Immunological characterization of peripheral blood leukocytes using vaccine for mycoplasmal pneumonia of swine (MPS) in swine line selected for resistance to MPS

This study was conducted to evaluate immunological changes in peripheral blood leukocytes in pigs that were genetically selected for their improved resistance to mycoplasmal pneumonia of swine (MPS), using MPS vaccine as an antigen. Twelve castrated MPS-selected Landrace pigs were compared with the same number of pigs from a nonselected line by using a time-course analysis at the hematological level. After the second sensitization with MPS vaccine, the percentages of B cells, CD4(+) T cells, and natural killer (NK) cells in total leukocytes were lower in the selected line than in the nonselected line, whereas the percentage of granulocytes in total leukocytes increased in the MPS-selected line. We also assessed the proliferative ability of peripheral blood mononuclear cells (PBMCs) stimulated with Mycoplasma hyopneumoniae, lipopolysaccharide or concanavalin A, and found that although the proliferative ability of the PBMC was not different between the two lines at a steady state, the nonselected line showed a significantly higher proliferative ability after sensitization with MPS vaccine than the selected line regardless of antigens used. These results thus indicate that the selection of pigs on the basis of MPS resistance changes their immunophenotype, and would give us beneficial information for the prevention of MPS infection.

Comparative proteomic and metabolomic profiling of citrus fruit with enhancement of disease resistance by postharvest heat treatment

BACKGROUND

From field harvest to the consumer's table, fresh citrus fruit spends a considerable amount of time in shipment and storage. During these processes, physiological disorders and pathological diseases are the main causes of fruit loss. Heat treatment (HT) has been widely used to maintain fruit quality during postharvest storage; however, limited molecular information related to this treatment is currently available at a systemic biological level.

RESULTS

Mature 'Kamei' Satsuma mandarin (Citrus unshiu Marc.) fruits were selected for exploring the disease resistance mechanisms induced by HT during postharvest storage. Proteomic analyses based on two-dimensional gel electrophoresis (2-DE), and metabolomic research based on gas chromatography coupled to mass spectrometry (GC-MS), and liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS) were conducted. The results show resistance associated proteins were up-regulated in heat treated pericarp, such as beta-1, 3-glucanase, Class III chitinase, 17.7 kDa heat shock protein and low molecular weight heat-shock protein. Also, redox metabolism enzymes were down-regulated in heat treated pericarp, including isoflavone reductase, oxidoreductase and superoxide dismutase. Primary metabolic profiling revealed organic acids and amino acids were down-regulated in heat treated pericarp; but significant accumulation of metabolites, including tetradecanoic acid, oleic acid, ornithine, 2-keto-d-gluconic acid, succinic acid, turanose, sucrose, galactose, myo-inositol, glucose and fructose were detected. Noticeably, H2O2 content decreased, while, lignin content increased in heat treated pericarp compared to the control, which might increase fruit resistibility in response to external stress. Also, flavonoids, substances which are well-known to be effective in reducing external stress, were up-regulated in heat treated pericarp.

CONCLUSIONS

This study provides a broad picture of differential accumulation of proteins and metabolites in postharvest citrus fruit, and gives new insights into HT improved fruit disease resistance during subsequent storage of 'Kamei' Satsuma mandarin. Interpretation of the data for the proteins and metabolites revealed reactive oxygen species (ROS) and lignin play important roles in heat treatment induced fruit resistance to pathogens and physiological disorders.

Molecular mapping of a sunflower rust resistance gene from HAR6

Sunflower rust, caused by Puccinia helianthi Schw., can result in significant yield losses in cultivated sunflower (Helianthus annuus L. var. macrocarpus Ckll.). HAR6 is a germplasm population resistant to most predominant rust races. The objectives of this study were to map the resistance factor present in HAR6 (R HAR6 ), and to provide and validate molecular tools for the identification of this gene for marker assisted selection purposes. Virulence reaction of seedlings for the F2 population and F2:3 families suggested that a single dominant gene confers rust resistance in HAR6-1, a selected rust resistance line from the original population. Genetic mapping with eight markers covered 97.4 cM of genetic distance on linkage group 13 of the sunflower consensus map. A co-dominant marker ZVG61 is the closest marker distal to R HAR6 at a genetic distance of 0.7 cM, while ORS581, a dominant marker linked in the coupling phase, is proximal to R HAR6 at a genetic distance of 1.5 cM. Validation of these markers was assessed by converting a susceptible line into a rust resistant isoline by means of marker assisted backcrossing. The application of these results to assist the breeding process and to design new strategies for rust control in sunflower is discussed.

