Author: Rico A. CaldoPublisher:
ISBN:
Category :
Languages : en
Pages : 190
Book Description
Changes in Gene Expression by Wheat in Response to Infection by Puccinia Triticina, Causal Fungus of Wheat Leaf Rust
Author: Rico A. CaldoIdentification of Wheat Genes Induced by Puccinia Triticina
Author: Kerri Allison NeugebauerPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Bread wheat (Triticum aestivum L.) is an important staple crop for 35% of the world population. One economically important pathogen of wheat is Puccinia triticina, the causal agent of leaf rust, can cause up to 50% yield loss during epidemics. Despite the lack of an alternate host to complete the sexual stages, P. triticina still has variation within the population, which can make achieving durable resistance difficult. This study aims to gain a better understanding of the P. triticina-wheat interaction by identifying wheat genes that are induced by individual and multiple races. Six P. triticina races were evaluated on a susceptible variety of wheat at six days post inoculation. RNA was sequenced and 63 wheat genes were identified that showed varying expression in response to the six P. triticina races. Fifty-four wheat genes were characterized during the first seven days of infection using real-time PCR. Race specific gene expression was found in three wheat genes with race differences on Lr2A, Lr2C, and Lr17A. Wheat genes that had similar expression in response to all six races were also identified. Seven of the characterized genes were then silenced using RNAi hairpin constructs. The transgenic plants were molecularly characterized and inoculated with a virulent P. triticina race in the T2 generation. However, the endogenous genes were not silenced and the transgenic plants maintained susceptibility. A mutation approach was also used to identify wheat genes involved in infection. A mutant population of 3780 wheat plants was created using EMS. Fifteen hundred mutants from the M1 population were screened for plants with a different infection phenotype compared to the non-mutated control and 570 were selected. After two additional generations of selection, eight resistant mutants were obtained. The gene expression of the seven previously identified genes were evaluated and one mutant showed reduced expression of an ER molecular chaperone gene. This research uses a forward and reverse genetics approach to identify and evaluate the function of wheat genes in the wheat-P. triticina interaction. Although RNAi could not determine the gene function, the knockout mutant shows that the identified genes may have a crucial role in infection.
Identification of Wheat Leaf Rust (Puccinia Triticina. ERIKS.) Genes Expressed During the Early Stages of Infection
Author: Vanesa SegoviaPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
In Kansas, wheat (Triticum aestivum L.) is severely affected by the biotrophic fungus Puccinia triticina (leaf rust). Although resistant varieties have been developed, the fungus tends to overcome new sources resistance very quickly. Plants have evolved a single gene (R genes) defense network that can recognize specific pathogen effectors (Avr), in a gene-for-gene manor. In rusts, effectors are secreted proteins responsible for inducing the uptake of nutrients and inhibit host defense responses. Identification of secreted proteins during the infection may help to understand the mode of infection of P. triticina. Little is known about molecular interactions in the pathosystem wheat-leaf rust and no Avr genes from cereal rusts have been cloned. In order to understand pathogenicity in leaf rust and generate new alternatives for disease control, the goal of this research is identify P. triticina secreted proteins from a collection of expressed genes during the infection, and to characterize putative Avr function for three candidates. From 432 EST's derived from haustoria and infected plants, fifteen secreted proteins were identified and 10 were selected as potential avirulence candidates. Pt3 and Pt 51 are two P. triticina (Pt) candidates expressed specifically in the haustoria and encode small cysteine-rich secreted proteins. Eight candidates are expressed at early stages of infection, during spore germination and 6 days after inoculation. They are small-secreted proteins. None are repetitive elements or have nuclear localization signals. They also do not share a conserved motif with known filamentous fungus Avr proteins. Five candidates are novel proteins, two have similarity with predicted proteins, one is homologous with Hesp-379-like protein, one is homologous with superoxide dismutase, and one has a cell glucanase predicted function. Pt3, Pt12 and Pt27 were tested by transient expression experiments using co-bombardment with GUS into leaf rust resistant isogenic lines. Reduction in the expression of reporter gene GUS co-expressed with Pt27 indicates a potential avirulence factor for Lr26 in wheat.
Wheat Rusts
Author: RA McIntoshPublisher: CSIRO PUBLISHING
ISBN: 0643103023
Category : Technology & Engineering
Languages : en
Pages : 308
Book Description
Although stem rust has been controlled by means of resistant cultivars, leaf and stripe rust continue as problems for many growing areas of the world. Wheat Rusts: An Atlas of Resistance Genes has been prepared by specialists from one of the leading international laboratories, and illustrates with colour photographs typical resistance phenotypes associated with most known genes for resistance to the three rust diseases of wheat. Relevant details for each gene include chromosome location, aspects of genetics and pathogen variation, the effects of environment on expression, origin, availability in genetic and breeding stocks, and use in agriculture. This atlas includes an introduction to host:pathogen genetics, methodologies for wheat rust research and breeding for resistance.
