M.Sc. (Biochemistry) / Plant innate immunity occurs in two interconnected branches, the first being the recognition of pathogen conserved surface structures known as pathogen- or microbe-associated molecular patterns (P/MAMPs) by the plant plasma membrane pathogen recognition receptors (PRRs), leading to activation of P/MAMP-triggered immunity (P/MTI). The second branch involves the recognition of pathogen avirulence (Avr) genes by the corresponding plant disease resistance (R) genes, known as the ‘gene-for-gene‘ interaction, and results in a more efficient or stronger defence response, namely effector-triggered immunity (ETI). Lipopolysaccharide (LPS) acts as a P/MAMP that induces an innate immune response in both plants and animals. LPS, especially the lipid A component, has been shown to play a vital role in activating immune responses in animals. Other LPS components such as lipooligosaccharide (LOS) and the core-oligosaccharide have also been shown to trigger an immune response in plants such as Arabidopsis thaliana. In mammalian cells, LPS binds to the LPS-binding protein (LBP) forming a LPS-LBP complex, which binds to a Toll-like receptor 4/myeloid differentiation-2 (TLR4/MD-2) complex together with the co-receptor CD14, a glycosylphosphatidylinositol (GPI)-linked protein, and activates an immune response. To date, there is still no knowledge about the LPS receptor(s) in plants.....

M.Sc. / Plants have evolved a complex array of biochemical pathways that enable them to recognise and respond to signals from the environment. At present, little is known about the signal transduction pathways that are activated during a plant's response to attack by a pathogen, although this knowledge is central to our understanding of disease susceptibily and resistance. A common form of plant resistance is the restriction of pathogen proliferation to a small zone surrounding the site of infection. In many cases, this restriction is accompanied by localized death of host tissues, known as the hypersensitive response. In addition to local defense responses, many plants respond to infection by activating defenses in uninfected parts of the plant. As a result, the entire plant is more resistant to a secondary infection. This systemic acquired resistance can persist for several weeks or more and often confers crossresistance to unrelated pathogens. Fungal polygalacturonases (PGs) catalyze the fragmentation and the solubilisation of the homogalacturonan in the plant cell wall. These enzymes might have important functions during plant colonization by a fungus. PGs have also been shown to activate plant defense responses, likely because they generate oligogalacturonides with elicitor activity from the plant cell wall. A polygalacturonase inhibiting protein (PGIP), found in the plant cell wall of many plants, forms a specific complex with fungal PGs and favours the accumulation of elicitor-active oligogalacturonides in vitro. An agarose diffusion assay was used to screen the extracts from Verticillium dahliae for PG activity and ensuing inhibition by purified cotton PGIP. Quantitative determination of differences in polygalacturonase activity in the extracts were performed using a reducing sugar assay. There may be more than one isoform of PG present since the polygalacturonases produced by fungi are likely to be to a mixture of exo- and endo-PGs. Polygalacturonase was therefore isolated from 18-day-old culture filtrates of V. dahliae. The enzyme was partially purified by means of ammonium sulphate precipitation and gel chromatography. The band responsible for PG activity was identified and characterized, having a molecular weight of approximately 28-31 kDa, and a pl of 5.1 - 5.9. Kinetic studies indicate a Km of 0.33% and V,„,,of 0.85 pmoles reducing units / min. A commercial preparation of endo-PG from Aspergillus niger was used as a control. This endo-PG had a molecular weight of 68 kDa and a pl point of 3.6 and 5.1, suggesting there were at least two isoforms of endo-PG present. Kinetic studies indicate a K m of 0.33% and V,,„ of 1.07 gmoles reducing units / min.

O objetivo deste projeto foi entender a organização genômica e o conteúdo de genes de dois fitopatógenos relacionados geneticamente, mas que infectam diferentes hospedeiros: Leifsonia xyli subsp. xyli (Lxx), um patógeno de cana-de-açúcar; e Leifonia xyli subsp. cynodontis (Lxc), um patógeno de gramíneas do gênero Cynodon. Os resultados do seqüenciamento parcial do genoma de Lxc são descritos, incluindo as seqüências comuns ao genoma de Lxx e os fragmentos de organização distinta e genes específicos de Lxc. Para alcançar o objetivo, bibliotecas genômicas do genoma de Lxc foram construídas. A estratégia revelou seqüências específicas, algumas provavelmente adquiridas por transferência horizontal, e regiões não sintênicas do genoma de Lxc, quando comparadas com Lxx. Regiões específicas somaram 311.353 pb e foram anotadas. Devido a associação de elementos genéticos móveis com reorganização cromossômica e transferência horizontal de genes, um estudo detalhado dos transposons do tipo IS, presentes em ambos os genomas, foi realizado. A análise revelou um número variável de elementos para cada genoma atuando na diversificação dos mesmos. / This study aimed to understand genome organization and gene content of two closely related plant pathogens that infect different hosts: Leifsonia xyli subsp. xyli (Lxx), a sugarcane pathogen; and Leifonia xyli subsp. cynodontis (Lxc), a Cynodon grass pathogen. We describe the results of a partial genome sequence of Lxc, assessing the similarity to Lxx completely sequenced genome, describing differences in genome organization and uncovering genes specific to Lxc genome. To accomplish the objective, genomic libraries were constructed. The strategy uncovered specific sequences, some probably acquired by horizontal transfer and non-syntenic regions of Lxc genome compared to Lxx. Specific regions of Lxc genome accounted for 311,353 bp and were annotated. Because mobile genetic elements are often associated with rearrangements and horizontal gene transfer, a detailed study of all insertion sequence (IS) elements presented in both genomes were realized. The analysis revealed a variable number of transposable elements acting upon genomic diversity.