Groundnut improvement: use of genetic and genomic tools

Groundnut (Arachis hypogaea L.), a self-pollinated legume is an important crop cultivated in 24 million ha world over for extraction of edible oil and food uses. The kernels are rich in oil (48-50%) and protein (25-28%), and are source of several vitamins, minerals, antioxidants, biologically active polyphenols, flavonoids, and isoflavones. Improved varieties of groundnut with high yield potential were developed and released for cultivation world over. The improved varieties belong to different maturity durations and possess resistance to diseases, tolerance to drought, enhanced oil content, and improved quality traits for food uses. Conventional breeding procedures along with the tools for phenotyping were largely used in groundnut improvement programs. Mutations were used to induce variability and wide hybridization was attempted to tap variability from wild species. Low genetic variability has been a bottleneck for groundnut improvement. The vast potential of wild species, reservoir of new alleles remains under-utilized. Development of linkage maps of groundnut during the last decade was followed by identification of markers and quantitative trait loci for the target traits. Consequently, the last decade has witnessed the deployment of molecular breeding approaches to complement the ongoing groundnut improvement programs in USA, China, India, and Japan. The other potential advantages of molecular breeding are the feasibility to target multiple traits for improvement and provide tools to tap new alleles from wild species. The first groundnut variety developed through marker-assisted back-crossing is a root-knot nematode-resistant variety, NemaTAM in USA. The uptake of molecular breeding approaches in groundnut improvement programs by NARS partners in India and many African countries is slow or needs to be initiated in part due to inadequate infrastructure, high genotyping costs, and human capacities. Availability of draft genome sequence for diploid (AA and BB) and tetraploid, AABB genome species of Arachis in coming years is expected to bring low-cost genotyping to the groundnut community that will facilitate use of modern genetics and breeding approaches such as genome-wide association studies for trait mapping and genomic selection for crop improvement.

Genome-wide copy number variant analysis in inbred chickens lines with different susceptibility to Marek's disease

Breeding of genetically resistant chickens to Marek’s disease (MD) is a vital strategy to poultry health. To find the markers underlying the genetic resistance to MD, copy number variation (CNV) was examined in inbred MD-resistant and -susceptible chicken lines. A total of 45 CNVs were found in four lines of chickens, and 28 were potentially involved in immune response and cell proliferation, etc. Importantly, two CNVs related with MD resistance were transmitted to descendent recombinant congenic lines that differ in susceptibility to MD. Our findings may lead to better strategies for genetic improvement of disease resistance in poultry.

Genomic prediction of northern corn leaf blight resistance in maize with combined or separated training sets for heterotic groups

Northern corn leaf blight (NCLB), a severe fungal disease causing yield losses worldwide, is most effectively controlled by resistant varieties. Genomic prediction could greatly aid resistance breeding efforts. However, the development of accurate prediction models requires large training sets of genotyped and phenotyped individuals. Maize hybrid breeding is based on distinct heterotic groups that maximize heterosis (the dent and flint groups in Central Europe). The resulting allocation of resources to parallel breeding programs challenges the establishment of sufficiently sized training sets within groups. Therefore, using training sets combining both heterotic groups might be a possibility of increasing training set sizes and thereby prediction accuracies. The objectives of our study were to assess the prospect of genomic prediction of NCLB resistance in maize and the benefit of a training set that combines two heterotic groups. Our data comprised 100 dent and 97 flint lines, phenotyped for NCLB resistance per se and genotyped with high-density single-nucleotide polymorphism marker data. A genomic BLUP model was used to predict genotypic values. Prediction accuracies reached a maximum of 0.706 (dent) and 0.690 (flint), and there was a strong positive response to increases in training set size. The use of combined training sets led to significantly greater prediction accuracies for both heterotic groups. Our results encourage the application of genomic prediction in NCLB-resistance breeding programs and the use of combined training sets.

