Endophytes: a Novel Source for Bioactive Molecules
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Endophytes:Proc Indian Natn A Novel Sci Acad Source 74 No.2 for Bioactivepp. 73-86 (2008)Molecules 73 Review Article Endophytes: A Novel Source for Bioactive Molecules VIJESHWAR VERMA*, PANKAJ SUDAN and AMARDEEP KOUR Dean College of Sciences, Shri Mata Vaishno Devi University (SMVDU), Katra (J&K State) Fast track postal address: PRO Office of SMVDU,15-C (2nd Ext.) Gandhi Nagar, Opp. Bahu Plaza, Jammu 180 003 (Received 15 Feb 2008; Accepted 7 may 2008) Endophytes inhabit theoretically every plant on the earth. They have gained increased importance after these have been reported as a novel source of potentially useful bioactive molecules e.g., anticancer, immunosuppressive and anti-viral compounds, alkaloids, antibiotics, anti-oxidants, cytochalacins etc. This has raised the hope that medicinally important plants might escape the wrath of mankind in their over exploitation for extraction of bioactive molecules from them and might survive the danger of getting extinct in near future. One of the major problems facing the future of endophyte biology is the rapidly diminishing rainforests, which hold the greatest possible resource for acquiring novel microorgan- isms and their products. The present review is to consolidate the data available on the role of endophytes producing various important bioactive molecules of therapeutic importance. Key Words: Endophytic Microorganisma; Bioactive Molecules; Life Cycle; Isolating Endophytes; Eco-friendly; Torreyanic Acid; Cytochalacine; Antibiotics; Alkaloids; Pesticides; Biodiversity. 1 Introduction plant species inhabiting the world, each individual plant The term endophyte refers here to microorganisms is a host to these unique microorganisms (Strobel, mostly fungi inhabiting plant organs without causing unpublished data). Only a few of these plants (grass apparent harm to their host [1]. Plant tissues remain entire species) have been studied relatively complete for their and functional. Since the discovery of fungal endophytes endophytic biology. Consequently, the opportunity to find in conifers [2] numerous investigations on their new and interesting endophytic microorganisms among abundance, species composition and response to various myriad of plants in different settings and ecosystems is environmental factors have been published. Endophytes not only very great but also a thrilling challenge. have one or more varieties of interactions with their host Plants may benefit from the presence of endophytes plant: Some fungi are widespread and are found on many in many ways. Potential plant benefits have been different plant species; others are highly specific to a examined in only a few cases. Rhabdocline parkeri single host in a specific environment. Further, a diverse produces a compound that reduces needle attack by array of interactions between plant and fungus have been borers. Metabolites produced by Phomopsis sp in cotton found. Given that a huge array of fungi may be isolated appear to deter larvae of Helicoverpa from feeding on from any one host, it seems possible that endophytes leaves. Similar properties have been reported with will have one or more arrays of functions, most of which Neotyphodium. In addition, aphids feeding on leaves of are unknown at present [3]. However, in some thoroughly cotton may become colonised by Lecanicillium lecanii, investigated cases, the fungus-plant relationship has when conditions permit. Thus the aphid may be killed turned out to be mutualistic/symbiotic, as the endophyte or it may transfer the fungus to another leaf. In addition, acts antagonistically against insect herbivores [4], [5]. endophytes may upregulate host responses to pathogens Hence, it has been proposed that short-cycle (one or and pests. Chaetomium globosum has been shown to several generations each year) endophytes increase the increase host resistance to rust and tan spot pathogens resistance potential of long-living trees against the effects in wheat. Direct interactions appear to be too small to of short-cycle insects [6]. measure in this case. Presence of Lecanicillium lecanii Endophytic microorganisms are to be found in appears to reduce the feeding by aphids from leaves of virtually every plant on earth. These organisms reside in cotton. The interaction is probably due to induction of a symbiotic relationship with its host plant, obtaining host responses, which is perplexing because plant nutrients from it and in return providing it protection regulatory pathways for responses to insects and against insect pests. Endophytes are invisible to the naked pathogens are not thought to be complementary. eye and must be stained and viewed under a microscope Endophytes appear to have direct and induced effects