Genetic Basis Of Variation Research Articles

Causes of lifetime fitness of Darwin's finches in a fluctuating environment

The genetic basis of variation in fitness of many organisms has been studied in the laboratory, but relatively little is known of fitness variation in natural environments or its causes. Lifetime fitness (recruitment) may be determined solely by producing many offspring, modified by stochastic effects on their subsequent survival up to the point of breeding, or by an additional contribution made by the high quality of the offspring owing to nonrandom mate choice. To investigate the determinants of lifetime fitness, we measured offspring production, longevity, and lifetime number of mates in four cohorts of two long-lived species of socially monogamous Darwin's finch species, Geospiza fortis and G. scandens, on the equatorial Galápagos Island of Daphne Major. Regression analysis showed that the lifetime production of fledglings was predicted by lifetime number of clutches and that recruitment was predicted by lifetime number of fledglings and longevity. There was little support for a hypothesis of selective mating by females. The offspring sired by extrapair mates were no more fit in terms of recruitment than were half-sibs sired by social mates. These findings provide insight into the evolution of life history strategies of tropical birds. Darwin's finches deviate from the standard tropical pattern of a slow pace of life by combining tropical (long lifespan) and temperate (large clutch size) characteristics. Our study of fitness shows why this is so in terms of selective pressures (fledgling production and adult longevity) and ecological opportunities (pulsed food supply and relatively low predation).

Opportunities to improve nutrient efficiency in pigs and poultry through breeding

Efficiency of food and nutrient (including energy) use are considered the key factors in the economic and environmental performance of livestock systems. The aim of this paper is to consider the basis of genetic variation in the components that constitute dietary nutrient efficiency; and to conclude whether there would be benefit, in any relevant terms, in including these components in breeding programmes that aim to improve nutrient efficiency within pig and poultry systems of production. The components considered are (i) external, pre-ingestion losses, such as food spillage and its relation to feeding behaviour traits, (ii) digestive efficiency, (iii) maintenance requirements, (iv) net efficiency of energy and nutrient utilisation and (v) partitioning of scarce resources within productive and between productive and fitness functions. It is concluded that opportunities to exploit genetic variation exist mainly in the potential to improve the digestive efficiency of pigs and to reduce the maintenance requirements for resources mainly in hens, but also potentially in pigs. Current evidence suggests that there are very weak genetic and phenotypic correlations between components of feeding behaviour and productive traits, and little genetic variation in the net efficiency of nutrient utilisation among poultry and pig genotypes. The implication of the latter is that there would be little exploitable genetic variation in the partitioning of scarce nutrients between productive functions. Currently, there is a lack of understanding of the genetic basis of the partitioning of scarce nutrients between productive and fitness functions, and how this may impact upon the efficiency of nutrient use in pig and poultry systems. This is an area of research to which further effort might usefully be devoted.

Evolutionary genetics of genital size and lateral asymmetry in the earwig Euborellia plebeja (Dermaptera: Anisolabididae)

Male genitalia show several evolutionary characteristics, including rapid morphological divergence between closely related species and low within-species phenotypic variability. In addition, genital asymmetry is widespread despite the essentially bilaterally symmetric external morphology of insects. Several hypotheses, such as sexual selection and lock-and-key hypotheses, have been proposed to explain these characteristics of genital evolution. Although these hypotheses provide different predictions about the genetic basis of variation in genitalia, detailed quantitative genetic studies have been conducted in only three insect taxa: heteropterans, dung beetles (Scarabaeidae), and drosophilid flies. For an anisolabidid earwig, Euborellia plebeja, characterized by paired elongated intromittent organs, we estimated the heritabilities and genetic correlations of genital laterality, size of genitalia, and body size. No statistically significant additive genetic, dominance, maternal, or common environmental effects were detected for genital laterality (readiness to use either the left or the right intromittent organ). This result lends further support to the general rule that the direction of antisymmetric variations is randomly determined by non-genetic factors. Irrespective of the restricted phenotypic variation in genitalia compared with body size (allometric slope < 1), as observed in previous studies for other insects, these two traits showed a similar level of genetic variation, measured as the narrow sense heritability (h2) and the coefficient of additive genetic variation (CVA). Comparison suggests the causes of interspecific differences in genetic variability/correlation structures were developmental processes (holo- or hemimetabolous) and/or mode of sexual selection. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 103–112.

