Genetics Of Disease Resistance Research Articles

Genetic resilience in chickens against bacterial, viral and protozoal pathogens.

The genome contributes to the uniqueness of an individual breed, and enables distinctive characteristics to be passed from one generation to the next. The allelic heterogeneity of a certain breed results in a different response to a pathogen with different genomic expression. Disease resistance in chicken is a polygenic trait that involves different genes that confer resistance against pathogens. Such resistance also involves major histocompatibility (MHC) molecules, immunoglobulins, cytokines, interleukins, T and B cells, and CD4+ and CD8+ T lymphocytes, which are involved in host protection. The MHC is associated with antigen presentation, antibody production, and cytokine stimulation, which highlight its role in disease resistance. The natural resistance-associated macrophage protein 1 (Nramp-1), interferon (IFN), myxovirus-resistance gene, myeloid differentiation primary response 88 (MyD88), receptor-interacting serine/threonine kinase 2 (RIP2), and heterophile cells are involved in disease resistance and susceptibility of chicken. Studies related to disease resistance genetics, epigenetics, and quantitative trait loci would enable the identification of resistance markers and the development of disease resistance breeds. Microbial infections are responsible for significant outbreaks and have blighted the poultry industry. Breeding disease-resistant chicken strains may be helpful in tackling pathogens and increasing the current understanding on host genetics in the fight against communicable diseases. Advanced technologies, such as the CRISPR/Cas9 system, whole genome sequencing, RNA sequencing, and high-density single nucleotide polymorphism (SNP) genotyping, aid the development of resistant breeds, which would significantly decrease the use of antibiotics and vaccination in poultry. In this review, we aimed to reveal the recent genetic basis of infection and genomic modification that increase resistance against different pathogens in chickens.

Action Mechanisms of Effectors in Plant-Pathogen Interaction.

Plant pathogens are one of the main factors hindering the breeding of cash crops. Pathogens, including oomycetes, fungus, and bacteria, secrete effectors as invasion weapons to successfully invade and propagate in host plants. Here, we review recent advances made in the field of plant-pathogen interaction models and the action mechanisms of phytopathogenic effectors. The review illustrates how effectors from different species use similar and distinct strategies to infect host plants. We classify the main action mechanisms of effectors in plant-pathogen interactions according to the infestation process: targeting physical barriers for disruption, creating conditions conducive to infestation, protecting or masking themselves, interfering with host cell physiological activity, and manipulating plant downstream immune responses. The investigation of the functioning of plant pathogen effectors contributes to improved understanding of the molecular mechanisms of plant-pathogen interactions. This understanding has important theoretical value and is of practical significance in plant pathology and disease resistance genetics and breeding.

Breeding and genetics of disease resistance in temperate fruit trees: challenges and new opportunities.

Climate change, large monocultures of disease-susceptible cultivars, overuse of pesticides, and the emergence of new pathogens or pathogenic strains causing economic losses are all major threats to our environment, health, food, and nutritional supply. Temperate tree fruit crops belonging to the Rosaceae family are the most economically important and widely grown fruit crops. These long-lived crops are under attack from many different pathogens, incurring major economic losses. Multiple chemical sprays to control various diseases annually is a common practice, resulting in significant input costs, as well as environmental and health concerns. Breeding for disease resistance has been undertaken primarily in pome fruit crops (apples and pears) for a few fungal and bacterial diseases, and to a lesser extent in some stone fruit crops. These breeding efforts have taken multiple decades due to the biological constraints and complex genetics of these tree fruit crops. Over the past couple of decades, major advances have been made in genetic and physical mapping, genomics, biotechnology, genome sequencing, and phenomics, along with accumulation of large germplasm collections in repositories. These valuable resources offer opportunities to make significant advances in greatly reducing the time needed to either develop new cultivars or modify existing economic cultivars for enhanced resistance to multiple diseases. This review will cover current knowledge, challenges, and opportunities in breeding for disease resistance in temperate tree fruit crops.

Plant immunity: Rice XA21-mediated resistance to bacterial infection

In this article, we describe the development of the plant immunity field, starting with efforts to understand the genetic basis for disease resistance, which ∼30 y ago led to the discovery of diverse classes of immune receptors that recognize and respond to infectious microbes. We focus on knowledge gained from studies of the rice XA21 immune receptor that recognizes RaxX (required for activation of XA21 mediated immunity X), a sulfated microbial peptide secreted by the gram-negative bacterium Xanthomonas oryzae pv. oryzae. XA21 is representative of a large class of plant and animal immune receptors that recognize and respond to conserved microbial molecules. We highlight the complexity of this large class of receptors in plants, discuss a possible role for RaxX in Xanthomonas biology, and draw attention to the important role of sulfotyrosine in mediating receptor-ligand interactions.

