Tomato yellow leaf curl geminivirus (TYLCV-Is) is transmitted among whiteflies (Bemisia tabaci) in a sex-related manner

Tomato yellow leaf curl virus (TYLCV) is the name given to a complex of geminiviruses infecting tomato cultures worldwide. TYLCV is transmitted by a single insect species, the whitefly Bemisia tabaci. Herein we show that a TYLCV isolate from Israel (TYLCV-Is) can be transmitted among whiteflies in a sex-dependent manner, in the absence of any other source of virus. TYLCV was transmitted from viruliferous males to females and from viruliferous females to males but not among insects of the same sex. Transmission took place when insects were caged in groups or in couples, in a feeding chamber or on cotton plants, a TYLCV nonhost. The recipient insects were able to efficiently inoculate tomato test plants. Insect-to-insect virus transmission was instrumental in increasing the number of whiteflies capable of infecting tomato test plants in a whitefly population. TYLCV was present in the hemolymph of whiteflies caged with viruliferous insects of the other sex; therefore, the virus follows, at least in part, the circulative pathway associated with acquisition from infected plants. Taken as a whole, these results imply that a plant virus can be sexually transmitted from insect to insect.     

Analyzing and Modeling the Kinetics of Amyloid Beta Pores Associated with Alzheimer’s Disease Pathology

Amyloid beta (Aβ) oligomers associated with Alzheimer’s disease (AD) form Ca²⁺-permeable plasma membrane pores, leading to a disruption of the otherwise well-controlled intracellular calcium (Ca²⁺) homeostasis. The resultant up-regulation of intracellular Ca²⁺ concentration has detrimental implications for memory formation and cell survival. The gating kinetics and Ca²⁺ permeability of Aβ pores are not well understood. We have used computational modeling in conjunction with the ability of optical patch-clamping for massively parallel imaging of Ca²⁺ flux through thousands of pores in the cell membrane of Xenopus oocytes to elucidate the kinetic properties of Aβ pores. The fluorescence time-series data from individual pores were idealized and used to develop data-driven Markov chain models for the kinetics of the Aβ pore at different stages of its evolution. Our study provides the first demonstration of developing Markov chain models for ion channel gating that are driven by optical-patch clamp data with the advantage of experiments being performed under close to physiological conditions. Towards the end, we demonstrate the up-regulation of gating of various Ca²⁺ release channels due to Aβ pores and show that the extent and spatial range of such up-regulation increases as Aβ pores with low open probability and Ca²⁺ permeability transition into those with high open probability and Ca²⁺ permeability.     

Recruitment of the Host Plant Heat Shock Protein 70 by Tomato Yellow Leaf Curl Virus Coat Protein Is Required for Virus Infection

A functional capsid protein (CP) is essential for host plant infection and insect transmission of Tomato yellow leaf curl virus (TYLCV) and other monopartite begomoviruses. We have previously shown that TYLCV CP specifically interacts with the heat shock protein 70 (HSP70) of the virus insect vector, Bemisia tabaci. Here we demonstrate that during the development of tomato plant infection with TYLCV, a significant amount of HSP70 shifts from a soluble form into insoluble aggregates. CP and HSP70 co-localize in these aggregates, first in the cytoplasm, then in the nucleus of cells associated with the vascular system. CP-HSP70 interaction was demonstrated by co-immunopreciptation in cytoplasmic - but not in nuclear extracts from leaf and stem. Inhibition of HSP70 expression by quercetin caused a decrease in the amount of nuclear CP aggregates and a re-localization of a GFP-CP fusion protein from the nucleus to the cytoplasm. HSP70 inactivation resulted in a decrease of TYLCV DNA levels, demonstrating the role of HSP70 in TYLCV multiplication in planta. The current study reveals for the first time the involvement of plant HSP70 in TYLCV CP intracellular movement. As described earlier, nuclear aggregates contained TYLCV DNA-CP complexes and infectious virions. Showing that HSP70 localizes in these large nuclear aggregates infers that these structures operate as nuclear virus factories.     

Modeling Ca2+ signaling differentiation during oocyte maturation

Ca2+ is a fundamental intracellular signal that mediates a variety of disparate physiological functions often in the same cell. Ca2+ signals span a wide range of spatial and temporal scales, which endow them with the specificity required to induce defined cellular functions. Furthermore, Ca2+ signaling is highly plastic as it is modulated dynamically during normal physiological development and under pathological conditions. However, the molecular mechanisms underlying Ca2+ signaling differentiation during cellular development remain poorly understood. Oocyte maturation in preparation for fertilization provides an exceptionally well-suited model to elucidate Ca2+ signaling regulation during cellular development. This is because a Ca2+ signal with specialized spatial and temporal dynamics is universally essential for egg activation at fertilization. Here we use mathematical modeling to define the critical determinants of Ca2+ signaling differentiation during oocyte maturation. We show that increasing IP3 receptor (IP3R) affinity replicates both elementary and global Ca2+ dynamics observed experimentally following oocyte maturation. Furthermore, our model reveals that because of the Ca2+ dependency of both SERCA and the IP3R, increased IP3R affinity shifts the system's equilibrium to a new steady state of high cytosolic Ca2+, which is essential for fertilization. Therefore our model provides unique insights into how relatively small alterations of the basic molecular mechanisms of Ca2+ signaling components can lead to dramatic alterations in the spatio-temporal properties of Ca2+ dynamics.     

