Abstract:Fusarium head blight (FHB) is a devastating disease of wheat throughout the world. FHB is primarily caused by the fungal pathogen Fusarium graminearum. In wheat, benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH) induces the wheat chemically-induced (WCI) genes and provides resistance to several pathogens. The objectives of this study were two-fold: (1) to investigate the effects of BTH application and F. graminearum infection on selected defense response genes in wheat spikes; and (2) to study the potential of BTH for inducing FHB resistance in wheat. Wheat spikes were treated with BTH prior to anthesis and transcript accumulation and resistance to FHB were measured. BTH-treated wheat spikes were examined for expression of six defense response genes (PR-1, PR-2, PR-3, PR-4, PR-5 and peroxidase) and the five WCI genes that are induced by BTH in wheat leaves. All five WCI genes were induced by BTH in spikes; however none of the six defense response genes were induced. Conversely, the defense response genes were induced by F. graminearum infection, whereas the WCI genes were not. These data indicate that the pathway for induction of the defense response genes by F. graminearum infection is distinct from the BTH-induced pathway. In the disease evaluations of BTH-treated plants, we found that BTH did not provide significant Type I or Type II resistance to wheat spikes spray- or point-inoculated with F. graminearum, respectively. These data indicate that BTH application and the induction of WCI gene expression does not provide resistance to FHB.
Abstract: Four chemicals [salicylic acid (SA), sodium salt of salicylic acid (NaSA), isonicotinic acid (INA), and DL-b-amino-n-butyric acid (BABA)] and the yeast antagonist Cryptococcus flavescens (=C. nodaensis nomen nudum) OH 182.9 were evaluated separately or together for the ability to reduce Fusarium head blight (FHB) of wheat in the greenhouse. When sprayed onto wheat heads at 3 days prior to pathogen challenge with Gibberella zeae, NaSA and INA at 10 mM significantly reduced FHB severity compared to the non-treated disease control. Applied at concentrations of 1 and 5 mM at 3 days before pathogen challenge, NaSA or INA in combination with OH 182.9 did not significantly reduce FHB severity compared to either treatment alone, though the lowest disease severity values frequently were associated with the combination treatments. When sprayed onto wheat heads just beginning to emerge from boot at 10 days prior to pathogen inoculation, NaSA, INA, and BABA at 1 mM significantly reduced FHB severity indicating that induced systemic resistance was at least partially responsible for the reduction of FHB disease. Induced FHB resistance was achieved by treating wheat with INA at concentrations as low as 0.1 mM. In only one instance was 100-kernel weight affected by any chemical or combination of chemicals with OH 182.9 treatment. Data from our studies in the greenhouse suggest that chemical inducers can induce resistance in wheat against FHB, and that further efforts are warranted to explore the potential of improved control of FHB disease by incorporating chemical inducers with the FHB biocontrol agent OH 182.9.
Abstract: Previously identified as breeding line MSJ461-1, Missaukee is a round white chip processing potato variety resulting from a cross between Tollocan and NY88 and has foliar resistance to potato late blight (Phytophthora infestans de Bary). This variety has an attractive round shape and mildly netted, bright skin. Seven years of field testing in Michigan indicate that the yield of total marketable tubers in Missaukee is similar to that of Snowden. However, Missaukee has a lower incidence of internal defects than Snowden. Specific gravity ranged from 1.069 to 1.086 in Michigan trials and out-of-the-field chip scores were similar to those of Snowden. Missaukee showed some resistance to Verticillium wilt in 2-years of trials. DNA marker and greenhouse tests indicate that Missaukee is also resistant to the golden cyst nematode (Globodera rostochiensis Woll) pathotype Ro1.