The role of nitric oxide in the interaction of Arabidopsis thaliana with the biotrophic fungi, Golovinomyces orontii and Erysiphe pisi

Powdery mildews are a diverse group of pathogenic fungi that can infect a large number of plant species, including many economically important crops. However, basic and applied research on these devastating diseases has been hampered by the obligate biotrophic lifestyle of the pathogens, which require living host cells for growth and reproduction, and lacking genetic and molecular tools for important host plants. The establishment of Arabidopsis thaliana as a host of different powdery mildew species allowed pursuing new strategies to study the molecular mechanisms governing these complex plant-pathogen interactions. Nitric oxide (NO) has emerged as an important signaling molecule in plants, which is produced upon infection and involved in activation of plant immune responses. However, the source and pathway of NO production and its precise function in the regulatory network of reactions leading to resistance is still unknown. We studied the response of Arabidopsis thaliana to infection with the adapted powdery mildew, Golovinomyces orontii (compatible interaction) and the non-adapted, Erysiphe pisi (incompatible interaction). We observed that NO accumulated rapidly and transiently at infection sites and we established a correlation between the resistance phenotype and the amount and timing of NO production. Arabidopsis mutants with defective immune response accumulated lower NO levels compared to wild type. Conversely, increased NO levels, generated by treatment with chemicals or expression of a NO-synthesizing enzyme, resulted in enhanced resistance, but only sustained NO production prevented excessive leaf colonization by the fungus, which was not achieved by a short NO burst although this reduced the initial penetration success. By contrast, lowered NO levels did not impair the ultimate resistance phenotype. Although our results suggest a function of NO in mediating plant immune responses, a direct impact on pathogen growth and development cannot be excluded.

Activation of R-mediated innate immunity and disease susceptibility is affected by mutations in a cytosolic O-acetylserine (thiol) lyase in Arabidopsis

O-acetylserine (thiol) lyases (OASTLs) are evolutionarily conserved proteins among many prokaryotes and eukaryotes that perform sulfur acquisition and synthesis of cysteine. A mutation in the cytosolic OASTL-A1 protein ONSET OF LEAF DEATH3 (OLD3) was previously shown to reduce the OASTL activity of the old3-1 protein in vitro and cause auto-necrosis in specific Arabidopsis accessions. Here we investigated why a mutation in this protein causes auto-necrosis in some but not other accessions. The auto-necrosis was found to depend on Recognition of Peronospora Parasitica 1 (RPP1)-like disease resistance R gene(s) from an evolutionarily divergent R gene cluster that is present in Ler-0 but not the reference accession Col-0. RPP1-like gene(s) show a negative epistatic interaction with the old3-1 mutation that is not linked to reduced cysteine biosynthesis. Metabolic profiling and transcriptional analysis further indicate that an effector triggered-like immune response and metabolic disorder are associated with auto-necrosis in old3-1 mutants, probably activated by an RPP1-like gene. However, the old3-1 protein in itself results in largely neutral changes in primary plant metabolism, stress defence and immune responses. Finally, we showed that lack of a functional OASTL-A1 results in enhanced disease susceptibility against infection with virulent and non-virulent Pseudomonas syringae pv. tomato DC3000 strains. These results reveal an interaction between the cytosolic OASTL and components of plant immunity.

A nuclear localization for Avr2 from Fusarium oxysporum is required to activate the tomato resistance protein I-2

Plant pathogens secrete effector proteins to promote host colonization. During infection of tomato xylem vessels, Fusarium oxysporum f. sp. lycopersici (Fol) secretes the Avr2 effector protein. Besides being a virulence factor, Avr2 is recognized intracellularly by the tomato I-2 resistance protein, resulting in the induction of host defenses. Here, we show that AVR2 is highly expressed in root- and xylem-colonizing hyphae three days post inoculation of roots. Co-expression of I-2 with AVR2 deletion constructs using agroinfiltration in Nicotiana benthamiana leaves revealed that, except for the N-terminal 17 amino acids, the entire AVR2 protein is required to trigger I-2-mediated cell death. The truncated Avr2 variants are still able to form homo-dimers, showing that the central region of Avr2 is required for dimerization. Simultaneous production of I-2 and Avr2 chimeras carrying various subcellular localization signals in N. benthamiana leaves revealed that a nuclear localization of Avr2 is required to trigger I-2-dependent cell death. Nuclear exclusion of Avr2 prevented its activation of I-2, suggesting that Avr2 is recognized by I-2 in the nucleus.

