Sangeeta Saxena

Strategy for a generic resistance to geminiviruses infecting tomato and papaya through in silico siRNA search.

Use of siRNA is a powerful methodology to particularly knockdown the targeted genes in a sequence specific manner. The potential of siRNA can be harnessed for silencing specific geminiviral genes in papaya and tomato plant hosts, thus making them resistant to the respective viruses. The challenge is in designing exogenous siRNA which can trigger silencing of viral genes irrespective of the genetic variability in different viral isolates and at the same time the selected siRNA does not target any plant gene (off target silencing). In this study, we have designed siRNA from the most conserved regions of viral coat protein (AV1) and replicase (AC1) genes retrieved from different isolates of geminiviruses infecting papaya (PLCV), and tomato (TLCV & TLCV, Northern India), so as to give a broad spectrum resistance and efficient silencing as it is highly homology-dependent strategy. Software siRNA finder (Ambion) was used on the selected conserved sequences in order to select only those putative siRNA oligonucleotides which fulfill all the basic criteria required as per the algorithm. Finally, a cross search using BLAST was performed to confirm that the designed siRNAs do not have any homology to plant genome sequences. The putative siRNA sequences thus designed to target essential genes of geminiviruses and introduced into the plants may facilitate developing papaya and tomato crops with generic resistance to geminiviruses.

Role of HCMV miR-UL70-3p and miR-UL148D in overcoming the cellular apoptosis

The studies into the pathophysiology of viral miRNAs are still in infancy; the interspecies regulation at the miRNA level fuels the spark of the investigation into the repertoire of virus–host interactions. Reports pertaining to the viral miRNAs role in modulating/evading the host immune response are surging up; we initiated this in silico study to speculate the role of human cytomegalovirus (HCMV)-encoded miRNAs on human antiviral mechanisms such as apoptosis and autophagy. The results indicate that both the above mechanisms were targeted by the HCMV miRNAs, located in the unique long region of the HCMV genome. The proapoptotic genes MOAP1, PHAP, and ERN1 are identified to be the potential targets for the miR-UL70-3p and UL148D, respectively. The ERN1 gene plays a role in the initiation of Endoplasmic reticulum stress-induced apoptosis as well as autophagosome formation. This study shows that HCMV employs its miRNA repertoire for countering the cellular apoptosis and autophagy, particularly the mitochondrial-dependent intrinsic pathway of apoptosis. In addition, the homology studies reveal no HCMV miRNA bears sequence homology with human miRNAs.

Designing of putative siRNA against geminiviral suppressors of RNAi to develop geminivirus-resistant papaya crop

Geminiviruses are single-stranded circular DNA viruses causing leaf curl disease in papaya crop. Post-Transcriptional Gene Silencing (PTGS), also known as RNAi, acts as a natural antiviral defence mechanism and plays a role in genome maintenance and development in plants. PTGS suppression by viruses makes the plant RNA silencing machinery inefficient. Three geminiviral genes namely AV2, AC2 and AC4 are found to play the role in suppression of RNA silencing. siRNA degrades the target mRNA in a homology-dependent manner. In-silico designing of siRNA against these three genes of geminiviruses infecting Carica papaya was done using bioinformatics tools. This strategy may provide PTGS by specifically targeting the viral genes involved in suppression of plant RNA silencing machinery.

A molecular insight into papaya leaf curl—a severe viral disease

Papaya leaf curl disease (PaLCuD) caused by papaya leaf curl virus (PaLCuV) not only affects yield but also plant growth and fruit size and quality of papaya and is one of the most damaging and economically important disease. Management of PaLCuV is a challenging task due to diversity of viral strains, the alternate hosts, and the genomic complexities of the viruses. Several management strategies currently used by plant virologists to broadly control or eliminate the viruses have been discussed. In the absence of such strategies in the case of PaLCuV at present, the few available options to control the disease include methods like removal of affected plants from the field, insecticide treatments against the insect vector (Bemisia tabaci), and gene-specific control through transgenic constructs. This review presents the current understanding of papaya leaf curl disease, genomic components including satellite DNA associated with the virus, wide host and vector range, and management of the disease and suggests possible generic resistance strategies.

