Domain movement within a gene: a novel evolutionary mechanism for protein diversification

A protein function is carried out by a specific domain localized at a specific position. In the present study, we report that, within a gene, a specific amino acid sequence can move between a certain position and another position. This was discovered when the sequences of restriction-modification systems within the bacterial species Helicobacter pylori were compared. In the specificity subunit of Type I restriction-modification systems, DNA sequence recognition is mediated by target recognition domain 1 (TRD1) and TRD2. To our surprise, several sequences are shared by TRD1 and TRD2 of genes (alleles) at the same locus (chromosomal location); these domains appear to have moved between the two positions. The gene/protein organization can be represented as x-(TRD1)-y-x-(TRD2)-y, where x and y represent repeat sequences. Movement probably occurs by recombination at these flanking DNA repeats. In accordance with this hypothesis, recombination at these repeats also appears to decrease two TRDs into one TRD or increase these two TRDs to three TRDs (TRD1-TRD2-TRD2) and to allow TRD movement between genes even at different loci. Similar movement of domains between TRD1 and TRD2 was observed for the specificity subunit of a Type IIG restriction enzyme. Similar movement of domain between TRD1 and TRD2 was observed for Type I restriction-modification enzyme specificity genes in two more eubacterial species, Streptococcus pyogenes and Mycoplasma agalactiae. Lateral domain movements within a protein, which we have designated DOMO (domain movement), represent novel routes for the diversification of proteins.     

Transmission distortion and genetic incompatibilities between alleles in a multigenerational mouse advanced intercross line

While direct additive and dominance effects on complex traits have been mapped repeatedly, additional genetic factors contributing to the heterogeneity of complex traits have been scarcely investigated. To assess genetic background effects, we investigated transmission ratio distortions (TRDs) of alleles from parent to offspring using an advanced intercross line (AIL) of an initial cross between the mouse inbred strains C57BL/6NCrl (B6N) and BFMI860-12 [Berlin Fat Mouse Inbred (BFMI)]. A total of 341 males of generation 28 and their respective 61 parents and 66 grandparents were genotyped using Mega Mouse Universal Genotyping Arrays. TRDs were investigated using allele transmission asymmetry tests, and pathway overrepresentation analysis was performed. Sequencing data were used to test for overrepresentation of nonsynonymous SNPs (nsSNPs) in TRD regions. Genetic incompatibilities were tested using the Bateson–Dobzhansky–Muller two-locus model. A total of 62 TRD regions were detected, many in close proximity to the telocentric centromere. TRD regions contained 44.5% more nsSNPs than randomly selected regions (182 vs 125.9 ± 17.0, P < 1 × 10⁻⁴). Testing for genetic incompatibilities between TRD regions identified 29 genome-wide significant incompatibilities between TRD regions [P_(BF) < 0.05]. Pathway overrepresentation analysis of genes in TRD regions showed that DNA methylation, epigenetic regulation of RNA, and meiotic/meiosis regulation pathways were affected independent of the parental origin of the TRD. Paternal BFMI TRD regions showed overrepresentation in the small interfering RNA biogenesis and in the metabolism of lipids and lipoproteins. Maternal B6N TRD regions harbored genes involved in meiotic recombination, cell death, and apoptosis pathways. The analysis of genes in TRD regions suggests the potential distortion of protein–protein interactions influencing obesity and diabetic retinopathy as a result of disadvantageous combinations of allelic variants in Aass, Pgx6, and Nme8. Using an AIL significantly improves the resolution at which we can investigate TRD. Our analysis implicates distortion of protein–protein interactions as well as meiotic drive as the underlying mechanisms leading to the observed TRD in our AIL. Furthermore, genes with large amounts of nsSNPs located in TRD regions are more likely to be involved in pathways that are related to the phenotypic differences between the parental strains. Genes in these TRD regions provide new targets for investigating genetic adaptation, protein–protein interactions, and determinants of complex traits such as obesity.     

Identification of a subdomain within DNA-(cytosine-C5)-methyltransferases responsible for the recognition of the 5' part of their DNA target.