The molecular pathways underlying host resistance and tolerance to pathogens

Breeding livestock that are better able to withstand the onslaught of endemic- and exotic pathogens is high on the wish list of breeders and farmers world-wide. However, the defense systems in both pathogens and their hosts are complex and the degree of genetic variation in resistance and tolerance will depend on the trade-offs that they impose on host fitness as well as their life-histories. The genes and pathways underpinning resistance and tolerance traits may be distinct or intertwined as the outcome of any infection is a result of a balance between collateral damage of host tissues and control of the invading pathogen. Genes and molecular pathways associated with resistance are mainly expressed in the mucosal tract and the innate immune system and control the very early events following pathogen invasion. Resistance genes encode receptors involved in uptake of pathogens, as well as pattern recognition receptors (PRR) such as the toll-like receptor family as well as molecules involved in strong and rapid inflammatory responses which lead to rapid pathogen clearance, yet do not lead to immunopathology. In contrast tolerance genes and pathways play a role in reducing immunopathology or enhancing the host's ability to protect against pathogen associated toxins. Candidate tolerance genes may include cytosolic PRRs and unidentified sensors of pathogen growth, perturbation of host metabolism and intrinsic danger or damage associated molecules. In addition, genes controlling regulatory pathways, tissue repair and resolution are also tolerance candidates. The identities of distinct genetic loci for resistance and tolerance to infectious pathogens in livestock species remain to be determined. A better understanding of the mechanisms involved and phenotypes associated with resistance and tolerance should ultimately help to improve livestock health and welfare.

A gene for plant protection: expression of a bean polygalacturonase inhibitor in tobacco confers a strong resistance against Rhizoctonia solani and two oomycetes

We have tested whether a gene encoding a polygalacturonase-inhibiting protein (PGIP) protects tobacco against a fungal pathogen (Rhizoctonia solani) and two oomycetes (Phytophthora parasitica var. nicotianae and Peronospora hyoscyami f. sp. tabacina). The trials were performed in greenhouse conditions for R. solani and P. parasitica and in the field for P. hyoscyami. Our results show that expression of PGIP is a powerful way of engineering a broad-spectrum disease resistance.

Imprimatins A and B: novel plant activators targeting salicylic acid metabolism in Arabidopsis thaliana

Plant activators are agrochemicals that protect plants from a broad range of pathogens by activating the plant immune system. Unlike pesticides, they do not target pathogens; therefore, plant activators provide durable effects that are not overcome by pathogenic microbes. Although certain plant activators have been applied to paddy fields for more than 30 years, the molecular basis of the underlying immune induction are unclear. From the screening of 10,000 diverse chemicals by a high-throughput screening procedure to identify compounds that specifically enhance pathogen-induced cell death in Arabidopsis cultured cells, we identified 7 compounds, which we designated as immune priming chemicals (Imprimatins). These compounds increased disease resistance against pathogenic Pseudomonas bacteria in Arabidopsis plants. Pretreatments increased the accumulation of endogenous salicylic acid (SA) but reduced its metabolite, SA-O-β-D-glucoside (SAG). Imprimatins inhibited the enzymatic activities of 2 SA glucosyltransferases (SAGTs) in vitro at concentrations effective for immune priming. Single and double knockout Arabidopsis plants for both SAGTs consistently exhibited enhanced disease resistance and SA accumulation. Our results demonstrate that the control of the free SA pool through SA-inactivating enzymes can be a useful methodology to confer disease resistance in plants. SAGTs can pave the way for target-based discovery of novel crop protectants.

Isolation and characterization of the plant immune-priming compounds Imprimatin B3 and -B4, potentiators of disease resistance in Arabidopsis thaliana

Plant activators are chemical crop protectants that fortify the immune system in plants. Unlike pesticides that target pathogens, plant activators provide durable effects against a broad spectrum of diseases, which have not been overcome by pathogenic microbes. Plant activators are not only useful agrochemicals, but can also help to elucidate the details of the plant immune system. Using an established high-throughput screening procedure, we previously identified 5 compounds, designated as Imprimatins, which prime plant immune response. These compounds increased disease resistance against pathogenic Pseudomonas bacteria in Arabidopsis plants by inhibiting 2 salicylic acid (SA) glucosyltransferases (SAGTs), resulting in accumulation of the phytohormone SA. Here, we report the isolation of 2 additional Imprimatins, B3 and B4, which are structurally similar to Imprimatin B1 and B2. Because these compounds did not have strong inhibitory effects on SAGTs in vitro, they may exert their function after metabolic conversion in vivo.

