Most higher plant species can enter a root symbiosis with arbuscular mycorrhizal fungi, in which plant carbon is traded for fungal phosphate. This is an ancient symbiosis, which has been detected in fossils of early land plants. In contrast, the nitrogen-fixing root nodule symbioses of plants with bacteria evolved more recently, and are phylogenetically restricted to the rosid I clade of plants. Both symbioses rely on partially overlapping genetic programmes. We have identified the molecular basis for this convergence by cloning orthologous SYMRK ('symbiosis receptor-like kinase') genes from Lotus and pea, which are required for both fungal and bacterial recognition. SYMRK is predicted to have a signal peptide, an extracellular domain comprising leucine-rich repeats, a transmembrane and an intracellular protein kinase domain. Lotus SYMRK is required for a symbiotic signal transduction pathway leading from the perception of microbial signal molecules to rapid symbiosis-related gene activation. The perception of symbiotic fungi and bacteria is mediated by at least one common signalling component, which could have been recruited during the evolution of root nodule symbioses from the already existing arbuscular mycorrhiza symbiosis.

SummaryVirus diseases are widespread threats for crop production, which can, in many cases, be controlled efficiently by exploiting naturally occurring resistance. Barley, an important cereal species of the Triticeae, carries two genes, rym4 and rym5, which are located in the telomeric region of chromosome 3HL and confer recessive resistance to various strains of the Barley yellow mosaic virus complex. The barley 'eukaryotic translation initiation factor 4E' (Hv-eIF4E) was identified as a candidate for resistance gene function by physical mapping on a 650 kb contig. It is located in a chromosomal region characterized by suppressed recombination, in a position collinear to its homologue on rice chromosome 1L. Sequence diversity in the coding region of Hv-eIF4E, as calculated from a collection of unrelated barley accessions, revealed non-silent single nucleotide polymorphisms (SNPs) in four of its five exons. Stable transformation of a resistant barley genotype with a genomic fragment or a full-length cDNA of Hv-eIF4E derived from susceptible cultivars induced susceptibility to Barley mild mosaic virus. Moreover, the identification of SNPs diagnostic for rym4 and rym5 provides evidence that these are two alleles, which confer different resistance specificities. These findings demonstrate that variants of Hv-eIF4E confer multiallelic recessive virus resistance in a monocot species. The identification of eIF4E as the causal host factor for bymovirus resistance illustrates that mutations in this basic component of the eukaryotic translation complex form a seminal mechanism for recessive virus resistance in both dicot and monocot plants.

The interaction between members of a gene network has an important impact on the variation of quantitative traits, and can inXuence the outcome of phenotype/ genotype association studies. Three genes (Ppd-H1, HvCO1, HvFT1) known to play an essential role in the regulation of Xowering time under long days in barley were subjected to an analysis of nucleotide diversity in a collection of 220 spring barley accessions. The coding region of Ppd-H1 was highly diverse, while both HvCO1 and HvFT1 showed a rather limited level of diversity. Within all three genes, the extent of linkage disequilibrium was variable, but on average only moderate. Ppd-H1 is strongly associated with Xowering time across four environments, showing a diVerence of Wve to ten days between the most extreme haplotypes. The association between Xowering time and the variation at HvFT1 and HvCO1 was strongly dependent on the haplotype present at Ppd-H1. The interaction between HvCO1 and Ppd-H1 was statistically signiWcant, but this association disappeared when the analysis was corrected for the geographical origin of the accessions. No association existed between Xowering time and allelic variation at HvFT1. In contrast to Ppd-H1, functional variation at both HvCO1 and HvFT1 is limited in cultivated barley.

Association mapping offers a tool to identify plant resources that carry important alleles for crop improvement and breeding. A necessary prerequisite for association mapping is a collection of genotypes representing a cross section of the examined germplasm. This study describes the genetic and phenotypic characterization of a collection of 224 spring barley (Hordeum vulgare L.) accessions sampled from the IPK gene bank. The analysis of the genetic structure of the collection was based on 45 EST-derived simple sequence repeat (SSR) markers and it revealed two major subgroups, mainly comprising two-rowed and six-rowed barleys, respectively. The phenotypic data were based on field trials performed at three locations in Germany in 2004 and 2005. Significant genotypic variation and genotype · environment interaction were observed for all traits under study (thousand-grain weight, crude protein content, starch content, plant height, and flowering time). For all analysed traits entry mean-based heritability estimates exceeded 0.9. After appropriately correcting for population structure and geographic origin significant associations between SSR markers and all traits under study were detected.

Cytoplasmatic male sterility (CMS) is the basis for commercial hybrid seed production of rye. Nuclear restorer genes are indispensable for a complete restoration of fertility of the CMS lines. The drawbacks of current European restorer lines require the utilisation of new genetic resources that have been recently detected in an Iranian primitive rye population (IRAN IX) and an Argentinean landrace (Pico Gentario). The introgression of these effective restorer genes (Rfp1 and Rfp2, respectively) into breeding material can be facilitated by marker-assisted selection. Using two F(2) populations based on crosses between the non-restorer inbred line Lo6 and the restorer IRAN IX, as well as Pico Gentario, RAPDs and AFLPs were screened and led to a closely linked marker set for each of these genes. The conversion of the closest markers into fragment-specific sequence-characterised amplified region (SCAR) markers resulted in flanking ranges of 2.9 cM (Rfp1) and 5.2 cM (Rfp2). The application of these markers in backcross programmes is discussed.