In previous work on DNA-(cytosine-C5)-methyltransferases (C5-MTases), domains had been identified which are responsible for the sequence specificity of the different enzymes (target-recognizing domains, TRDs). Here we have analyzed the DNA methylation patterns of two C5-MTases containing reciprocal chimeric TRDs, consisting of the N- and C-terminal parts derived from two different parental TRDs specifying the recognition of 5'-CC(A/T)GG-3' and 5'-GCNGC-3'. Sequences recognized by these engineered MTases were non-symmetrical and degenerate, but contained at their 5' part a consensus sequence which was very similar to the 5' part of the target recognized by the parental TRD which contributed the N-terminal moiety of the chimeric TRD. The results are discussed in connection with the present understanding of the mechanism of DNA target recognition by C5-MTases. They demonstrate the possibility of designing C5-MTases with novel DNA methylation specificities.     

The Medicago truncatula reference accession A17 has an aberrant chromosomal configuration

Medicago truncatula (barrel medic) has emerged as a model legume and accession A17 is the reference genotype selected for the sequencing of the genome. In the present study we compare the A17 chromosomal configuration with that of other accessions by examining pollen viability and genetic maps of intraspecific hybrids. Hybrids derived from crosses between M. truncatula accessions, representative of the large genetic variation within the germplasm collection, were evaluated for pollen viability using Alexander's stain. Genetic maps were generated for the following crosses: SA27063 x SA3054 (n = 94), SA27063 x A17 (n = 92), A17 x Borung (n = 99) and A17 x A20 (n = 69). All F(1) individuals derived from crosses involving A17 showed 50% pollen viability or less. Examination of the recombination frequencies between markers of chromosomes 4 and 8 revealed an apparent genetic linkage between the lower arms of these chromosomes in genetic maps derived from A17. Semisterility and unexpected linkage relationship are both good indicators of a reciprocal translocation. The implications of the A17 distinctive chromosomal rearrangement on studies of genetic mapping, genome sequencing and synteny between species are discussed.     

Genome scans for transmission ratio distortion regions in mice

Transmission ratio distortion (TRD) is the departure from the expected genotypic frequencies under Mendelian inheritance. This departure can be due to multiple physiological mechanisms during gametogenesis, fertilization, fetal and embryonic development, and early neonatal life. Although a few TRD loci have been reported in mouse, inheritance patterns have never been evaluated for TRD. In this article, we developed a Bayesian binomial model accounting for additive and dominant deviation TRD mechanisms. Moreover, this model was used to perform genome-wide scans for TRD quantitative trait loci (QTL) on six F2 mouse crosses involving between 296 and 541 mice and between 72 and 1854 genetic markers. Statistical significance of each model was checked at each genetic marker with Bayes factors. Genome scans revealed overdominance TRD QTL located in mouse chromosomes 1, 2, 12, 13, and 14 and additive TRD QTL in mouse chromosomes 2, 3, and 15, although these results did not replicate across mouse crosses. This research contributes new statistical tools for the analysis of specific genetic patterns involved in TRD in F2 populations, our results suggesting a relevant incidence of TRD phenomena in mouse with important implications for both statistical analyses and biological research.     

Allelic variation at high-molecular-weight glutenin subunit loci in Aegilops biuncialis Vis

Alleles at the high-molecular-weight glutenin subunit loci Glu-U1 and Glu-M(b)1 were analyzed in the tetraploid species Aegilops biuncialis (UUM(b)M(b)). The material for the investigation included the collection of 39 accessions of Ae. biuncialis from Ukraine (the Crimea), one Hellenic accession, one accession of unknown origin, F2 seeds from different crosses, as well as samples from natural populations from the Crimea. Ae. umbellulata and Ae. comosa accessions were used to allocate components of the HMW glutenin subunit patterns of Ae. biuncialis to U or M(b) genomes. Eight alleles were identified at the Glu-U1 locus and ten alleles were revealed at the Glu-M(b) 1 locus. Among alleles at the Glu-M(b) 1 locus ofAe. biuncialis there were two alleles controlling the y-type subunit only and one allele encoding the x-subunit only.     

The specificity of sty SKI, a type I restriction enzyme, implies a structure with rotational symmetry.