Exploring the Genetic Basis of Variation in Gene Predictions with a Synthetic Association Study

Identifying DNA polymorphisms that affect molecular processes like transcription, splicing, or translation typically requires genotyping and experimentally characterizing tissue from large numbers of individuals, which remains expensive and time consuming. Here we introduce an alternative strategy: a “synthetic association study” in which we computationally predict molecular phenotypes on artificial genomes containing randomly sampled combinations of polymorphic alleles, and perform a classical association study to identify genotypes underlying variation in these computationally predicted annotations. We applied this method to characterize the effects on gene structure of 32,792 single-nucleotide polymorphisms between two strains of the antibiotic producing fungus Penicilium chrysogenum. Although these SNPs represent only 0.1 percent of the nucleotides in the genome, they collectively altered 1.8 percent of predicted gene models between these strains. To determine which SNPs or combinations of SNPs were responsible for this variation, we predicted protein-coding genes in 500 intermediate genomes, each identical except for randomly chosen alleles at each SNP position. Of 30,468 gene models in the genome, 557 varied across these 500 genomes. 226 of these polymorphic gene models (40%) were perfectly correlated with individual SNPs, all of which were within or immediately proximal to the affected gene. The genetic architectures of the other 321 were more complex, with several examples of SNP epistasis that would have been difficult to predict a priori. We expect that many of the SNPs that affect computational gene structure reflect a biologically unrealistic sensitivity of the gene prediction algorithm to sequence changes, and we propose that genome annotation algorithms could be improved by minimizing their sensitivity to natural polymorphisms. However, many of the SNPs we identified are likely to affect transcript structure in vivo, and the synthetic association study approach can be easily generalized to any computed genome annotation to uncover relationships between genotype and important molecular phenotypes.

Genotype-dependent recovery from acute exposure to heavy metal contamination in the freshwater clam Sphaerium novaezelandiae

The ability to recover from environmental perturbations is essential for the sustainability of ecological systems. Variation in the ability of individual organisms to recover from stressors influences overall resilience at higher levels of biological organisation. Such variation is likely to be genetically based. To investigate this hypothesis we examined the genetic basis of both resistance to and recovery from zinc, a common stormwater contaminant, in the New Zealand freshwater clam Sphaerium novaezelandiae. We undertook a 4-day toxicity test using zinc exposure concentrations ranging from 0.31 to 5.00 mg/L. These concentrations are consistent with levels recorded in urban streams during the first flush of storms. As our response measures we recorded mortality at the end of the 4-day period, as well as reburial rate (time to rebury in sediment) following the 4-day exposure (“exposure”) and then again following a 24 h period of recovery (“recovery”). Genotypic composition was determined using allozyme electrophoresis, focusing on the enzyme Pgm (phosphoglucomutase). Overall, a significant effect on mortality was observed, with an average value of 78.6% (±7.9) at 5.00 mg/L zinc, compared with only 3.8% (±3.8) mortality at 0.31 mg/L zinc. An inhibition concentration (IC 50) of 1.16 mg/L was recorded, when considered regardless of genotypes. There was no significant genotype-specific differences in mortality. There was a significant difference in reburial rates across all genotypes at the end of the exposure period with an average reburial time of 83.0 ± 3.6 min at 5.00 mg/L (22.8 ± 2.9 min at 0.31 mg/L). There was a near-significant ( p = 0.058) difference in time taken to rebury when comparing between genotypes at the “exposure” stage for any concentration. Significant differences in reburial rates across all genotypes were also observed following 24 h recovery. When individual genotypes were compared at this stage, genotype 33 reburied on average significantly faster (24.0 ± 4.5 min) than other genotypes at the highest exposure concentration and was also significantly faster than genotype 44 at 1.25 mg/L. Studies investigating the genetic basis to recovery from stressors at an individual level are limited. This study has shown that populations of organisms display genetically-based variation in their ability to recover from zinc exposure in the laboratory and that such variation is linked to a physiological trait (reburial). The potential effects on other life history traits (e.g. feeding), possible physiological trade-offs and the implications for such variation on ecosystem resilience requires further investigation.

