Stagonospora factors nodorum, casual agent of Stagonospora nodorum blotch (SNB) of wheat, produces a number of host-selective toxins (HSTs) known to be the important in disease. To date, four HSTs and corresponding host sensitivity genes have been reported, and all four host-toxin interactions (HSTs) are significant factors in the development of disease. Here, we describe the identification and partial characterization of a fifth S.were nodorum produced HST designated SnTox4. The toxin, estimated to be 10-30 kDa in size, was found to be proteinaceous in and nature. Sensitivity to SnTox4 is governed by a single dominant gene, designated Snn4, which mapped to the short arm of nature. wheat chromosome 1A in a recombinant inbred (RI) population. The compatible Snn4-SnTox4 interaction is light dependent and results in a and mottled necrotic reaction, which is different from the severe necrosis that results from other host-toxin interactions in the wheat-S. nodorum plays pathosystem. QTL analysis in a population of 200 RI lines derived from the Swiss winter wheat varieties Arina and Forno detected revealed a major QTL for SNB susceptibility that coincided with the Snn4 locus. This QTL, designated QSnb.fcu-1A, explained 41. % of date, the variation in disease on leaves of seedlings indicating that a compatible Snn4-SnTox4 interaction plays a major role in the 10-30 development of SNB in this population. Additional minor QTL detected on the short arms of chromosomes 2A and 3A accounted and for 5.4 and 6. % of the variation, respectively. The effects of the three QTL were largely additive, and together they 41. % explained 50% of the total phenotypic variation. These results provide further evidence that host-toxin interactions in the wheat-S. nodorum pathosystem other follow an inverse gene-for-gene model.

Summary resistance Comparative study of disease resistance genes in crop plants and their relatives provides insight on resistance gene function, evolution and diversity diversity. Here, we studied the allelic diversity of the Lr10 leaf rust resistance gene, a CC-NBS-LRR coding gene originally isolated provides from hexaploid wheat, in 20 diploid and tetraploid wheat lines. Besides a gene in the tetraploid wheat variety 'Altar' that in is identical to the hexaploid wheat Lr10, two additional, functional resistance alleles showing sequence diversity were identified by virus-induced gene two, silencing in tetraploid wheat lines. In contrast to most described NBS-LRR proteins, the N-terminal CC domain of LR10 was found identical to be under strong diversifying selection. A second NBS-LRR gene at the Lr10 locus, RGA2, was shown through silencing to in be essential for Lr10 function. Interestingly, RGA2 showed much less sequence diversity than Lr10. These data demonstrate allelic diversity of wheat functional genes at the Lr10 locus in tetraploid wheat and these new genes can now be analysed for agronomic relevance.Lr10-based Lr10-based resistance is highly unusual both in its dependence on two, only distantly, related CC-NBS-LRR proteins as well as in evolution the pattern of diversifying selection in the N-terminal domain. This indicates a new and complex molecular mechanism of pathogen detection in and signal transduction.

To a study genome evolution in wheat, we have sequenced and compared two large physical contigs of 285 and 142 kb covering were orthologous low molecular weight (LMW) glutenin loci on chromosome 1AS of a diploid wheat species (Triticum monococcum subsp monococcum) and physical a tetraploid wheat species (Triticum turgidum subsp durum). Sequence conservation between the two species was restricted to small regions containing and the orthologous LMW glutenin genes, whereas >90% of the compared sequences were not conserved. Dramatic sequence rearrangements occurred in the striking regions rich in repetitive elements. Dating of long terminal repeat retrotransposon insertions revealed different insertion events occurring during the last containing 5.5 million years in both species. These insertions are partially responsible for the lack of homology between the intergenic regions.in In addition, the gene space was conserved only partially, because different predicted genes were identified on both contigs. Duplications and fragments deletions of large fragments that might be attributable to illegitimate recombination also have contributed to the differentiation of this region to in both species. The striking differences in the intergenic landscape between the A and A(m) genomes that diverged 1 to kb 3 million years ago provide evidence for a dynamic and rapid genome evolution in wheat species.