Abstract: Mapping resistance genes is usually accomplished by phenotyping a segregating population for the resistance trait and genotyping it using a large number of
markers. Most resistance genes are of the NBS-LRR type, of which an increasing number is sequenced. These genes and their analogs (RGAs) are often organized in clusters. Clusters tend to be rather homogenous, viz. containing genes that show high sequence similarity with each other. From many of these clusters the map position is known. In this study we present and test a novel method to quickly identify to which cluster a new resistance gene belongs and to produce markers that can be used for introgression breeding. We used NBS profiling to identify markers in bulked DNA samples prepared from resistant and susceptible genotypes of small segregating populations. Markers co-segregating with resistance can be tested on individual plants and directly used for breeding. To identify the resistance gene cluster a gene belongs to, the fragments were sequenced and the sequences analyzed using bioinformatics tools. Putative map positions arising from this analysis were validated using markers mapped in the segregating population. The versatility of the approach is demonstrated with a number of populations derived from wild Solanum species segregating for P.infestans resistance. Newly identified P.infestans resistance genes originating from S.verrucosum, S.schenckii, and S.capsicibaccatum could be mapped to potato chromosomes 6, 4, and 11,
respectively.
Abstract: Transcriptome profiling in chile (Capsicum annuum) roots was used to determine those genes with expression profiles correlated with a resistance phenotype to the pathogen, Phytophthora capsici. Two microarrays were generated; a 10K element array printed with cDNAs from a library of transcripts expressed in Criollo de Morelos-334 variety of C. annuum 6 h post-challenge with P. capsici and a 2K element array printed with sequenced cDNA clones selected based on their preliminary patterns of expression. This second array was enriched for clones that were differentially expressed in susceptible (New Mexico 6-4) vs. resistant (CM334) varieties of C. annuum. Gene expression profiles were revaluated at 0, 4 and 24 h post-inoculation. Control treatments included samples collected at 0, 4, and 24 h post-mock-inoculation. In addition to the parental CM334, a resistant backcross line (01-1688) was also used to identify gene expression patterns associated with the resistance phenotype. Based on a principal component analysis, CM334 samples showed the most significant transcription induction at 4 and 24 h post-inoculation, while the predominant variability in the susceptible line was in genes repressed at 24 h. A set of 168 genes with significant changes in expression following P. capsici challenge was identified; of these, 22 were uniquely expressed only in the resistant lines (CM334 or 01-1688). This set of genes represent candidates for further study as markers for recurrent selection programs and as candidate genes for the mechanism of disease resistance.
Abstract: Initial screening of 14 Solanum dulcamara accessions enabled the identification of individuals resistant and susceptible to Phytophthora infestans. Crosses between contrasting genotypes resulted in three F2–BC1 populations segregating for resistance to late blight in a laboratory assay and under field conditions. Genetic profiling of one of these populations using 128 AFLP primers generated three markers linked to the resistant phenotype. Blast analysis of the sequenced markers resulted in a plausible gene position on the distal end of the long arm of chromosome 9 that could be confirmed by CAPS markers. Thus, we describe a first resistant gene, named Rpi-dlc1, from S. dulcamara, a Solanum species native to Europe. In addition, one population was tested for broadness of resistance responses using a set of seven additional P. infestans isolates, varying in virulence. This indicated the possible presence of additional Rpi genes.
Abstract: StPUB17, a novel UND/PUB/ARM repeat type gene, was isolated from leaves of potato (Solanum tuberosum L.) clone 386209.10 using the rapid amplification of cDNA ends strategy with the primers designed according to a potato EST fragment up-regulated by Phytophthora infestans. StPUB17 was confirmed intron-free by comparison of the cDNA and genomic DNAs. The RT-PCR analysis showed that StPUB17 was constitutively and differentially expressed in all tissues, and was significantly induced in detached leaves subjected to P. infestans, signal molecules such as salicylic acid, methyl jasmonate, ethylene, abscisic acid and wounding. The gene expression was also strongly up-regulated when in vitro plantlets were exposed to high (40°C) and low (4°C) temperatures and dehydration induced by polyethylene glycol and NaCl. The function of StPUB17 was further clarified by silencing it in potato using RNAi-based post-transcriptional gene silencing (PTGS). The results demonstrated that StPUB17-silenced plants exhibited more susceptible to the infection of P. infestans and more sensitive to the stress of NaCl. Present data indicated that StPUB17 is a gene harboring broad-spectrum responses to both biotic and abiotic stresses in the potato and may play crucial roles in late blight resistance and salt tolerance of the crop.
