Effect of balancing selection on spatial genetic structure within populations: theoretical investigations on the self-incompatibility locus and empirical studies in Arabidopsis halleri

The effect of selection on patterns of genetic structure within and between populations may be studied by contrasting observed patterns at the genes targeted by selection with those of unlinked neutral marker loci. Local directional selection on target genes will produce stronger population genetic structure than at neutral loci, whereas the reverse is expected for balancing selection. However, theoretical predictions on the intensity of this signal under precise models of balancing selection are still lacking. Using negative frequency-dependent selection acting on self-incompatibility systems in plants as a model of balancing selection, we investigated the effect of such selection on patterns of spatial genetic structure within a continuous population. Using numerical simulations, we tested the effect of the type of self-incompatibility system, the number of alleles at the self-incompatibility locus and the dominance interactions among them, the extent of gene dispersal, and the immigration rate on spatial genetic structure at the selected locus and at unlinked neutral loci. We confirm that frequency-dependent selection is expected to reduce the extent of spatial genetic structure as compared to neutral loci, particularly in situations with low number of alleles at the self-incompatibility locus, high frequency of codominant interactions among alleles, restricted gene dispersal and restricted immigration from outside populations. Hence the signature of selection on spatial genetic structure is expected to vary across species and populations, and we show that empirical data from the literature as well as data reported here on three natural populations of the herb Arabidopsis halleri confirm these theoretical results.     

Natural and synthetic alleles provide complementary insights into the nature of selection acting on the Men polymorphism of Drosophila melanogaster

Two malic enzyme alleles, Men^113A and Men^113G, occur at approximately equal frequency in North American populations of Drosophila melanogaster, while only Men^113A occurs in African populations. We investigated the population genetics, biochemical characteristics, and selective potential of these alleles. Comparable levels of nucleotide polymorphism in both alleles suggest that the Men^113G allele is not recently derived, but we find no evidence in the DNA sequence data for selection maintaining the polymorphism. Interestingly, the alleles differ in both V_max and K_m for the substrate malate. Triglyceride concentration and isocitrate dehydrogenase (IDH) and glucose-6-phosphate dehydrogenase (G6PD) activities are negatively correlated with the in vivo activities of the Men alleles. We examined the causality of the observed correlations using P-element excision-derived knockout alleles of the Men gene and found significant changes in the maximum activities of both IDH and G6PD, but not in triglyceride concentration, suggesting compensatory interactions between MEN, IDH, and G6PD. Additionally, we found significantly higher than expected levels of MEN activity in knockout heterozygotes, which we attribute to transvection effects. The distinct differences in biochemistry and physiology between the naturally occurring alleles and between the engineered alleles suggest the potential for selection on the Men locus.     

Local selection of human populations shapes complex evolution patterns of CXCL10 gene

CXC motif chemokine 10 (CXCL10) is a small cytokine belonging to the CXC chemokine family, and it is secreted by several cell types in response to IFN-γ and regulates immune responses through the recruitment and activation of lymphocytes. As CXCL10 is very important in T-cell immunity and infectious diseases, we studied the effect of natural selection on the CXCL10 locus. By sequencing 74 individuals from three human populations, we found a complex pattern of natural selection acting on the CXCL10 locus. We discovered a signature of balancing selection in the European population with a significant positive Tajima’s D value (2.57, P?=?0.005) and an excess of intermediate frequency alleles. However, we observed an excess of high frequency-derived alleles and a significant Fay and Wu’s test statistics (P?=?0.015) in the Chinese population, which suggests that recent selective sweeps under positive selection had occurred. Also, there are a lot of alleles showing great frequency difference among populations. These results demonstrate that local selection has shaped CXCL10 evolution and indicates that there exist different actions of natural selection on the CXCL10 locus in different populations. This study provides insights into the likely relative roles of natural selection and population history in shaping today’s genetic variation at the CXCL10 locus, indicates the relationship between adaptation to past infection and predisposition to autoimmunity in modern populations, improves our understanding of CXCL10 evolution, and motivates further investigations of the role of CXCL10 in infectious diseases and autoimmune diseases.     