A simple means for MHC-Y genotyping in chickens using short tandem repeat sequences.

Described here is a new, more efficient method for defining major histocompatibility complex-Y (MHC-Y) genotypes in chickens. The MHC-Y region is genetically independent from the classical MHC (MHC-B) region. MHC-Y is highly polymorphic and potentially important in the genetics of disease resistance. MHC-Y haplotypes contain variable numbers of specialized MHC class I-like genes, along with members of four additional gene families. Previously, MHC-Y haplotypes were defined by patterns of restriction fragments (RF) generated in labor-intensive procedures that were difficult to use to define MHC-Y genotypes for large numbers of samples. The method reported here is much simpler. MHC-Y genotypes are distinguished via patterns of PCR products generated from heritable short tandem repeat (STR) regions found immediately upstream of the MHC class I-like genes located throughout MHC-Y haplotypes. To validate the method, fully pedigreed families were analyzed for STR-defined haplotypes in light of haplotypes defined previously by RF patterns. STR-defined MHC-Y patterns segregate in fully pedigreed families as expected and correspond with haplotypes assigned by RF patterns. The patterns provided in STR chromatograms generated by capillary electrophoresis are distinct for different haplotypes and can be scored easily. Investigations into the influence of MHC-Y genetics on immune responses can now realistically be conducted with large sample sets.

Disease Resistance Genetics and Genomics in Octoploid Strawberry

Octoploid strawberry (Fragaria ×ananassa) is a valuable specialty crop, but profitable production and availability are threatened by many pathogens. Efforts to identify and introgress useful disease resistance genes (R-genes) in breeding programs are complicated by strawberry’s complex octoploid genome. Recently-developed resources in strawberry, including a complete octoploid reference genome and high-resolution octoploid genotyping, enable new analyses in strawberry disease resistance genetics. This study characterizes the complete R-gene collection in the genomes of commercial octoploid strawberry and two diploid ancestral relatives, and introduces several new technological and data resources for strawberry disease resistance research. These include octoploid R-gene transcription profiling, dN/dS analysis, expression quantitative trait loci (eQTL) analysis and RenSeq analysis in cultivars. Octoploid fruit eQTL were identified for 76 putative R-genes. R-genes from the ancestral diploids Fragaria vesca and Fragaria iinumae were compared, revealing differential inheritance and retention of various octoploid R-gene subtypes. The mode and magnitude of natural selection of individual F. ×ananassa R-genes was also determined via dN/dS analysis. R-gene sequencing using enriched libraries (RenSeq) has been used recently for R-gene discovery in many crops, however this technique somewhat relies upon a priori knowledge of desired sequences. An octoploid strawberry capture-probe panel, derived from the results of this study, is validated in a RenSeq experiment and is presented for community use. These results give unprecedented insight into crop disease resistance genetics, and represent an advance toward exploiting variation for strawberry cultivar improvement.

Genetics of footrot resistance in small ruminants.

Abstract Footrot is a highly contagious disease with significant economic and animal welfare impacts on the small ruminant livestock industry. Host genetics, environmental conditions, nutrition, foot shape and structure, and age contribute to small ruminants' susceptibility to footrot. Selection for footrot resistance is a promising way to classify susceptible or resistant small ruminants without subjecting them to a pathogenic challenge, to reduce disease prevalence, to improve small ruminants' health and welfare and to produce safe, high-quality food. To date, there has been little focus on footrot resistance heritability and response to selection in small ruminants. This review paper (a) explains footrot and its aetiology in small ruminants, (b) describe genetics of disease resistance and marker-assisted selection, (c) discusses footrot resistance heritability, (d) addresses phenotypic and genetic variation in footrot resistance and selection for footrot resistance, and (e) defines phenotypic and genetic assessment for footrot resistance and footrot gene-marker screening test.

