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Research project (§ 26 & § 27)
Duration : 2018-04-01 - 2020-05-31

In higher plants, organ development occurs mostly post-embryonically. Organ initiation requires tightly controlled cell division patterning and cell fate reprogramming. Auxin, a key plant hormone, plays a crucial role in these processes, ultimately through significantly altering the gene expression landscape. On the other hand, gene expression can also be defined by manipulating locus accessibility, both on protein- (i.e. nucleosomes, histones and their modifications) as well as on DNA level: methylation status of cytosines in coding genes, mainly in their promoter regions, severely affects their expression rate and regulation. The interplay between auxin signaling and DNA methylation is poorly understood and we are planning to address this question in our research. We will characterize “freak show” (fks), a novel missense mutant of NRPE5, a subunit of RNA Polymerase V (Pol V) involved in RNA-directed DNA Methylation (RdDM). We isolated fks in a forward genetic screen aimed at identifying auxin-dependent determinants of lateral root development. fks is absolutely unique among all known Pol V mutants as it shows a series of very strong phenotypic traits in its inbred progenies such as organogenesis defects, dwarfism, sterility, homeotic organ transformations or delayed flowering time. Several of these features had already been described as potentially caused by epialleles, i.e. alterations of DNA methylation at target loci. However, to our knowledge, this is the first example that a mutant in de novo DNA methylation displays such a diverse palette of epigenetic features. Characterization of fks will help us, besides gaining new knowledge about auxin action, to understand how Pol V functions and how RdDM can be directed or regulated on a general level, with insight into developmental and physiological processes regulated by this machinery. We will use next generation sequencing (NGS) for determining the transcriptome and methylome of fks. To couple auxin-dependent gene expression and DNA methylation, we will combine auxin treatment with the NGS analysis. Besides, we will identify epialleles causing aberrant lateral root development and other selected traits with physical mapping, when and where feasible. We will perform double mutant analyses to investigate genetically whether the fks mutation specifically affects any of the known RdDM sub-pathways and whether it interferes with DNA methylation maintenance too. We will obtain triple mutants of NRPE5 and its two homologs of unknown function to further elaborate their role in RdDM and development. Additionally, we will address the function of NRPE5 and its homologs biochemically: protein interaction assays with other RNA polymerase subunits will tell us about possible subunit composition and –affinity of Pol V.
Research project (§ 26 & § 27)
Duration : 2017-11-01 - 2020-10-31

Plants undergo several developmental transitions in the course of their life cycle, marked by specific morphological changes such as altered leaf morphology, the formation of leaf hairs (trichomes) and the onset of flowering. Mutants in the putative O-GlcNAc transferase SPINDLY show an accelerated transition from the juvenile to the adult phase, as well as early flowering, but a potential connection between O-GlcNAcylation and phase change has not been adressed as yet. O-GlcNAcylation is a common posttranslational modification, where a single N-acetyl-β-D glucosamine (GlcNAc) is O-linked to side chains of serine- or threonine residues in nuclear and cytoplasmic proteins. The targets and molecular function of O-GlcNAcylation in plants are not well characterized. In animals, this modification serves an important signalling role in a range of different cellular processes, often in response to stress and nutrients. As the availability of the donor molecule UDP-GlcNAc reflects the overall state of nutrition within cells, it has been suggested that O-GlcNAcylation may integrate information on stress and nutrients to basic cellular processes on a global level. On the other hand, the timing of developmental transitions in plants is regulated by the amount of available sugar accumulating during plant growth. This process is mediated by balancing the ratio between miRNA156 and miRNA172, therefore regulating the downstream miRNA156 target genes, a family of SPL-transcription factors. Given the observed early transition phenotypes in spy-mutants, this project aims to investigate a potential role of SPY in developmental transitions, focusing on the juvenile to adult phase change and the regulation of flowering time. Levels of miRNA156 and its target genes in spy-mutant backgrounds will be analysed, and genetic analysis will be performed to establish the interaction of SPY and SPL transcription factors. These experiments will establish if SPY regulates developmental transitions via the miRNA156 pathway and/or SPL transcription factors. Additional experiments will adress a potential role of gibberellin signaling in this interaction.
Research project (§ 26 & § 27)
Duration : 2017-09-01 - 2020-08-31

Fungal-plant interactions constitute fine-tuned interplays where each of the participating organisms has evolved efficient strategies to win over the other. To establish a successful infection of a plant host the invading fungal pathogen has to quickly respond and adapt to numerous plant defence mechanisms. This implies a coordinated expression of metabolic and virulence-associated genes, and there is compelling evidence that part of the communication between both interacting organisms is regulated at the level of chromatin. In this project, we strive to unravel chromatin-based mechanisms that govern adequate transcriptomic responses during the host-pathogen interaction using the notorious plant pathogen Fusarium graminearum and wheat (Triticum aestivum) as pathosystem. We have previously identified and characterised a heterochromatin-deficient mutant (Δhep1) that exhibited a hypervirulent phenotype. While most strains deficient for a specific chromatin regulator exhibit a hypo- or avirulent phenotype, deletion of the heterochromatin protein 1-encoding gene (hep1), exhibited a hypervirulence of F. graminearum towards its plant host wheat (J. Strauss and colleagues, unpublished data). This phenotype provides a unique advantage in terms of in planta analyses.

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