Genetik, Ökologie, Forstwirtschaft: Zusammenhänge und Perspektiven | Genetics, ecology, forest management: connections and perspectives

Our understanding of the genetic variation of forest trees and its dynamics is rapidly increasing. The glacial eras, postglacial migration and human transfer of reproductive material had deep impacts on genetic variation patterns of European forest trees. The genetic basis of variation at adaptive traits and traits of economic importance is currently investigated by molecular genetic approaches eventually leading to a better understanding of the functional importance of intraspecific variation for forest ecosystems. Important applications of forest genetic research including breeding, conservation and adaptation to changing environments are briefly described based on current fields of research. The establishment and observation of field trials, complemented by a molecular investigation of variation patterns in genes coding for adaptive traits, continues to be a main field of research. The potential for the use of transgenic trees is regarded as low in central Europe. The origin of forest reproductive material is routinely tested based on genetic markers in Germany. Forest genetics contributes to the protection of natural resources by the development and implementation of methods to conserve forest genetic resources. In addition, molecular genetic tools are developed to test the origin of wood and wood products and to identify illegally traded wood; first encouraging results have been obtained. Evolutionary processes must not be neglected within the context of adaptation to global change. The development of strategies to mitigate climate change effects on forests in central Europe should consider the genetic variation of tree species by the promotion of adaptive potentials. The current knowledge does not allow to propose long-distance seed transfer from south to north as a universal approach to promote adaptation to climate warming in Europe.

Naltrexone for the Treatment of Alcoholism: Clinical Findings, Mechanisms of Action, and Pharmacogenetics

Naltrexone is an opioid receptor antagonist with established efficacy, albeit moderate, for the treatment of alcohol dependence. This manuscript provides a critical review of the literature on naltrexone as a pharmacotherapy for alcoholism by covering the following areas: (a) clinical findings from treatment studies; (b) pharmacokinetics and safety data; (c) medication compliance and persistence; and (d) neurobiological and biobehavioral mechanisms of action of naltrexone for the indication of alcohol dependence. This review will then focus on the emerging literature on naltrexone pharmacogenetics, which has the potential to identify responders on the basis of genetic variation and to use genetic tools to individualize the use of this medication. Limitations and future directions in the research and practice of naltrexone for alcoholism are also outlined.

Evidence for host variation in parasite tolerance in a wild fish population

Hosts can protect themselves against parasites by actively reducing parasites burden (i.e. resistance) or by limiting the damages caused by parasites (i.e. tolerance). Disentangling between tolerance and resistance is important for predicting the evolutionary outcomes of host-parasite interaction. Dace (Leuciscus leuciscus) are often parasitized by the ectoparasite Tracheliastes polycolpus which feeds on (and destroys) fins, reducing thus the host’s condition. We tested the hypothesis that genetically-based variation in ectoparasite tolerance exists in a wild dace population. We found that moderately heterozygous dace, which are less resistant than highly heterozygous or homozygous dace, tolerated better the effect imposed by T. polycolpus for a given parasite burden. However, tolerance also varied upon environmental conditions, suggesting that genetic and environmentally-based variation exists for both resistance and tolerance in this natural host-parasite system. Moreover, a negative genetic correlation may exist between tolerance and resistance, and hence several evolutionary outcomes are possible in this interacting system.