Quantitative genetics of disease resistance in different groups of Penaeus semisulcatus from preliminary controlled challenge test with Vibrio parahaemolyticus the aetiological agent of acute hepatopancreatic necrosis disease (AHPND)

ABSTRACTAcute hepatopancreatic necrosis disease (AHPND) has caused losses to shrimp farmers worldwide owing to Vibrio parahaemolyticus (VPAHPND). Selective breeding for disease resistance of shrimp was used as an alternative strategy for disease control. Five subsamples of shrimp from 20 full-sib families were subjected to a cohabitation challenge test. Juveniles of P. semisulcatus (mean weight 2.5 ± 0.17 g) were tested for survival after challenge with VPAHPND. Mortality in the challenge test was recorded daily, and the experiment was terminated after 96 days when the mortality ceased. Moderate heritabilities were estimated in resistance to VPAHPND based on a linear model (LM) and threshold model (TM). This indicates that disease resistance is a heritable trait, and a challenge test may serve as a basis for selection for resistance to VPAHPND in P. semisulcatus. However, further investigation is needed to confirm and quantify the additive genetic variation for resistance to VPAHPND in P. semisulcatus.

Annual Review of Phytopathology, 2016

Development of novel plant disease management strategies requires knowledge of the co-evolution or arms race, affecting phenotypic variations of disease in nature. Advances in understanding genetics of disease resistance and its functional aspects, especially pathogensecreted (elicitors/effectors) and host surveillance (effector targets) molecules, underpin the recognition and specificity in plant–pathogen interactions at the molecular level operating through cellautonomous, multilayered immune system in plants. Seven of the 25 reviews in this volume connect to this theme, demonstrating the significance and expectations from it for better crop improvement. Two of these chapters (Hawes et al. and Deleris et al. – annotated below) even take a step closer in connecting plant and animal immunity systems.

Quantitative Genetics of Disease Resistance in Wheat.

Wheat (Triticum aestivum L.) is one of the top three global food security crops. Fusarium head blight is one of the major constraints in sustainable wheat production and resistance to the disease is polygenic. This review provides an overview of recent efforts in mapping these genes/loci with the objective to aid marker-assisted selection breeding.

Animal genomics and infectious disease resistance in poultry.

Avian pathogens are responsible for major costs to society, both in terms of huge economic losses to the poultry industry and their implications for human health. The health and welfare of millions of birds is under continued threat from many infectious diseases, some of which are increasing in virulence and thus becoming harder to control, such as Marek's disease virus and avian influenza viruses. The current era in animal genomics has seen huge developments in both technologies and resources, which means that researchers have never been in a better position to investigate the genetics of disease resistance and determine the underlying genes/mutations which make birds susceptible or resistant to infection. Avian genomics has reached a point where the biological mechanisms of infectious diseases can be investigated and understood in poultry and other avian species. Knowledge of genes conferring disease resistance can be used in selective breeding programmes or to develop vaccines which help to control the effects of these pathogens, which have such a major impact on birds and humans alike.

An Ideal Job

A brief personal history illustrates how fortunate I was to have stumbled into a career in plant pathology, which turned out to be the ideal job for me. Several of the people who steered me or facilitated my development in research on plant diseases are mentioned. Starting with my PhD research, I have had the good fortune to indulge a career-long fascination with epidemiology and genetics of disease resistance in plants, particularly coevolution of gene-for-gene host-pathogen systems. I hope that my example may inspire others of like minds to consider a research career in plant pathology.

Bovine Genomics by James E. Womack

Bovine Genomics by James E. Womack

Quantitative genetics of disease resistance in vaccinated and unvaccinated Atlantic salmon (Salmo salar L.).

Furunculosis (Aeromonoas salmonicida) is an important disease in Atlantic salmon (Salmo salar) farming. Vaccination and selective breeding for increased resistance to the disease on the basis of challenge tests of unvaccinated fish are used as complementary prophylactic methods. An important issue is whether genetic predisposition to infection is consistent across vaccinated and unvaccinated fish. Hence, the main objective of this study was to determine the magnitude of the genetic associations (correlations) between resistance to furunculosis in vaccinated and unvaccinated fish, and to estimate the magnitude of the correlation of resistance to furunculosis with resistance to the viral diseases infectious pancreatic necrosis (IPN) and infectious salmon anaemia (ISA). Sub-samples of unvaccinated and vaccinated salmon from 150 full-sib families were subjected to separate cohabitation challenge tests. Substantial genetic variation was found in resistance to furunculosis in both the unvaccinated (heritabilities of 0.51 ± 0.05) and vaccinated (0.39 ± 0.06) fish. However, the genetic correlation between resistance to furunculosis in the two groups was low (0.32 ± 0.13), indicating a weak genetic association between resistance in the two groups. Hence, the current selection strategy on the basis of challenge tests of unvaccinated fish is likely to produce low genetic improvement in resistance to furunculosis under field conditions, where fish are vaccinated with an effective vaccine. Evidence was found of significantly favourable genetic associations of resistance to furunculosis in unvaccinated (but less so for vaccinated) fish with resistance to both IPN and ISA (unvaccinated fish), indicating that vaccination 'mask' genetic associations between resistance to different diseases.