to be identified. Of the approximately 300,000 higher on plant responses to biotic agents. The interaction with abiotic agents remains largely unexplored. *Corresponding Author: E-mail: [email protected] / [email protected] 74 Vijeshwar Verma et al. Because of what appears to be their contribution to probably the first researcher who reported an example the host plant, the endophytes may produce ample of protection given by an endophytic fungus to plant by substances of potential use to modern medicine, resisting the growth of insects, in which the endophyte agriculture and industry. Novel antibiotics, antimycotics, Phomopsis oblonga protected elm trees against the beetle immunosuppressant, topoisomerase inhibitors [7] and Physocnemum brevilineum. After four years , Claydon antineoplastic compounds [7], [8] are only a few et al. [15] confirmed it and showed that endophytic fungi examples of what has been found after the isolation, belonging to the Xylariaceae family synthesize culture, purification, and characterization of some novel secondary metabolites in hosts of the genus Fagus and endophytes in the recent studies. The potential prospects that these substances affect the beetle larvae. of finding new drugs that may be effective candidates The best studied endophytic plant/microbes system for treating newly developing diseases in humans, plants, to date is the grass species/Neotyphodium species and animals are great. relationship (Plate 1). This fungal species provides a host Endophytic fungi are an important, yet relatively of biologically active compounds [16] including toxic unstudied group of microbial plant symbionts. alkaloids such as Peramine (deters insect pests), Lolitrem Endophytic fungi live asymptomatically, and sometimes B (deters larvae feeding) and Ergovaline (provides systemically, within plant tissues [6]. Endophytes usually resistance to black beetle). However, enormous inhabit above-ground plant tissues (leaves, stems, bark, opportunities exist for the recovery of novel forms, petioles and reproductive structures), which distinguishes including genera, biotypes and species in the myriad of them from better known mycorrhizal symbionts. The plants yet to be studied. It is now well established that distinction is not firm, because endophytes may also endophytes are a rich and reliable source of genetic inhabit root tissues. Overall, endophytic fungi are diversity and may represent morphological and molecular ubiquitous and extremely diverse in host plants. Every levels, often have been associated with them novel natural plant examined to date harbors at least one species of products [17]. However, there has to be a sound and endophytic fungus and many plants, especially woody specific rationale for the selection of each plant for plants, may contain literally hundreds or thousands of endophyte isolation and natural product/secondary species [9-14]. metabolite discovery. The most accepted such rationale In the past two decades, a great deal of information is the following: on the role of endophytic microorganisms in nature has a) Plants from unique environmental settings, especially been collected. The capability of colonizing internal host those with unusual biology and possessing novel strategies for survival; tissues has made endophytes valuable for agriculture as a tool to improve crop performance. Webber [4] was The Endophyte Lifecycle In infected seed, As the seed germinates, endophyte is the endophyte grows found in the into the emerging leaf embryo Endophyte is When the grass goes concentrated in reproductive, the the base of the endophyte grows up plant, not in the the stem and into the roots seed head Plate 1: Endophyte life-cycle Endophytes: A Novel Source for Bioactive Molecules 75 b) Plants that have an ethanobotanical history or use Table 1. Sterilization of samples for the isolation of endophytes by the indigenous people that is related to the specific Plant species Minutes in Dilution of Reference uses or applications of interest i.e., through direct NaOCl NaOCl contact with local people or via local literature e.g., Lichens 1 1:5 Petrini (1986) healing powers of a botanical source, in fact, may Mosses 1 1:5 Petrini (1986) Ferns 3 1:5 Dreyfuss & Petrini(1984) have nothing to do with the natural products of the Conifer needles 5 1:2 Carroll & Carroll (1978) plant, but of the endophyte inhabiting the plant; Conifer twigs 7 1:2 Carroll & Carroll (1978) c) Plants that are endemic, having an unusual longevity, Monocots-leaves & 3 1:5 Petrini (1986) culms (Triticum) or that have occupied certain ancient land mass, such Dicots (general) 3 1:5 Petrini (1986) as Gondwanaland, are also more likely to lodge Erica leaves 3 1:5 Petrini (1986) endophytes with active natural products than other Erica stems 5 1:5 Petrini (1986) Rhododendron