Swati Tripathi

Piriformospora indica, a cultivable root endophyte with multiple biotechnological applications.

Piriformospora indica is a wide-host root-colonizing endophytic fungus which allows the plants to grow under extreme physical and nutrient stress. The fungus can be cultivated on complex and minimal substrates. It belongs to the Sebacinales in Basidiomycota. P. indica has a vast geographical distribution and is reported from Asia, South America and Australia. The fungus is interesting for basic research as well as biotechnological applications because: (i) it functions as a plant promoter and biofertilizer in nutrient-deficient soils, (ii) as a bioprotector against biotic and abiotic stresses including root and leaf fungus pathogens and insect invaders, (iii) as a bioregulator for plant growth development, early flowering, enhanced seed production, and stimulation of active ingredients in medicinal plants (iv) as well as a bio-agent for the hardening of tissue-culture-raised plants. Positive interaction are established for many plants of economic importance in arboriculture, agro-forestry, flori-horticulture including Orchids, and those utilized for energy production and paper industry. P. indica also interacts with members of bryophyte, Aneura pinguis, pteridophyte, Pteris ensiormis, Gymnosperms (Pinus halepensis) and a large number of angiosperms (145 tested till date) including the model plant Arabidopsis thaliana and other members of the mustard family. Similar to arbuscular mycorrhizal fungi, P. indica stimulates nutrient uptake in the roots and solubilizes insoluble phosphatic and sulphur components in the soil. The interaction of P. indica with the model plants Arabidopsis thaliana and barley (Hordeum vulgare L.) is used to understand the molecular basis of this beneficial plant/microbe interaction. We describe the current knowledge about the molecular basis of the interaction of plants with P. indica. An attempt is made to compare it with pathogenic and mycorrhizal plant/microbe interactions and also propose possible biotechnological applications.

The Root-Colonizing Endophyte Pirifomospora indica Confers Drought Tolerance in Arabidopsis by Stimulating the Expression of Drought Stress–Related Genes in Leaves

Piriformospora indica is an endophytic fungus that colonizes the roots of many plant species, including Arabidopsis. We exposed 18-day-old Arabidopsis seedlings, which were either cocultivated with the fungus or mock-treated for the last 9 days, to mild drought stress for 84 h. During the first 36 to 48 h, seedlings cocultivated with the fungus continued to grow, while the uncolonized controls did not. This results in a threefold difference in the fresh weight and a more than twofold difference in the chlorophyll content. The photosynthetic efficiency was only slightly reduced in the colonized (F variable/F maximum [Fv/Fm] at t(0 h) = 0.82 and t(36 h) = 0.79) and was severely impaired in the uncolonized (Fv/Fm at t(0 h) = 0.81 and (t)(36 h) = 0.49) seedlings, which also showed symptoms of withering. When seedlings exposed to drought stress for 72 or 84 h were transferred to soil, 10% (72 h) and none (84 h) of uncolonized seedlings reached the flowering stage and produced seeds, while 59% (72 h) and 47% (84 h) of the colonized seedlings flowered and produced seeds. After exposure to drought stress for 3 h, the message levels for RESPONSE TO DEHYDRATION 29A, EARLY RESPONSE TO DEHYDRATION1, ANAC072, DEHYDRATION-RESPONSE ELEMENT BINDING PROTEIN2A, SALT-, AND DROUGHT-INDUCED RING FINGER1, phospholipase Ddelta, CALCINEURIN B-LIKE PROTEIN (CBL)1, CBL-INTERACTING PROTEIN KINASE3, and the histone acetyltransferase (HAT) were upregulated in the leaves of P. indica-colonized seedlings. Uncolonized seedlings responded 3 to 6 h later, and the message levels increased much less. We identified an Arabidopsis ethylmethane-sulfonate mutant that is less resistant to drought stress and in which the stress-related genes were not upregulated in the presence of P. indica. Thus, P. indica confers drought-stress tolerance to Arabidopsis, and this is associated with the priming of the expression of a quite diverse set of stress-related genes in the leaves. Transfer to soil was again associated with a faster and stronger upregulation of the message levels for phospholipase Ddelta, CBL1, and HAT in P. indica-colonized seedlings, indicating that this response might also contribute to better survival on soil.