Intramolecular Interaction Influences Binding of the Flax L5 and L6 Resistance Proteins to their AvrL567 Ligands

L locus resistance (R) proteins are nucleotide binding (NB-ARC) leucine-rich repeat (LRR) proteins from flax (Linum usitatissimum) that provide race-specific resistance to the causal agent of flax rust disease, Melampsora lini. L5 and L6 are two alleles of the L locus that directly recognize variants of the fungal effector AvrL567. In this study, we have investigated the molecular details of this recognition by site-directed mutagenesis of AvrL567 and construction of chimeric L proteins. Single, double and triple mutations of polymorphic residues in a variety of AvrL567 variants showed additive effects on recognition strength, suggesting that multiple contact points are involved in recognition. Domain-swap experiments between L5 and L6 show that specificity differences are determined by their corresponding LRR regions. Most positively selected amino acid sites occur in the N- and C-terminal LRR units, and polymorphisms in the first seven and last four LRR units contribute to recognition specificity of L5 and L6 respectively. This further confirms that multiple, additive contact points occur between AvrL567 variants and either L5 or L6. However, we also observed that recognition of AvrL567 is affected by co-operative polymorphisms between both adjacent and distant domains of the R protein, including the TIR, ARC and LRR domains, implying that these residues are involved in intramolecular interactions to optimize detection of the pathogen and defense signal activation. We suggest a model where Avr ligand interaction directly competes with intramolecular interactions to cause activation of the R protein.     

Mating-type locus of Cryptococcus neoformans: a step in the evolution of sex chromosomes

The sexual development and virulence of the fungal pathogen Cryptococcus neoformans is controlled by a bipolar mating system determined by a single locus that exists in two alleles, α and a. The α and a mating-type alleles from two divergent varieties were cloned and sequenced. The C. neoformans mating-type locus is unique, spans >100 kb, and contains more than 20 genes. MAT-encoded products include homologs of regulators of sexual development in other fungi, pheromone and pheromone receptors, divergent components of a MAP kinase cascade, and other proteins with no obvious function in mating. The α and a alleles of the mating-type locus have extensively rearranged during evolution and strain divergence but are stable during genetic crosses and in the population. The C. neoformans mating-type locus is strikingly different from the other known fungal mating-type loci, sharing features with the self-incompatibility systems and sex chromosomes of algae, plants, and animals. Our study establishes a new paradigm for mating-type loci in fungi with implications for the evolution of cell identity and self/nonself recognition.     

Incest versus abstinence: reproductive trade‐offs between mate limitation and progeny fitness in a self‐incompatible invasive plant

Plant mating systems represent an evolutionary and ecological trade‐off between reproductive assurance through selfing and maximizing progeny fitness through outbreeding. However, many plants with sporophytic self‐incompatibility systems exhibit dominance interactions at the S‐locus that allow biparental inbreeding, thereby facilitating mating between individuals that share alleles at the S‐locus. We investigated this trade‐off by estimating mate availability and biparental inbreeding depression in wild radish from five different populations across Australia. We found dominance interactions among S‐alleles increased mate availability relative to estimates based on individuals that did not share S‐alleles. Twelve of the sixteen fitness variables were significantly reduced by inbreeding. For all the three life‐history phases evaluated, self‐fertilized offspring suffered a greater than 50% reduction in fitness, while full‐sib and half‐sib offspring suffered a less than 50% reduction in fitness. Theory indicates that fitness costs greater than 50% can result in an evolutionary trajectory toward a stable state of self‐incompatibility (SI). This study suggests that dominance interactions at the S‐locus provide a possible third stable state between SI and SC where biparental inbreeding increases mate availability with relatively minor fitness costs. This strategy allows weeds to establish in new environments while maintaining a functional SI system.     

Diversity and evolution of the highly polymorphic tandem repeat LEI0258 in the chicken MHC-B region

The chicken major histocompatibility complex (MHC) is located on the microchromosome 16 and is described as the most variable region in the genome. The genes of the MHC play a central role in the immune system. Particularly, genes encoding proteins involved in the antigen presentation to T cells. Therefore, describing the genetic polymorphism of this region is crucial in understanding host–pathogen interactions. The tandem repeat LEI0258 is located within the core area of the B region of the chicken MHC (MHC-B region) and its genotypes correlate with serology. This marker was used to provide a picture of the worldwide diversity of the chicken MHC-B region and to categorize chicken MHC haplotypes. More than 1,600 animals from 80 different populations or lines of chickens from Africa, Asia, and Europe, including wild fowl species, were genotyped at the LEI0258 locus. Fifty novel alleles were described after sequencing. The resulting 79 alleles were classified into 12 clusters, based on the SNPs and indels found within the sequences flanking the repeats. Furthermore, hypotheses were formulated on the evolutionary dynamics of the region. This study constitutes the largest variability report for the chicken MHC and establishes a framework for future diversity or association studies.     