Abstract: Using degenerate primers based on the conserved nucleotide binding site (NBS) and protein kinase domain (PKD), 100 resistance gene analogs (RGAs) were isolated from tobacco variety Nicotiana repanda. BLASTx search against the GenBank database revealed that 27 belong to the NBS class and 73 belong to the protein kinase (PK) class. Cluster analysis and multiple sequence alignment of the deduced protein sequences indicate that RGAs of the NBS class can be divided into two groups: toll/interleukin receptor (TIR) and non-TIR types. Both types possess 6 conserved motifs (P-loop, RNBS-A, Kinase-2, RNBS-B, RNBS-C, GLPL). Based on their sequence similarity, the tobacco RGAs of the PK class were assigned to 8 subclasses. We examined their expression after infection with either Tobacco mosaic virus (TMV) or the tobacco black shank pathogen (Phytophthora parasitica var. nicotianae). The expression levels of 4 RGAs of the PK class were significantly elevated by TMV and 1 RGA of the PK class and 3 RGAs of the NBS class were up-regulated by P. parasitica var. nicotianae. The expression of two RGAs of the PK class was induced by P. parasitica var. nicotianae. Infection by either TMV or P. parasitica var. nicotianae enhanced the expression of NtRGA2, a RGA of the PK class. The present study shows that RGAs are abundant in the tobacco genome and the identification of tobacco RGAs induced by pathogens should provide valuable information for cloning related resistance genes in tobacco.
Abstract: The selective induction of heat shock protein(s) (HSP) in human cells during bacterial, parasitic or viral infection and the accompanying cytoprotection initiated an interest in this conserved group of proteins – either as markers of disease outcome and severity or in novel therapeutic approaches. Knowledge concerning the induction and role of HSP in plant-pathogen interactions is however limited. The objective of this study was to investigate the expression of constitutive and inducible members of the 70-kDa HSP family (Hsp70/Hsc70) during compatible and incompatible interactions in tomato Lycopersicon esculentum L. cv. UC82B. Cell suspensions were co-cultured with virulent (biovar III) or avirulent (biovar II) strains of Ralstonia solanacearum, the causative agent of bacterial wilt, and samples harvested at specific time points for the analysis of pathogenesis-related protein-1 (PR-1) accumulation, phenylalanine ammonia-lyase (EC 4.3.1.5, PAL) activity, Hsp70/Hsc70 accumulation and cell survival. Besides inducing PR-1 (6–18 h, P < 0.05), biovar II caused a virulence-dependent induction of Hsp70/Hsc70 (24–48 h, P < 0.05) coinciding with the induction of PAL activity (24–48 h, P < 0.05) and maintenance of cell viability (48 h). It is proposed that, at least in tomato, Hsp70/Hsc70 is induced by avirulent strains of R. solanacearum as part of the defence response to chaperone newly synthesized defence proteins and to maintain cellular homeostasis essential for the execution of a defence response.
Abstract: A strategy to control the devastating late blight disease is providing potato cultivars with genes that are effective in resistance to a broad spectrum of Phytophthora infestans isolates. Thus far, most late blight resistance (R) genes that were introgressed in potato were quickly defeated. In contrast, the Rpi-blb1 gene originating from Solanum bulbocastanum has performed as an exclusive broad-spectrum R gene for many years. Recently, the RXLR effector family ipiO was identified to contain Avr-blb1. Monitoring the genetic diversity of the ipiO family in a large set of isolates of P. infestans and related species resulted in 16 ipiO variants in three distinct classes. Class I and class II but not class III ipiO variants induce cell death when coinfiltrated with Rpi-blb1 in Nicotiana benthamiana. Class I is highly diverse and is represented in all analyzed P. infestans isolates except two Mexican P. infestans isolates, and these were found virulent on Rpi-blb1 plants. In its C-terminal domain, IPI-O contains a W motif that is essential for triggering Rpi-blb1–mediated cell death and is under positive selection. This study shows that profiling the variation of Avr-blb1 within a P. infestans population is instrumental for predicting the effectiveness of Rpi-blb1–mediated resistance in potato.
Abstract