PYK10, a β-glucosidase located in the endoplasmatic reticulum, is crucial for the beneficial interaction between Arabidopsis thaliana and the endophytic fungus Piriformospora indica

Piriformospora indica, an endophyte of the Sebacinaceae family, promotes growth and seed production of many plant species, including Arabidopsis. Growth of a T-DNA insertion line in PYK10 is not promoted and the plants do not produce more seeds in the presence of P. indica, although their roots are more colonized by the fungus than wild-type roots. Overexpression of PYK10 mRNA did not affect root colonization and the response to the fungus. PYK10 codes for a root- and hypocotyl-specific beta-glucosidase/myrosinase, which is implicated to be involved in plant defences against herbivores and pathogens. Expression of PYK10 is activated by the basic helix-loop-helix domain containing transcription factor NAI1, and two Arabidopsis lines with mutations in the NAI1 gene show the same response to P. indica as the PYK10 insertion line. PYK10 transcript and PYK10 protein levels are severely reduced in a NAI1 mutant, indicating that PYK10 and not the transcription factor NAI1 is responsible for the response to the fungus. In wild-type roots, the message level for a leucine-rich repeat protein LRR1, but not for plant defensin 1.2 (PDF1.2), is upregulated in the presence of P. indica. In contrast, in lines with reduced PYK10 levels the PDF1.2, but not LRR1, message level is upregulated in the presence of the fungus. We propose that PYK10 restricts root colonization by P. indica, which results in the repression of defence responses and the upregulation of responses leading to a mutualistic interaction between the two symbiotic partners.

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

Ascorbate is a major antioxidant and radical scavenger in plants. Monodehydroascorbate reductase (MDAR) and dehydroascorbate reductase (DHAR) are two enzymes of the ascorbate-glutathione cycle that maintain ascorbate in its reduced state. MDAR2 (At3g09940) and DHAR5 (At1g19570) expression was upregulated in the roots and shoots of Arabidopsis seedlings co-cultivated with the root-colonizing endophytic fungus Piriformospora indica, or that were exposed to a cell wall extract or a culture filtrate from the fungus. Growth and seed production were not promoted by Piriformospora indica in mdar2 (SALK_0776335C) and dhar5 (SALK_029966C) T-DNA insertion lines, while colonized wild-type plants were larger and produced more seeds compared to the uncolonized controls. After 3 weeks of drought stress, growth and seed production were reduced in Piriformospora indica-colonized plants compared to the uncolonized control, and the roots of the drought-stressed insertion lines were colonized more heavily by the fungus than were wild-type plants. Upregulation of the message for the antimicrobial PDF1.2 protein in drought-stressed insertion lines indicated that MDAR2 and DHAR5 are crucial for producing sufficient ascorbate to maintain the interaction between Piriformospora indica and Arabidopsis in a mutualistic state.

Mycorrhizal Fungi and Other Root Endophytes as Biocontrol Agents Against Root Pathogens

In nature, production of disease-free plants with enhanced yield and compounds of therapeutic value can be mediated through rhizospheric microorganisms. There are increasing environmental concerns over the widespread use of biocontrol measures in general, and alternatively, more sustainable methods of disease control are now being sought. Plant diseases caused by root pathogens need to be controlled in order to maintain the quality and abundance of food, feed and fiber, the prime necessities of life. Different approaches are used for prevention and control of these root pathogens. Among these alternatives are those referred to as biological control; the most obvious and apparently biological control is a potent means of reducing the damage caused by plant pathogens. The potential agents for biocontrol activity are rhizosphere-competent fungi and bacteria which, in addition to their antagonistic activity, are capable of inducing growth responses by either controlling minor pathogens or by producing growth-stimulating factors. A variety of biological controls are available for use, but further development and effective adoption requires a greater understanding of the complex interactions among plants, people, and the environment. This article emphasizes: (1) information about mycorrhiza and root endophytes, (2) various definitions and key mechanisms of biocontrol, and (3) the relationships between microbial diversity and biological control.

In vitro plant development and root colonization of Coleus forskohlii by Piriformospora indica

The present study was conducted for optimization of in vitro substrates under aseptic conditions for interaction of Piriformospora indica with the medicinal plant Coleus forskohlii. It aims to test the effects of different substrates on P. indica colonization as well as growth parameters of the in vitro raised C. forskohlii. Interaction of in vitro C. forskohlii with root endophyte P. indica under aseptic condition resulted in increase in growth parameters in fungus colonized plants. It was observed that P. indica promoted the plant’s growth in all irrespective of substrates used for co-culture study. The growth was found inferior in liquid compared to semisolid medium as well as there was problem of hyperhydricity in liquid medium. P. indica treated in vitro plantlets were better adapted for establishment under green house compared to the non treated plants due to fungal intervention.

Inhibitory Interactions of Rhizobacteria with the Symbiotic Fungus Piriformospora indica

