performance in gene selection. In this paper, we draw into class information via the total scatter matrix and put forward a class-information-based penalized matrix decomposition (CIPMD) method to improve the gene identification performance of PMD-based method. Firstly, the total scatter matrix is obtained based on different samples of the gene expression data. Secondly, a new data matrix is constructed by decomposing the total scatter matrix. Thirdly, the new data matrix is decomposed by PMD to obtain the sparse eigensamples. Finally, the core genes are identified according to the nonzero entries in eigensamples. The results on simulation data show that CIPMD method can reach higher identification accuracies than the conventional gene identification methods. Moreover, the results on real gene expression data demonstrate that CIPMD method can identify more core genes closely related to the abiotic stresses than the other methods.

The maturation zone is an important target of Piriformospora indica in Chinese cabbage roots

The mutualistic symbiont Piriformospora indica exhibits a great potential in agriculture. The interaction between P. indica and Chinese cabbage (Brassica campestris cv. Chinensis) results in growth and biomass promotion of the host plant and in particular in root hair development. The resulting highly bushy root phenotype of colonized Chinese cabbage seedlings differs substantially from reports of other plant species, which prompted the more detailed study of this symbiosis. A large-scale expressed sequence tag (EST) data set was obtained from a double-subtractive EST library, by subtracting the cDNAs of Chinese cabbage root tissue and of P. indica mycelium from those of P. indica-colonized root tissue. The analysis revealed ~700 unique genes rooted in 141 clusters and 559 singles. A total of 66% of the sequences could be annotated in the NCBI GenBank. Genes which are stimulated by P. indica are involved in various types of transport, carbohydrate metabolism, auxin signalling, cell wall metabolism, and root development, including the root hair-forming phosphoinositide phosphatase 4. For 20 key genes, induction by fungal colonization was confirmed kinetically during the interaction by real-time reverse transcription-PCR. Moreover, the auxin concentration increases transiently after exposure of the roots to P. indica. Microscopic analyses demonstrated that the development of the root maturation zone is the major target of P. indica in Chinese cabbage. Taken together, the symbiotic interaction between Chinese cabbage and P. indica is a novel model to study root growth promotion which, in turn, is important for agriculture and plant biotechnology.

Root endophyte Piriformospora indica DSM 11827 alters plant morphology, enhances biomass and antioxidant activity of medicinal plant Bacopa monniera

Unorganized collections and over exploitation of naturally occurring medicinal plant Bacopa monniera is leading to rapid depletion of germplasm and is posing a great threat to its survival in natural habitats. The species has already been listed in the list of highly threatened plants of India. This calls for micropropagation based multiplication of potential accessions and understanding of their mycorrhizal associations for obtaining plants with enhanced secondary metabolite contents. The co-cultivation of B. monniera with axenically cultivated root endophyte Piriformospora indica resulted in growth promotion, increase in bacoside content, antioxidant activity and nuclear hypertrophy of this medicinal plant.

The mutualistic fungus Piriformospora indica protects barley roots from a loss of antioxidant capacity caused by the necrotrophic pathogen Fusarium culmorum

Fusarium culmorum causes root rot in barley (Hordeum vulgare), resulting in severely reduced plant growth and yield. Pretreatment of roots with chlamydospores of the mutualistic root-colonizing basidiomycete Piriformospora indica (subdivision Agaricomycotina) prevented necrotization of root tissues and plant growth retardation commonly associated with Fusarium root rot. Quantification of Fusarium infections with a real-time polymerase chain reaction assay revealed a correlation between root rot symptoms and the relative amount of fungal DNA. Fusarium-infected roots showed reduced levels of ascorbate and glutathione (GSH), along with reduced activities of antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, GSH reductase, dehydroascorbate reductase, and monodehydroascorbate reductase. Consistent with this, Fusarium-infected roots showed elevated levels of lipid hydroperoxides and decreased ratios of reduced to oxidized forms of ascorbate and GSH. In clear contrast, roots treated with P. indica prior to inoculation with F. culmorum showed levels of ascorbate and GSH that were similar to controls. Likewise, lipid peroxidation and the overall reduction in antioxidant enzyme activities were largely attenuated by P. indica in roots challenged by F. culmorum. These results suggest that P. indica protects roots from necrotrophic pathogens, at least partly, through activating the plant's antioxidant capacity.

Trichoderma-plant root colonization: escaping early plant defense responses and activation of the antioxidant machinery for saline stress tolerance

Trichoderma spp. are versatile opportunistic plant symbionts which can colonize the apoplast of plant roots. Microarrays analysis of Arabidopsis thaliana roots inoculated with Trichoderma asperelloides T203, coupled with qPCR analysis of 137 stress responsive genes and transcription factors, revealed wide gene transcript reprogramming, proceeded by a transient repression of the plant immune responses supposedly to allow root colonization. Enhancement in the expression of WRKY18 and WRKY40, which stimulate JA-signaling via suppression of JAZ repressors and negatively regulate the expression of the defense genes FMO1, PAD3 and CYP71A13, was detected in Arabidopsis roots upon Trichoderma colonization. Reduced root colonization was observed in the wrky18/wrky40 double mutant line, while partial phenotypic complementation was achieved by over-expressing WRKY40 in the wrky18 wrky40 background. On the other hand increased colonization rate was found in roots of the FMO1 knockout mutant. Trichoderma spp. stimulate plant growth and resistance to a wide range of adverse environmental conditions. Arabidopsis and cucumber (Cucumis sativus L.) plants treated with Trichoderma prior to salt stress imposition show significantly improved seed germination. In addition, Trichoderma treatment affects the expression of several genes related to osmo-protection and general oxidative stress in roots of both plants. The MDAR gene coding for monodehydroascorbate reductase is significantly up-regulated and, accordingly, the pool of reduced ascorbic acid was found to be increased in Trichoderma treated plants. 1-Aminocyclopropane-1-carboxylate (ACC)-deaminase silenced Trichoderma mutants were less effective in providing tolerance to salt stress, suggesting that Trichoderma, similarly to ACC deaminase producing bacteria, can ameliorate plant growth under conditions of abiotic stress, by lowering ameliorating increases in ethylene levels as well as promoting an elevated antioxidative capacity.