Project

Wheat; host-pathogen interactions; Powdery mildew; host specificity; Leaf rust; resistance gene

Lead
Pflanzen werden von einer Vielzahl von Krankheitserregern befallen. Die Züchtung von Nutzpflanzen hat im Verlauf der letzten hundert Jahre zur Entdeckung von natürlicherweise vorkommender Resistenz gegen Pathogene geführt. Die Funktionsweisen dieser Resistenzen sind auf molekularer Ebene noch wenig verstanden. Das Projekt widmet sich der Frage, wie Pflanzen auf molekularer Ebene die Anwesenheit von pilzlichen Pathogenen (z.B. dem Weizenmehltau) erkennen können, und wie dadurch Abwehrreaktionen ausgelöst werden.
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 entweder gar mehr wachsen können, oder zumindest in ihrer Vermehrung stark eingeschränkt sind. Das vorliegende Projekt soll zum Verständis der Erkennungsmechanismen von Krankheitserregern durch eine Reihe von pflanzliche Immunrezeptoren beitragen. Dabei stehen Pilzpathogene wie z.B. Mehltau und Braunrost bei Weizen im Vordergrund. Die Immunrezeptoren stammen aus Weizen oder Mais und gehören zu ganz unterschiedlichen Proteinklassen. Basierend auf diesen verschiedenen Typen von Rezeptoren wollen wir verstehen, wie die biochemische Erkennung auf Proteinebene stattfindet, welche Strukturen auf Pathogen- wie auf Wirtsseite für die spezifische Erkennung verantwortlich sind, und schliesslich wie diese Erkennung zur einer Abwehrantwort der Pflanze führt  Zudem wollen wir Wege finden, wie diese Erkenntnisse für die praktisch Pflanzenzüchtung nutzbar gemacht werden können. Das Projekt beschäftigt sich mit der biologischen Funktionsweise von Krankheitsresistenz bei Getreidepflanzen und leistet einen 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: 30.11.2018

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The focus of our work is on the molecular determinants of resistance interactions between the wheat (Triticum aestivum) host plant and the obligate biotrophic, fungal pathogens powdery mildew (Blumeria graminis, Bgt) and leaf rust. In the last three years, the genomic tools both for wheat and its pathogens (particularly powdery mildew) have been greatly improved, allowing efficient map-based cloning of genes as well as genome-wide association studies (GWAS). The new resources have allowed us to identify the first avirulence as well as avirulence suppressor genes from powdery mildew three years ago (AvrPm3a2f2, SvrPm3). This work on the pathogen side was complemented by the development of more efficient approaches for resistance gene isolation from wheat, e.g. MutChromSeq which was used for the identification of the Pm2 mildew resistance gene. In the last two years we have isolated a number of novel molecular determinants of the race-specific resistance interaction of mildew and wheat. The AvrPm2, AvrPm3b2c2, AvrPm3d and AvrPm17 genes specifically recognized by the immune receptors Pm2, Pm3b, Pm3c, Pm3d and Pm17, respectively, have been identified and found to encode small effector-like proteins. Each of them belongs to a gene family with close relatives that are not recognized by the respective immune receptor. On the host side we have recently isolated genes for two new immune receptors. In wheat, at total of 77 Pm (powdery mildew resistance) genes/alleles have been genetically described at 53 loci. Each of them confers resistance to a specific set of mildew isolates. In the past, we have cloned a number of these genes which encode immune receptors, and we want to understand the immune network of host and pathogen factors contributing to agricultural resistance which is highly diverse and specific, depending on host-genotype and pathogen race. Thus, the overall goal of the first proposal part is to understand the molecular basis of disease resistance specificity in the agriculturally important wheat-mildew pathosystem. This will help to understand the evolution of pathogen adaptation as well as contribute to strategies for improved resistance gene management in plant breeding. We will analyze the interactions at the molecular level in a transient system to identify by mutagenesis the AVR and host protein domains involved in resistance. Furthermore, we will perform domain swaps between active AVR proteins and the highly similar proteins encoded by closely related gene family members which exist for all our cloned AVR genes. Such domain swaps will give further insight into the protein recognition surfaces and the sub-domains involved in the recognition. We will also study these interactions at the biochemical level, using yeast-2-hybrid systems, co-immunoprecipitation experiments, bimolecular fluorescence complementation assays and a split-LUC complementation assay. At the protein structural level, we want to purify some of the AVR proteins for protein structure determination. As these proteins have relatively small sizes of around 100 amino acids, structure determinations should be feasible once crystals are obtained. Structural information will then be combined with functional and biochemical studies. This should result in a detailed mechanistic understanding of the specificity of the interactions. Finally, we will continue our genetic approaches on both the host and the pathogen to identify novel factors involved in the determination of specificity of interactions within one host as well as of adaptation to new host species. Building on ongoing work, we will perform a molecular analysis of wheat Lr34 and maize Htn1 gene functions which are both contributing to quantitative disease resistance against fungal diseases in cereals. We want to study allelic and functional diversity of the maize Htn1 resistance gene and possibly related genes. Furthermore, the durable, quantitatively acting wheat resistance gene Lr34 will be functionally analyzed in heterologous cereal species such as barley, rice and maize for its role in conferring a unique, partial resistance phenotype. The work should also allow us to generate hypotheses on additional components involved in durable pathogen resistance.