Disentangling cause and consequence: genetic dissection of the DANGEROUS MIX2 risk locus,and activation of the DM2h NLR in autoimmunity

Nucleotide-binding domain–leucine-rich repeat-type immune receptors (NLRs) protect plants against pathogenic microbes through intracellular detection of effector proteins. However, this comes at a cost, as NLRs can also induce detrimental autoimmunity in genetic interactions with foreign alleles. This may occur when independently evolved genomes are combined in inter- or intraspecific crosses, or when foreign alleles are introduced by mutagenesis or transgenesis. Most autoimmunity-inducing NLRs are encoded within highly variable NLR gene clusters with no known immune functions, which were termed autoimmune risk loci. Whether risk NLRs differ from sensor NLRs operating in natural pathogen resistance and how risk NLRs are activated in autoimmunity is unknown. Here, we analyzed the DANGEROUS MIX2 risk locus, a major autoimmunity hotspot in Arabidopsis thaliana. By gene editing and heterologous expression, we show that a single gene, DM2h, is necessary and sufficient for autoimmune induction in three independent cases of autoimmunity in accession Landsberg erecta. We focus on autoimmunity provoked by an EDS1-yellow fluorescent protein (YFP)^NLS fusion protein to characterize DM2h functionally and determine features of EDS1-YFP^NLS activating the immune receptor. Our data suggest that risk NLRs function in a manner reminiscent of sensor NLRs, while autoimmunity-inducing properties of EDS1-YFP^NLS in this context are unrelated to the protein's functions as an immune regulator. We propose that autoimmunity, at least in some cases, may be caused by spurious, stochastic interactions of foreign alleles with coincidentally matching risk NLRs.     

Genetic separation of autonomous endosperm formation (AutE) from the two other components of apomixis in Hieracium

In apomictic Hieracium subgenus Pilosella species, embryo sacs develop in ovules without meiosis. Embryo and endosperm formation then occur without fertilization, producing seeds with a maternal genotype encased in a fruit (achene). Genetic analyses in H. praealtum indicate a dominant locus (LOA) controls meiotic avoidance, and another dominant locus (LOP) controls both fertilization-independent embryogenesis and endosperm formation. While cytologically examining developmental events in ovules of progeny from crosses between different wild-type and mutant Hieracium apomicts, and a sexual Hieracium species, we identified two plants, AutE196 and AutE24, which have lost the capacity for meiotic avoidance and fertilization-independent embryo formation. AutE196 and AutE24 exhibit autonomous endosperm formation and set parthenocarpic, seedless achenes at a penetrance of 18 %. Viable seed form after pollination. Cytological examination of 102 progeny from a backcross of AutE196 with sexual H. pilosella showed that autonomous endosperm formation is a heritable, dominant, qualitative trait, detected in 51 % of progeny. Variation in quantitative trait penetrance indicates other factors influence its expression. The correlation between autonomous endosperm development and mature parthenocarpic achene formation suggests the former is sufficient to trigger fruit maturation in Hieracium. The developmental component of autonomous endosperm formation is therefore genetically separable from those controlling meiotic avoidance and autonomous embryogenesis in Hieracium and has been denoted as AutE. We postulate that tight linkage of AutE and genes controlling autonomous embryogenesis at the LOP locus in H. praealtum may explain why inheritance of autonomous seed formation is typically observed as a single component.     

Polymorphism of hordein-coding loci in barley (Hordeum vulgare L.) populations from the countries of Eastern Asia (China, Nepal, Pakistan, India)

In this study, starch gel electrophoresis was used to examine polymorphism of hordeins encoded by the Hrd A, Hrd B, and Hrd F loci in 201 accessions of barley landraces from China (including Tibet), Nepal, Pakistan, and India. Altogether, 50 alleles with the frequencies of 0.001?C0.2269 were determined for the Hrd A locus, 65 alleles with the frequencies of 0.001?C0.1612 were determined for the Hrd B locus, and five alleles with the frequencies of 0.001?C0.4537 were determined for the Hrd F locus. In barley populations from these countries, irregular distribution of alleles and allele frequencies was observed. Cluster analysis of the matrix of allele frequencies in populations from known sampling sites revealed cluster structure of local barley populations within each country. Local populations formed five differently sized clusters in Nepal, four such clusters in India, three clusters in China, and three clusters, in Pakistan. These results suggest that variation and allele frequency distribution of the hordein-coding loci in the countries of Eastern Asia resulted from the introduction and spreading of barley forms through the husbandmen migrations.     

