ENDOPHYTIC FUNGI: AS A POOL OF SECONDARY METABOLITES.

R. Kuralarasi 1 , M. Sundar 1 and * K. Lingakumar 2 . 1. Research scholar, Centre for Research and PG studies in Botany, Ayya Nadar Janaki Ammal College, Sivakasi-626124. 2. Head and Associate Professor of Botany, Centre for Research and PG studies in Botany, Ayya Nadar Janaki Ammal College, Sivakasi-626124. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History


A. Secondary metabolites from endophytes as antimycotic agents
Endophytic fungi are mitosporic and meiosporicascomycetes that asymptomatically reside in the internal t issues of plants beneath the epidermal cell layer, where fungi colonize healthy and living tissues. The ir biological diversity is enormous, especially in temperate and tropical rainforests. The fungi are hosted in nearly 300,000 land plant species, with each plant hosting one or more of these fungi. Wagenaaret al., (2000) three novel cytochalasins have recently been reported from Rhinocladiella sp. as an endophyte on Tripterygiumwilfordiithese compounds have antitumor activity and have been identified as 22-o xa-cytochalasins. Muscodorvitigenus, isolated from Paullina paullinioides yields naphthalene as its major product naphthalene, the active ingredient in common mothballs, is a widely exploited insect repellant. Worapong et al., (2001). Muscodoralbus is a newly described endophyticfungus obtained fro m s mall limbs of Cinnamomumzeylanicum. Daisy and Castillo, and Strobelet al., (2002.) reported M. vitigenus shows promising preliminary results as an insect deterrent and has exhibited potent insect repellency against the wheat stem sawfly (Cephuscinctus). An interesting observation is that in the case of co-cultivation between A. niger and actinomycetes, an intimate physical interaction is required to activate silent gene clusters in As. niger (Schroeckhet al. 2009) A lthough the topic of volatile antibiot ics would perfectly fit into th e previous section, they have been put it under a separate heading because special techniques are required to detect these compounds. Because microbes in nature live in commun ities, growth of various fungi in co -culture with other organisms has been tested. Co-culture can indeed result in activation of silent gene clusters or in strongly increased expression (Ola et al. 2013;Wu et al. 2015b). Little-studied groups of fungi are considered to be potential sources of novel natural products for medicine and agriculture ). The function of invasive fungal infections has increased significantly during cancer organ transplantation, chemotherapy and bone marrow transplantation. Endophytes are presumably ubiquitous in plants, with populations dependent on host species and location. During long research only a few numbers of antifungal agents are available for the treatment of various life threatening fungal infections. The search for new antifungal agents to overcome the growing human problems of drugs resistance in microorganis ms is growing. Ongoing global efforts to discover new compounds from EF of medicinal plants are yielding valuable results . Co mpounds produced by EF are being recognized as a versatile arsenal of antifungal agents. Their anti-microbial activity is detected using air contact between the volatileproducing fungus and the target pathogen.

B. Secondary metabolites from endophytes as anti viral agent
Endophytes have also been studied for their antiviral activ ity, the emergence of mu lti resistance against existing drugs, and high cost of current therapies as well as the AIDS associated opportunistic infections, such as Cytomegalo virus and Polyoma virus needs essential antiviral agent. Cytonic acid A and B were recognized as human cytomegalo virus protease inhibitors fro m endophytic fungus Cytonaema Sp. isolated Bioprospecting for Microbial Endophytes and their Natural Products fromQuercus Sp. (Guoet al., 2000). A novel quinine related metabolites xanthoviridicatins E and F was also produced by an endophyticPenicilliumchrysogenum able to inhibit the cleavage reaction of HIV-1 integrase. Fermentation of endophytic fungi with potential fo r bioactive co mpound production has several advantages like reproducible and dependable productivity. These endophytes can be grown on large scale in fermenters to provide inexhaustible supply of bioactive compound and thus can be commercially exploited. In order to optimize various biosynthetic pathways, changes in the culture conditions should be explored which leads to the production of derivatives and analogues of novel compounds (Goutamet al. 2014). Endophyticactinobacteria are examined to be a substitute to combat mult idrug -resistant human pathogens as they serve as a latent source of novel antimicrobial co mpounds (Ravi and Vasantba. 2017).

