Differential Evolutionary History in Visual and Olfactory Floral Cues of the Bee-Pollinated Genus Campanula (Campanulaceae).

Visual and olfactory floral signals play key roles in plant-pollinator interactions. In recent decades, studies investigating the evolution of either of these signals have increased considerably. However, there are large gaps in our understanding of whether or not these two cue modalities evolve in a concerted manner. Here, we characterized the visual (i.e., color) and olfactory (scent) floral cues in bee-pollinated Campanula species by spectrophotometric and chemical methods, respectively, with the aim of tracing their evolutionary paths. We found a species-specific pattern in color reflectance and scent chemistry. Multivariate phylogenetic statistics revealed no influence of phylogeny on floral color and scent bouquet. However, univariate phylogenetic statistics revealed a phylogenetic signal in some of the constituents of the scent bouquet. Our results suggest unequal evolutionary pathways of visual and olfactory floral cues in the genus Campanula. While the lack of phylogenetic signal on both color and scent bouquet points to external agents (e.g., pollinators, herbivores) as evolutionary drivers, the presence of phylogenetic signal in at least some floral scent constituents point to an influence of phylogeny on trait evolution. We discuss why external agents and phylogeny differently shape the evolutionary paths in floral color and scent of closely related angiosperms.

Absence of strong linkage disequilibrium between odorant receptor alleles and the major histocompatibility complex.

The odorant receptor (OR) genes constitute the largest gene family among vertebrates. While over 800 loci are present in the human genome, their allele diversity is still poorly characterized. It has been hypothesized that the products of OR genes can be relevant in the reproductive context, thereby interacting with products of genes of the major histocompatibility complex (MHC). Here we investigated the genetic diversity of the OR2W6P, OR2B8P, OR1F12 and OR12D2 genes, in order to define haplotypes and haplotype frequencies. We measured levels of linkage disequilibrium (LD) between these OR genes and the MHC genes HLA-A, HLA-B and HLA-DRB1. This was accomplished through the assessment of 30 single nucleotide polymorphisms (SNPs) in samples from 61 family trios. We characterized 26 alleles among the four OR genes and identified three SNPs that had not yet been reported. Based on our haplotype analysis, LD spanning the OR-HLA region is not very strong, and therefore not enough to enable selection regarding specific HLA-OR haplotypes.

Genomic architecture of MHC-linked odorant receptor gene repertoires among 16 vertebrate species.

The recent sequencing and assembly of the genomes of different organisms have shown that almost all vertebrates studied in detail so far have one or more clusters of genes encoding odorant receptors (OR) in close physical linkage to the major histocompatibility complex (MHC). It has been postulated that MHC-linked OR genes could be involved in MHC-influenced mate choice, comprising both pre- as well as post-copulatory mechanisms. We have therefore carried out a systematic comparison of protein sequences of these receptors from the genomes of man, chimpanzee, gorilla, orangutan, rhesus macaque, mouse, rat, dog, cat, cow, pig, horse, elephant, opossum, frog and zebra fish (amounting to a total of 559 protein sequences) in order to identify OR families exhibiting evolutionarily conserved MHC linkage. In addition, we compared the genomic structure of this region within these 16 species, accounting for presence or absence of OR gene families, gene order, transcriptional orientation and linkage to the MHC or framework genes. The results are presented in the form of gene maps and phylogenetic analyses that reveal largely concordant repertoires of gene families, at least among tetrapods, although each of the eight taxa studied (primates, rodents, ungulates, carnivores, proboscids, marsupials, amphibians and teleosts) exhibits a typical architecture of MHC (or MHC framework loci)-linked OR genes. Furthermore, the comparison of the genomic organization of this region has implications for phylogenetic relationships between closely related taxa, especially in disputed cases such as the evolutionary history of even- and odd-toed ungulates and carnivores. Finally, the largely conserved linkage between distinct OR genes and the MHC supports the concept that particular alleles within a given haplotype function in a concerted fashion during self-/non-self-discrimination processes in reproduction.

Variation and linkage disequilibrium within odorant receptor gene clusters linked to the human major histocompatibility complex.

Odorant receptors (OR) are G-protein-coupled receptors that are predominantly expressed in the membrane of olfactory neurons. Members of the two OR gene clusters on the short arm of human chromosome 6 could be involved in major histocompatibility complex (MHC)-associated behavioral traits, such as olfaction-influenced mate selection and cryptic female choice. In this context, OR gene polymorphisms and haplotypes are likely to play an important role. Here we report an investigation of polymorphisms within 12 MHC-linked OR genes in 10 human cell lines. Eight of these OR loci belong to the telomeric, smaller OR gene cluster, whereas four are located centromeric, between the first cluster and the MHC. We also assessed part of this genomic region using sequence data from eight additional cell lines that had previously been sequenced. Thirteen novel OR variants were found through direct DNA sequencing and cloning, in addition to the detection of OR polymorphisms already known, and the number of OR cluster haplotypes could be increased to 21. Two loci belonging to the telomeric cluster (OR2B8P and OR1F12) were found to exhibit nonfunctional and potentially functional alleles and should therefore be considered as segregating pseudogenes. The results provide a detailed picture regarding polymorphisms and phenotypic variation in an ethnically diverse sample of major histocompatibility complex-linked OR clusters and identify a subregion of unusually pronounced genetic variability. We expand these data by analyzing linkage disequilibrium both within these OR clusters as well as between them and the HLA complex in 11 unrelated HapMap populations. The sequence data described in this paper have been submitted to the GenBank database under the accession numbers GU251059, GU251060, GU251061, GU251062, GU251063, GU251064, GU251065, GU251066, GU251067, GU251068, GU251069, GU251070, GU251071, and GU251072.