Identificaiton of a clubroot resistance locus conferring resistance to a Plasmodiophora brassicae classified into pathotype group 3 in Chinese cabbage (Brassica rapa L.)

In Chinese cabbage (Brassica rapa), the clubroot resistance (CR) genes Crr1 and Crr2 are effective against the mild Plasmodiophora brassicae isolate Ano-01 and the more virulent isolate Wakayama-01, but not against isolate No. 14, classified into pathotype group 3. 'Akiriso', a clubroot-resistant F(1) cultivar, showed resistance to isolate No. 14. To increase the durability of resistance, we attempted to identify the CR locus in 'Akiriso'. CR in 'Akiriso' segregated as a single dominant gene and was linked to several molecular markers that were also linked to CRb, a CR locus from cultivar 'CR Shinki'. We developed additional markers around CRb and constructed partial genetic maps of this region in 'Akiriso' and 'CR Shinki'. The positions and order of markers in the genetic maps of the two cultivars were very similar. The segregation ratios for resistance to isolate No. 14 in F(2) populations derived from each of the two cultivars were also very similar. These results suggest that the CR locus in 'Akiriso' is CRb or a tightly linked locus. The newly developed markers in this study were more closely linked to CRb than previously reported markers and will be useful for marker-assisted selection of CRb in Chinese cabbage breeding.

Molecular Linkage Mapping and Marker-Trait Associations with NlRPT, a Downy Mildew Resistance Gene in Nicotiana langsdorffii

Nicotiana langsdorffii is one of two species of Nicotiana known to express an incompatible interaction with the oomycete Peronospora tabacina, the causal agent of tobacco blue mold disease. We previously showed that incompatibility is due to the hypersensitive response (HR), and plants expressing the HR are resistant to P. tabacina at all stages of growth. Resistance is due to a single dominant gene in N. langsdorffii accession S-4-4 that we have named NlRPT. In further characterizing this unique host-pathogen interaction, NlRPT has been placed on a preliminary genetic map of the N. langsdorffii genome. Allelic scores for five classes of DNA markers were determined for 90 progeny of a "modified backcross" involving two N. langsdorffii inbred lines and the related species N. forgetiana. All markers had an expected segregation ratio of 1:1, and were scored in a common format. The map was constructed with JoinMap 3.0, and loci showing excessive transmission distortion were removed. The linkage map consists of 266 molecular marker loci defined by 217 amplified fragment length polymorphisms (AFLPs), 26 simple-sequence repeats (SSRs), 10 conserved orthologous sequence markers, nine inter-simple sequence repeat markers, and four target region amplification polymorphism markers arranged in 12 linkage groups with a combined length of 1062 cM. NlRPT is located on linkage group three, flanked by four AFLP markers and one SSR. Regions of skewed segregation were detected on LGs 1, 5, and 9. Markers developed for N. langsdorffii are potentially useful genetic tools for other species in Nicotiana section Alatae, as well as in N. benthamiana. We also investigated whether AFLPs could be used to infer genetic relationships within N. langsdorffii and related species from section Alatae. A phenetic analysis of the AFLP data showed that there are two main lineages within N. langsdorffii, and that both contain populations expressing dominant resistance to P. tabacina.

GhWRKY15, a member of the WRKY transcription factor family identified from cotton (Gossypium hirsutum L.), is involved in disease resistance and plant development

BACKGROUND

As a large family of regulatory proteins, WRKY transcription factors play essential roles in the processes of adaptation to diverse environmental stresses and plant growth and development. Although several studies have investigated the role of WRKY transcription factors during these processes, the mechanisms underlying the function of WRKY members need to be further explored, and research focusing on the WRKY family in cotton crops is extremely limited.