C. Secondary metabolites from endophytes as antioxidant compounds
Natural antio xidants and might substitute synthetic antio xidants which produce many undesirable secondary effects. Antioxidants are the substances that when present in low concentrations compared to those of an oxidizable substrate significantly delays or prevents oxidation of that substance. Reactive o xygen species (ROS) produced during the cellular metabolism are essential fo r cell signaling, apoptosis, gene expression and ion transportation1. Phenolic and flavonoid co mpound seem to have an important role in stabilizing lip id pero xidation, associated with antioxidant activity Yanishlieva-Maslarova, (2001). Fungal endophytes are a store house of novel secondary metabolites including antibiotic, antio xidant, anticancer and immunosuppressant compounds . Free radicals are reactive o xygen and nitrogen species which are generated by various physiologica l processes in the body. Uncontrolled generation of free radicals leads to attack on memb rane lipids, proteins, enzy mes and DNA 250 causing oxidative stress and ultimately cell death. Cephalosporium sp., an endophytic fungus isolated from the root of Trachelospermumjasminoidesproduce a phenolic co mpound with strong free radical scavenging and antioxidant activity .
The free radical scavenging ability of phenols is attributed to the occurrence of hydroxyl groups. Phenols and alkaloids were the major phytochemical constituents of endophytes in the study which supports the views of Huang et al., (2007).Preliminary phytochemical investigation of ethyl acetate extracts of endophytic fungi associated with Eugenia jambolanaconfirms the presence of alkaloids, phenols, flavonoids, saponins, and terpenes. Phenols and terpenes are the main chemical constituents responsible for reducing lipid pero xidation and hence act as primary and secondary antioxidants (Hajduet al.,2007).There is 22% of endophytic fungi extract isolated fro m five More than 51% o f s mall mo lecule drugs approved between 1981 and 2014 were based on natural products, the rest being synthetic . With the increasing demand for herbal drugs, natural health products and secondary metabolites, the use of medicinal plants is growing rapidly throughout the world. However, we are facing the accelerated loss of wild medicinal plant species; one third of the estimated 50.000-80.000 medicinal p lant species are threatened with ext inction fro m overharvesting and natural anthropogenic habitat destruction . Antio xidants have become the topic of interest recently. The field of free radical chemistry is gaining more attention now a days. Free radicals are reactive oxygen and nitrogen species which are generated by various physiologic al processes in the body. Uncontrolled generation of free radicals leads to attack on membrane lip ids, proteins, enzymes and DNA causing oxidative stress and ultimately cell death. These ROS are responsible for many degenerative human diseases like neurodegenerative disorders, cancer, Alzheimer's disease, ageing, Parkinson's disease, diabetes mellitus, atherosclerosis, and inflammatory diseases. Protection against free radicals can be enhanced by taking sufficient amounts of exogenous antioxidants. An antioxidant is a stable mo lecule which donates an electron to a rampaging free radical and terminates the chain reaction before vital mo lecules are damaged. Dietary antio xidants, including polyphenolic co mpounds, vitamin E and C are believed to be the effective nutrients in the prevention of oxidative stress related diseases. Fungal endophytes represent an abundant and dependable source of novel antioxidant compounds (Yadavet al., 2014). Lot of studies were conducted as antiviral, anticancer, antidiabetic and antimicrobial effects to test the potential effects of fungal endophytes, but very few scientists worked on their antioxidant capacity (Seemadhankharet al., 2012). Srin ivasanet al., 2010 was conducted antioxidant properties using EF Phyllostictasp. which is isolated fro m medicinal plant Guazumatomentosaand also quantified phenol and flavonoid content. Antioxidant was screened (Zenget al.,2011) with the 2,2'-azinodi(3-ethylbenzthiazoline-6sulfonic acid) (ABTS) decolorizat ion assay and 2,2'-diphenyl-1-p icrylhydrazyl (DPPH) found this EF have potential novel source of natural antioxidants. Antioxidant was screened for EF in medicinal p lants Rhodiolacrenulata, R. angusta, and R. sachalinensis (Cui et al., 2015). DPPH, FRAP, and Iron chelating activity are conducted using endophytesAsperigillusniger ,Penicillium sp. and Trichoderma sp. (Gov indappaet al., 2013).

