Manoj K. Dhar

Endophytic fungi from medicinal plants: a treasure hunt for bioactive metabolites

Endophytic fungi are ubiquitous organisms found in the plants, residing intercellular or intracellular, at least for a portion of their lives without causing apparent symptoms of infection. Almost all plants are known to harbor endophytes. The choice of the plant to be used for exploring endophytes for bioactives is important. Therefore, medicinal plants which are known to be used since centuries as an alternative source of medicine, are a valuable source for bioprospecting endophytes. Nevertheless, due to many reasons there is a dire need for novel resources for novel drugs which can be an answer to many deadly diseases. It is in this context that the present review was envisaged. The review reveals the importance of endophytic fungi from medicinal plants as a source of bioactive and chemically novel compounds. The bioactive metabolites produced by endophytic fungi originate from different biosynthetic pathways and belong to diverse structural groups such as terpenoids, steroids, quinones, phenols, coumarins etc. Endophytes therefore, represent a chemical reservoir for new compounds such as, anticancer, immunomodulatory, antioxidant, antiparasitic, antiviral, antitubercular, insecticidal etc. for use in the pharmaceutical and agrochemical industries. Although, efforts have been made to accommodate as many examples as possible but the depth of the subject is so vast that it cannot be covered in one single review. This in itself speaks of the fact that endophytic fungi from medicinal plants is indeed a treasure worth searching. In the present review only some selected examples have been covered.

Origin of an apparent B chromosome by mutation, chromosome fragmentation and specific DNA sequence amplification

Abstract. The present study documents the de novo origin of an apparent B chromosome in Plantago lagopus. The origin was associated with mutation (aneuploidy), chromosome fragmentation, specific DNA sequence amplification, addition of telomeric repeats, and centromeric misdivision. It originated in the progeny of trisome 2, from the excision of 5S rDNA and 18S, 5.8S, 25S rDNA sequences located on chromosome 2, and within a few generations acquired many characteristics of an apparent B chromosome. The B chromosome has preferential transmission through the male (41%, P<0.025) and female gametes (42%, P<0.01) but does not affect plant phenotype. The B chromosome is completely heterochromatic, has a functional centromere and does not pair at meiosis with any A chromosomes of the standard complement. Fluorescence in situ hybridization analysis showed that it arose from massive amplification of 5S rDNA sequences, has 18S, 5.8S, 25S rDNA sequences at the ends of both arms and telomeric repeats at both termini. Ag-NOR-banding and determination of the maximum number of nucleoli in interphase cells indicate that the nucleolar organizer regions at the ends of both arms of the B chromosome are active in organizing nucleoli. RNA blot analysis showed that the 5S rDNA sequences are not transcribed. To our knowledge, this is the first report that fully documents one of the mechanisms by which B chromosomes may arise in nature.

Farnesyl pyrophosphate synthase: a key enzyme in isoprenoid biosynthetic pathway and potential molecular target for drug development

As isoprenoid biosynthetic pathway has gained importance since last few years, key enzymes of this pathway have been characterized and their functional roles in the cell metabolism have been explored using molecular biology approaches. A key enzyme in this pathway is farnesyl pyrophosphate (EC 2.5.1.10) synthase (FPPS) which supplies precursors for the biosynthesis of essential isoprenoids like carotenoids, withanolides, ubiquinones, dolichols, sterols, among others and also helps in farnesylation and geranylation of proteins. It is a chain elongation enzyme which catalyzes head to tail condensation of two molecules of isopentenyl diphosphate with dimethylallyl diphosphate to form farnesyl pyrophosphate (FPP). Recent studies have validated FPPS as a molecular target of bisphosphonates for drug development against tumors as well as human pathogens. The present paper synthesizes the information on characterization, structural and functional relationships, evolution, localization as well as advances on FPPS enzyme as a target for drug development.

