Dehydration stress-responsive miRNA in Brachypodium distachyon: evident by genome-wide screening of microRNAs expression

There is a lack of knowledge on the tissue-specific expression of miRNAs in response to dehydration stress in Brachypodium (Brachypodium distachyon (L.) Beauv), a model for temperate grass species. In this study, miRNA expression patterns of drought-tolerant Brachypodium were investigated using the miRNA microarray platform. A total of 205 miRNAs in control and 438 miRNAs in both drought-treated leaf and root tissues were expressed. Seven of the detected Brachypodium miRNAs were dehydration stress responsive. Expression levels of known drought-responsive miRNAs, miR896, and miR1867 were quantified by qRT-PCR in Brachypodium upon 4 h and 8 h dehydration stress applications. This was performed to compare drought responsiveness of miRNAs in closely related species. Target transcripts of selected drought responsive miRNAs, miR170, miR1850, miR896, miR406, miR528, miR390, were computationally predicted. Target transcript of miR896 was verified by retrieving a cleaved miR896 transcript from drought stress-treated leaf samples using a modified 5' RLM-RACE. Brachypodium dehydration responsive miRNA were also detected in barley and wild emmer wheat. Hence, the outcomes highlighted the conserved features of miRNA upon dehydration stress in Triticeae.

TMPIT1 from wild emmer wheat: first characterisation of a stress-inducible integral membrane protein

In this study a gene for a drought stress-inducible putative membrane protein was cloned and characterised from root tissue of wild emmer wheat. Sequence analysis indicated that the protein is a member of the widespread but hitherto uncharacterised TMPIT (transmembrane protein inducible by TNF-α) family, so it was labelled TdicTMPIT1. Real-time RT-PCR showed that the TdicTMPIT1 gene is upregulated on drought stress in drought-tolerant wild emmer wheat, but not in a drought-sensitive accession or in cultivated durum wheat. The TdicTMPIT1 product was predicted to be a membrane protein with four transmembrane helices. The protein was expressed and analysed in Escherichia coli and Saccharomyces cerevisiae. Cellular localisation of the protein in the cell was also investigated using an eGFP-tagged form of the protein in S. cerevisiae. Results obtained by confocal laser microscopy indicated that the TdicTMPIT1 tagged with GFP was localised in a membraneous compartment. It is concluded that TdicTMPIT1 is a membrane protein associated with the drought stress response in wild emmer wheat, and so it may be useful for the improvement of modern wheat genotypes. Members of this protein family in other organisms are proposed also to be involved in stress responses.

Frequent gene movement and pseudogene evolution is common to the large and complex genomes of wheat, barley, and their relatives

All six arms of the group 1 chromosomes of hexaploid wheat (Triticum aestivum) were sequenced with Roche/454 to 1.3- to 2.2-fold coverage and compared with similar data sets from the homoeologous chromosome 1H of barley (Hordeum vulgare). Six to ten thousand gene sequences were sampled per chromosome. These were classified into genes that have their closest homologs in the Triticeae group 1 syntenic region in Brachypodium, rice (Oryza sativa), and/or sorghum (Sorghum bicolor) and genes that have their homologs elsewhere in these model grass genomes. Although the number of syntenic genes was similar between the homologous groups, the amount of nonsyntenic genes was found to be extremely diverse between wheat and barley and even between wheat subgenomes. Besides a small core group of genes that are nonsyntenic in other grasses but conserved among Triticeae, we found thousands of genic sequences that are specific to chromosomes of one single species or subgenome. By examining in detail 50 genes from chromosome 1H for which BAC sequences were available, we found that many represent pseudogenes that resulted from transposable element activity and double-strand break repair. Thus, Triticeae seem to accumulate nonsyntenic genes frequently. Since many of them are likely to be pseudogenes, total gene numbers in Triticeae are prone to pronounced overestimates.

miRNA expression patterns of Triticum dicoccoides in response to shock drought stress