D. Secondary metabolites from endophytes as antibiotics
Antibiotics are used to treat bacterially infected animals but are also admin istered as a preventive measure. From an animal and human health perspective, Antibiotics are used to treat infections caused by bacteria and other microorganisms. Trad itionally, the term "antibiotics" is used to describe any substance produced by a micro -organis m that is effective against the growth of another microorganism. Antibiotics are used to treat bacterially infected animals but are also administered as a preventive measure. Important group of antibiotics was introduced by Duggar,(1948) the tetracyclines, of wh ich chlortetracycline, isolated fro m the soil bacteria Strepromycesaureofaciens, was the first . In the same year, David Gottlieb reported the isolation of a new broad spectrum antibiot ic fro m the soil bacteriu m Streptomyces venezuelaecalled chloramphenicol (Carter et al., 1948).
Different antibiotics have different antibacterial mechanisms of activity. The main mechanis ms of antimicrobial action inhibit the bacteria cell wall synthesis by covalently binding with penicillin -binding proteins (PBP), wh ich catalyse the synthesis of peptidoglycan, the major co mponent of the cell wall (Jovetic et al., 2010). Chloramphenicol binds to the active site of transfer ribonucleic acid (tRNA) and thus inhibits the protein synthesis at the ribosome (McCoy et al., 2011). The carbapenems are structurally very similar to the penicillins the sulfur ato m has been replaced by a carbon atom and an unsaturation has been introduced. As a result the carbapenems possess the broadest antimicrobial activ ity amongst the ß-lactams Nord mannet al., (2011). The most common carbapenems are imipenem, meropenem, ertapenem, doripenem and biapenem.