Identification of Leaf Rust Susceptibility Genes in Wheat
Author: Joseph FenoglioPublisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
Leaf Rust, caused by Puccinia triticina, is a major disease of wheat. Leaf rust has proven to be a resilient pathogen, overcoming resistance genes multiple times. Plants have factors, known as susceptibility genes, that facilitate the ability of pathogens to cause disease. Altering susceptibility genes may provide a more durable defense against infection than resistance genes but have yet to be identified for susceptibility to leaf rust in wheat. By characterizing random mutants created through chemical mutagenesis, mechanisms determining wheat susceptibility to leaf rust can be determined. The susceptible wheat variety Thatcher was mutagenized using ethyl methanesulfonate (EMS). Surviving plants were scored for a reduction in pustule size or quantity when challenged with leaf rust. From these plants, three mutant lines (1995, 2048, and 2348) have been obtained. Mutant lines 1995 and 2048 exhibit a constitutive hypersensitive-like response (HR-like). Mutant line 2348 exhibits no evidence of a HR. Microscopic analysis of the initial 5 days of the infection process revealed the ability of P. triticina to form appressoria, early colonization, and pustule development was altered in 1995 and 2048. In 2348, P. triticina was less able to progress beyond appressoria formation and intercellular hyphae than in Thatcher. Bulked segregant RNAseq analysis of F[subscript 2:3] pools of tissue originating from a backcross to the wild type parent revealed an induction of the plant defense response in 1995 and 2048. Genotypic studies were conducted to identify regions that may contain the causative mutation. A F4 mapping population was generated by crossing each mutant line with the hard red winter wheat variety KS061705M11 and utilizing single seed descent. Association mapping identified SNPs within each population that associated with the mutant phenotype. Confidence intervals surrounding each identified SNP were created through haplotype blocking. A second genotyping method, exome capture, identified SNPs in M8 lines for each mutant. Using the confidence intervals from association mapping, the list of SNPs from exome capture was narrowed. Mutant line 1995 mapped to a 3.89Mb window on 2D, a 7Mb window on 3A, and a 4.85Mb window on 4B. Mutant line 2048 mapped to a 3.89Mb window on 3B and a 4.52Mb window on 4B. These intervals narrow the region of interest for future fine mapping studies that seek to identify the causative mutation.
The Rust Diseases of Wheat
Author: William Quenn LoegeringPublisher:
ISBN:
Category : Barley
Languages : en
Pages : 24
Book Description
Changes in Gene Expression in Wheat Leaves During Rust and Powdery Mildew Infection
Author: Paul M. EalingPublisher:
ISBN:
Category : Wheat powdery mildew fungus
Languages : en
Pages : 322
Book Description
Unraveling the Mechanisms of Sr35-based Resistance in the Wheat-Puccinia Graminis F.sp. Tritici Pathosystem
Author: Andrés Felipe SalcedoPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
The fungus Puccinia graminis f. sp. tritici (Pgt) is the causal agent of the wheat stem rust disease. Wheat stem rust has attracted a lot of attention after the emergence of the Ug99 race group, which at the time of its origin was virulent on most of the wheat varieties cultivated around the world. The evolution and spread of the Pgt isolates from the Ug99 race group posed a serious threat to worldwide wheat production. To mitigate the potential impact of new rust epidemics in major wheat production areas, it remains critical to identify new strategies for breeding durable resistance traits. A detailed understanding of the plant-pathogen interaction mechanisms in the wheat-Pgt pathosystem should be the foundation of these strategies. The interaction between the matching pair of resistance (R) and avirulence (Avr) genes, an important element of the plant-pathogen interactions, is described by the broadly documented gene-for-gene model. The cloning of the Sr35 gene, which confers near immunity against all isolates from the Ug99 race group provided a unique opportunity to investigate the molecular mechanisms of resistance to stem rust in wheat. The goals of the present study were: (1) to determine whether the Sr35 gene alone is sufficient for conferring resistance against Ug99, (2) to assess the Sr35 transcript levels during the time course of infection, and (3) to identify and validate the corresponding Avr gene interacting with Sr35. The cloning of Avr genes from the biotrophic fungi represents a substantial challenge due to the variability, redundant nature, the lack of similarity to known proteins, and lack of adequate functional tools to validate them. To overcome these limitations, we performed a comparative genomic analysis using multiple Sr35-avirulent and Sr35-virulent races, including 15 chemically mutagenized Pgt strains that acquired virulence on the Sr35 gene. Whole genome shotgun sequencing of the Pgt mutants identified a single candidate gene, which