The soil ecosystem consists of the largest reservoir of biodiversity on Earth. Microbial communities are unseen drivers in soil ecosystems and they play an important role in determining a wide... Show moreThe soil ecosystem consists of the largest reservoir of biodiversity on Earth. Microbial communities are unseen drivers in soil ecosystems and they play an important role in determining a wide variety of soil processes in terrestrial ecosystems. Soil microbial communities can influence plant performance and can drive plant species composition on a particular soil. Soil microbes are associated with an extensive range of ecosystem processes, in turn, affect plant growth. While these processes can benefit plant growth, the soil microbial community also harbors microbes that compete with plants for nutrients or are pathogenic and impair plant growth. This leads to the question if plants can manipulate the composition of the soil microbial community to their advantage.In agriculture, the physical structure of the soil is often altered to improve crop production and this modifies biological components and microbial properties of the soil. Moreover, green crop management technologies, such as regulation of soil microbial biodiversity, application of beneficial microbial agents and induction of plant hormonal resistance, are regarded as promising approaches against pests and microbial pathogens. Although many experiments have shown that activation of hormonal signaling pathways can boost a plant’s immunity against pathogenic microbial attacks, whether and how these hormonal signaling pathways affect the soil microbial community and consequently plant growth is still poorly understood. Therefore, to better understand the roles of soil microbial communities at both taxonomic and functional level, studies from a plant defensive perspective are timely and needed, and this is the main focus of this thesis. Show less
Salicylic acid (SA) is a plant hormone, which is involved in the defense responses to pathogens and to abiotic stress, and in the regulation of plant growth and development. The shikimate pathway... Show moreSalicylic acid (SA) is a plant hormone, which is involved in the defense responses to pathogens and to abiotic stress, and in the regulation of plant growth and development. The shikimate pathway end product chorismic acid serves as the precursor for salicylic acid. In the model plant Arabidopsis thaliana. Chorismate is converted to salicylic acid by a chloroplast-localized isochorismate synthase and an unidentified isochorismate pyruvate lyase. EDS5, a member of the multidrug and toxin extrusion (MATE) transporter family, localized in the chloroplast envelope is responsible for SA transport from the chloroplasts to the cytosol. SA triggers a local defense response as well as a systemic defense response through the whole plant. The first objective in this thesis focused on transcription factors for the regulation of EDS5 gene expression. The second objective was to identify the missing enzyme with isochorismate pyruvate lyase activity. Show less
Cutaneous warts are caused by the human papillomavirus (HPV). Although warts are one of the most common reasons to consult general practice, there is a considerable lack of evidence on the... Show moreCutaneous warts are caused by the human papillomavirus (HPV). Although warts are one of the most common reasons to consult general practice, there is a considerable lack of evidence on the transmission and treatment of warts. This thesis presents epidemiological data from a cohort of primary school children, and two pragmatic multicenter randomized trials on common treatments for warts in general practice. The results reveal that current recommendations on both prevention and treatment of warts should be revised. In addition, this thesis explores the clinical use of determining specific wart-associated HPV type. Show less
The salicylic acid (SA) signaling pathway triggered by attack of biotrophic pathogens leads to broad spectrum resistance against a plethora of pathogenic fungi, bacteria and viruses and is known as... Show moreThe salicylic acid (SA) signaling pathway triggered by attack of biotrophic pathogens leads to broad spectrum resistance against a plethora of pathogenic fungi, bacteria and viruses and is known as systemic acquired resistance (SAR). One of the hallmarks of SAR is the accumulation of PR proteins and the induced expression of the PR-1 gene is often used as a marker for SAR. In this thesis we describe the characterization of a WRKY-class transcription factor (NtWRKY12) that specifically binds to the sequence TTTTCCAC. This sequence differs significantly from the consensus WRKY protein binding site TTGAC[C/T] (W-box), and was designated as the __WK-box__. The activation of PR-1a has always been proposed to occur mainly via TGA-factors. We show that NtWRKY12 can bind to TGA2.2 and has a more essential role in PR-1a activation. Using bioinformatic analysis various candidate genes have been prospected to have a role in regulation of the SA, jasmonate (JA) and ethylene (ET) biosynthesis or signaling pathways. The connection between AtWRKY28 and ICS1 was further studied. In protoplasts AtWRKY28 can activate ICS1 promoter::GUS reporter constructs and endogenous ICS1 mRNA levels. Using EMSA assays and ChIP experiments the bindingsite has been determined in vitro and confirmed in vivo. Show less
Salicylic acid (SA) is a signal molecule that plays an important role in plant defense against pests and diseases. Introducing the gene(s) that overexpressed SA would be an advantage where the crop... Show moreSalicylic acid (SA) is a signal molecule that plays an important role in plant defense against pests and diseases. Introducing the gene(s) that overexpressed SA would be an advantage where the crop performance could be improved by enhancing its resistance to pathogen attack. This thesis aimed at developing transgenic Brassica rapa plants with a bacterial SA pathway gene, the entC gene (encoding for isochorismate synthase) and subsequently investigating the effect of introducing this gene on the B. rapa secondary metabolite profile. The transgenic B. rapa carrying the entC gene was developed by using Agrobacterium tumefaciens-mediated transformation. The level of SA and its glucosides (SAG) were increased in transgenic plants which means that the bacterial entC gene was functional in B. rapa. In contrast, the introduction of the gene was expected to have an effect on other isochorismate derived products, but did not have a significant effect on the phylloquinone accumulation. However, the glucosinolate profiles particularly for indole and aliphatic glucosinolates was altered. The altered profile of the glucosinolates might be due to the increased level of SA produced via isochorismate that leads to activation of plant defense. Metabolome analysis of the transgenic plants showed that some phenylpropanoid compounds and indole glucosinolate (neoglucobrassicin) were increased in comparison to the control plants. These results suggest that the expression of the bacterial entC gene in B. rapa did not affect fluxes into pathways to the other groups of secondary metabolites through competition for the same precursor (chorismate). On the contrary, the biosynthesis of chorismate derived products (SA) seems to induce the competitive pathways via phenylalanine and tryptophan, pathways that are known to play a role in plant resistance. Future studies on the resistance of the transgenic plants are required to proof an increased resistance as it previously has been reported for tobacco plants overproducing salicylic acid Show less
Salicylic acid (SA) is an important signal compound in systemic acquired resistance in plants. The level of this C6C1 compound in plants increases after a pathogenic attack. There are two... Show moreSalicylic acid (SA) is an important signal compound in systemic acquired resistance in plants. The level of this C6C1 compound in plants increases after a pathogenic attack. There are two biosynthetic pathways of SA, the phenylalanine pathway, which is thought to occur in plants, and the isochorismate pathway, which is found in microorganisms. The biosynthetic pathway of SA in plant is still a matter of debate and some studies showed that the presence of the microbial pathway in plants is also plausible. The present study deals with the production of SA in Catharanthus roseus cell suspension cultures after elicitation with a fungal elicitor (Pythium aphanidermatum extract), the development of a purification method for salicylic acid from plant extract using an ion exchange chromatography, 13C-NMR analysis of purified SA-containing extracts of Catharanthus roseus cells after a labeling experiment with [1-13C]glucose and metabolic profiling of Catharanthus roseus cells elicited with SA. Catharanthus roseus is an important medicinal plant for the production of the anti-tumor agents vincristine and vinblastine, and an excellent model for a retrobiosynthetic study as shown in some studies. We showed by chemistry that in Catharanthus roseus cell suspension cultures, SA is synthesized via the isochorismate pathway. Show less