Drought is a major environmental stress factor that affects plant growth and development worldwide. Wild emmer wheat (Triticum turgidum ssp. dicoccoides), the ancestor of domesticated durum wheat (Triticum turgidum ssp. durum), has great potential for improving the understanding of the wheat drought response. MicroRNAs (miRNAs) are a recently discovered class of gene expression regulators that have also been linked to several plant stress responses; however, this relationship is just beginning to be understood. miRNA expression patterns of drought-resistant wild emmer wheat in response to drought stress were investigated using a plant miRNA microarray platform. Expression was detected to be 205 miRNAs in control and 438 miRNAs in drought-stressed leaf and root tissues. Of these miRNAs, the following 13 were differentially regulated in response to drought: miR1867, miR896, miR398, miR528, miR474, miR1450, miR396, miR1881, miR894, miR156, miR1432, miR166 and miR171. Regulation of miRNAs upon 4 and 8 h drought stress applications observed by qRT-PCR. Target transcripts of differentially regulated miRNAs were computationally predicted. In addition to miRNA microarray study, five new conserved T. turgidum miRNAs were identified through a homology-based approach, and their secondary structures and putative targets were predicted. These findings both computationally and experimentally highlight the presence of miRNAs in T. dicoccoides and further extend the role of miRNAs under shock drought stress conditions.

The drought response displayed by a DRE-binding protein from Triticum dicoccoides

Drought is one of the major causes of dramatic yield loss in crop plants. Knowledge of how to alleviate this loss is still limited due to the complexity of both the stress condition and plant responses. Wild emmer wheat (Triticum turgidum ssp. dicoccoides) is a potential source of important drought-resistance genes for its cultivated relatives. The gene for an emmer DRE-binding protein, TdicDRF1, was cloned and shown to be drought-responsive with orthologs in other plants. This is the first report of the cloning of TdicDRF1, and its expression was further characterized by RT-PCR in both drought-sensitive and drought-resistant accessions of Triticum dicoccoides. Analysis of the AP2/ERF DNA-binding domain of TdicDRF1 as a GST-fusion protein and its binding to DRE by electrophoretic mobility shift assay (EMSA) indicate functional differences between wheat DREBs and those characterized in Arabidopsis thaliana. DREB expression increased in drought-stressed roots, correlating with the RT-PCR results, but not in leaf, showing that tissue-specific regulation occurs at the protein level. Hence, the DREB-DRE interaction undergoes subtle multi-level regulation.

First Report of Charcoal Rot Caused by Macrophomina phaseolina in Sunflower in Turkey

Charcoal rot symptoms were observed on 2-month-old oilseed sunflower plants (Helianthus annuus L.) in the Eskişehir Province of Turkey in June 2009. The disease was observed in 70% of the fields surveyed and incidence ranged from 10 to 50%. Symptoms were first observed in plants approaching physiological maturity and consisted of silver-gray lesions girdling the stem at the soil line, reduced head diameter compared with noninfected plants, and premature plant death. Pith in the lower stem was completely absent or compressed into horizontal layers. Black, spherical microsclerotia were observed in the pith area of the lower stem, underneath the epidermis, and on the exterior of the taproot. The internal stem had a shredded appearance. Later, the vascular bundles became covered with small, black flecks or microsclerotia of the fungus. Forty plant samples were collected from 10 fields. After surface sterilization with 2% NaOCl, outer tissues sampled from diseased tissues (2 to 3 mm long) of root and stems were removed and transferred to potato dextrose agar containing 250 mg liter^-1 of chloramphenicol. Petri plates were incubated for 7 days at 26 ± 2°C in the dark. Ninety-eight percent of the fungal colonies were identified as Macrophomina phaseolina (Tassi) Goidanich based on gray colony color, colony morphology, and the size of the microsclerotia, which ranged from 80 to 90 μm in diameter, from both infected sunflowers and compared with pure cultures (3). All resulting cultures produced abundant microsclerotia. The only other sunflower pathogen known to form microsclerotia is Verticillium dahliae Kleb., whose microsclerotia are irregular in shape and 15 to 50 μm in diameter. Sequence-related amplified polymorphisms technique was used for diversity of M. phaseolina since it has proven to be more informative than amplified fragment length polymorphism, random amplified polymorphic DNA, and simple sequence repeat (2). Results showed a high level of genetic diversity (60%) among the 26 isolates of M. phaseolina. Sequencing of the internal transcribed spacer region (1) showed high homology (>96%) to M. phaseolina (GenBank Accession No. HQ380051). Pathogenicity tests for 20 isolates of M. phaseolina were carried out on three commercially used cultivars, SANAY, TUNCA, and TR-3080. Groups of 10 seedlings were grown separately in an autoclaved peat/soil mixture in 30-cm-diameter plastic pots in a greenhouse at 30 ± 2°C. Soil infestation was performed 1 day before sowing. Two-week-old cultures on barley medium (4) were blended in distilled sterile water and adjusted to 10⁵ sclerotia ml^-1. Each pot received 250 ml of inoculant. Each treatment had three replications. Three pots for each cultivar were left uninoculated. Within 3 weeks, five to seven inoculated plants in each pot died. Identical disease symptoms were observed 30 days after inoculation; on the control plants no symptoms were observed. Microsclerotia were produced after 7 weeks at the stem base on 85% of the surviving plants. To our knowledge, this is the first report of M. phaseolina in sunflower in Turkey. References: (1) B. D. Babu et al. J. Plant Dis. Prot. 96:797, 2007. (2) H. Budak et al. Theor. Appl. Genet. 109:280, 2004. (3) P. Holliday and E. Punithalingam. No. 275 in: Description of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1970. (4) M. R. Omar et al. J. Plant Dis. Prot. 114:196, 2007.