Self/nonself perception, reproduction and the extended MHC.

Self/nonself perception governs mate selection in most eukaryotic species. It relies on a number of natural barriers that act before, during and after copulation. These hurdles prevent a costly investment into an embryo with potentially suboptimal genetic and immunological properties and aim at discouraging fertilization when male and female gametes exhibit extensive sharing of alleles. Due to the fact that several genes belonging to the extended major histocompatibility complex (xMHC) carry out crucial immune functions and are the most polymorphic within vertebrate genomes, it is likely that securing heterozygosity and the selection of rare alleles within this gene complex contributes to endowing the offspring with an advantage in fighting infections. Apart from MHC class I and II antigens, the products of several other genes within the xMHC are candidates for participating in mate choice, especially since the respective loci are subject to long-range linkage disequilibrium which may aid to preserve functionally connected alleles within a given haplotype. Among these loci are polymorphic odorant receptor genes that are expressed not only in the olfactory epithelium, but also within male reproductive tissues. They may thus not only be of importance in olfaction-influenced mate choice, by recognizing MHC-dependent individual-specific olfactory signals, but could also guide spermatozoa along chemical gradients to their target, the oocyte. By focusing on the human HLA complex and genes within its vicinity, we show here that the products of several xMHC-specified molecules might be involved in self/nonself perception during reproduction. Although the molecular details are often unknown, the existence of highly diverse, yet intertwined pre- and post-copulatory barriers suggests that xMHC-encoded proteins may be important for various stages of mate choice, germ cell development, as well as embryonic and foetal life in mammals and other vertebrates. Many of these genes should thus be regarded as crucial not only within the immune system, but also in reproduction.

Assessment of transmission distortion on chromosome 6p in healthy individuals using tagSNPs.

The best-documented example for transmission distortion (TD) to normal offspring are the t haplotypes on mouse chromosome 17. In healthy humans, TD has been described for whole chromosomes and for particular loci, but multiple comparisons have presented a statistical obstacle in wide-ranging analyses. Here we provide six high-resolution TD maps of the short arm of human chromosome 6 (Hsa6p), based on single-nucleotide polymorphism (SNP) data from 60 trio families belonging to two ethnicities that are available through the International HapMap Project. We tested all approximately 70,000 previously genotyped SNPs within Hsa6p by the transmission disequilibrium test. TagSNP selection followed by permutation testing was performed to adjust for multiple testing. A statistically significant evidence for TD was observed among male parents of European ancestry, due to strong and wide-ranging skewed segregation in a 730 kb long region containing the transcription factor-encoding genes SUPT3H and RUNX2, as well as the microRNA locus MIRN586. We also observed that this chromosomal segment coincides with pronounced linkage disequilibrium (LD), suggesting a relationship between TD and LD. The fact that TD may be taking place in samples not selected for a genetic disease implies that linkage studies must be assessed with particular caution in chromosomal segments with evidence of TD.

Association of smoking behavior with an odorant receptor allele telomeric to the human major histocompatibility complex.

Smoking behavior has been associated in two independent European cohorts with the most common Caucasian human leukocyte antigen (HLA) haplotype (A1-B8-DR3). We aimed to test whether polymorphic members of the two odorant receptor (OR) clusters within the extended HLA complex might be responsible for the observed association, by genotyping a cohort of Hungarian women in which the mentioned association had been found. One hundred and eighty HLA haplotypes from Centre d'Etude du Polymorphisme Humain families were analyzed in silico to identify single-nucleotide polymorphisms (SNPs) within OR genes that are in linkage disequilibrium with the A1-B8-DR3 haplotype, as well as with two other haplotypes indirectly linked to smoking behavior. A nonsynonymous SNP within the OR12D3 gene (rs3749971(T)) was found to be linked to the A1-B8-DR3 haplotype. This polymorphism leads to a (97)Thr --> Ile exchange that affects a putative ligand binding region of the OR12D3 protein. Smoking was found to be associated in the Hungarian cohort with the rs3749971(T) allele (p = 1.05 x 10(-2)), with higher significance than with A1-B8-DR3 (p = 2.38 x 10(-2)). Our results link smoking to a distinct OR allele, and demonstrate that the rs3749971(T) polymorphism is associated with the HLA haplotype-dependent differential recognition of cigarette smoke components, at least among Caucasian women.

New evidence that the MHC influences odor perception in humans: a study with 58 Southern Brazilian students.

Increasing evidence suggests a correlation between mate choice, odor preference, and genetic similarity at the Major Histocompatibility Complex (MHC) in a variety of animals, including our species. The MHC is a highly polymorphic group of genes that play an important role in the immunological self/nonself recognition. Its products have been reported to take part on the variety of compounds and reactions that together build an individual's body odor. It has been suggested, therefore, that animals use body odor as a guide to identify possible mates as MHC-similar or MHC-dissimilar from their own genotype. Preference for a MHC-dissimilar partner enhances MHC heterozygosity of an individual's offspring. The possible adaptive advantages are clear: it is a mechanism of avoiding inbreeding and MHC-heterozygous offspring may have enhanced immunocompetence. The aim of this study was to search, in our species, new evidence on the correlation between specificities at HLA-A and HLA-B and assessments of pleasantness regarding specific body odors. HLA is the name for the human MHC. Four olfactory sessions were performed with 58 young Southern Brazilian students, in order to investigate whether assessments of pleasantness of body odors from individuals correlate to a person's HLA phenotype. Body odors were collected via sweat and urine from all participants. Women smelled and scored all male odor samples and men did the same with all female samples. We found a significant correlation only when female smellers evaluated male sweat odors.