The type I restriction and modification (R-M) enzyme from Salmonella enterica serovar kaduna ( Sty SKI) recognises the DNA sequence 5'-CGAT(N)7GTTA, an unusual target for a type I R-M system in that it comprises two tetranucleotide components. The amino target recognition domain (TRD) of Sty SKI recognises 5'-CGAT and shows 36% amino acid identity with the carboxy TRD of Eco R124I which recognises the complementary, but degenerate, sequence 5'-RTCG. Current models predict that the amino and carboxy TRDs of the specificity subunit are in inverted orientations within a structure with 2-fold rotational symmetry. The complementary target sequences recognised by the amino TRD of Sty SKI and the carboxy TRD of Eco R124I are consistent with the predicted inverted positions of the TRDs. Amino TRDs of similar amino acid sequence have been shown to recognise the same nucleotide sequence. The similarity reported here, the first example of one between amino and carboxy TRDs, while consistent with a conserved mechanism of target recognition, offers additional flexibility in the evolution of sequence specificity by increasing the potential diversity of DNA targets for a given number of TRDs. Sty SKI identifies the first member of the IB family in Salmonella species.     

Population differentiation in the beetleTribolium castaneum. I. Genetic architecture

We used joint-scaling analyses in conjunction with rearing temperature variation to investigate the contributions of additive, non-additive, and environmental effects to genetic divergence and incipient speciation among 12 populations of the red flour beetle, Tribolium castaneum, with small levels of pairwise nuclear genetic divergence (0.033 < Nei's D < 0.125). For 15 population pairs we created a full spectrum of line crosses (two parental, two reciprocal F1's, four F2's, and eight backcrosses), reared them at multiple temperatures, and analyzed the numbers and developmental defects of offspring. We assayed a total of 219,388 offspring from 5147 families. Failed crosses occurred predominately in F2's, giving evidence of F2 breakdown within this species. In all cases where a significant model could be fit to the data on offspring number, we observed at least one type of digenic epistasis. We also found maternal and cytoplasmic effects to be common components of divergence among T. castaneum populations. In some cases, the most complex model tested (additive, dominance, epistatic, maternal, and cytoplasmic effects) did not provide a significant fit to the data, suggesting that linkage or higher order epistasis is involved in differentiation between some populations. For the limb deformity data, we observed significant genotype-by-environment interaction in most crosses and pure parent crosses tended to have fewer deformities than hybrid crosses. Complexity of genetic architecture was not correlated with either geographic distance or genetic distance. Our results support the view that genetic incompatibilities responsible for postzygotic isolation, an important component of speciation, may be a natural but serendipitous consequence of nonadditive genetic effects and structured populations.     

Cytosine-specific type II DNA methyltransferases. A conserved enzyme core with variable target-recognizing domains

Comparisons of the amino acid sequences of m5C DNA methyltransferases (Mtases) from 11 prokaryotes and one eukaryote reveal a very similar organization. Among all the enzymes one can distinguish highly conserved "core" sequences and "variable" regions. The core sequences apparently mediate steps of the methylation reaction that are common to all the enzymes. The major variable region has been shown in our previous studies on multispecific phage Mtases to contain the target-recognizing domains (TRDs) of these enzymes. Here we have compared the amino acid sequences of various TRDs from phage Mtases. This has revealed the presence of both highly conserved and variable amino acids. We postulate that the conserved residues represent a "consensus" sequence defining a TRD, whereas the specificity of the TRD is determined by the variable residues. We have observed similarity between this consensus sequence and sequences in the variable region of the monospecific Mtases. We predict that the regions thus identified represent part of the TRDs of monospecific Mtases.     

Genetic diversity of three Elymus species indigenous to Japan and East Asia (E. tsukushiensis,E. humidus and E. dahuricus) detected by AFLP

With the aim of broadening the gene pool of Triticeae for crop improvement, the genetic diversity of three hexaploid Elymus species indigenous to Japan and East Asia (E. tsukushiensis, E. humidus and E. dahuricus) was evaluated using amplified fragment length polymorphism (AFLP) markers. A total of 34 accessions: five of E. tsukushiensis, 13 of E. humidus, 15 of E. dahuricus, and one tetraploid Elymus species as an outgroup, were analyzed. The AFLP analysis was conducted with 12 selective primer combinations. In all, 329 bands were scored. The average number of bands scored per accession was 135.3. Among the 34 accessions, no polymorphism was detected among 10 accessions of E. humidus and among three accessions of E. tsukushiensis. Each species showed a diagnostic band pattern. One accession of E. humidus showed a band pattern intermediate between those of E. humidus and E. tsukushiensis, suggesting the occurrence of interspecific introgression. The level of intraspecific variation was highest in E. dahuricus (1-psb = 0.17, pi = 0.010), followed by E. tsukushiensis (1-psb = 0.14, pi = 0.008) and E. humidus (1-psb = 0.03, pi = 0.002). The level of interspecific variation was higher than that of intraspecific variation in all the pairs compared. The level of divergence between E. humidus and E. tsukushiensis was relatively low, but even so it was two times higher than that of the intraspecific variation for each species. The phylogenetic tree constructed here showed clear separations of all the species. The results of this study indicate a clear divergence of E. humidus from E. tsukushiensis in spite of the morphological similarity between these two species. Based on the values of nucleotide diversity, the time of divergence between E. humidus and E. tsukushiensis was estimated to be 0.9-1.2 million years ago.     