Caenorhabditis elegans as a Toolkit for Studying Mammalian Aging Pathways

During the last few decades the free living soil nematode Caenorhabditis elegans has been highlighted as an important model organism to decipher the role of several conserved signaling pathways in longevity determination. C. elegans is a most effective in vivo model for studying aging due to its cellular complexity and high homology with mammalian biochemical and genetic pathways. Despite its apparent simplicity, lately the nematode C. elegans has been developed into an important model for biomedical research, mostly in the functional characterization of novel drug targets identified using genomics technologies. For many decades, aging was considered to be a passive, entropic process of tissue decline that occurred in a haphazard way. We know now, however, that the aging process, like so many other biological processes, is subject to regulation by classical signaling pathways viz. insulin signaling pathway, mitochondrial pathway etc. Some of these genetic pathways were first of all reported in small, short-lived organisms such as yeast, worms and flies, and a genetic alteration in same pathways turned out to extend lifespan in mammals as well. C. elegans aging mechanism provides a basis to understand how age regulation of a genetic pathway might be conserved between distantly related species. Here we review some aging pathways that are evolutionary conserved and modulates lifespan from worms to mammals viz. Insulin signaling (ILS), Dietary restriction (DR), Mitochondrial respiration and Sirtuin pathway.

Profiling of triterpenoid saponin content variation in different chemotypic accessions of Centella asiatica L.

Centella asiatica (L.) Urban is an important herbaceous medicinal plant with a worldwide distribution. The herb possesses a medicinal value and is used extensively in traditional systems of medicine. The medicinal properties of the herb are attributed to the presence of characteristic triterpenoids and their saponins in the leaves. The major triterpenoids are asiaticoside, madecassoside and their aglycones asiatic acid and madecassic acid, respectively, among others. The present study reports a remarkable qualitative and quantitative variability in secondary metabolites in different accessions of C. asiatica L. as determined by high-performance liquid chromatography (HPLC) analysis. The accessions analyzed in this study can be considered as the core set of discrete chemotypes of C. asiatica . Considerable and contrasting biochemical variations were observed in the terpenoid profiles of the chemotypes. From the basic and applied phytochemical utility, this chemotypic variability in the total content of triterpenoids is important and interesting.

Application of four novel fungal strains to remove arsenic from contaminated water in batch and column modes

Immobilized biomass of novel indigenous fungal strains FNBR_3, FNBR_6, FNBR_13, and FNBR_19 were evaluated for arsenic (As) removal from aqueous solution. Alginate beads containing 0.1 g biomass were used in a batch experiment (200 mg l-1 As; pH 6). Biosorption equilibrium established in first 2 h with As adsorption (mg g-1) as 70, 68, 113 and 90 by FNBR_3, FNBR_6, FNBR_13 and FNBR_19, respectively. The equilibrium was fitted to the Langmuir model (r2 = 0. 90-0.97). The absorption kinetic followed the pseudo second order. Changes in the surface of fungal cells and intracellular As-uptake by fungal biomass were also confirmed by scanning electron microscopy combined with X-ray energy dispersive spectrometer. The presence of different functional groups on fungal cells capable of As-binding was investigated by FTIR. The As-removal by immobilized fungal beads tested in the packed columns also. The As-adsorption by biomass (qe as mg g-1) were recorded as 59.5 (FNBR_3 and FNBR_6), 74.8 (FNBR_13), and 66.3 (FNBR_19) in the column and validated by Thomas model. This is the first report concerning the arsenic removal by immobilized biomass of these novel fungal strains from aqueous solution both in batch and column studies with a prospect of their further industrial application.