E. Secondary metabolites from endophytes as anticancer agents
Endophyte hold main position in drug discovery as it has antibiotic, antiviral and anticancer properties, due to their ability to produce chemical which can be used as drug. The discovery of novel antimicrobial metabolites from endophytes is an important alternative to overcome the increasing levels of drug resistance by plant and human pathogens, the insufficient nu mber of effective antibiotics against diverse bacterial species, and few new antimicrobial agents in development, probably due to relatively unfavorable returns on investment. For this reason, seeking new ways of obtaining Taxo l is the key to protecting this limited resources and reducing the cost of drug theraphy with this end goal in mind, scientists all over the world are researc hing arras related to Taxol production including chemical synthesis, plant tissue cell culture microbial fermentation .In particular microbial fermentation has demonstrated that he isolation and identification of Taxo l producing endophytic fungi is new and feasible approach to the production of Taxol (Sun et al.,2008).Presently, the develop ment and utilizat ion of Taxol producing fungi have made significant progress worldwide. Extensive research such as searching for paclitaxel producing endophytic fungi fro m Taxus species as well as fro m other related plant species, microbial fermentation processes and genetic engineering for improving paclitaxel production has been developed, and much progress has been achieved during the past two decades.
In the case Taxomycesandrenae, Pestalotiopsismicrospora, Alternariasp, Fusariumlateritium, F.solni, F.mairie and Perconiasp were screened to have the ability to produce Paclitaxel and its derivatives (Chakravarthiet al.,2008).This early work set the stage for a more comp rehensive examination of the ability of other Taxus species and other plants to yield endophytes producing taxol. Developing new anticancer drugs with a higher potency and specificity against cancer cells has therefore become an important goal in bio med ical research and concern for the medical fraternity. Many bioactive co mpounds, including antifungal agents, have been isolated fro m the genus Xylariaresiding in different plant hosts, such as "sordaricin" with antifungal activ ity ag ainst Candida albicans (Pongcharoenet al., 2008).
The anticancer drugs show nonspecific to xicity to proliferating normal cells, possess enormous side effects, and are not effective against many forms of cancer. Thus, the cure of cancer has been enhanced mainly due to diagnosis improvements, which allow earlier and more precise treatments. The rediscovery of known secondary metabolites that are typically produced under standard in vitro conditions has been an under-standable consequence of such an approach Scherlach and Hertweck (2009). The importance of compounds bearing antioxidant activity lies in the fact that they are highly effective against damage caused by reactive oxygen species (ROSs) and oxygen -derived free radicals, wh ich contribute to a variety of pathological effects, for instance, DNA damages, carcinogenesis, and cellu lar degeneration. These free radicals occur in the body during an imbalance between ROS and antioxidants. Hence, the role of antio xidant is necessary and important to balance the antioxidant status that would reduce the pathological conditions induced by free radicals. Fungi are remarkably a diverse group including approximately 1.5 million species, which can potentially provide a wide variety of metabolites such as alkaloids, ben zoquinones, 252 flavonoids, phenols, steroids, terpenoids, tetralones, and, xanthones and t axol, also known as paclitaxel,a chemical substance of tetracyclicditerpene lactam was first isolated from the bark,roots and branches of western coniferous tree Taxusbrevifolia Zhou et al.,(2010).Traditional methods of extract ing taxol fro m the bark of Taxus species are inefficient and environmentally costly. Alyet al., (2010) isolated the bioactive metabolites and showed different biological activ ities that metabolites antitumor, herbicide, antimicrobial, antimalarial, and antileishmanial. Gayathriet al., (2010) pointed out theemergence of antibiotic resistance among pathogenic microorganisms limits treatment options.
Scientific studies have investigated the anticancer activity of several anthracenedione derivatives, which was separated from the secondary metabolites of themangroveendophytic fungus Haloroselliniasp. and Guignardiasp.

Conclusion:-
This review explains the traditional importance of endophyteswith comparative view in modern med icine.A ll isolated chemical constituents as a promising antibioticentity. Theherbal formulations or purification of novel compound so as toovercome the obstacles in the path of discovery of pure herbaldrug. The use of the secondary metabolites of plants or microorganisms has gained substantial attention in the treatment of cancer. Endophytes have 253 proven to be rich sources of novel natural compounds with a wide-spectrum of biological activ ities and a high level of structural diversity. The use of endophytesas biocatalysts in the biotransformation process of natural products assumes greater importance. However, the application of microorganisms by the food and pharmaceutical industries to obtain compounds of interest is still modest, considering the great availability of useful microorganisms and the large scope of reactions that can be accomplished by them.
Endophytic fungi can produce same or similar compounds originated from their host plants. Endophytic microorganis ms are a huge reservoir of genetic diversity. Insights gained into endophyte -endophyte and plantendophyte communication can be beneficial to bio medical co mmunity and the endophyte synthesized and secreted chemicals can be of importance to the society for the development of novel antibiotics against deadly pathogens. However, only a few numbers of antifungal agents are now available for the treatment of various life threatening fungal infections. There is an ongoing need for novel drugs that are highly effective in the treatment of cancer, drug resistant bacteria, and fungal infections. However, the application of microorganisms by the pharmaceutical and food industries to obtain different co mpounds of interest is still modest. Antioxidants have become the topic of interest recently. Fungal endophytes represent an abundant and dependable source of novel antioxidant compounds. There has been increasing interest in systematics, evolutionary biology, ecology and applied research of endophytic fungi. During the developments of modern biotechnology and taking advantage of genetic engineering, metabolic technology and their better use to manipulate this impo rtant microbial resource, and to make benefit of mankind.