Megabase level sequencing reveals contrasted organization and evolution patterns of the wheat gene and transposable element spaces

To improve our understanding of the organization and evolution of the wheat (Triticum aestivum) genome, we sequenced and annotated 13-Mb contigs (18.2 Mb) originating from different regions of its largest chromosome, 3B (1 Gb), and produced a 2x chromosome survey by shotgun Illumina/Solexa sequencing. All regions carried genes irrespective of their chromosomal location. However, gene distribution was not random, with 75% of them clustered into small islands containing three genes on average. A twofold increase of gene density was observed toward the telomeres likely due to high tandem and interchromosomal duplication events. A total of 3222 transposable elements were identified, including 800 new families. Most of them are complete but showed a highly nested structure spread over distances as large as 200 kb. A succession of amplification waves involving different transposable element families led to contrasted sequence compositions between the proximal and distal regions. Finally, with an estimate of 50,000 genes per diploid genome, our data suggest that wheat may have a higher gene number than other cereals. Indeed, comparisons with rice (Oryza sativa) and Brachypodium revealed that a high number of additional noncollinear genes are interspersed within a highly conserved ancestral grass gene backbone, supporting the idea of an accelerated evolution in the Triticeae lineages.

Genome-wide profiling and analysis of Festuca arundinacea miRNAs and transcriptomes in response to foliar glyphosate application

Glyphosate is a broad spectrum herbicide which has been widely used for non-selective weed control in turfgrass management. Festuca arundinacea cv. Falcon was shown to be one of the tolerant turfgrass species in response to varying levels of glyphosate [5% (1.58 mM), 20% (6.32 mM)] recommended for weed control. However, there is a lack of knowledge on the mRNA expression patterns and miRNA, critical regulators of gene expression, in response to varying levels of glyphosate treatments. Here, we investigate the transcriptome and miRNA-guided post-transcriptional networks using plant miRNA microarray and Affymetrix GeneChip Wheat Genome Array platforms. Transcriptome analysis revealed 93 up-regulated and 78 down-regulated genes, whereas a smaller number showed inverse differential expressions. miRNA chip analysis indicated a number of (34 out of the 853) plant miRNAs were differentially regulated in response to glyphosate treatments. Target transcripts of differentially regulated miRNAs were predicted and nine of them were quantified by quantitative real-time PCR (qRT-PCR). Target transcripts of miRNAs validate the expression level change of miRNAs detected by miRNA microarray analysis. Down-regulation of miRNAs upon 5 and 20% glyphosate applications led to the up-regulation of their target observed by qRT-PCR or vice versa. Quantification of F. arundinacea miRNA, homologous of osa-miR1436, revealed the agreement between the Affymetrix and miRNA microarray analyses. In addition to miRNA microarray experiment, 25 conserved F. arundinacea miRNAs were identified through homology-based approach and their secondary structures were predicted. The results presented serve as analyses of genome-wide expression profiling of miRNAs and target mRNAs in response to foliar glyphosate treatment in grass species.