Chromosome healing by addition of telomeric repeats in wheat occurs during the first mitotic divisions of the sporophyte and is a gradual process

Alien gametocidal chromosomes cause extensive chromosome breakage prior to S-phase in the first mitotic division of gametophytes lacking the alien chromosome. The broken chromosomes may be healed either by addition of telomeric repeats in the gametophyte or undergo fusions to form dicentric or translocation chromosomes. We show that dicentric chromosomes undergo breakage–fusion–bridge (BFB) cycles in the first few mitotic divisions of the sporophyte, are partially healed before the germ line differentiation regimen, and are healed completely in the ensuing gametophytic stage. The gametocidal factor on chromosome 4Mg of Aegilopsgeniculata was used to induce dicentrics involving the satellite chromosomes1B and 6B of wheat, Triticumaestivum. The dicentrics 1BS·1BL-2AL·2AS and 6BS·6BL-4BL·4BS initiated BFB cycles that ceased 2 to 4 weeks after seed germination. At the end of the BFB cycles, we observed deficient 1B and 6B chromosomes with breakpoints in proximal regions of the 1BL and 6BL arms. The process of chromosome healing was analyzed in root tip meristems, at meiotic metaphase I, and in the derived progenies by fluorescence in-situ hybridization analysis using a telomeric probe pAtT4. The results show that chromosome healing in wheat occurs during very early mitotic divisions in the sporophyte by de-novo addition of telomeric repeats and is a gradual process. Broken chromosome ends have to pass through several cell divisions in the sporophyte to acquire the full telomeric repeat length.

Plantago ovata : genetic diversity, cultivation, utilization and chemistry

Plantago ovata is the cultivated and economically important species in the monotypic genus Plantago. P. ovata is a short-stemmed annual herb, 10–45 cm tall. The species is generally an in-breeder. The seed husk of this plant is commonly called Psyllium or Isabgol (in Hindi), which is a very effective laxative. Other usages of Isabgol are in ice cream making, cosmetics, printing and finishing. The intake of husk also reduces blood cholesterol levels. Isabgol is commercially very important as its export earns India foreign exchange worth INR 2.5 billion (US

“Omics” Tools for Better Understanding the Plant–Endophyte Interactions

1=44 INR). The plant is cultivated on a large scale in western India. In Gujarat, it is cultivated in about 144,000 ha of land, yielding 720 kg/ha. P. ovata has a narrow genetic base, and the lack of variability is on account of low chromosome number, small chromosome size, presence of high heterochromatin in the chromosomes, low chiasmata frequency and low recombination index. The genome size of the species is ∼500 Mb. Different breeding methods, namely selection, hybridization, induced mutations, polyploidy and tissue culture, have been used for genetic improvement of this plant. Except selections, which have led to isolation of a few varieties, the results of other methods have not been encouraging. P. ovata has about 200 wild allies, some of which are medicinally important. These wild species constitute a rich resource of important genes, which if transferred to cultivated species could revolutionize the production of Isabgol. The present paper highlights various aspects of genetic diversity, cultivation and utilization of this important medicinal plant, and suggests the prospects of genetic manipulation.

Replication of Type 2 Diabetes Candidate Genes Variations in Three Geographically Unrelated Indian Population Groups

Endophytes, which mostly include bacteria, fungi and actinomycetes, are the endosymbionts that reside asymptomatically in plants for at least a part of their life cycle. They have emerged as a valuable source of novel metabolites, industrially important enzymes and as stress relievers of host plant, but still many aspects of endophytic biology are unknown. Functions of individual endophytes are the result of their continuous and complex interactions with the host plant as well as other members of the host microbiome. Understanding plant microbiomes as a system allows analysis and integration of these complex interactions. Modern genomic studies involving metaomics and comparative studies can prove to be helpful in unraveling the gray areas of endophytism. A deeper knowledge of the mechanism of host infestation and role of endophytes could be exploited to improve the agricultural management in terms of plant growth promotion, biocontrol and bioremediation. Genome sequencing, comparative genomics, microarray, next gen sequencing, metagenomics, metatranscriptomics are some of the techniques that are being used or can be used to unravel plant–endophyte relationship. The modern techniques and approaches need to be explored to study endophytes and their putative role in host plant ecology. This review highlights “omics” tools that can be explored for understanding the role of endophytes in the plant microbiome.