Genetic diversity of Artemisia populations in central and north Saudi Arabia based on morphological variation and RAPD polymorphism

The analysis of morphological variation and RAPD polymorphism distinguished populations of A. herba alba from populations of A. judaica and A. monosperma. Higher morphological diversity is found in A. herba alba compared to the other two species, but molecular data derived from RAPD polymorphism also indicated that A. herba alba is more polymorphic than the other two species. However, RAPD fingerprinting also indicated sharp polymorphism among populations of both A. judaica and A. monosperma. Geographic and local ecological variations related to elevation of the sites of the examined populations may be regarded to have played a role in the genetic diversity of the examined populations of Artemisia species in the study area. The results are important for future plans for sustainable conservation of medicinal plants in Saudi Arabia. However, extensive sampling of the examined Artemisia species populations is required, and more regional data should be obtained from other distribution areas.     

A novel bacterial symbiont in the nematode Spirocerca lupi

ABSTRACT: BACKGROUND: The parasitic nematode Spirocerca lupi (Spirurida: Thelaziidae), the canine esophagealworm, is the causative agent of spirocercosis, a disease causing morbidity and mortality indogs. Spirocerca lupi has a complex life cycle, involving an obligatory coleopteranintermediate host (vector), an optional paratenic host, and a definitive canid host. Thediagnosis of spirocercosis is challenging, especially in the early disease stages, when adultworms and clinical signs are absent. Thus, alternative approaches are needed to promote earlydiagnosis. The interaction between nematodes and their bacterial symbionts has recentlybecome a focus of novel treatment regimens for other helminthic diseases. RESULTS: Using 16S rDNA-based molecular methods, here we found a novel bacterial symbiont in S.lupi that is closely related to Comamonas species (Brukholderiales: Comamonadaceae) of thebeta-proteobacteria. Its DNA was detected in eggs, larvae and adult stages of S. lupi. Usingfluorescent in situ hybridization technique, we localized Comamonas sp. to the gut epithelialcells of the nematode larvae. Specific PCR enabled the detection of this symbiont's DNA inblood obtained from dogs diagnosed with spirocercosis. CONCLUSIONS: The discovery of a new Comamonas sp. in S. lupi increase the complexity of the interactionsamong the organisms involved in this system, and may open innovative approaches fordiagnosis and control of spirocercosis in dogs.     

Niche partitioning and stochastic processes shape community structure following whitefly invasions

One of the most detrimental impacts of invasive species is the exclusion of native species, which reduces biodiversity and can alter community structure. Coexistence between invaders and native species across large scales, however, might be promoted by niche partitioning and/or stochastic processes, even when one species is excluded in some habitats. Here, we examined the effects of species traits, stochastic processes, and niche partitioning on coexistence of two morphocryptic whitefly species in the Bemisia tabaci complex: the invasive Mediterranean (MED) species and the native Middle East-Asia Minor 1 (MEAM1) species. These species engage in intense reproductive interference, which can result in the exclusion of one species or the other in shared habitats. Both species, however, have coexisted in sympatry in Israel for many years, where MED is invasive and MEAM1 is native. Using a spatially explicit model, we show that both stochastic processes and niche partitioning can promote coexistence between MEAM1 and MED, although predicted community structure differs drastically in each scenario. Comparison of field observations with model results indicated that variation in habitat use leading to niche partitioning was a primary factor driving coexistence between MEAM1 and MED across landscapes, although stochastic processes affected the establishment of rare species within habitats. In many systems, combining models with field surveys can be used to isolate and test mechanisms underlying patterns of community structure following invasions.     

Nuclear DNA content of the whitefly Bemisia tabaci (Aleyrodidae: Hemiptera) estimated by flow cytometry

The nuclear DNA content of the whitefly Bemisia tabaci (Gennnadius) was estimated using flow cytometry. Male and female nuclei were stained with propidium iodide and their DNA content was estimated using chicken red blood cells and Arabidopsis thaliana L. (Brassicaceae) as external standards. The estimated nuclear DNA content of male and female B. tabaci was 1.04 and 2.06 pg, respectively. These results corroborated previous reports based on chromosome counting, which showed that B. tabaci males are haploid and females are diploid. Conversion between DNA content and genome size (1 pg DNA=980 Mbp) indicate that the haploid genome size of B. tabaci is 1020 Mbp, which is approximately five times the size of the genome of the fruitfly Drosophila melanogaster Meigen. These results provide an important baseline that will facilitate genomics-based research for the B. tabaci complex.     

Mode switching of Inositol 1,4,5-trisphosphate receptor channel shapes the Spatiotemporal scales of Ca<Superscript>2+</Superscript> signals

The inositol 1,4,5-trisphosphate (InsP₃) receptor (InsP₃R) channel is crucial for the generation and modulation of highly specific intracellular Ca²⁺ signals performing numerous functions in animal cells. However, the single channel behavior during Ca²⁺ signals of different spatiotemporal scales is not well understood. To elucidate the correlation between the gating dynamics of single InsP₃Rs and spatiotemporal Ca²⁺ patterns, we simulate a cluster of InsP₃Rs under varying ligand concentrations and extract comprehensive gating statistics of all channels during events of different sizes and durations. Our results show that channels gating predominantly in the low activity mode with negligible occupancy of intermediate and high modes leads to single channel Ca²⁺ release event blips. Increasing occupancies of intermediate and high modes results in events with increasing size. When the channel has more than 50% probability of gating in the intermediate and high modes, the cluster generates very large puffs that would most likely result in global Ca²⁺ signals. The size, duration and frequency of Ca²⁺ signals all increase linearly with the total probability of channel gating in the intermediate and high modes. To our knowledge, this is the first study that quantitatively relates the modal characteristics of InsP₃R to the shaping of different spatiotemporal scales of Ca²⁺ signals.