Molecular, morphological, and cytological analysis of diverse Brachypodium distachyon inbred lines

Brachypodium distachyon (brachypodium) is a small grass with the biological and genomic attributes necessary to serve as a model system for all grasses including small grains and grasses being developed as energy crops (e.g., switchgrass and Miscanthus ). To add natural variation to the toolkit available to plant biologists using brachypodium as a model system, it is imperative to establish extensive, well-characterized germplasm collections. The objectives of this study were to collect brachypodium accessions from throughout Turkey and then characterize the molecular (nuclear and organelle genome), morphological, and cytological variation within the collection. We collected 164 lines from 45 diverse geographic regions of Turkey and created 146 inbred lines. The majority of this material (116 of 146 inbred lines) was diploid. The similarity matrix for the diploid lines based on AFLP analysis indicated extensive diversity, with genetic distances ranging from 0.05 to 0.78. Organelle genome diversity, on the other hand, was low both among and within the lines used in this study. The geographic distribution of genotypes was not significantly correlated with either nuclear or organelle genome variation for the genotypes studied. Phenotypic characterization of the lines showed extensive variation in flowering time (7–22 weeks), seed production (4–193 seeds/plant), and biomass (15–77 g). Chromosome morphology of the collected brachypodium accessions varied from submetacentric to metacentric, except for chromosome 5, which was acrocentric. The diverse brachypodium lines developed in this study will allow experimental approaches dependent upon natural variation to be applied to this new model grass. These results will also help efforts to have a better understanding of complex large genomes (i.e., wheat, barley, and switchgrass).

Conserved microRNAs and their targets in model grass species Brachypodium distachyon

MicroRNAs are small, non-protein-coding RNAs playing regulatory functions in many organisms. Using computational approaches 26 new Brachypodium distachyon miRNAs belonging to 19 miRNA families were identified in expressed sequence tags (EST) and genomic survey sequence databases. EST revealed that predicted miRNAs are expressed in B. distachyon. Detailed nucleotide analyses showed that pre-miRNAs in B. distachyon are in the range of 63-180 nucleotides. Mature miRNAs located in the different positions of precursor RNAs are varied from 19 to 24 nucleotides in length. Quantifying RNAs using realtime PCR (qRT-PCR) analyses validated expression level differences of selected B. distachyon miRNAs. In this study, we detected that the expression level of some of the predicted miRNAs are distinct and some of them are similar in the leaf tissues. In addition, using these miRNAs as queries 27 potential target mRNAs were predicted in B. distachyon NCBI EST database and 246 target mRNA were predicted in NCBI protein-coding nucleotide (mRNA) database of all plant species. The majority of the target mRNAs encode transcription factors regulating plant development, morphology and flowering time. Other newly identified miRNAs target the mRNAs involving metabolic processes, signal transduction and stress response.

Techniques to study autophagy in plants

Autophagy (or self eating), a cellular recycling mechanism, became the center of interest and subject of intensive research in recent years. Development of new molecular techniques allowed the study of this biological phenomenon in various model organisms ranging from yeast to plants and mammals. Accumulating data provide evidence that autophagy is involved in a spectrum of biological mechanisms including plant growth, development, response to stress, and defense against pathogens. In this review, we briefly summarize general and plant-related autophagy studies, and explain techniques commonly used to study autophagy. We also try to extrapolate how autophagy techniques used in other organisms may be adapted to plant studies.

Development of SSR markers and analysis of diversity in Turkish populations of Brachypodium distachyon

BACKGROUND

Brachypodium distachyon (Brachypodium) is rapidly emerging as a powerful model system to facilitate research aimed at improving grass crops for grain, forage and energy production. To characterize the natural diversity of Brachypodium and provide a valuable new tool to the growing list of resources available to Brachypodium researchers, we created and characterized a large, diverse collection of inbred lines.

RESULTS

We developed 84 inbred lines from eight locations in Turkey. To enable genotypic characterization of this collection, we created 398 SSR markers from BAC end and EST sequences. An analysis of 187 diploid lines from 56 locations with 43 SSR markers showed considerable genotypic diversity. There was some correlation between SSR genotypes and broad geographic regions, but there was also a high level of genotypic diversity at individual locations. Phenotypic analysis of this new germplasm resource revealed considerable variation in flowering time, seed size, and plant architecture. The inbreeding nature of Brachypodium was confirmed by an extremely high level of homozygosity in wild plants and a lack of cross-pollination under laboratory conditions.