RESULTS

In the present study, a gene encoding a putative WRKY family member, GhWRKY15, was isolated from cotton. GhWRKY15 is present as a single copy gene, and a transient expression analysis indicated that GhWRKY15 was localised to the nucleus. Additionally, a group of cis-acting elements associated with the response to environmental stress and plant growth and development were detected in the promoter. Consistently, northern blot analysis showed that GhWRKY15 expression was significantly induced in cotton seedlings following fungal infection or treatment with salicylic acid, methyl jasmonate or methyl viologen. Furthermore, GhWRKY15-overexpressing tobacco exhibited more resistance to viral and fungal infections compared with wild-type tobacco. The GhWRKY15-overexpressing tobacco also exhibited increased RNA expression of several pathogen-related genes, NONEXPRESSOR OF PR1, and two genes that encode enzymes involved in ET biosynthesis. Importantly, increased activity of the antioxidant enzymes POD and APX during infection and enhanced expression of NtAPX1 and NtGPX in transgenic tobacco following methyl viologen treatment were observed. Moreover, GhWRKY15 transcription was greater in the roots and stems compared with the expression in the cotyledon of cotton, and the stems of transgenic plants displayed faster elongation at the earlier shooting stages compared with wide type tobacco. Additionally, exposure to abiotic stresses, including cold, wounding and drought, resulted in the accumulation of GhWRKY15 transcripts.

CONCLUSION

Overall, our data suggest that overexpression of GhWRKY15 may contribute to the alteration of defence resistance to both viral and fungal infections, probably through regulating the ROS system via multiple signalling pathways in tobacco. It is intriguing that GhWRKY15 overexpression in tobacco affects plant growth and development, especially stem elongation. This finding suggests that the role of the WRKY proteins in disease resistance may be closely related to their function in regulating plant growth and development.

Phenotypic and histochemical traits of the interaction between Plasmopara viticola and resistant or susceptible grapevine varieties

BACKGROUND

Grapevine downy mildew, caused by Plasmopara viticola, is a very serious disease affecting mainly Vitis vinifera cultivated varieties around the world. Breeding for resistance through the crossing with less susceptible species is one of the possible means to reduce the disease incidence and the application of fungicides. The hybrid Bianca and some of its siblings are considered very promising but their resistance level can vary depending on the pathogen strain. Moreover, virulent strains characterized by high fitness can represent a potential threat to the hybrid cultivation.

RESULTS

The host response and the pathogen virulence were quantitatively assessed by artificially inoculating cv Chardonnay, cv Bianca and their siblings with P. viticola isolates derived from single germinating oospores collected in various Italian viticultural areas. The host phenotypes were classified as susceptible, intermediate and resistant, according to the Area Under the Disease Progress Curve caused by the inoculated strain. Host responses in cv Bianca and its siblings significantly varied depending on the P. viticola isolates, which in turn differed in their virulence levels. The fitness of the most virulent strain did not significantly vary on the different hybrids including Bianca in comparison with the susceptible cv Chardonnay, suggesting that no costs are associated with virulence. Among the individual fitness components, only sporangia production was significantly reduced in cv Bianca and in some hybrids. Comparative histological analysis revealed differences between susceptible and resistant plants in the pathogen diffusion and cytology from 48 h after inoculation onwards. Defence mechanisms included callose depositions in the infected stomata, increase in peroxidase activity, synthesis of phenolic compounds and flavonoids and the necrosis of stomata and cells immediately surrounding the point of invasion and determined alterations in the size of the infected areas and in the number of sporangia differentiated.

CONCLUSIONS

Some hybrids were able to maintain an intermediate-resistant behaviour even when inoculated with the most virulent strain. Such hybrids should be considered for further field trials.

miRNA regulation in the early development of barley seed

BACKGROUND

During the early stages of seed development many genes are under dynamic regulation to ensure the proper differentiation and establishment of the tissue that will constitute the mature grain. To investigate how miRNA regulation contributes to this process in barley, a combination of small RNA and mRNA degradome analyses were used to identify miRNAs and their targets.

RESULTS

Our analysis identified 84 known miRNAs and 7 new miRNAs together with 96 putative miRNA target genes regulated through a slicing mechanism in grain tissues during the first 15 days post anthesis. We also identified many potential miRNAs including several belonging to known miRNA families. Our data gave us evidence for an increase in miRNA-mediated regulation during the transition between pre-storage and storage phases. Potential miRNA targets were found in various signalling pathways including components of four phytohormone pathways (ABA, GA, auxin, ethylene) and the defence response to powdery mildew infection. Among the putative miRNA targets we identified were two essential genes controlling the GA response, a GA3oxidase1 and a homolog of the receptor GID1, and a homolog of the ACC oxidase which catalyses the last step of ethylene biosynthesis. We found that two MLA genes are potentially miRNA regulated, establishing a direct link between miRNAs and the R gene response.