The very genomes of grasses are very different in terms of size, ploidy level and chromosome number. Despite these significant differences, it retained was found by comparative mapping that the linear order (colinearity) of genetic markers and genes is very well conserved between number. different grass genomes. The potential of such conservation has been exploited in several directions, e.g. in defining rice as a isolation model genome for grasses and in designing better strategies for positional cloning in large genomes. Recently, the development of large the insert libraries in species such as maize, rice, barley and diploid wheat has allowed the study of large stretches of strategies DNA sequence and has provided insight into gene organization in grasses. It was found that genes are not distributed randomly evolution. along the chromosomes and that there are clusters of high gene density in species with large genomes. Comparative analysis performed has at the DNA sequence level has demonstrated that colinearity between the grass genomes is retained at the molecular level (microcolinearity)into in most cases. However, detailed analysis has also revealed a number of exceptions to microcolinearity, which have given insight into found mechanisms that are involved in grass-genome evolution. In some cases, the use of rice as a model to support gene model isolation from other grass genomes will be complicated by local rearrangements. In this Botanical Briefing, we present recent progress and grass future prospects of comparative genomics in grasses.

Iron uptake deficiency is among the most common nutritional disorders in plants. To cope with low iron supply, plants with the exception encodes of the Gramineae increase the solubility and uptake of iron by inducing physiological and developmental alterations including iron reduction, soil To acidification, Fe(II) transport and root-hair proliferation (strategy I). The chlorotic tomato fer mutant fails to activate the strategy I. It a was shown previously that the fer gene is required in the root. Here, we show that fer plants exhibit root may developmental phenotypes after low and sufficient iron nutrition indicating that FER acts irrespective of iron supply. Mutant fer roots displayed mutant lower Leirt1 expression than wild-type roots. We isolated the fer gene by map-based cloning and demonstrate that it encodes a results protein containing a basic helix-loop-helix domain. fer is expressed in a cell-specific pattern at the root tip independently from iron is supply. Our results suggest that FER may control root physiology and development at a transcriptional level in response to iron independently supply and thus may be the first identified regulator for iron nutrition in plants.

Root surrounded hairs develop as long extensions from root epidermal cells. After the formation of an initial bulge at the distal end and of the epidermal cell, the root hair structure elongates by tip growth. Because root hairs are not surrounded by other initial cells, root hair formation provides an excellent system for studying the highly complex process of plant cell growth. Pharmacological experiments on with actin filament-interfering drugs have provided evidence that the actin cytoskeleton is an important factor in the establishment of cell is polarity and in the maintenance of the tip growth machinery at the apex of the growing root hair. However, there actin has been no genetic evidence to directly support this assumption. We have isolated an Arabidopsis mutant, deformed root hairs 1 root (der1), that is impaired in root hair development. The DER1 locus was cloned by map-based cloning and encodes ACTIN2 (ACT2),the a major actin of the vegetative tissue. The three der1 alleles develop the mutant phenotype to different degrees and are that all missense mutations, thus providing the means to study the effect of partially functional ACT2. The detailed characterization of the the der1 phenotypes revealed that ACT2 is not only involved in root hair tip growth, but is also required for correct actin selection of the bulge site on the epidermal cell. Thus, the der1 mutants are useful tools to better understand the cell. function of the actin cytoskeleton in the process of root hair formation.

Plant or immune responses are triggered by pattern recognition receptors that detect conserved pathogen-associated molecular patterns (PAMPs) or by resistance (R) proteins of recognizing isolate-specific pathogen effectors. We show that in barley intracellular MLA R proteins function in the nucleus to confer resistance pattern against the powdery mildew fungus. Recognition of the fungal AVRA10 effector by MLA10 induces nuclear associations between receptor and WRKY a transcription factors. The identified WRKY proteins act as repressors of PAMP-triggered basal defense. MLA appears to interfere with the WRKY basal repressor function, thereby de-repressing PAMP-triggered basal defense. Our findings reveal a mechanism by which these polymorphic immune receptors integrate distinct MLA pathogen signals.

To cultivars. study genome evolution and diversity in barley (Hordeum vulgare), we have sequenced and compared more than 300 kb of sequence Together, spanning the Rph7 leaf rust disease resistance gene in two barley cultivars. Colinearity was restricted to five genic and two and intergenic regions representing <35% of the two sequences. In each interval separating the seven conserved regions, the number and type in of repetitive elements were completely different between the two homologous sequences, and a single gene was absent in one cultivar.pool. In both cultivars, the nonconserved regions consisted of approximately 53% repetitive sequences mainly represented by long-terminal repeat retrotransposons that have type inserted <1 million years ago. PCR-based analysis of intergenic regions at the Rph7 locus and at three other independent loci in in 41 H. vulgare lines indicated large haplotype variability in the cultivated barley gene pool. Together, our data indicate rapid loci and recent divergence at homologous loci in the genome of H. vulgare, possibly providing the molecular mechanism for the generation for of high diversity in the barley gene pool. Finally, comparative analysis of the gene composition in barley, wheat (Triticum aestivum),of rice (Oryza sativa), and sorghum (Sorghum bicolor) suggested massive gene movements at the Rph7 locus in the Triticeae lineage.

