Project

wheat; avirulence; fungal pathogens ; receptor-like kinase; durable resistance; maize; rice; disease resistance; effectors; host specificity

Lead
Pflanzen werden von einer Vielzahl von Krankheitserregern befallen. Die Züchtung von Nutzpflanzen hat im Verlauf der letzten 100 Jahre zur Entdeckung von natürlicherweise vorkommender Resistenz gegen Pathogene geführt. Die Funktionsweisen dieser Resistenzen sind auf molekularer Ebene noch wenig verstanden. Das Projekt soll dazu wichtige Erkenntnisse liefern.
Lay summary
Wir haben in den letzten Jahren in Weizen und Mais drei molekular sehr unterschiedliche Resistenzmechanismen gegen pilzliche Krankheitserreger entdeckt. Dabei handelt es sich um Abwehrstrategien, die entweder spezifische Moleküle der mikrobiellen Invasoren entdecken können, oder aber den Stoffwechsel der Pflanze so verändern, dass die Pathogene nicht mehr wachsen können. Im vorliegenden Projekt sollen die Erkennungsmechanismen in Mais durch das Htn1 Gen gegen die Helminthosporium-Blattfleckenkrankheit sowie in Weizen durch das Pm3 Gen gegen Mehltau analysiert werden. Für das Pm3 Gen kennen wir inzwischen ein Protein aus dem Pathogen, das spezifisch erkannt wird. Dies erlaubt es, eine genaue molekulare Beschreibung der Interaktion der beiden Moleküle und damit des Erkennungsmechanismus zwischen Pflanze und Krankheitserreger anzustreben. Schliesslich sollen die physiologischen Veränderungen in Weizensorten erforscht werden, die das Lr34 Gen enthalten. Lr34 vermittelt eine Resistenz gegenüber verschiedenen Pilzarten und stellt damit eines der interessantesten und bedeutendsten Resistenzgene dar. Das Projekt beschäftigt sich mit der biologischen Funktionsweise von Krankheitsresistenz bei Getreide und leistet einen wichtigen Beitrag zu einer sehr dynamischen, global relevanten Forschungsrichtung. Da Pflanzenkrankheiten und ihre Bekämpfung ökonomisch wie ökologisch von grosser Bedeutung sind, steht diese Forschungsrichtung auch im Brennpunkt gesellschaftlicher Aufmerksamkeit.

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Last update: 30.10.2015

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The three cereal crop species wheat, rice and maize directly or indirectly contribute about 50% of the globally consumed calories for humans. Fungal diseases are a major limiting factor in cereal production. There is an enormous natural diversity of disease resistance sources in the gene pool of the three species, but the molecular nature and function of the involved genes is largely unexplored. We want to use some of these resources for improving our mechanistic understanding of different forms of disease resistance providing efficient defense in agro-ecosystems. We propose to study the molecular mechanisms of three resistance types that we have identified in wheat and maize: the wheat genes Lr34 and Lr75 are quantitative resistance genes, the maize Htn1 gene is possibly a damage induced molecular pattern (DAMP) receptor and the Pm3-AvrPm3 interaction is based on an allelic series of R genes interacting with the pathogen in a genetically highly complex way.We have found that the durable wheat resistance gene Lr34 is also functional in the diploid species barley and rice and, therefore, its function in grasses must be based on a widely conserved mechanism. To identify biochemically the substrate of the LR34 transporter, yeast and plant protoplast assays will be used, focusing on the recently identified candidate substrate abscisic acid. Based on the Lr34-induced, senescence-like phenotype observed in N. benthamiana, protein function and localization studies will be done. Lr34 together with Lr75 confer durable leaf rust resistance in winter wheat cultivar Forno. We will clone Lr75 (already well-advanced work in the lab) and functionally study this gene and its interaction with a seedling resistance gene. Our recent isolation of the maize Htn1 gene conferring quantitative, broad-spectrum resistance against Northern Corn Leaf Blight has shown that it encodes a WAK-domain receptor-like kinase, putatively acting as DAMP receptor recognizing degradation products from cell wall attack. We want to identify the ligand of HTN1 by carbohydrate microarray analysis and study protein kinase function, protein localization and the transcriptome network induced by HTN1.For the Pm3-AvrPm3 interaction involving a major resistance (R) gene, we will build on our recent cloning of the first avirulence factor, AvrPm3a/f. Using site-directed mutagenesis and natural diversity analysis, critical R and Avr protein sequences involved in the interaction will be identified. Protein partners interacting with AvrPm3a/f will be isolated by co-immuno-precipitation and yeast-2-hybrid screens. Besides the established N. benthiamana system for functional analysis, we will also test the transformable hemibiotrophic fungal pathogen Zymoseptoria tritici as a novel delivery system. Transcriptomic studies of effector gene expression in several isolates as well as genetic studies will be used for the identification of one or more additional AvrPm3 genes. The genetic network of AvrPm3a/f will be further studied by the molecular isolation of an allele-specific mutant (exp3) at a new genetic locus. This project part should contribute to the development of pathogen-informed strategies in resistance breeding.Finally, we want to continue our work on mildew evolution and the genetics of host specialization of different mildew forms in cereals. This analysis will use genetic crosses between mildews specialized on wheat and triticale/wheat, or on tetraploid wheat and tetraploid/hexaploid wheat. This will allow the genetic mapping of factors relevant for host expansions. Depending on the outcome of these experiments, single genes or QTL will be mapped at high resolution to identify candidate genes underlying host specialization. This work can rely on our advanced genetic and genomic resources in mildew that we developed in the last grant phase. The work proposed in our application is expected to significantly contribute to an improved molecular understanding of agronomically important, fungal disease resistance.