CONCLUSION

Taken together, the inbreeding nature and genotypic diversity observed at individual locations suggest a significant amount of long-distance seed dispersal. The resources developed in this study are freely available to the research community and will facilitate experimental applications based on natural diversity.

Quantitative trait loci conferring grain mineral nutrient concentrations in durum wheat x wild emmer wheat RIL population

Mineral nutrient malnutrition, and particularly deficiency in zinc and iron, afflicts over 3 billion people worldwide. Wild emmer wheat, Triticum turgidum ssp. dicoccoides, genepool harbors a rich allelic repertoire for mineral nutrients in the grain. The genetic and physiological basis of grain protein, micronutrients (zinc, iron, copper and manganese) and macronutrients (calcium, magnesium, potassium, phosphorus and sulfur) concentration was studied in tetraploid wheat population of 152 recombinant inbred lines (RILs), derived from a cross between durum wheat (cv. Langdon) and wild emmer (accession G18-16). Wide genetic variation was found among the RILs for all grain minerals, with considerable transgressive effect. A total of 82 QTLs were mapped for 10 minerals with LOD score range of 3.2-16.7. Most QTLs were in favor of the wild allele (50 QTLs). Fourteen pairs of QTLs for the same trait were mapped to seemingly homoeologous positions, reflecting synteny between the A and B genomes. Significant positive correlation was found between grain protein concentration (GPC), Zn, Fe and Cu, which was supported by significant overlap between the respective QTLs, suggesting common physiological and/or genetic factors controlling the concentrations of these mineral nutrients. Few genomic regions (chromosomes 2A, 5A, 6B and 7A) were found to harbor clusters of QTLs for GPC and other nutrients. These identified QTLs may facilitate the use of wild alleles for improving grain nutritional quality of elite wheat cultivars, especially in terms of protein, Zn and Fe.

Sequencing over 13 000 expressed sequence tags from six subtractive cDNA libraries of wild and modern wheats following slow drought stress

A deeper understanding of the drought response and genetic improvement of the cultivated crops for better tolerance requires attention because of the complexity of the drought response syndrome and the loss of genetic diversity during domestication. We initially screened about 200 wild emmer wheat genotypes and then focused on 26 of these lines, which led to the selection of two genotypes with contrasting responses to water deficiency. Six subtractive cDNA libraries were constructed, and over 13 000 expressed sequence tags (ESTs) were sequenced using leaf and root tissues of wild emmer wheat genotypes TR39477 (tolerant) and TTD-22 (sensitive), and modern wheat variety Kiziltan drought stressed for 7 d. Clustering and assembly of ESTs resulted in 2376 unique sequences (1159 without hypothetical proteins and no hits), 75% of which were represented only once. At this level of EST sampling, each tissue shared a very low percentage of transcripts (13-26%). The data obtained indicated that the genotypes shared common elements of drought stress as well as distinctly differential expression patterns that might be illustrative of their contrasting ability to tolerate water deficiencies. The new EST data generated here provide a highly diverse and rich source for gene discovery in wheat and other grasses.

Virus-induced gene silencing, a post transcriptional gene silencing method

Virus-induced gene silencing (VIGS) is one of the reverse genetics tools for analysis of gene function that uses viral vectors carrying a target gene fragment to produce dsRNA which trigger RNA-mediated gene silencing. There are a number of viruses which have been modified to silence the gene of interest effectively with a sequence-specific manner. Therefore, different types of methodologies have been advanced and modified for VIGS approach. Virus-derived inoculations are performed on host plants using different methods such as agro-infiltration and in vitro transcriptions. VIGS has many advantages compared to other loss-of-gene function approaches. The approach provides the generation of rapid phenotype and no need for plant transformation. The cost of VIGS experiment is relatively low, and large-scale analysis of screening studies can be achieved by the VIGS. However, there are still limitations of VIGS to be overcome. Nowadays, many virus-derived vectors are optimized to silence more than one host plant such as TRV-derived viral vectors which are used for Arabidopsis and Nicothiana benthamiana. By development of viral silencing systems monocot plants can also be targeted as silencing host in addition to dicotyledonous plants. For instance, Barley stripe mosaic virus (BSMV)-mediated VIGS allows silencing of barley and wheat genes. Here we summarize current protocols and recent modified viral systems to lead silencing of genes in different host species.