Stable expression of a single-copy rolA gene in transgenic Arabidopsis thaliana plants allows an exhaustive mutagenic analysis of the transgene-associated phenotype

Several publications have documented the instability of transgene expression in plants. Previous genetic approaches to the study of transgene-associated phenotypes in plants were limited by this phenomenon. Here we show that a transgene can be expressed in plants with sufficient stability to allow an exhaustive mutagenic analysis of the resulting phenotype. We have expressed the morphogenic rolA gene from the TL-DNA of Agrobacterium rhizogenes Ri plasmid in transgenic Arabidopsis thaliana plants. The resulting pleiotropic RolA phenotype allows a visual screen for reversion to detect germinal as well as somatic instability of transgene expression. However no spontaneous reversions of the RolA phenotype were observed in 65 000 progeny of two independent transgenic A. thaliana lines, each carrying a single homozygous rolA locus. In contrast, 12 revertants of the RolA phenotype were isolated from 360000 ethyl methane sulphonate (EMS)-mutagenized M2 progeny. All revertants were shown genetically to carry stable recessive mutations in the rolA locus, thus establishing a series of loss-of-function alleles. Molecular characterization revealed that the loss-of-function alleles were structurally intact and expressed in all rolA mutants. A wild-type rolA locus and two loss-of-function alleles were reisolated and sequenced; base pair substitutions were found in each loss-of-function allele leading to single amino acid substitutions in the rolA open reading frame. Therefore no instability of expression of the rolA locus was detected in any of the 425 000 individuals studied in this analysis. Furthermore even under conditions of saturation mutagenesis, no extragenic suppressor locus was detected.     

Selection at the Esterase-2 Locus of Drosophila buzzatii? Perturbation-Reperturbation Experiments

Apparent selection affecting starch gel electrophoretic alleles at the Esterase-2 locus of Drosophila buzzatii has been detected in laboratory and natural populations. Perturbation-reperturbation of allele frequencies in replicated laboratory populations attempts to test direct selective effects at the locus versus effects of linked loci. Sequential gel electrophoresis has identified more alleles within starch classes, and three of these alleles (within the a, b and c starch alleles) were used in cage population experiments. Allele a/1.00/1.00/1.00 was set up in 10 replicate populations with allele c/1.00/1.00/1.00, and in an independent 10 replicate populations with allele b/0.99/1.01/1.00. For each set, three reperturbations were done. Replicate populations generally showed similar patterns of allele frequency change and clear directionality: effects of selection, not drift. However, four populations deviated from their replicates, indicating dissipation of linkage disequilibrium. Estimates of pre-adult viability in the F₂ of pair-wise crosses among 12 sequential gel electrophoretic alleles showed very variable modes of inheritance and relative viability fitnesses. Together with the diversity of patterns of allele frequency change in the cage populations, these results suggest a gene complex, with selection acting on an interacting set of loci which may include Esterase-2.     

Use of immunochemical and SSCP analyses to test homozygosity at theS locus ofBrassica oleracea genotypes

The self-incompatibility reaction of cruciferous plants prevents self-fertilization and has been shown to be controlled by at least two genes situated at a single multiallelic locus, theS locus. One of these two genes, theS locus glycoprotein (SLG) gene, encodes an abundant glycoprotein secreted to the cell wall of stigma papillae. Identification of thoseS alleles present at theS locus is of prime interest when studying the self-incompatibility response and can be achieved by identifying the SLG of the stigma. Here, we show that using anti-SLG antibodies in an immunochemical analysis, combined with a SSCP (single-strand conformation polymorphism) approach to characterize the corresponding stigma-specific, SLG mRNA, allowed the identification of plants heterogeneous at theS locus among populations of plants that were thought to be homozygous for known SLG alleles. This analysis stresses the importance of testing the homozygosity at theS locus of lines considered inbred for a knownS allele as mix-up of seeds may occur during the breeding programme.     