Reconstructing Fragaria × ananassa utilizing wild F. virginiana and F. chiloensis: inheritance of winter injury, photoperiod sensitivity, fruit size, female fertility and disease resistance in hybrid progenies

The genetics of disease resistance, winter hardiness, spring bloom date, fruit set, ovule set, fruit size, and photoperiod sensitivity was investigated in crosses between sets of elite selections of F. virginiana and F. chiloensis in Minnesota and Ontario. In Minnesota, family means varied considerably for all traits except ovule set. For all other traits, general combining ability was significant for at least one species, while specific combining ability was significant for only spring bloom date. In Ontario, general combining ability was significant for all traits in at least one species except flower number. Just as they were in previous crosses with F. × ananassa cultivars, the F. virginiana parents High Falls 22 and Montreal River 10 were notable for producing offspring with large fruit and high fertility. Fragaria chiloensis parents exhibited strong combining ability effects for short day-induced flowering and suppressed the expression of day-neutral flowering in these progeny compared to progeny of these F. virginiana in previous crosses with F. × ananassa. These results indicate that substantial breeding progress can be made by reconstructing F. × ananassa if care is taken to select elite, complementary genotypes of F. virginiana and F. chiloensis.

Genetics of disease resistance in sheep and goats

This review summarises the current state of knowledge of the genetic control of resistance to infectious and metabolic diseases in small ruminants. Diseases covered include gastrointestinal nematode infections, diseases due to mycotoxins, bacterial diseases including footrot and mastitis, ectoparasites such as flies and lice, and scrapie, the small ruminant transmissible spongiform encephalopathy. In all cases there is well-documented evidence for between-animal genetic variation in resistance to the disease and, in the case of some of the infectious diseases, resistance to infection. These heritable differences between animals lead to opportunities to breed animals for enhanced resistance to the disease. For some diseases, including nematode parasite infections, resistance to various forms of mycotoxin poisoning and fly-strike, the feasibility of breeding for resistance has been demonstrated in experimental flocks. Importantly, in other cases, including (again) nematode parasite infections and some forms of mycotoxin poisoning, but also mastitis, footrot and scrapie, there are now breeding programmes selecting commercial animals for enhanced resistance. In almost all cases, the evidence for genetic variation and the documented success of breeding for resistance occurs in sheep rather than goats. For nearly all the diseases discussed, there are now concerted efforts to find genetic markers associated with resistance to infection, potentially allowing selection for increased resistance in the absence of infection. Such selection is now implemented for scrapie, as a part of national scrapie eradication programmes, and selection using genetic markers is currently being explored for nematode parasite resistance, footrot resistance and resistance to facial eczema, a mycotoxin poisoning example. Functional genomics, combining gene mapping and gene expression studies, is now being applied to a number of diseases, an example being the identification of genes whose expression underlies genetic differences in resistance to nematode parasites. It is likely that integrated studies combining quantitative and functional genomics, large-scale data collection (both within and between breeds) and epidemiological prediction will lead to new opportunities for breeders to select sheep and goats for enhanced resistance to a variety of diseases.

Molecular genetics of disease resistance in cereals.

This Botanical Briefing attempts to summarize what is currently known about the molecular bases of disease resistance in cereal species and suggests future research directions. An increasing number of resistance (R) genes have been isolated from rice, maize, wheat and barley that encode both structurally related and unique proteins. This R protein diversity may be attributable to the different modus operandi employed by pathogen species in some cases, but it is also a consequence of multiple defence strategies being employed against phytopathogens. Mutational analysis of barley has identified additional genes required for activation of an R gene-mediated defence response upon pathogen infection. In some instances very closely related barley R proteins require different proteins for defence activation, demonstrating that, within a single plant species, multiple resistance signalling pathways and different resistance strategies have evolved to confer protection against a single pathogen species. Despite the apparent diversity of cereal resistance mechanisms, some of the additional molecules required for R protein function are conserved amongst cereal and dicotyledonous species and even other eukaryotic species. Thus the derivation of functional homologues and interacting partner proteins from other species is contributing to the understanding of resistance signalling in cereals. The potential and limit of utilizing the rice genome sequence for further R gene isolation from cereal species is also considered, as are the new biotechnological possibilities for disease control arising from R gene isolation. Molecular analyses in cereals have further highlighted the complexity of plant-pathogen co-evolution and have shown that numerous active and passive defence strategies are employed by plants against phytopathogens. Many advances in understanding the molecular basis of disease resistance in cereals have focused on monogenic resistance traits. Future research targets are likely to include less experimentally tractable, durable polygenic resistances and nonhost resistance mechanisms.