A genomewide study of reproductive barriers between allopatric populations of a homosporous fern, Ceratopteris richardii

Biological factors involved in reproductive barriers between two divergent races of Ceratopteris richardii were investigated. We used a combination of spore germination rates, QTL analysis of spore germination rates, and transmission ratio distortion (TRD) of 729 RFLPs, AFLPs, and isozyme markers distributed across the genome on the basis of hybrid populations of 488 doubled haploid lines (DHLs) and 168 F(2)'s. Substantial reproductive barriers were found between the parental races, predominantly in the form of spore inviability (23.7% F(1) spore viability). Intrinsic genetic factors such as Bateson-Dobzhansky-Muller (BDM) incompatibilities involving both nuclear-nuclear and nuclear-cytoplasmic factors and chromosomal rearrangements appear to contribute to intrinsic postzygotic isolation. The genomewide distribution patterns of TRD loci support the hypothesis that reproductive barriers are a byproduct of divergence in allopatry and that the strong reproductive barriers are attributable to a small number of genetic elements scattered throughout the genome.     

The recombination landscape in Arabidopsis thaliana F2 populations

Recombination during meiosis shapes the complement of alleles segregating in the progeny of hybrids, and has important consequences for phenotypic variation. We examined allele frequencies, as well as crossover (XO) locations and frequencies in over 7000 plants from 17 F(2) populations derived from crosses between 18 Arabidopsis thaliana accessions. We observed segregation distortion between parental alleles in over half of our populations. The potential causes of distortion include variation in seed dormancy and lethal epistatic interactions. Such a high occurrence of distortion was only detected here because of the large sample size of each population and the number of populations characterized. Most plants carry only one or two XOs per chromosome pair, and therefore inherit very large, non-recombined genomic fragments from each parent. Recombination frequencies vary between populations but consistently increase adjacent to the centromeres. Importantly, recombination rates do not correlate with whole-genome sequence differences between parental accessions, suggesting that sequence diversity within A. thaliana does not normally reach levels that are high enough to exert a major influence on the formation of XOs. A global knowledge of the patterns of recombination in F(2) populations is crucial to better understand the segregation of phenotypic traits in hybrids, in the laboratory or in the wild.     

Complex genetic nature of sex-independent transmission ratio distortion in Asian rice species: the involvement of unlinked modifiers and sex-specific mechanisms

Transmission ratio distortion (TRD), in which one allele is transmitted more frequently than the opposite allele, is presumed to act as a driving force in the emergence of a reproductive barrier. TRD acting in a sex-specific manner has been frequently observed in interspecific and intraspecific hybrids across a broad range of organisms. In contrast, sex-independent TRD (siTRD), which results from preferential transmission of one of the two alleles in the heterozygote through both sexes, has been detected in only a few plant species. We previously reported an S(6) locus-mediated siTRD, in which the S(6) allele from an Asian wild rice strain (Oryza rufipogon) was transmitted more frequently than the S(6)(a) allele from an Asian cultivated rice strain (O. sativa) through both male and female gametes in heterozygous plants. Here, we report on the effect of a difference in genetic background on S(6) locus-mediated siTRD, based on the analysis using near-isogenic lines and the original wild strain as a parental strain for crossing. We found that the degree of TRD through the male gametes varied depending on the genetic background of the female (pistil) plants. Despite the occurrence of TRD through both male and female gametes, abnormality was detected in ovules, but not in pollen grains, in the heterozygote. These results suggest the involvement of unlinked modifiers and developmentally distinct, sex-specific genetic mechanisms in S(6) locus-mediated siTRD, raising the possibility that siTRD driven by a single locus may be affected by multiple genetic factors harbored in natural populations.     