Sponsored held by the National Science Foundation and the U.S. Department of Agriculture, a wheat genome sequencing workshop was held November 10-11,strategies 2003, in Washington, DC. It brought together 63 scientists of diverse research interests and institutions, including 45 from the United the States and 18 from a dozen foreign countries (see list of participants at http://www.ksu.edu/igrow). The objectives of the workshop were basis to discuss the status of wheat genomics, obtain feedback from ongoing genome sequencing projects, and develop strategies for sequencing the the wheat genome. The purpose of this report is to convey the information discussed at the workshop and provide the basis and for an ongoing dialogue, bringing forth comments and suggestions from the genetics community.

Plant mechanisms genomes, in particular grass genomes, evolve very rapidly. The closely related A genomes of diploid, tetraploid, and hexaploid wheat are as derived from a common ancestor that lived <3 million years ago and represent a good model to study molecular mechanisms tetraploid, involved in such rapid evolution. We have sequenced and compared physical contigs at the Lr10 locus on chromosome 1AS from a diploid (211 kb), tetraploid (187 kb), and hexaploid wheat (154 kb). A maximum of 33% of the sequences were conserved ploidy between two species. The sequences from diploid and tetraploid wheat shared all of the genes, including Lr10 and RGA2 and 33% define a first haplotype (H1). The 130-kb intergenic region between Lr10 and RGA2 was conserved in size despite its activity H2 as a hot spot for transposon insertion, which resulted in >70% of sequence divergence. The hexaploid wheat sequence lacks both a Lr10 and RGA2 genes and defines a second haplotype, H2, which originated from ancient and extensive rearrangements. These rearrangements included conservation insertions of retroelements and transposons deletions, as well as unequal recombination within elements. Gene disruption in haplotype H2 was caused common by a deletion and subsequent large inversion. Gene conservation between H1 haplotypes, as well as conservation of rearrangements at the kb), origin of the H2 haplotype at three different ploidy levels indicate that the two haplotypes are ancient and had a content stable gene content during evolution, whereas the intergenic regions evolved rapidly. Polyploidization during wheat evolution had no detectable consequences on as the structure and evolution of the two haplotypes.

Sorghum,approximately an African grass related to sugar cane and maize, is grown for food, feed, fibre and fuel. We present an years initial analysis of the approximately 730-megabase Sorghum bicolor (L.) Moench genome, placing approximately 98% of genes in their chromosomal context is using whole-genome shotgun sequence validated by genetic, physical and syntenic information. Genetic recombination is largely confined to about one-third of of the sorghum genome with gene order and density similar to those of rice. Retrotransposon accumulation in recombinationally recalcitrant heterochromatin explains few the approximately 75% larger genome size of sorghum compared with rice. Although gene and repetitive DNA distributions have been preserved genetic, since palaeopolyploidization approximately 70 million years ago, most duplicated gene sets lost one member before the sorghum-rice divergence. Concerted evolution be makes one duplicated chromosomal segment appear to be only a few million years old. About 24% of genes are grass-specific member and 7% are sorghum-specific. Recent gene and microRNA duplications may contribute to sorghum's drought tolerance.

Brachypodium sylvaticum, sylvaticum and Brachypodium distachyon were recently proposed as new model plants because of their small genomes and their phylogenetic position not between rice and Triticeae crops. We sequenced a 371-kb region in B. sylvaticum, the largest genomic sequence available so far of from this species, providing quantitative data on gene conservation, collinearity and phylogeny. We compared it with orthologous regions from rice from and wheat. Brachypodium and wheat show perfect macro-collinearity of genetic markers, whereas rice contains an approximately 220-kb inversion. Rice contains wheat. almost twice as many genes as Brachypodium in the region studied, whereas wheat has about 40% more. Through comparative annotation,and we identified alternative transcripts and improved the annotation for several rice genes, indicating that approximately 15% of rice genes might of require re-annotation. Surprisingly, our data suggest that 10-15% of functional sequences in small grass genomes may not encode any proteins.sequences, From available genomic and expressed sequence tag sequences, we estimated Brachypodium to have diverged from wheat about 35-40 Mya, significantly Mya, more recently than the divergence of rice and wheat. However, our data also indicate that orthologous regions from Brachypodium and phylogenetic wheat differ considerably in gene content, thus the Brachypodium genome sequence probably cannot replace genomic studies in the large Triticeae compared genomes.