Transmission of Begomoviruses

Transmission is the mechanism of pathogen transfer from an infected plant to another host. Begomoviruses are emerging and economically very important phloem-bound plant pathogens that choose the single species of whitefly, i.e. B. tabaci, as vector for their spread in many crops. Mouthparts of whiteflies are designed to detain begomoviruses while feeding on phloem sap of plants. An interaction between mouthparts and coat protein of virus confers Begomovirus-whitefly specificity. High-degree conservation of capsid protein of begomoviruses is the main reason for the choice of their vector. Once virus particle enters, it further moves along in the body of vector in a persistent circulative manner and is introduced back into the plant with salivary secretion during next feeding. There are many proteins present inside the vector that facilitate the efficient transmission of begomoviruses. Variations in the begomoviral coat protein can change their vector preferences. Viruses have the ability to manipulate the behaviour of their vector to enhance their transmission; as a result, begomoviruses negatively affect the longevity and fertility of their whitefly vector, whereas behaviour of whiteflies and their feeding habits can also affect the population genetics, behaviour and evolution of viruses. Whitefly-Begomovirus relationship is an example of co-evolution, and the studies on transmission mechanism, virus-vector interactions and proteins involved in virus translocation inside the vector can help in developing new virus management strategies.

Effect of explanting season and source of explants on in vitro morphogenetic responses of shoot tip explants of sugarcane

Micro propagation is an efficient technique used for seed development of sugarcane. Protocol for the rapid propagation of Co 05011, a newly released variety, was optimized in the present study with a view to find out the best explanting season and source for obtaining optimum morphogenetic responses. Shoot tip explants were collected at monthly interval on 20th of each month from the field grown crops of sugarcane variety Co 05011 and inoculated on MS medium. The highest frequency of establishment (75%) of explants inoculated in the month of March was recorded followed by October, February, September, April and November as compared to those explanted in other months. Explants inoculated in the months of March to November required a minimum period of about 40 to 45 days for establishment of shoot cultures, whereas those inoculated in the months of December and January which required 60 to 70 days to complete the establishment. In an another set of experiment, shoot tip explants were collected from different sources e. g. spring planted, autumn planted and ratoon of spring planted crop. Results revealed that explants collected from spring planted crop gave the best responses regarding frequency of shoot initiation (85%), establishment of shoot cultures (65%), number of shoots/culture (24.3) and rooting responses (86.7%) followed by those collected from autumn planted crop and ratoon of spring planted crop. These results indicated a remarkable effect of season of explanting and source of explants on various in vitro morphogenetic responses. The aforesaid results suggested that the season of explanting and source of explant were important factors which should be taken into consideration during micropropagation of sugarcane varieties.

Plant miRNAs and Phytomolecules As Anticancer Therapeutics

In Indian health-care system, plants are used as a source of medicine to cure various ailments and also provide high quality of food and raw materials for human beings. In due course of time, gradually the expertise developed in selective uses of different plants and their secondary metabolites in treating certain disease conditions. Many such plant parts are now used as alternative medicines for treating diverse forms of diseases including cancer. Research is going on to identify active component/phytomolecules present in plant extracts to cure certain ailments and to be used as therapeutics. In this chapter, we are emphasizing on the role of different plants and their phytomolecules in the treatment of cancer with a detailed overview, and the specific plant parts are discussed in the later part of this chapter. As a second line of thought, authors believe that one of the major genetic components, i.e., plant microRNA, has been overlooked since years and may prove to play a major role as a therapeutic molecule. MicroRNAs are attributed to control gene expression at a very fine level both transcriptionally and posttranscriptionally. Studies have indicated that aberrant expression of several genes leads to cancer and damages normal cellular processes related to many human diseases. Plant miRNAs may play a major role in regulating such gene expression, thereby impacting the development of physiology and development of the human body. Interestingly, many reports are suggesting the possible cross-kingdom regulation of mammalian gene expression by plant-derived microRNAs. The possibility that food-derived miRNA can inhibit cancer growth in mammals is appealing as plant-derived microRNAs are reported to pass through the gastrointestinal tract and are found in human serum regulating the expression of endogenous mRNA. The present chapter highlights the plants and their derived phytomolecules having anticancer properties and also explored the potential of miRNA as a new therapeutic in the field of cancer biology.