Selection and genetic drift in captive versus wild populations: an assessment of neutral and adaptive (MHC-linked) genetic variation in wild and hatchery brown trout (<Emphasis Type="Italic">Salmo trutta</Emphasis>) populations

Captive bred individuals are often released into natural environments to supplement resident populations. Captive bred salmonid fishes often exhibit lower survival rates than their wild brethren and stocking measures may have a negative influence on the overall fitness of natural populations. Stocked fish often stem from a different evolutionary lineage than the resident population and thus may be maladapted for life in the wild, but this phenomenon has also been linked to genetic changes that occur in captivity. In addition to overall loss of genetic diversity via captive breeding, adaptation to captivity has become a major concern. Altered selection pressure in captivity may favour alleles at adaptive loci like the Major Histocompatibility Complex (MHC) that are maladaptive in natural environments. We investigated neutral and MHC-linked genetic variation in three autochthonous and three hatchery populations of Austrian brown trout (Salmo trutta). We confirm a positive selection pressure acting on the MHC II β locus, whereby the signal for positive selection was stronger in hatchery versus wild populations. Additionally, diversity at the MHC II β locus was higher, and more uniform among hatchery samples compared to wild populations, despite equal levels of diversity at neutral loci. We postulate that this stems from a combination of stronger genetic drift and a weakening of positive selection at this locus in wild populations that already have well adapted alleles for their specific environments.     

SNP assay to detect the ‘Hyuuga’ red-brown lesion resistance gene for Asian soybean rust

Asian soybean rust (ASR), caused by Phakopsora pachyrhizi Syd., has the potential to become a serious threat to soybean, Glycine max L. Merr., production in the USA. A novel rust resistance gene, Rpp?(Hyuuga), from the Japanese soybean cultivar Hyuuga has been identified and mapped to soybean chromosome 6 (Gm06). Our objectives were to fine-map the Rpp?(Hyuuga) gene and develop a high-throughput single nucleotide polymorphism (SNP) assay to detect this ASR resistance gene. The integration of recombination events from two different soybean populations and the ASR reaction data indicates that the Rpp?(Hyuuga) locus is located in a region of approximately 371 kb between STS70887 and STS70923 on chromosome Gm06. A set of 32 ancestral genotypes which is predicted to contain 95% of the alleles present in current elite North American breeding populations and the sources of the previously reported ASR resistance genes (Rpp1, Rpp2, Rpp3, Rpp4, Rpp5, and rpp5) were genotyped with five SNP markers. We developed a SimpleProbe assay based on melting curve analysis for SNP06-44058 which is tighly linked to the Rpp?(Hyuuga) gene. This SNP assay can differentiate plants/lines that are homozygous/homogeneous or heterozygous/heterogeneous for the resistant and susceptible alleles at the Rpp?(Hyuuga) locus.     

Selection, trans-species polymorphism, and locus identification of major histocompatibility complex class IIβ alleles of New World ranid frogs

Genes encoded by the major histocompatibility complex (MHC) play key roles in the vertebrate immune system. However, our understanding of the evolutionary processes and underlying genetic mechanisms shaping these genes is limited in many taxa, including amphibians, a group currently impacted by emerging infectious diseases. To further elucidate the evolution of the MHC in frogs (anurans) and develop tools for population genetics, we surveyed allelic diversity of the MHC class II β1 domain in both genomic and complementary DNA of seven New World species in the genus Rana (Lithobates). To assign locus affiliation to our alleles, we used a “gene walking” technique to obtain intron 2 sequences that flanked MHC class IIβ exon 2. Two distinct intron sequences were recovered, suggesting the presence of at least two class IIβ loci in Rana. We designed a primer pair that successfully amplified an orthologous locus from all seven Rana species. In total, we recovered 13 alleles and documented trans-species polymorphism for four of the alleles. We also found quantitative evidence of selection acting on amino acid residues that are putatively involved in peptide binding and structural stability of the β1 domain of anurans. Our results indicated that primer mismatch can result in polymerase chain reaction (PCR) bias, which influences the number of alleles that are recovered. Using a single locus may minimize PCR bias caused by primer mismatch, and the gene walking technique was an effective approach for generating single-copy orthologous markers necessary for future studies of MHC allelic variation in natural amphibian populations.     

A non-additive interaction in a single locus causes a very short root phenotype in wheat

Non-additive allelic interactions underlie over dominant and under dominant inheritance, which explain positive and negative heterosis. These heteroses are often observed in the aboveground traits, but rarely reported in root. We identified a very short root (VSR) phenotype in the F₁ hybrid between the common wheat (Triticum aestivum L.) landrace Chinese Spring and synthetic wheat accession TA4152-71. When germinated in tap water, primary roots of the parental lines reached ~15 cm 10 days after germination, but those of the F₁ hybrid were ~3 cm long. Selfing populations segregated at a 1 (long-root) to 1 (short-root) ratio, indicating that VSR is controlled by a non-additive interaction between two alleles in a single gene locus, designated as Vsr1. Genome mapping localized the Vsr1 locus in a 3.8-cM interval delimited by markers XWL954 and XWL2506 on chromosome arm 5DL. When planted in vermiculite with supplemental fertilizer, the F₁ hybrid had normal root growth, virtually identical to the parental lines, but the advanced backcrossing populations segregated for VSR, indicating that the F₁ VSR expression was suppressed by interactions between other genes in the parental background and the vermiculite conditions. Preliminary physiological analyses showed that the VSR suppression is independent of light status but related to potassium homeostasis. Phenotyping additional hybrids between common wheat and synthetics revealed a high VSR frequency and their segregation data suggested more Vsr loci involved. Because the VSR plants can be regularly maintained and readily phenotyped at the early developmental stage, it provides a model for studies of non-additive interactions in wheat.     

