Host Pathogen Interaction

Durable resistance to apple scab (Venturia inaequalis (Cke) Wint; anamorph Spilocaea pomi Fries) is one of the major goals of apple (Malus) breeding programs. Since current scab resistance breeding is heavily reliant on genes with gene-for-gene relationships, a good understanding of the genetic basis of host-pathogen interactions needs to be developed for this strategy to be successful. While the genomic organization of apple scab resistance genes has been studied extensively, little is known about the avirulence genes in the pathogen. The progeny of a cross of European V. inaequalis race (1) isolate EU-B04 and race (1,2,8,9) isolate 1639 was used to generate a genetic map based on microsatellite and AFLP markers, and investigated for inheritance of avirulence traits on 20 Malus accessions representing 17 scab resistance genes. The accessions comprised scab differential hosts (0), (1), (2), (8), and (9), and hosts carrying known as well as not previously reported secondary resistance genes, including some identified in crosses that have resistant accessions 'Geneva', 'Dolgo', Malus baccata jackii, M. micromalus, or 'Antonovka' in their pedigree. The latter genes appear to be narrow spectrum genes that showed gene-for-gene relationships as a segregation ratio of Avr:avr=1:1 was observed on 12 accessions, while a ratio of 3:1 was observed on five accessions and a ratio of 7:1 on one host. All progenies were shown to be pathogenic, as all of them were able to infect hosts (0) and (1). A genetic map consisting of 15 major linkage groups (LGs) and spanning 972cM was generated with the aid of 156 markers. The map position of 12 avirulence traits was determined: eight avirulence genes mapped into two separate clusters (1: AvrVdg2, AvrVv1, AvrVu1, AvrVrjrd; and 2: AvrVu2, AvrVh3.2, AvrVs1, AvrVu4), while four avirulence genes (AvrRvi8, AvrVv2, AvrVt57 and AvrVsv) mapped to different LGs. AvrRvi2 and AvrRvi9 also are genetically linked, but showed an interaction with AvrRvi8, the nature of which is unclear. While AvrRvi8 segregated at 1:1 ratio, the other two Avrs segregated at 3:1 ratios. However, all progeny avirulent on hosts (2) and (9) were also avirulent on host (8) and further research is required to determine the avirulence gene relationships. A further two independently segregating loci, AvrRvi1 and AvrRvi6, identified in previous studies, were mapped by inference based on their known linkage to SSR markers. The clustering of avirulence genes in V. inaequalis reflecting the clustering of resistance genes in Malus suggests this pathosystem is a classical example of an…

The development of vaccines to prevent infectious diseases has been one of the most important contributions of biomedical sciences. Increasing understanding in biochemistry, molecular biology, molecular genetics and related fields have provided an opportunity for the development of new generation vaccines that are based on rational design approaches. This is possible because of proper understanding of the microbial-genetics, biochemistry, host-pathogen interaction and recent developments in molecular immunology. Another important improvement made in the quality of vaccine production is the incorporation of immunomodulators or adjuvants with modified delivery vehicles viz liposomes, Iscoms and microspheres apart from alum being used as a gold standard. This article reviews the art of vaccination from Jenner period to present day context highlighting all the developments made at each stage of the vaccine development. Various criteria have been discussed regarding the selection of epitopes that expand B & T cells, its linkage with other accessory cells of the immune system, means to overcome MHC linked immune unresponsiveness, enhanced antigen processing and presentations that specially induce either helper or cytotoxic or mucosal immune responses were critically discussed.

Despite the compulsory test and slaughter campaigns in cattle, bovine tuberculosis (bTB) is still present in Spain, and the role of wildlife reservoirs is increasingly recognized. We provide an update on recent progress made in bTB control in Spanish wildlife, including aspects of epidemiology, surveillance, host–pathogen interaction and wildlife vaccination.At the high densities and in the particular circumstances of Mediterranean environments, wild ungulates, mainly Eurasian wild boar and red deer, are able to maintain Mycobacterium bovis circulation even in absence of domestic livestock. Infection is widespread among wild ungulates in the south of the country, local infection prevalence being as high as 52% in wild boar and 27% in red deer. Risk factors identified include host genetic susceptibility, abundance, spatial aggregation at feeders and waterholes, scavenging, and social behaviour. An increasing trend of bTB compatible lesions was reported among wild boar and red deer inspected between 1992 and 2004 in Southwestern Spain. Sporadic cases of badger TB have been detected, further complicating the picture.Gene expression profiles were characterized in European wild boar and Iberian red deer naturally infected with M. bovis. The comparative analysis of gene expression profiles in wildlife hosts in response to infection advanced our understanding of the molecular mechanisms of infection and pathogenesis, revealed common and distinctive host responses to infection and identified candidate genes associated with resistance to bTB and for the characterization of host response to infection and vaccination.Ongoing research is producing valuable knowledge on vaccine delivery, safety and efficacy issues. Baits for the oral delivery of BCG vaccine preparations to wild boar piglets were developed and evaluated. The use of selective feeders during the summer was found to be a potentially reliable bait-deployment strategy. Safety experiments yielded no isolation of M. bovis BCG from faeces, internal organs at necropsy and the environment, even after oral delivery of very high doses. Finally, preliminary vaccination and challenge experiments suggested that a single oral BCG vaccination may protect wild boar from infection by a virulent M. bovis field strain.