CONCLUSION

Our dataset provides a useful source of information on miRNA regulation during the early development of cereal grains and our analysis suggests that miRNAs contribute to the control of development of the cereal grain, notably through the regulation of phytohormone response pathways.

Molecular characterization and comparative sequence analysis of defense-related gene, Oryza rufipogon receptor-like protein kinase 1

Many of the plant leucine rich repeat receptor-like kinases (LRR-RLKs) have been found to regulate signaling during plant defense processes. In this study, we selected and sequenced an LRR-RLK gene, designated as Oryza rufipogon receptor-like protein kinase 1 (OrufRPK1), located within yield QTL yld1.1 from the wild rice Oryza rufipogon (accession IRGC105491). A 2055 bp coding region and two exons were identified. Southern blotting determined OrufRPK1 to be a single copy gene. Sequence comparison with cultivated rice orthologs (OsI219RPK1, OsI9311RPK1 and OsJNipponRPK1, respectively derived from O. sativa ssp. indica cv. MR219, O. sativa ssp. indica cv. 9311 and O. sativa ssp. japonica cv. Nipponbare) revealed the presence of 12 single nucleotide polymorphisms (SNPs) with five non-synonymous substitutions, and 23 insertion/deletion sites. The biological role of the OrufRPK1 as a defense related LRR-RLK is proposed on the basis of cDNA sequence characterization, domain subfamily classification, structural prediction of extra cellular domains, cluster analysis and comparative gene expression.

Genetic and genomic approaches for R-gene mediated disease resistance in tomato: retrospects and prospects

Tomato (Solanum lycopersicum) is one of the world's most important vegetable crops. Managing the health of this crop can be particularly challenging; crop resistance may be overcome by new pathogen races while new pathogens have been introduced by global agricultural markets. Tomato is extensively used as a model plant for resistance studies and much has been attained through both genetic and biotechnological approaches. In this paper, we illustrate genomic methods currently employed to preserve resistant germplasm and to facilitate the study and transfer of resistance genes, and we describe the genomic organization of R-genes. Patterns of gene activation during disease resistance response, identified through functional approaches, are depicted. We also describe the opportunities offered by the use of new genomic technologies, including high-throughput DNA sequencing, large-scale expression data production and the comparative hybridization technique, whilst reporting multifaceted approaches to achieve genetic tomato disease control. Future strategies combining the huge amount of genomic and genetic data will be able to accelerate development of novel resistance varieties sustainably on a worldwide basis. Such strategies are discussed in the context of the latest insights obtained in this field.

A deletion in the nitrate high affinity transporter NRT2.1 alters metabolomic and transcriptomic responses to Pseudomonas syringae

A deletion in the high affinity nitrate trasporter NRT2.1 in Arabidopsis results in a reduced susceptibility to Pseudomonas syringae by two different mechanisms, the SA priming and an interference in the effector triggered susceptibility. In the present research we further characterized the metabolic and genetic profiles of the mutant nrt2 in the interaction with P. syringae. Despite the priming found in the SA-dependent pathway, the metabolic changes in nrt2 compared with wild-type plants are more remarkable prior infection. This is associated mainly to a pre-existing over representation of signals attributed to aromatic amino acids and phenylpropanoids in the nrt2. Genomic analysis confirms the implication of aromatic aminoacids and phenylpropanoids, but additionally, suggests a new role in ribosomal proteins as the major changes observed in nrt2 upon infection by the bacterium.

Cotton GhMKK5 affects disease resistance, induces HR-like cell death, and reduces the tolerance to salt and drought stress in transgenic Nicotiana benthamiana