Interactions between plant growth-promoting rhizobacteria (PGPRs) and the symbiotic plant growth-promoting fungus Piriformospora indica were demonstrated by adopting several working models. Different rhizobacteria either inhibit, promote, or have no influence on stimulatory effect of P. indica in gnotobiotic barley plants. In particular, it was demonstrated that, e.g., Pseudomonas fluorescens WS5 and Burkholderia cepacia LA3 inhibited the growth and development of P. indica including complete blockage of sporulation (chlamydospores). The interaction with Ps. fluorescens turned out to be “fungistatic” as well as “fungicidal” in nature. TEM study showed the degradation of cell walls. Gas chromatography/mass spectrometry ion fragmentation pattern suggests that one of the interactive compounds is pyoverdine—a potent siderophore. On the other hand, the severe inhibition of the P. indica by the excreted metabolites of B. cepacia was described at the metabolome level applying high accurate mass spectrometer measurements. It was observed that several pathways were deactivated in the fungus, but a few of them, like ubiquinone biosynthesis, limonene, and pinene degradation, were activated since increased number of metabolites was annotated. Saponin, a biosurfactant, also inhibited the fungus but did not affect the ubiquinone biosynthesis and the limonene–pinene degradation. The study clearly demonstrated that there is intense interaction at metabolome level between rhizobacteria, P. indica, and plant components. A balance maintained due to stimulation and inhibition of the fungus by different rhizobacteria appears to be one of the major factors responsible for fungal diversity, abundance, and function in the rhizosphere. The study opens new vistas to understand delicate balance among mycorrhizospheric organisms that largely allow diverse microbes to coexist and share common resources.

Mycorrhizal Fungi as Control Agents Against Plant Pathogens

Biofertilizers comprise single or consortia of living microorganisms which are responsible for the direct or indirect benefits rendered to growth of various plants. These microbial inoculants are produced from cultures of certain soil organisms that can improve soil fertility and crop productivity. They solubilise phosphorous, fix atmospheric nitrogen, oxidize sulfur, decompose organic material and alter the dynamics and properties of soil resulting in various benefits to plant growth and crop production. Biofertilizers help to increase access to nutrients thus providing growth-promoting factors for plants. This increased availability and efficient absorption of nutrients stimulates plant growth by hormone action and improves crop yield. One of the most abundant fungi in agricultural soil, the arbuscular mycorrhizal (AM) fungi, play a very important role as biofertilizers. They form mutualistic relationships with roots of 90% of plants, promote absorption of nutrients and water, control plant diseases, and improve soil structure. Plants colonized by mycorrhizae grow better than those without them and are beneficial in natural and agricultural systems. The use of AM fungi as biofertilizers is not new; they have been produced for use in agriculture, horticulture, landscape restoration, and soil remediation for almost two decades.

Protective and therapeutic potential of ginger (Zingiber officinale) extract and [6]-gingerol in cancer: A comprehensive review: Ginger extract and [6]-gingerol as anticancer agents

Natural dietary agents have attracted considerable attention due to their role in promoting health and reducing the risk of diseases including cancer. Ginger, one of the most ancient known spices, contains bioactive compounds with several health benefits. [6]‐Gingerol constitutes the most pharmacologically active among such compounds. The aim of the present work was to review the literature pertaining to the use of ginger extract and [6]‐gingerol against tumorigenic and oxidative and inflammatory processes associated with cancer, along with the underlying mechanisms of action involved in signaling pathways. This will shed some light on the protective or therapeutic role of ginger derivatives in oxidative and inflammatory regulations during metabolic disturbance and on the antiproliferative and anticancer properties. Data collected from experimental (in vitro or in vivo) and clinical studies discussed in this review indicate that ginger extract and [6]‐gingerol exert their action through important mediators and pathways of cell signaling, including Bax/Bcl2, p38/MAPK, Nrf2, p65/NF‐κB, TNF‐α, ERK1/2, SAPK/JNK, ROS/NF‐κB/COX‐2, caspases‐3, ‐9, and p53. This suggests that ginger derivatives, in the form of an extract or isolated compounds, exhibit relevant antiproliferative, antitumor, invasive, and anti‐inflammatory activities.

Mycotoxin-assisted mitochondrial dysfunction and cytotoxicity: Unexploited tools against proliferative disorders: MYCOTOXIN-ASSISTED MITOCHONDRIAL DYSFUNCTION AND CYTOTOXICITY

Mitochondria are the powerhouse of cells, which upon dysfunctions may lead to several diseases. Mycotoxins are the toxic secondary metabolites from fungi which are capable of causing diseases and death in humans and animals. They have a versatile mechanism of action in biological systems and can be used as lead compounds to treat some diseases including cancer. The present work encompasses analysis on the effects of mycotoxins on mitochondrial dysfunction. Electronic databases such as PubMed, ScienceDirect, Scopus, Web of Science, and Google Scholar were thoroughly searched for up‐to‐date published information associated with those mycotoxins and their effect on mitochondrial dysfunction. Findings suggest that mycotoxins such as citrinin, aflatoxin, and T‐2 toxin exert multi‐edged sword‐like effects in test systems causing mitochondrial dysfunction. Mycotoxins can induce oxidative stress even at low concentration/dose that may be one of the major causes of mitochondrial dysfunction. On the other hand, activation of apoptotic caspases and other proteins by mycotoxins may lead to apoptotic cell death. Thus, mycotoxins‐mediated mitochondrial dysfunction may be related to several chronic diseases which also makes these mycotoxins considerable as lead compounds for inducing toxic effects in cells. Their cytotoxic effects on cancer cells suggest their possible application as chemotherapeutic tools.