Nucleosome patterning evolution: steady aim despite moving targets

Mol Syst Biol. 6: 376 Molecular systems are the scaffolding on which natural selection builds. Comparing the tendency of different molecular mechanisms to generate tolerable and useful raw genetic variation is a challenging interdisciplinary problem. Modulation of gene expression is thought to be an important source of interspecific phenotypic divergence, and as new mechanisms are revealed, their potential roles must be considered. In this issue of Molecular Systems Biology , Tirosh et al (2010) use an interspecies hybrid approach to examine the genetic basis of variation in nucleosome arrangement and its potential to explain differences in gene expression. They find that most nucleosome occupancy and position differences are explained by changes in nearby DNA, and these differences prove to be surprisingly poor predictors of gene expression differences between species. If a gene differs in expression between two species, the causal genetic locus of variation could either be linked to the gene itself ( cis ) or located somewhere else ( trans ). With a few assumptions, whether the locus of change is in cis or trans can often be determined by examining gene expression in a hybrid of the two species (Wittkopp et al , 2004; Tirosh et al , 2009). In purely trans cases, the alleles of both species will be expressed identically in the hybrid, whereas alleles will …

Melanocyte-stimulating Hormone Receptor (MC1R) Genotype and Its Effects on Coat Color in Korean Jindo Dogs

The Jindo dog is a Korean natural monument and is recognized by the Federation Cynologique Internationale. A prominent feature is the diverse coat color within the breed. To analyze the genetic basis of variation in the Jindo coat color, we sequenced the protein-coding regions of the melanocortin I receptor gene (MC1R). The MC1R coding sequence was determined from 154 dogs in five breeds (Jindo, Labrador Retriever, English Springer Spaniel, Belgian Malinois, and German Shepherd). To confirm the genetic structure of sampled populations, we tested for Hardy-Weinberg equilibrium (HWE) and computed F st . The sample populations did not significantly deviate from HWE. F st was 0.02 between white and fawn Jindo dogs; this was lower than F st between breeds. Six single nucleotide polymorphisms (SNPs) were detected in the MC1R coding region. Among the six SNPs, five were non-synonymous (S90G, T105A, Q159P, M264V, and R306ter) and one was synonymous SNP (Y298Y). From the SNPs, we predicted four haplotypes (H1, H2, H3, and H4) for Jindo MC1R. Jindo dogs had different haplotypes corresponding to different coat colors. H1 was frequently observed in white Jindo dogs with an odds ratio of 5.03 (95% CI: 2.27-11.18, p<0.0001), whereas H2 and H4 were observed only in fawn Jindo dogs. Our findings indicate that SNP haplotype can influence coat color. Knowledge of MCIR haplotypes can help discriminate white and fawn coats in Jindo dogs. We hope this report will trigger more research into the genetics of this traditional Korean dog and will be a reference for dogs of Asian origin. Also, our results will provide a useful genetic marker for Jindo dog breeders who have selected for specific colors.

A Gene-Centric Approach to Elucidating Cardiovascular Risk

Although behavioral precedents including diet and cigarette smoking play an important role, coronary artery disease (CAD) exhibits significant heritability,1 a part of which can be attributable to genetic variants affecting known biochemical and metabolic risk factors. In the last 2 years, impressive progress has been made in understanding the genetic basis of several of these using both candidate gene and genome-wide association study (GWAS) approaches. Article see p 16 Candidate genes, coding for proteins of known biological significance in a disease process, provide a logical first step in understanding the genetics of common disease states. Populations of affected and unaffected individuals can be studied by genotyping common single-nucleotide polymorphisms (SNPs) within a gene and its regulatory sequences. Although economically attractive, this approach is acknowledged to have a number of limitations. By definition, studies are limited to genes with a known or suspected role in defining a given phenotype and do not provide new insight into biological pathways leading to disease. Furthermore, candidate gene associations often fail to replicate for multiple reasons. Sample sizes have often been inadequate to provide the statistical power required when multiple variants of small effect are tested. The original observation may have been false positive, emphasizing the need for stringent statistical thresholds. Other issues include heterogeneity of causality. For example, genetic variants affecting plasma lipid traits may have significant effects on CAD risk, but these may be less important than or interact with other risk factors including diabetes and smoking. Finally, appropriate measures must be taken to test for population stratification. Genome wide association studies (GWASs) are is an alternative approach, facilitated by the International HapMap Project and advances in genotyping technology, permitting analysis of a million or more markers across the human genome. GWASs provides an unbiased approach that has led to the identification …

Genetic basis of variation for lint color, yield, and quality in cotton (Gossypium hirsutum L.)