Background: Many patients with obsessive-compulsive disorder (OCD) do not receive first-line treatment according to the current guidelines (cognitive behavioral therapy with exposure and response prevention, CBT with ERP) due to barriers to treatment. Internet-based therapy is designed to overcome these barriers. The present study evaluates the efficacy of an Internet-based writing therapy with therapeutic interaction based on the concept of CBT with ERP for patients with OCD. Methods: Thirty-four volunteers with OCD according to DSM-IV-criteria were included in the trial and randomized according to a waiting-list control design with follow-up measures at 8 weeks and 6 months. The intervention consisted of 14 sessions, either starting directly after randomization or with an 8-week delay. Main outcome measure was the change in the severity of OCD symptoms (Yale-Brown Obsessive Compulsive Scale Self-Rating, Y-BOCS SR, and Obsessive-Compulsive Inventory-Revised, OCI-R). Results: Obsessive-compulsive symptoms were significantly improved in the treatment group compared to the waiting-list control group with large effect sizes of Cohen's d = 0.82 (Y-BOCS SR) and d = 0.87 (OCI-R), using an intention-to-treat analysis. This effect remained stable at 6-month follow-up. Only 4 participants (12%) dropped out prematurely from the study. Of the 30 completers, 90% rated their condition as improved and would recommend the program to their friends. Conclusions: Internet-based writing therapy led to a significant improvement of obsessive-compulsive symptoms. Even though replications with larger sample sizes are needed, the results support the notion that Internet-based approaches have the potential for improving the treatment situation for patients with OCD.

The transcription factor GAMYB is involved in gibberellin signalling in cereal aleurone cells and in plant developmental processes. Nucleotide diversity of HvG-AMYB and TaGAMYB was investigated in 155 barley (Hordeum vulgare) and 42 wheat (Triticum aestivum) accessions, respectively. Polymorphisms defined 18 haplotypes in the barley collection and 1, 7 and 3 haplotypes for the A, B, and D genomes of wheat, respectively. We found that (1) Hv-and TaGAMYB genes have identical structures.(2) Both genes show a high level of nucleotide identity ([95%) in the coding sequences and the distribution of polymorphisms is similar in both collections. At the protein level the functional domain is identical in both species. (3) GAMYB genes map to a syntenic position on chromosome 3. GAMYB genes are different in both collections with respect to the Tajima D statistic and linkage disequilibrium (LD). A moderate level of LD was observed in the barley collection. In wheat, LD is absolute between polymorphic sites, mostly located in the first intron, while it decays within the gene. Differences in Tajima D values might be due to a lower selection pressure on HvGAMYB, compared to its wheat orthologue. Altogether our results provide evidence that there have been only few evolutionary changes in Hv-and TaGAMYB. This confirms the close relationship between these species and also highlights the functional importance of this transcription factor.

We present a detailed analysis of linkage disequilibrium (LD) in the physical and genetic context of the barley gene Hv-eIF4E, which confers resistance to the barley yellow mosaic virus (BYMV) complex. Eightythree SNPs distributed over 132 kb of Hv-eIF4E and six additional fragments genetically mapped to its flanking region were used to derive haplotypes from 131 accessions. Three haplogroups were recognized, discriminating between the alleles rym4 and rym5, which each encode for a spectrum of resistance to BYMV. With increasing map distance, haplotypes of susceptible genotypes displayed diverse patterns driven mainly by recombination, whereas haplotype diversity within the subgroups of resistant genotypes was limited. We conclude that the breakdown of LD within 1 cM of the resistance gene was generated mainly by susceptible genotypes. Despite the LD decay, a significant association between haplotype and resistance to BYMV was detected up to a distance of 5.5 cM from the resistance gene. The LD pattern and the haplotype structure of the target chromosomal region are the result of interplay between low recombination and recent breeding history.T HE ever-increasing availability of nucleotide sequence, and the concomitant improvement that this brings to our understanding of the organization of complex crop plant genomes, has created the opportunity to identify trait-related genes and to analyze their allelic diversity. The association between phenotype and genotype in diverse populations represents a powerful approach, but the applicability and design of such analyses depend critically on the extent and pattern of linkage disequilibrium (LD) present in the study population. Cultivated barley (Hordeum vulgare ssp. vulgare) has many of the hallmarks known to be associated with a high level of LD. Its effective recombination rate is dramatically reduced by its predominantly inbreeding habit, with an estimated outcrossing rate of 5% in winter barley and ,0.5% in spring barley (Giles et al. 1974;Doll 1987;Abdel-Ghani et al. 2005). Domestication and intensive selection have introduced major bottlenecks in genetic variation, and these are thought to be largely responsible for the perceived narrowness of the modern gene pool (Badr et al. 2000;Russell et al. 2000;Matus and Hayes 2002). LD in modern spring barley, as estimated from a whole-genome survey, extends over distances of at least 10 cM, indicative of an extensive conservation of the genetic identity of barley chromosomes (Kraakman et al. 2004). However, estimates of genomewide LD conceal localized variation, which, as has been shown for a number of species, can be substantial and independent of the mating system (Gupta et al. 2005). In the self-pollinating species Arabidopsis thaliana LD varies from ,10 kb in global (Tian et al. 2002) to 50-250 kb in local populations (Nordborg et al. , 2005Aranzana et al. 2005). Within a given set of maize (an outbreeding species) accessions, the extent of LD has been documented to vary widely around different genes and chr...