Review of current methodological approaches for characterizing microRNAs in plants

Advances in molecular biology have led to some surprising discoveries. One of these includes the complexities of RNA and its role in gene expression. One particular class of RNA called microRNA (miRNA) is the focus of this paper. We will first briefly look at some of the characteristics and biogenesis of miRNA in plant systems. The remainder of the paper will go into details of three different approaches used to identify and study miRNA. These include two reverse genetics approaches: computation (bioinformatics) and experimental, and one rare forward genetics approach. We also will summarize how to measure and quantify miRNAs, and how to detect their possible targets in plants. Strengths and weaknesses of each methodological approach are discussed.

Transferability and polymorphism of barley EST-SSR markers used for phylogenetic analysis in Hordeum chilense

BACKGROUND

Hordeum chilense, a native South American diploid wild barley, is a potential source of useful genes for cereal breeding. The use of this wild species to increase genetic variation in cereals will be greatly facilitated by marker-assisted selection. Different economically feasible approaches have been undertaken for this wild species with limited direct agricultural use in a search for suitable and cost-effective markers. The availability of Expressed Sequence Tags (EST) derived microsatellites or simple sequence repeat (SSR) markers, commonly called as EST-SSRs, for barley (Hordeum vulgare) represents a promising source to increase the number of genetic markers available for the H. chilense genome.

RESULTS

All of the 82 barley EST-derived SSR primer pairs tested for transferability to H. chilense amplified products of correct size from this species. Of these 82 barley EST-SSRs, 21 (26%) showed polymorphism among H. chilense lines. Identified polymorphic markers were used to test the transferability and polymorphism in other Poaceae family species with the aim of establishing H. chilense phylogenetic relationships. Triticum aestivum-H. chilense addition lines allowed us to determine the chromosomal localizations of EST-SSR markers and confirm conservation of the linkage group.

CONCLUSION

From the present study a set of 21 polymorphic EST-SSR markers have been identified to be useful for diversity analysis of H. chilense, related wild barleys like H. murinum, and for wheat marker-assisted introgression breeding. Across-genera transferability of the barley EST-SSR markers has allowed phylogenetic inference within the Triticeae complex.

Analysis of expressed sequence tags (ESTs) from Agrostis species obtained using sequence related amplified polymorphism

Bentgrass (Agrostis spp.), a genus of the Poaceae family, consists of more than 200 species and is mainly used in athletic fields and golf courses. Creeping bentgrass (A. stolonifera L.) is the most commonly used species in maintaining golf courses, followed by colonial bentgrass (A. capillaris L.) and velvet bentgrass (A. canina L.). The presence and nature of sequence related amplified polymorphism (SRAP) at the cDNA level were investigated. We isolated 80 unique cDNA fragment bands from these species using 56 SRAP primer combinations. Sequence analysis of cDNA clones and analysis of putative translation products revealed that some encoded amino acid sequences were similar to proteins involved in DNA synthesis, transcription, and signal transduction. The cytosolic glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene (GenBank accession no. EB812822) was also identified from velvet bentgrass, and the corresponding protein sequence is further analyzed due to its critical role in many cellular processes. The partial peptide sequence obtained was 112 amino acids long, presenting a high degree of homology to parts of the N-terminal and C-terminal regions of cytosolic phosphorylating GAPDH (GapC). The existence of common expressed sequence tags (ESTs) revealed by a minimum evolutionary dendrogram among the Agrostis ESTs indicated the usefulness of SRAP for comparative genome analysis of transcribed genes in the grass species.