Colored cotton produces naturally colored lint, which can help reduce the use of toxic dyes in textile. Four naturally colored lint accessions were crossed with eight white lint varieties of Gossypium hirsutum L. to study the genetic basis of variation of lint color, fiber yield, and quality traits. Various shades of lint appeared in the F1 progenies and the inheritance of lint colors appeared to be controlled by dominant genes with varying degrees of dominance. There was also some indication for the involvement of maternal effects in the manifestation of lint colors. Additive and dominance genetic effects were involved in the inheritance of fiber traits, dominance effects being greater. The estimate of narrow sense heritability was very low for seed cotton yield and therefore direct selection for yield would not be effective in isolating superior genotypes. As non‐additive gene effects predominated in the inheritance of most fiber yield and quality characters, the development of colored cotton hybrids and recurrent crossing and selection would be useful for the genetic improvement of colored cottons.

Group Size and Density Effects on Physical Indices and Cell-Mediated Immunity in Two Genetic Lines of White Leghorn Layers

Social stress resulting from varied group sizes with density in caging systems is a common problem that affects bird welfare in the poultry industry in the United States. To examine whether there is a genetic basis for variations in response to group size and density, 2 genetic strains of White Leghorn hens were used in this study: HGPS, a line selected for high group productivity and survivability in multiple-bird cages and DXL (Dekalb XL), a commercial line individually selected for production. Birds from each line were housed in either 4-bird cages (542 cm(2)/bird) or 10-bird cages (434 cm(2)/bird) from 17 to 60 wk of age. Blood samples, BW, and adrenal weight were collected from the birds at 30, 45, and 60 wk of age (n = 12, respectively) after euthanasia. Subsets of T cells (CD4(+) and CD8(+)) were measured by flow cytometry. Hematological parameters were collected from blood smears. Results showed that there were no significant differences for BW, the relative adrenal glands, and the heterophil:lymphocyte ratio between and across lines after the treatments (P > 0.05, respectively). Compared with DXL birds, the HGPS birds had a greater ratio of CD4(+):CD8(+) at 30 and 45 wk of age. There was an age-associated decrease in CD4(+) cells in all groups from 45 to 60 wk of age. However, an age-related decrease in CD8(+) cells from 45 to 60 wk was found in the DXL birds only. The unique changes in T-cell subpopulations and the ratio of CD4(+):CD8(+) may suggest that HGPS birds had a greater cell-mediated immunity than DXL birds. The genetic basis of variations in immunity may correlate with the line-unique ability of birds to cope in social environments and their survivability.

Genetic basis of variation in tenofovir drug susceptibility in HIV-1

To develop an improved model for the genetic basis of reduced susceptibility to tenofovir in vitro. A dataset of 532 HIV-1 subtype B reverse transcriptase genotypes for which matched phenotypic susceptibility data were available was assembled, both as a continuous (transformed) dataset and a categorical dataset generated by imposing a cut-off on the basis of earlier studies of in-vivo response of 1.4-fold. Models were generated using stepwise regression, decision tree and random forest approaches on both the continuous and categorical data. Models were compared by mean squared error (continuous models), or by misclassification rates by nested crossvalidation. From the continuous dataset, stepwise linear regression, regression tree and regression forest methods yielded models with MSE of 0.46, 0.48 and 0.42 respectively. Amino acids 215, 65, 41, 67, 184 and 151 in HIV-1 reverse transcriptase were identified in all three models and amino acid 210 in two. The categorical data yielded logistic regression, classification tree and forest models with misclassification rates of 26, 24 and 23%, respectively. Amino acids 215, 65 and 67 appeared in all; 41, 184, 210 and 151 were also included in the classification forest model. The random forests approach has yielded a substantial improvement in the available models to describe the genetic basis of reduced susceptibility to tenofovir in vitro. The most important sites in these models are amino acid sites 215, 65, 41, 67, 184, 151 and 210 in HIV-1 reverse transcriptase.