Chromosomal basis of viability differences in Tigriopus californicus interpopulation hybrids

Crosses between populations of Tigriopus californicus result in backcross and F2 hybrid breakdown for a variety of fitness related measures. The magnitude of this hybrid breakdown is correlated with evolutionary divergence. We assessed the chromosomal basis of viability differences in nonrecombinant backcross hybrids using markers mapped to individual chromosomes. To assess effects of evolutionary divergence we crossed one population to three different populations: two distantly related (approximately 18% mitochondrial COI sequence divergence) and one closely related (approximately 1% mitochondrial COI sequence divergence). We found that all three interpopulation crosses resulted in significant deviations from expected Mendelian ratios at a majority of the loci studied. In all but one case, deviations were due to a deficit of parental homozygotes. This pattern implies that populations of T. californicus carry a significant genetic load, and that a combination of beneficial dominance and deleterious homozygote-heterozygote interactions significantly affects hybrid viability. Pairwise tests of linkage disequilibrium detected relatively few significant interactions. For the two divergent crosses, effects of individual chromosomes were highly concordant. These two crosses also showed higher heterozygote excess in females than males across the vast majority of chromosomes.     

Genetic variation in epigenetic inheritance of ribosomal RNA gene methylation in Arabidopsis

We investigated the fidelity of epigenetic inheritance in crosses between three accessions of the flowering plant Arabidopsis thaliana (Canary Islands, Cape Verde Islands, and Columbia). Specifically, we examined the cytosine methylation content of the ribosomal RNA genes at the two nucleolus organizer regions (NOR2 and NOR4) in F1 and F2 hybrid individuals derived from reciprocal crosses between the high NOR methylation strain, Columbia, and the two other accessions, both of which have less NOR methylation. In crosses between the Columbia and Cape Verde Islands strains, the cytosine methylation content segregated as an additive Mendelian trait: the high NOR methylation state was tightly associated with the inheritance of the two Columbia-derived NOR loci. First-generation hybrid individuals between the Canary Islands and Columbia strains also showed a cytosine methylation content at the NORs intermediate between the parental values, consistent with the epigenetic inheritance of parental methylation patterns. Interestingly, mapping data from F2 individuals derived from a Canary Islands x Columbia cross revealed that NOR2 accounted for nearly all of the NOR methylation variation segregating in the population. NOR4 retains a significant effect on total NOR methylation content only through a complex epistatic interaction with NOR2. Our results indicate that the inheritance of differential cytosine methylation states at NOR loci can be modified by their genetic context, opening up the possibility of genetic dissection of epigenetic inheritance.     

Tests of reproductive isolation among species in the <Emphasis Type="Italic">Fundulus notatus</Emphasis> (Cyprinodontiformes: Fundulidae) species complex

We assessed prezygotic (probability of spawning) and postzygotic (hatching success) reproductive isolation among the three ecologically and morphologically similar species in the Fundulus notatus species complex. We employed a multi-generation breeding experiment to test the hypotheses that karyotypic differences, body size differences, or geographic isolation among populations will increase pre or postzygotic reproductive barriers. Overall, prezygotic barriers were strong and postzygotic barriers weak in crosses of non-hybrid heterospecifics (F1 hybrid crosses) while prezygotic barriers were weaker and postzygotic barriers stronger in crosses involving hybrid individuals (F2 hybrid crosses and backcrosses). Prezygotic barriers among the two smaller species (Fundulus notatus and F. euryzonus) broke down rapidly; first generation hybrids spawned (F2 hybrid crosses and backcrosses) as frequently as parental forms in intraspecific crosses. There was no increase in postzygotic barriers among species with cytogenetic differences. There were increased prezygotic, but not postzygotic, barriers among geographically isolated populations of one species. While pure males and females were just as likely to spawn with hybrids, some types of hybrid females suffered from increased sterility, but not inviability, over hybrid males. Female sterility was only seen in hybrids with a Fundulus euryzonus parent, while other female hybrids produced viable eggs.     