Background Infections with Salmonella cause significant morbidity and mortality worldwide. Replication of Salmonella typhimurium inside its host cell is a model system for studying the pathogenesis of intracellular bacterial infections. Genome-scale modeling of bacterial metabolic networks provides a powerful tool to identify and analyze pathways required for successful intracellular replication during host-pathogen interaction. Results We have developed and validated a genome-scale metabolic network of Salmonella typhimurium LT2 (iRR1083). This model accounts for 1,083 genes that encode proteins catalyzing 1,087 unique metabolic and transport reactions in the bacterium. We employed flux balance analysis and in silico gene essentiality analysis to investigate growth under a wide range of conditions that mimic in vitro and host cell environments. Gene expression profiling of S. typhimurium isolated from macrophage cell lines was used to constrain the model to predict metabolic pathways that are likely to be operational during infection. Conclusion Our analysis suggests that there is a robust minimal set of metabolic pathways that is required for successful replication of Salmonella inside the host cell. This model also serves as platform for the integration of high-throughput data. Its computational power allows identification of networked metabolic pathways and generation of hypotheses about metabolism during infection, which might be used for the rational design of novel antibiotics or vaccine strains.

Fire blight, caused by the necrogenic Gram-negative bacterium Erwinia amylovora, is one of the most destructive bacterial diseases of apple (Malus × domestica) and pear (Pyrus communis), among other members of the Rosaceae family. This disease poses a major economic threat to pome production as there are no available effective control measures. Genetic enhancement of fire blight resistance in apples is the best alternative for averting disease damage, loss of crop, and loss of whole trees. In this review, current knowledge of the molecular mechanisms of E. amylovora pathogenesis will be presented, especially those of effector proteins during bacterial–host interactions, as well as assessment of current understanding of the molecular controls of plant host resistance. Recent studies are elucidating how type III effectors modulate plant susceptibility and promote growth and dissemination of the pathogen. The large multidomain protein DspE is essential for E. amylovora pathogenesis and plays an additional role(s) in inhibiting salicylic acid-mediated innate immunity. On the other hand, the apple host defends itself against E. amylovora invasion by relying on quantitative resistance genes that likely respond to and/or complex with E. amylovora effectors. Thus far, a total of 27 quantitative trait loci (QTL) linked to fire blight resistance have been identified in different apple genetic backgrounds and in response to different E. amylovora strains. In addition to quantitative genetic approaches, microarray analysis of E. amylovora-challenged apple genotypes identified differential transcriptional expression in susceptible and resistant apples. Mechanisms of bacterial pathogenicity and plant host resistance offer intriguing scenarios as to how effector proteins in E. amylovora interact with groups of genes for resistance in the apple host, particularly when considering that these quantitative genes have small effects in plant defense against the invading bacterial pathogen. This collective knowledge will provide insights into bacterial pathogenesis and plant host resistance, as well as highlight implications and opportunities for developing fire blight-resistant apple cultivars.

Trees occupy more than 30% of the land biosphere. They are important from both ecological and environmental standpoints and provide some of the most valuable commodities in the world economy. The perennial nature and size of trees are the critical determinants of their survival in response to biotic and abiotic stresses. The identification of the defense pathways at biochemical and genetic levels in tree pathosystems are beginning to be addressed. The basic physiological and biochemical mechanisms in woody perennials in response to pathogen is homologous to the model annual crop like Arabidopsis, but their secondary metabolic processes and ecological survival strategies are likely to be divergent from their annual counterparts. The limited domestication in tree species makes its molecular mechanisms less comparable to the highly pedigreed crop species. Recent reports have highlighted that the possible difference in genetic programs responding to invasive pathogens between annuals and perennials could be the spatial and temporal pattern of gene regulation. Several reviews on pathogen defense with reference to crop species are available, while similar reports from the tree species are limited to few commercially important species like Populus, Pinus, Picea, Eucalyptus, Castanea, and Pseudotsuga. This paper reviews the present status of pathogenesis-related genes and proteins from tree species with emphasis on the resistant genes and the proteins induced during systemic acquired resistance and highlights the ecological and evolutionary significance of defense-related genes from tree species.

The production of reactive oxygen species (ROS) by the consumption of molecular oxygen during host–pathogen interactions is termed the oxidative burst. The most important ROS are singlet oxygen (1O2), the hydroxyperoxyl radical (HO2·), the superoxide anion \(\left( {{\text{O}}_{\text{2}} ^ - } \right)\) , hydrogen peroxide (H2O2), the hydroxyl radical (OH-) and the closely related reactive nitrogen species, nitric oxide (NO). These ROS are highly reactive, and therefore toxic, and participate in several important processes related to defence and infection. Furthermore, ROS also play important roles in plant biology both as toxic by-products of aerobic metabolism and as key regulators of growth, development and defence pathways. In this review, we will assess the different roles of ROS in host–pathogen interactions with special emphasis on fungal and Oomycete pathogens.

Phoma tracheiphila is the causative agent of the disease mal secco. Citrus cultivars differ substantially in respect to their sensitivity to the pathogenP. tracheiphila and its toxin. Some cultivars (e.g., ‘Femminello’ lemon) are inherently sensitive while others (e.g., ‘Tarocco’ orange) are tolerant. Cell lines derived from nucellar tissue of ‘Femminello’, ‘Tarocco’ and a cell line selected for tolerance to the

During infection of host cells by HIV-1, active host-pathogen interactions take place. The final balance between these interactions determines the efficiency of viral infection and subsequent disease progression. HIV-infected cells respond to viral invasion with various antiviral strategies such as innate, cellular and humoral immune antiviral defense mechanisms. On the other hand, the virus has also developed tactics to suppress these host cellular responses. Among the many viral offensive strategies, viral protein R (Vpr) plays a particularly active role. Vpr involved in nuclear transport of the viral pre-integration complex, activation of viral transcription, induction of cell cycle G2/M arrest and apoptosis of the host cells. However, specific roles of these Vpr activities in viral pathogenesis and their contribution to disease progression are not fully understood. HIV-1 defective for some or all of these Vpr activities have been associated with slow disease progression in some ...