The evolution of senescence from a comparative perspective

Summary 1Comparative studies of ageing address the evolutionary lability of the rate of ageing as an indication of potential for, and constraints on, the extension of life span. 2Experimental studies on ageing have focused on damage induced by reactive oxygen species (ROS) and other stresses, and on the mechanisms to prevent or repair this damage. Research on animal models has revealed genes with large effects on life span. However, the relevance of some animal models to human ageing is unclear and it is not known whether evolved differences in ageing involve such major gene effects. 3Studies on the demography of populations of vertebrates in the wild show that animals suffer from senescence in nature. Variation in the rate of ageing is consistent with evolutionary theory in that senescence is delayed in populations that suffer relatively low extrinsic mortality. 4Populations of longer-lived individuals suffer a higher proportion of ageing-related mortality, and thus stronger selection against early ageing. The presence of ageing-related deaths in these populations suggests a lack of suitable mechanisms that would further extend life span. 5Similar patterns of ageing-related mortality in wild and captive or domesticated populations indicate that most ageing-related death is caused by intrinsic factors, such as tumours and cardiovascular failure, rather than increasing vulnerability to extrinsic causes of mortality. 6Studies of several wild populations of long-lived birds suggest that ageing-related mortality is often catastrophic, with individuals maintaining high levels of condition until shortly before their demise. 7Comparative studies of many species suggest connections between early development and the pattern of ageing later in life, consistent with laboratory studies on variation within individual species. The physiological connections across the life span are not well understood. 8Comparative studies have provided important insights into the ageing process. However, we still lack information on important issues, including the causes of death in natural populations, the relationship of within- and between-population variation in the rate of ageing, the genetic basis of variation in rate of ageing in natural populations, and detailed longitudinal studies of individual health and reproductive success in relation to age at death.

Different Behavioral and Physiological Responses in Two Genetic Lines of Laying Hens After Transportation

Physiological and behavioral responses to transportation stress were examined in a chicken strain selected for high group productivity and survivability (HGPS) resulting from reduced cannibalism and flightiness in colony cages and in chickens from Dekalb XL (DXL) commercial strain. At 13 wk of age, 96 pullets per strain were randomly assigned to 4-bird cages within the same strain. At 17 wk of age, half of the cages of each strain (n = 12) were randomly used as experimental group. The birds of the experimental group were crated by line, with a caution to ensure all the birds in the same cage were unfamiliar to each other, and then transported for 2 h on a country road. After transportation, the birds were recaged in groups of 4 within the same line. Behavioral data were collected immediately after the recaging of the birds. Physical parameters (BW and organ weight), plasma corticosterone levels, blood and brain serotonin (5-HT) concentrations, and 5-HT1A receptor mRNA expressions were measured at 1 d posttransportation. Results showed that, compared with the control birds of each strain, transportation stress-induced behavioral changes in eating, drinking, and preening were found in the birds from both strains, but the HGPS birds showed a greater increase in drinking and preening (P < 0.01). In addition, after transportation stress, the HGPS birds had heavier adrenal glands (P < 0.01) with higher concentrations of plasma corticosterone (P < 0.01) and a trend to higher central 5-HT levels (P = 0.09) with a downregulated 5-HT1A receptor gene expression (P < 0.05), whereas the DXL birds had a higher H:L ratio (P < 0.05). The data indicate that there are a genetic basis of variations in chickens in response to transportation stress. The HGPS birds may have a better coping capability to transportation stress than DXL birds.