Glenn Snow, 1930 to 2003

Glenn Austin Snow passed away 5 August 2003 after a long fight with cancer. He is survived by his wife of 49 years, Dolores, his children Alan Mark, Albert Lee, Carroll Wayne, and Barbara Frances, and seven grandchildren. He was born in Carrizozo, New Mexico, in 1930. He attended primary and secondary school in Carrizozo, and later received a Bachelor of Science degree in Agricultural Biology from New Mexico State University. He received a Master of Science degree in plant pathology from Colorado State University and a Ph.D. degree in plant pathology from North Carolina State University. He served in Korea as a first lieutenant in the 24th Infantry Division of the United States Army. His professional career began with the New Mexico State Department of Health working as a District Sanitarian. In 1957, he joined the Southern Forest Experiment Station of the U.S. Forest Service in Gulfport, Mississippi. There he worked as a research plant pathologist and project leader until his retirement in 1990. Glenn’s major research was fusiform rust of slash pine and brown spot needle blight of longleaf pine. His early research on spore dispersal and infection biology of the rust pathogen contributed greatly to a better understanding of the epidemiology of the disease, including important developments in rust hazard evaluation, disease management and aspects of screening for disease resistance. He also contributed important research on control of fusiform rust in forest tree nurseries so that disease-free planting stock would be available. Glenn then turned his attention to characterizing variability in the fusiform rust–slash pine pathosystem where his studies were classical in forest pathology and set the stage for much of the current research on the genetics of disease resistance. Along the way, Glenn developed a quantitative inoculation system which is still a preferred way to challenge specific pine seedlings with sources of the pathogen. He collaborated in a paper describing several form species of Cronartium quercuum which renamed the fusiform rust pathogen C. quercuum f. sp. fusiforme. During his career, he published over 70 research papers. In 1983, he received the Southern Forest Pathologists Award. In addition to being a long-time member of The American Phytopathological Society, he was active in civic and church affairs. In retirement, he served as a consultant to a task-force seeking to determine the cause of the decline of the live oaks on the Mississippi Gulf Coast. He will long be remembered for his dedication to science, his mentorship, and his dry wit.

The molecular genetics of disease resistance in barley

The molecular genetics of disease resistance of barley and its wild relatives is reviewed, and the implications of recent findings for resistance breeding and the potential for disease control using gene technologies are discussed. As a resource for barley researchers and breeders, a chromosome map and list of mapped resistance genes, their source, and associated molecular markers are presented, updated to ultimo 2002. Genetic mapping of major genes and quantitative trait loci for many major diseases is revealing a heterogeneous distribution of resistance loci on chromosomes, with more than half of mapped loci occurring in clusters. Relatively few resistance loci have been identified in the cultivated barley germplasm. Studies have shown that wild Hordeum species contain resistance genes for the major diseases, although their allelic relationship to previously mapped genes is unknown. The structure of genes involved in race-specific and race-non-specific barley powdery mildew resistance has been determined. Isolation of resistance genes for other major diseases is essential and may be accelerated via genomics techniques such as EST sequencing, subtractive hybridisation, or expression profiling. Current strategies for molecular manipulation of barley disease resistance are based on the over-expression of defence-related or disease-signalling genes from other species.

Genetics of disease resistance in Arabidopsis to crop pathogens

Arabidopsis is universally resistant as a species to many crop pathogens, including examples from other crucifers such<br />as Albugo candida and Hyaloperonospora parasitica from Brassica oleracea. This species level trait could potentially<br />provide a source of durable disease resistance in crops if examples can be found which are amenable to molecular genetic<br />characterization. Our research has developed from the observation that null mutation in Arabidopsis of a defense regulatory<br />gene EDS1 (enhanced disease susceptibility) is susceptible to isolates of A. candida and H. parasitica from brassica.<br />EDS1 is required by a major structural class of R-genes to confer resistance in Arabidopsis. We have therefore focused<br />on identifying R-genes in Arabidopsis that are responsible for conferring resistance to brassica pathogens.