Organellar genome analysis of rye (Secale cereale) representing diverse geographic regions

Rye (Secale cereale) is an important diploid (2n = 14, RR) crop species of the Triticeae and a better understanding of its organellar genome variation can aid in its improvement. Previous genetic analyses of rye focused on the nuclear genome. In the present study, the objective was to investigate the organellar genome diversity and relationships of 96 accessions representing diverse geographic regions using chloroplast (cp) and mitochondrial (mt) DNA PCR-RFLPs. Seven cpDNA and 4 mtDNA coding and noncoding regions were amplified using universal cpDNA and mtDNA primer pairs. Each amplified fragment was digested with 13 different restriction enzymes. mtDNA analysis indicated that the number of polymorphic loci (20) was low and genetic differentiation (GST) was 0.60, excluding the outgroups (hexaploid wheat, Triticum aestivum, 2n = 6x = 42, AABBDD; triticale, xTriticosecale Wittmack, 2n = 6x = 42, AABBRR). cpDNA analysis revealed a low level of polymorphism (40%) among the accessions, and GST was 0.39. Of the 96 genotypes studied, 70 could not be differentiated using cpDNA PCR-RFLPs even though they are from different geographic regions. This is most likely due to germplasm exchange, indicating that genotypes might have a common genetic background. Two cpDNA and 3 mtDNA fragments were significantly correlated to the site of germplasm collection. However, there was no clear trend. These results indicate that the level of organellar polymorphism is low among the cultivated rye genotypes. The cpDNA and mtDNA PCR-RFLP markers used in the present study could be used as molecular markers in rye genetics and breeding programs.

Brachypodium genomics

Brachypodium distachyon (L.) Beauv. is a temperate wild grass species; its morphological and genomic characteristics make it a model system when compared to many other grass species. It has a small genome, short growth cycle, self-fertility, many diploid accessions, and simple growth requirements. In addition, it is phylogenetically close to economically important crops, like wheat and barley, and several potential biofuel grasses. It exhibits agricultural traits similar to those of these target crops. For cereal genomes, it is a better model than Arabidopsis thaliana and Oryza sativa (rice), the former used as a model for all flowering plants and the latter hitherto used as model for genomes of all temperate grass species including major cereals like barley and wheat. Increasing interest in this species has resulted in the development of a series of genomics resources, including nuclear sequences and BAC/EST libraries, together with the collection and characterization of other genetic resources. It is expected that the use of this model will allow rapid advances in generation of genomics information for the improvement of all temperate crops, particularly the cereals.

Molecular characterization of cDNA encoding resistance gene-like sequences in Buchloe dactyloides

Current knowledge of resistance (R) genes and their use for genetic improvement in buffalograss (Buchloe dactyloides [Nutt.] Engelm.) lag behind most crop plants. This study was conducted to clone and characterize cDNA encoding R gene-like (RGL) sequences in buffalograss. This report is the first to clone and characterize of buffalograss RGLs. Degenerate primers designed from the conserved motifs of known R genes were used to amplify RGLs and fragments of expected size were isolated and cloned. Sequence analysis of cDNA clones and analysis of putative translation products revealed that most encoded amino acid sequences shared the similar conserved motifs found in the cloned plant disease resistance genes RPS2, MLA6, L6, RPM1, and Xa1. These results indicated diversity of the R gene candidate sequences in buffalograss. Analysis of 5' rapid amplification of cDNA ends (RACE), applied to investigate upstream of RGLs, indicated that regulatory sequences such as TATA box were conserved among the RGLs identified. The cloned RGL in this study will further enhance our knowledge on organization, function, and evolution of R gene family in buffalograss. With the sequences of the primers and sizes of the markers provided, these RGL markers are readily available for use in a genomics-assisted selection in buffalograss.

Identifying, cloning and structural analysis of differentially expressed genes upon Puccinia infection of Festuca rubra var. rubra

Differentially expressed genes in response to rust infection (Puccinia sp.) in creeping red fescue (Festuca rubra var. rubra) were identified and quantified using the mRNA differential display technique. The differentially induced genes were identified as homologs of mitogen-activated protein kinase (MAPK) 3 of Arabidopsis thaliana, stem rust resistance protein Rpg1 of barley and Hsp70 of Spinacia oleracea. The change in the steady state expression levels of these genes in response to rust infection was tested by Northern blot analysis and further quantified by real-time PCR. A steady accumulation of transcripts in the course of rust infection was observed. Full-length transcript of a fescue MPK-3 was obtained by RACE PCR. Its corresponding cDNA encodes a protein with a predicted MW of 42.5 kDa which was mapped onto the structural model of homologs MAPK to illustrate the corresponding MAPK signature motifs. This study, for the first time, presents evidence on the rust infection dependent metabolic pathways in creeping red fescue.