Prospecting endophytic fungal assemblage of Digitalis lanata Ehrh. (foxglove) as a novel source of digoxin: a cardiac glycoside

Type 2 diabetes (T2D) is a syndrome of multiple metabolic disorders and is genetically heterogeneous. India comprises one of the largest global populations with highest number of reported type 2 diabetes cases. However, limited information about T2D associated loci is available for Indian populations. It is, therefore, pertinent to evaluate the previously associated candidates as well as identify novel genetic variations in Indian populations to understand the extent of genetic heterogeneity. We chose to do a cost effective high-throughput mass-array genotyping and studied the candidate gene variations associated with T2D in literature. In this case-control candidate genes association study, 91 SNPs from 55 candidate genes have been analyzed in three geographically independent population groups from India. We report the genetic variants in five candidate genes: TCF7L2, HHEX, ENPP1, IDE and FTO, are significantly associated (after Bonferroni correction, p<5.5E−04) with T2D susceptibility in combined population. Interestingly, SNP rs7903146 of the TCF7L2 gene passed the genome wide significance threshold (combined P value = 2.05E−08) in the studied populations. We also observed the association of rs7903146 with blood glucose (fasting and postprandial) levels, supporting the role of TCF7L2 gene in blood glucose homeostasis. Further, we noted that the moderate risk provided by the independently associated loci in combined population with Odds Ratio (OR)<1.38 increased to OR = 2.44, (95%CI = 1.67–3.59) when the risk providing genotypes of TCF7L2, HHEX, ENPP1 and FTO genes were combined, suggesting the importance of gene-gene interactions evaluation in complex disorders like T2D.

Genetic and epigenetic instability of amplification-prone sequences of a novel B chromosome induced by tissue culture in Plantago lagopus L.

Endophytes, the chemical synthesizers inside plants, are the microorganisms having mutualistic relationship with the host plant. They can be used by plants for defense in addition to the production of a wide variety of beneficial bioactive secondary metabolites. There are reports that microbial endophytes mimic the bioactive compounds as produced by the plant itself thus making them a promising source of novel compounds. During the present study, endophytes were isolated from the symptomless leaves and stem of the angiosperm, Digitalis lanata (foxglove). Digitalis lanata belongs to the family Plantaginaceae and is an important medicinal plant known for the production of an important glycoside, digoxin having valuable medicinal importance. Glycosides from Digitalis have been reported to be cardiotonic and are widely used in the treatment of various heart conditions namely atrial fibrillation, atrial flutter, heart failure, etc. Endophytic fungi were isolated from Digitalis to screen them for such glycosides as have been found in the plant itself. A total of 35 fungal endophytes were isolated and screened for the production of secondary metabolites. After preliminary analysis by thin layer chromatography for the presence of bioactive compounds, crude extracts of five fungal cultures were selected for HPLC. HPLC chromatograms revealed the production of glycoside digoxin from the five selected endophytic cultures, thus providing a novel, alternative and eco-friendly source for the production of such a pharmaceutically important and valuable drug.

Production and GC-MS trace analysis of methyl eugenol from endophytic isolate ofAlternaria from rose

Gene amplification is prevalent in many eukaryotes and has been found linked to various phenomena such as ontogenesis, carcinogenesis, in vitro culturing, neoplasia and drug resistance. Earlier, we reported a novel B chromosome in Plantago lagopus L., which was found to have arisen as a result of massive amplification of 5S rDNA. In addition, the chromosome is also composed of 45S rDNA and transposable elements. While the importance of gene amplification cannot be underestimated, its mechanism of origin is still unclear. Therefore, the aim of the present study was to determine whether amplification can be reactivated in the novel B chromosome. For this purpose, in vitro culture was used as stress. Three modes of tissue culture, i.e., direct, indirect and somatic embryogenesis were used for raising in vitro cultures. The variations due to genetic and epigenetic mechanisms were assessed in regenerants using molecular techniques, namely, PCR-RFLP, SSAP and MSAP. The retrotransposon-based molecular markers were applied to detect the polymorphism within transposable elements of in vitro regenerated and mother plants. We detected the variations that may be due to genetic changes either because of element recombination or activation of transposable elements which can lead to increase in the copy number. MSAP analysis revealed the differences in the DNA methylation pattern of the regenerants derived from novel chromosome bearing mother plants. Some regenerated plants were associated with increase and decrease in DNA methylation of both internal and external cytosine of the CCGG sequence.