Muhammad Shafiq

RNA Interference based Approach to Down Regulate Osmoregulators of Whitefly (Bemisia tabaci): Potential Technology for the Control of Whitefly

Over the past decade RNA interference (RNAi) technology has emerged as a successful tool not only for functional genomics, but in planta expression of short interfering RNAs (siRNAs) that could offer great potential for insect pest management. The diet of insects feeding exclusively on phloem sieves contains water and sugars as main components, and the uptake of the liquid food greatly depends on the osmotic pressure within the insect body. Based on this physiological mechanism, transgenic plants of Nicotiana tabacum were generated expressing double stranded RNA (dsRNA) against both aquaporin (AQP) and a sucrase gene, alpha glucosidase (AGLU). These two genes are involved in osmotic pressure maintenance particularly in sap sucking insects, and the aim was to disrupt osmoregulation within the insect ultimately leading to mortality. Real time quantitative PCR (RT-qPCR) was performed to assess the suppression of gene expression in Bemisia tabaci (B. tabaci) and mortality was recorded during transgenic tobacco feeding bioassays. Feeding of insects on plants expressing dsRNA significantly reduced the transcript level of the target genes in B. tabaci after six days of feeding and more than 70% mortality was observed in B. tabaci fed on transgenic plants compared to the control plants. Our data shows that down-regulation of genes related to osmoregulation may find practical applications for the control of this important pest in cotton and other crops.

An Investigation of Ac Impedance and Dielectric Spectroscopic Properties of Conducting Chitosan-silane Crosslinked-poly (Vinyl Alcohol) Blended Films

The films of chitosan (CS)-silane crosslinked-poly(vinyl alcohol) (PVA) with different weight % were prepared. The effect on conductivity of CS/PVA blended films due to change in the concentration of PVA and temperature was investigated by impedance spectroscopy and showed good conductance properties. The complex impedance plots revealed single semicircular arcs indicating the bulk contribution to overall electrical behavior of all synthesized samples. The ac conductivity obeyed the Jonschers power law for all samples in the frequency range of 2 kHz to 2 MHz. The ionic conductivity of the films was increased with the increase in temperature for all synthesized samples which showed an increase in the number of effective charge carriers while it was decreased at a specific higher temperature for each film. The observed activation energy for CP4, CP8 and CP10 were 0.431, 0.610 and 0.425 eV, respectively. These properties showed that the films were promising materials to be employed for conducting properties.

Real-time quantitative PCR assay for the quantification of virus and satellites causing leaf curl disease in cotton in Pakistan

Cotton leaf curl disease (CLCuD) is the major biotic constraint to cotton production in Pakistan and northwestern India. The disease is caused by monopartite begomoviruses in association with a specific DNA satellite, Cotton leaf curl Multan betasatellite. The virus-betasatellite complex is also frequently associated with another DNA satellite-like molecule; an alphasatellite. A quantitative real-time PCR (qPCR) assay to detect all three components of the monopartite begomovirus/betasatellite/alphasatellite complex which causes CLCuD was established. This was used to investigate the relationship between symptoms and virus/satellite titre. Not surprisingly the analysis showed that, overall, there was a reasonable correlation between symptom severity and virus/satellite titre - more severe symptoms usually being associated with more virus/satellite. However, cotton plants were identified with no or very mild symptoms with relatively high virus/satellite titres and plants with severe symptoms but relatively low virus/satellite titres. This may be attributed to the resistance/susceptibility of the cotton variety - tolerant plants being able to sustain a relatively high virus/satellite titre whilst exhibiting mild symptoms. The usefulness of this qPCR procedure in the screening for resistance in cotton against CLCuD is discussed.

Maintenance of Cotton Leaf Curl Multan Betasatellite by Tomato Leaf Curl New Delhi Virus—Analysis by Mutation

Viruses of the genus Begomovirus (family Geminiviridae) are economically important phytopathogens that are transmitted plant-to-plant by the whitefly Bemisia tabaci. Most Old World (OW) begomoviruses are monopartite and many of these interact with symptoms and host range determining betasatellites. Tomato leaf curl New Delhi virus (ToLCNDV) is one of only a few OW begomoviruses with a bipartite genome (components known as DNA A and DNA B). Four genes [AV2, coat protein (CP), transcriptional-activator protein (TrAP), and AC4] of ToLCNDV were mutated and the effects of the mutations on infectivity, symptoms and the ability to maintain Cotton leaf curl Multan betasatellite (CLCuMuB) were investigated. Infectivity and virus/betasatellite DNA titer were assessed by Southern blot hybridization, PCR, and quantitative PCR. The results showed TrAP of ToLCNDV to be essential for maintenance of CLCuMuB and AV2 to be important only in the presence of the DNA B. AC4 was found to be important for the maintenance of CLCuMuB in the presence of, but indispensable in the absence of, the DNA B. Rather than being required for maintenance, the CP was shown to possibly interfere with maintenance of the betasatellite. The findings show that the interaction between a bipartite begomovirus and a betasatellite is more complex than just trans-replication. Clearly, multiple levels of interactions are present and such associations can cause additional significant losses to crops although the interaction may not be stable.

High-temperature electrical properties of silane cross-linked chitosan/poly(vinyl alcohol) membrane: thermal, mechanical and surface characterization

Abstract Chitosan and poly(vinyl alcohol) were blended and cross-linked with tetraethoxysilane and showed conductive properties. Impedance spectroscopy was used to study the influence of temperature on the electrical properties of the membranes. The conductivity of the membranes was increased with an increase in temperature. Free water was decreased and bound water was increased with an increase in cross-linker contents. The tensile strength improved, whereas elongation at break decreased by increasing the amount of cross-linker contents. The water contact angle of the membranes lowered with time, exhibiting the hydrophilic nature of the membranes. The novel characteristics of biocompatible membranes can be used in biomedical applications including biological schemes that require smaller charge in medicinal apparatus, bioelectrode coatings, etc.