Predicting crown damage to Eucalyptus grandis by Paropsis atomaria with direct and indirect measures of leaf composition

A genetic basis for variation in resistance to defoliating insects within Eucalyptus species has been identified in many studies. This variation has frequently been ascribed to variation in secondary metabolites but studies investigating variation in resistance to defoliation by paropsine chrysomelids have failed to correlate foliar chemistry with resistance. We found that the extent of crown damage due to defoliation by Paropsis atomaria (Chrysomelidae: Colepoptera) in two matched progeny trials of Eucalyptus grandis was a heritable trait that exhibited a strong correlation with provenance latitude. Despite this, neither foliar nitrogen or concentrations of a recently discovered group of compounds, formylated phloroglucinol compounds, could account for significant variation in defoliation. We also investigated whether defoliation in the field could be predicted from foliar near-infrared reflectance spectra. Such an approach takes into account all compositional variation simultaneously rather than relying on a restricted number of measured traits. Modified partial least squares regression models performed poorly in predicting variation in crown defoliation between trees within a site primarily due to the high level of variability and coarseness of the calibration data. Discriminant analyses however demonstrated a consistent difference between spectra from trees in families suffering low level defoliation from families more susceptible to defoliation by P. atomaria suggesting chemical differences between the two groups are important in determining resistance to this insect.

Inheritance and joint segregation of biochemical loci in European whitefish, genus Coregonus

Crosses were made with whitefish of Coregonus lavaretus complex and vendace Coregonus albula L. to establish the genetic basis of variation at enzyme loci. The alleles of Gpi-2, Gpi-4, Ldh-1, Mdh-2, Mdh-3, 4 and Pgm-2 were found to segregate in a simple Mendelian fashion in whitefish. Ck-1 and Mdh-3, 4 were found to segregate normally in vendace. The results of 10 cases of pairwise segregation between these loci are presented. All pairs revealed random assortment except Gpi-4 with Ldh-1, which showed almost complete linkage.

The genetic basis of variation in susceptibility to infection with Histoplasma capsulatum in the mouse

The pathogenic fungus Histoplasma capsulatum causes disease ranging from mild to fatal in healthy and immunocompromised humans. Infection rates reach 80% in endemic areas, including the Midwestern United States. We used inbred mice to identify a 300-fold difference in fungal burden. A/J mice showed lower fungal burden and morbidity than C57BL/6J mice, a reversal of the trend observed for many bacterial pathogens. We mapped the differences in fungal burden to discrete locations on chromosomes 1, 6, 15 and 17 with high significance. Substitution of a single resistant chromosome 17 onto the susceptible background was sufficient to lower fungal burden. These loci will allow dissection of the fungal-specific immune program.

The CBF gene family in hexaploid wheat and its relationship to the phylogenetic complexity of cereal CBFs.

Most temperate plants tolerate both chilling and freezing temperatures whereas many species from tropical regions suffer chilling injury when exposed to temperatures slightly above freezing. Cold acclimation induces the expression of cold-regulated genes needed to protect plants against freezing stress. This induction is mediated, in part, by the CBF transcription factor family. To understand the evolution and function of this family in cereals, we identified and characterized 15 different CBF genes from hexaploid wheat. Our analyses reveal that wheat species, T. aestivum and T. monococcum, may contain up to 25 different CBF genes, and that Poaceae CBFs can be classified into 10 groups that share a common phylogenetic origin and similar structural characteristics. Six of these groups (IIIc, IIId, IVa, IVb, IVc and IVd) are found only in the Pooideae suggesting they represent the CBF response machinery that evolved recently during colonization of temperate habitats. Expression studies reveal that five of the Pooideae-specific groups display higher constitutive and low temperature inducible expression in the winter cultivar, and a diurnal regulation pattern during growth at warm temperature. The higher constitutive and inducible expression within these CBF groups is an inherited trait that may play a predominant role in the superior low temperature tolerance capacity of winter cultivars and possibly be a basis of genetic variability in freezing tolerance within the Pooideae subfamily.Electronic supplementary materialThe online version of this article (doi:10.1007/s00438-006-0206-9) contains supplementary material, which is available to authorized users.