carried strong effect mutations in each mutant strain. The Avr gene candidate (AvrSr35) was expressed at early stages of infection and had a signal peptide indicating that the gene product is secreted. Comparative microscopic analysis of the infected tissues at different time points after infection indicated that AvrSr35 secretion occurs before haustoria formation. The re-sequencing of the AvrSr35 candidate gene in a panel of Sr35-virulent and Sr35-avirulent isolates including isolates from the Ug99 race group, revealed the presence of a mobile DNA element inserted into the coding sequence of virulent isolates. This insertion resulted in a premature termination codon and explains the origin of Pgt field isolates virulent in the presence of the Sr35 gene. Co-expression of AvrSr35 with the Sr35 in N. benthamiana leaves induced a specific hypersensitive response confirming the avirulence function of the candidate effector gene. Subcellular localization, bi-molecular fluorescence complementation, and co-immunoprecipitation assays in N. benthamiana leaves revealed that the AvrSr35 and Sr35 proteins interact and are likely associated with the endoplasmic reticulum and plasma membrane. Thus, this study identified and functionally characterized the first matching pair of Avr/R genes for cereal rusts.
Differential Gene Expression in Wheat Roots in Response to Infection by the 'take-all' Fungus (Gaeumannomyces Graminis Var. Tritici)
Author: Timmy D. SamuelsStrategies for Wheat Stripe Rust Pathogenicity Identified by "omics" Technologies
Author: Diana Patricia Garnica MorenoPublisher:
ISBN:
Category : Haustoria
Languages : en
Pages :
Book Description
Stripe rust is a major constraint to wheat production worldwide. The causal agent is the fungus Puccinia striiformis f.sp. tritici (Pst). During infection, the fungus creates a specialized cellular structure within host cells called the haustorium which allows Pst to obtain the nutrients necessary for development and reproduction. The haustorium is also thought to secrete virulence molecules called 'effectors', which are suspected to manipulate the physiological and immune responses of host cells. Despite this broad outline, the molecular events that underlie host colonization and the produced effectors proteins are largely unknown. In my PhD, I extensively investigated Pst using transcriptomics and proteomics techniques to obtain a better understanding of how the pathogen establishes a compatible interaction with its host, and to identify the effector proteins that are synthesised and secreted during infection. First, by the use of next generation sequencing (454 and Illumina) the transcriptomes of two contrasting pathogenic stages (germinated spores and haustoria) were generated, de novo assembled and extensively annotated. A digital gene expression analysis revealed many differentially expressed genes which highlight key metabolic differences between these cell types, and provide insight into their different roles during infection. Spores turn on the metabolic pathways to derive energy from non carbohydrate sources, required to sustain growth and development. Conversely, haustoria deploy all the necessary machinery to take advantage of the abundant nutrients derived from the host nutrients and focus on energy production and biosynthetic pathways to support fungal growth and spore production. Further analysis of the haustoria transcriptome, allowed me to identify the first set of potential effector candidate genes of Pst, comprised of 437 genes, with two thirds of these up-regulated in haustoria compared to germinated spores. Using a bacterial system to synthesise and deliver proteins encoded by effector gene candidates, a small subset of these genes was cloned and used to establish two functional characterization methods. The first one aimed to test if these proteins could be recognised by wheat resistance genes and the second one tested their capacity to inhibit cell death triggered by a necrotic toxin. From the later one two effector gene candidates were found to partially inhibit plant cell death. In parallel, I have developed a method to isolate highly purified haustoria combining density gradients and flow cytometry. Haustoria purified by this method were successfully used for proteomics analysis. Proteomics data from haustoria, germinated and ungerminated spores were generated and analyzed preliminarily to determine the presence of effector candidates as well as non-effector proteins in each tissue. More than 3,000 proteins were validated by proteomic data, including 150 effector candidates. The correlation of transcriptomic and proteomic data suggested that the synthesis and deployment of some effector proteins could occur at different spatiotemporal sites and even could have destinations other than the host cell cytoplasm. Together, these studies have substantially increased our knowledge of Pst effectors and have provided insights into the pathogenic strategies of this important organism, opening new avenues of research with immense potential in the design of novel disease control strategies.