Mitogen-activated protein kinase (MAPK) cascades are involved in various processes from plant growth and development to biotic and abiotic stress responses. MAPK kinases (MAPKKs), which link MAPKs and MAPKK kinases (MAPKKKs), play crucial roles in MAPK cascades to mediate a variety of stress responses in plants. However, few MAPKKs have been functionally characterized in cotton (Gossypium hirsutum). In this study, a novel gene, GhMKK5, from cotton belonging to the group C MAPKKs was isolated and characterized. The expression of GhMKK5 can be induced by pathogen infection, abiotic stresses, and multiple defence-related signal molecules. The overexpression of GhMKK5 in Nicotiana benthamiana enhanced the plants' resistance to the bacterial pathogen Ralstonia solanacearum by elevating the expression of pathogen resistance (PR) genes, including PR1a, PR2, PR4, PR5, and NPR1, but increased the plants' sensitivity to the oomycete pathogen Phytophthora parasitica var. nicotianae Tucker. Importantly, GhMKK5-overexpressing plants displayed markedly elevated expression of reactive oxygen species-related and cell death marker genes, such as NtRbohA and NtCDM, and resulted in hypersensitive response (HR)-like cell death characterized by the accumulation of H(2)O(2). Furthermore, it was demonstrated that GhMKK5 overexpression in plants reduced their tolerance to salt and drought stresses, as determined by statistical analysis of seed germination, root length, leaf water loss, and survival rate. Drought obviously accelerated the cell death phenomenon in GhMKK5-overexpressing plants. These results suggest that GhMKK5 may play an important role in pathogen infection and the regulation of the salt and drought stress responses in plants.

Protein-protein interactions as a proxy to monitor conformational changes and activation states of the tomato resistance protein I-2

Plant resistance proteins (R) are involved in pathogen recognition and subsequent initiation of defence responses. Their activity is regulated by inter- and intramolecular interactions. In a yeast two-hybrid screen two clones (I2I-1 and I2I-2) specifically interacting with I-2, a Fusarium oxysporum f. sp. lycopersici resistance protein of the CC-NB-LRR family, were identified. Sequence analysis revealed that I2I-1 belongs to the Formin gene family (SlFormin) whereas I2I-2 has homology to translin-associated protein X (SlTrax). SlFormin required only the N-terminal CC I-2 domain for binding, whereas SlTrax required both I-2 CC and part of the NB-ARC domain. Tomato plants stably silenced for these interactors were not compromised in I-2-mediated disease resistance. When extended or mutated forms of I-2 were used as baits, distinct and often opposite, interaction patterns with the two interactors were observed. These interaction patterns correlated with the proposed activation state of I-2 implying that active and inactive R proteins adopt distinct conformations. It is concluded that the yeast two hybrid system can be used as a proxy to monitor these different conformational states.

In vivo role of nitric oxide in plant response to abiotic and biotic stress

Over the past few years, nitric oxide (NO) has emerged as an important regulator in many physiological events, especially in response to abiotic and biotic stress. However, the roles of NO were mostly derived from pharmacological studies or the mutants impaired NO synthesis unspecifically. In our recent study, we highlighted a novel strategy by expressing the rat neuronal NO synthase (nNOS) in Arabidopsis to explore the in vivo role of NO. Our results suggested that plants were able to perform well in the constitutive presence of nNOS, and provided a new class of plant experimental system with specific in vivo NO release. Furthermore, our findings also confirmed that the in vivo NO is essential for most of environmental abiotic stresses and disease resistance against pathogen infection. Proper level of NO may be necessary and beneficial, not only in plant response to the environmental abiotic stress, but also to biotic stress.

The effect of environmental heterogeneity on RPW8-mediated resistance to powdery mildews in Arabidopsis thaliana

BACKGROUND AND AIMS

The biotic and abiotic environment of interacting hosts and parasites may vary considerably over small spatial and temporal scales. It is essential to understand how different environments affect host disease resistance because this determines frequency of disease and, importantly, heterogeneous environments can retard direct selection and potentially maintain genetic variation for resistance in natural populations.

METHODS

The effect of different temperatures and soil nutrient conditions on the outcome of infection by a pathogen was quantified in Arabidopsis thaliana. Expression levels of a gene conferring resistance to powdery mildews, RPW8, were compared with levels of disease to test a possible mechanism behind variation in resistance.

KEY RESULTS

Most host genotypes changed from susceptible to resistant across environments with the ranking of genotypes differing between treatments. Transcription levels of RPW8 increased after infection and varied between environments, but there was no tight association between transcription and resistance levels.

CONCLUSIONS

There is a strong potential for a heterogeneous environment to change the resistance capacity of A. thaliana genotypes and hence the direction and magnitude of selection in the presence of the pathogen. Possible causative links between resistance gene expression and disease resistance are discussed in light of the present results on RPW8.