Identification of neutral genes at pollen sterility loci Sd and Se of cultivated rice (Oryza sativa) with wild rice (O. rufipogon) origin

Pollen sterility is one of the main hindrances against the utilization of strong intersubspecific (indica-japonica) heterosis in rice. We looked for neutral alleles at known pollen sterility loci Sd and Se that could overcome this pollen sterility characteristic. Taichung 65, a typical japonica cultivar, and its near isogenic lines E7 and E8 for pollen sterility loci Sd and Se were employed as tester lines for crossing with 13 accessions of wild rice (O. rufipogon). Pollen fertility and genotypic segregations of the molecular markers tightly linked with Sd and Se loci were analyzed in the paired F(1)s and F(2) populations. One accession of wild rice (GZW054) had high pollen fertility in the paired F(1)s between Taichung 65 and E7 or E8. Genotypic segregations of the molecular markers tightly linked with Sd and Se loci fit the expected Mendelian ratio (1:2:1), and non-significances were shown among the mean pollen fertilities with the maternal, parental, and heterozygous genotypes of each molecular markers tightly linked with Sd and Se loci. Evidentially, it indicated that the alleles of Sd and Se loci for GZW054 did not interact with those of Taichung 65 and its near isogenic lines, and, thus were identified as neutral alleles Sd(n) and Se(n). These neutral genes could become important germplasm resources for overcoming pollen sterility in indica-japonica hybrids, making utilization of strong heterosis in such hybrids viable.     

The genetic effects of Late Quaternary climatic changes over a tropical latitudinal gradient: diversification of an Atlantic Forest passerine

The increase in biodiversity from high to low latitudes is a widely recognized biogeographical pattern. According to the latitudinal gradient hypothesis (LGH), this pattern was shaped by differential effects of Late Quaternary climatic changes across a latitudinal gradient. Here, we evaluate the effects of climatic changes across a tropical latitudinal gradient and its implications to diversification of an Atlantic Forest (AF) endemic passerine. We studied the intraspecific diversification and historical demography of Sclerurus scansor, based on mitochondrial (ND2, ND3 and cytb) and nuclear (FIB7) gene sequences. Phylogenetic analyses recovered three well-supported clades associated with distinct latitudinal zones. Coalescent-based methods were applied to estimate divergence times and changes in effective population sizes. Estimates of divergence times indicate that intraspecific diversification took place during Middle-Late Pleistocene. Distinct demographic scenarios were identified, with the southern lineage exhibiting a clear signature of demographic expansion, while the central one remained more stable. The northern lineage, contrasting with LGH predictions, exhibited a clear sign of a recent bottleneck. Our results suggest that different AF regions reacted distinctly, even in opposite ways, under the same climatic period, producing simultaneously favourable scenarios for isolation and contact among populations.     

抽穗开花期耐高温的爪哇稻资源筛选

通过人工气候室鉴定和分期播种试验,对来自于不同国家和地区的95份爪哇稻进行抽穗开花期耐高温特性评价。以综合结实率为指标,通过聚类分析将95份爪哇稻分为耐热能力不同的3类。综合考虑大田分期播种的结实率和人工气候室鉴定结果,筛选出耐高温品种IRAT109 (IRRI编号38563)、260（IRRI编号14888）和L 4-34（IRRI编号13403）,它们可用于水稻耐高温新品种的选育及耐热性遗传研究。     

Genetic studies of leaf and stem rust resistance in six accessions of Triticum turgidum var. dicoccoides.

Six accessions of Triticum turgidum var. dicoccoides L. (4x, AABB) of diverse origin were tested with 10 races of leaf rust (Puccinia recondita f.sp. tritici Rob. ex Desm.) and 10 races of stem rust (P. graminis f.sp. tritici Eriks. &Henn.). Their infection type patterns were all different from those of lines carrying the Lr or Sr genes on the A or B genome chromosomes with the same races. The unique reaction patterns are probably controlled by genes for leaf rust or stem rust resistance that have not been previously identified. The six dicoccoides accessions were crossed with leaf rust susceptible RL6089 durum wheat and stem rust susceptible 'Kubanka' durum wheat to determine the inheritance of resistance. They were also crossed in diallel to see whether they carried common genes. Seedlings of F1, F2, and BC1F2 generations from the crosses of the dicoccoides accessions with RL6089 were tested with leaf rust race 15 and those from the crosses with 'Kubanka' were tested with stem rust race 15B-1. The F2 populations from the diallel crosses were tested with both races. The data from the crosses with the susceptible durum wheats showed that resistance to leaf rust race 15 and stem rust race 15B-1 in each of the six dicoccoides accessions is conferred by a single dominant or partially dominant gene. In the diallel crosses, the dominance of resistance appeared to be affected by different genetic backgrounds. With one exception, the accessions carry different resistance genes: CI7181 and PI 197483 carry a common gene for resistance to leaf rust race 15. Thus, wild emmer wheat has considerable genetic diversity for rust resistance and is a promising source of new rust resistance genes for cultivated wheats.