by Zeng Naiyan. / "December 2004." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (p. 185-213) / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 41-47). Also available on the World Wide Web.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 103-124).

Pseudomonas syringae pv. syringae strain B728a (P.s.s. B728a) is an economically significant plant pathogen that is capable of successful epiphytic colonization of leaf surfaces. Although the virulence factors associated with this pathogen’s ability to cause disease have been well studied, the transition from epiphyte to pathogen is not well understood. The research described in this dissertation utilizes high throughput sequencing transcriptome analyses to define an iron regulatory network that is predicted to be utilized during the epiphytic portion of the P.s.s. B728a lifecycle. This dissertation also describes a collaborative microarray analysis that analyzes the P.s.s. B728a transcriptome at a global level. An iron associated sigma factor, AcsS, encoded within a peptide synthesis rich region of the P.s.s. B728a genome is shown to regulate the citrate siderophore achromobactin. RNA-seq transcriptome analysis reveals that this sigma factor regulates expression of genes predicted to be involved in functions that are important during the epiphytic stage of P.s.s. B728a, including genes involved in iron response, secretion, extracellular polysaccharide production, and cell motility. As part of a collaboration, the transcriptomes of the P.s.s. B728a genome and nine deletion mutants in regulatory genes were analyzed by microarray analayses using seven treatment conditions, including epiphytic and in planta conditions. As part of these microarray analyses, results are described for the global regulator, GacS, and a downstream transcription factor, SalA. This study confirms the role of GacS and SalA in the regulation of major virulence components of P.s.s. B728a such as phytotoxin production and Type III secretion. This study also elucidates a role for GacS and SalA regulation of genes important for epiphytic survival and function, including the Type VI secretion system, iron acquisition, and EPS production.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: protein interaction; coat protein; resistance; arabidopsis; turnip crinkle virus. Includes bibliographical references (p. 58-62).

Thesis (Ph. D.)--Swedish University of Agricultural Sciences, 2001. / Includes bibliographical references.

The habitat diversity of the fungus Nectria haematococca MPVI has been shown to be due in part to conditionally dispensable (CD) chromosomes that carry habitat-defining genes. From a biological perspective, the CD chromosomes are analogous to plasmids that possess genes that determine the habitats of plant-associated bacteria. This study establishes that the N. haematococca CD chromosome that contains the genes for Pea Pathogenicity (PEP cluster) also carries genes for the utilization of homoserine, an amino acid found in pea root exudates. Competition studies presented here demonstrate that an isolate that lacks the PEP cluster, but carries a portion of the CD chromosome containing the homoserine utilization (HUT) genes, is more competitive in the pea rhizosphere than an isolate without the CD chromosome. Further competition studies show that both the PDA1 and PDA6 CD chromosomes confer a competitive advantage in the rhizosphere of soybean, whereas only the PDA6 CD chromosome confers a competitive advantage in the rhizospheres of tomato and alfalfa, and only the PDA1 CD chromosome confers a competitive advantage in the rhizosphere of pea. These studies suggest the presence of genes on the PDA6 and PDA1 CD chromosomes that enhance the ability of N. haematococca to expand its habitat and support the idea that fungal CD chromosomes are analogous to host-specifying plasmids in plant-associated bacteria. Transformation, insertional mutagenesis, and bioinformatics were used to identify a cluster of five genes on the PDA1 CD chromosome that was responsible for the HUT phenotype in N. haematococca. One of the genes was found only in N. haematococca, another was a fungal transcription factor, and the other three had homologs involved in the synthesis of the amino acids methionine, threonine, and isoleucine, in which homoserine is an intermediate. Competition experiments that compared isolates with or without the HUT cluster showed that the HUT cluster is responsible for increased competitive ability of HUT+ N. haematococca isolates in the rhizosphere of pea. This study establishes that homoserine utilization can be a rhizosphere competency trait for N. haematococca and, to our knowledge, is the first example of a rhizosphere competency trait identified in a fungus.