Non-additive effects of pollen limitation and self-incompatibility reduce plant reproductive success and population viability

Background and Aims

Mating system is a primary determinant of the ecological and evolutionary dynamics of wild plant populations. Pollen limitation and loss of self-incompatibility genotypes can both act independently to reduce seed set and these effects are commonly observed in fragmented landscapes. This study used a simulation modelling approach to assess the interacting effects of these two processes on plant reproductive performance and population viability for a range of pollination likelihood, self-incompatibility systems and S-allele richness conditions.

Methods

A spatially explicit, individual-based, genetic and demographic simulation model parameterized to represent a generic self-incompatible, short-lived perennial herb was used to conduct simulation experiments in which pollination probability, self-incompatibility type (gametophytic and sporophytic) and S-allele richness were systematically varied in combination to assess their independent and interacting effects on the demographic response variables of mate availability, seed set, population size and population persistence.

Key Results

Joint effects of reduced pollination probability and low S-allele richness were greater than independent effects for all demographic response variables except population persistence under high pollinator service (>50 %). At intermediate values of 15–25 % pollination probability, non-linear interactions with S-allele richness generated significant reductions in population performance beyond those expected by the simple additive effect of each independently. This was due to the impacts of reduced effective population size on the ability of populations to retain S alleles and maintain mate availability. Across a limited set of pollination and S-allele conditions (P = 0·15 and S = 20) populations with gametophytic SI showed reduced S-allele erosion relative to those with sporophytic SI, but this had limited effects on individual fecundity and translated into only modest increases in population persistence.

Conclusions

Interactions between pollen limitation and loss of S alleles have the potential to significantly reduce the viability of populations of a few hundred plants. Population decline may occur more rapidly than expected when pollination probabilities drop below 25 % and S alleles are fewer than 20 due to non-additive interactions. These are likely to be common conditions experienced by plants in small populations in fragmented landscapes and are also those under which differences in response between gameptophytic and sporophtyic systems are observed.     

Assessment of Genetic Relatedness of Crossbred Chicken Populations Using Microsatellite Markers

To measure genetic relatedness between populations, for breeding purposes, we analyzed 170 birds from six crossbred populations of three pure lines of White Leghorn chickens, using 14 microsatellite markers. All the microsatellites were polymorphic, with 2–6 alleles. The mean number of alleles per locus was 3.21. The effective number of alleles varied from 1.14 to 3.94. The observed heterozygosity varied from 0.133 to 1.00, with a mean of 0.748. The F _IS values were mostly negative, with an average of ?0.345. The mean F _ST value was 0.056. The Nm values ranged from 1.91 to 42.17. The highest genetic identity was observed between IWI × IWK and IWK × IWI. The relation between any two groups of crosses was more than 85%. The results suggest that the crossbred populations were very closely related.     

Mycobacterial Metabolic Syndrome: LprG and Rv1410 Regulate Triacylglyceride Levels,Growth Rate and Virulence in Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) mutants lacking rv1411c, which encodes the lipoprotein LprG, and rv1410c, which encodes a putative efflux pump, are dramatically attenuated for growth in mice. Here we show that loss of LprG-Rv1410 in Mtb leads to intracellular triacylglyceride (TAG) accumulation, and overexpression of the locus increases the levels of TAG in the culture medium, demonstrating a role of this locus in TAG transport. LprG binds TAG within a large hydrophobic cleft and is sufficient to transfer TAG from donor to acceptor membranes. Further, LprG-Rv1410 is critical for broadly regulating bacterial growth and metabolism in vitro during carbon restriction and in vivo during infection of mice. The growth defect in mice is due to disrupted bacterial metabolism and occurs independently of key immune regulators. The in vivo essentiality of this locus suggests that this export system and other regulators of metabolism should be considered as targets for novel therapeutics.