Project

wheat; disease resistance; fungal pathogenomics; avirulence genes; gene suppression; durable disease resistance; sustainable resistance

Lead
Lay summary
Pilzliche Krankheitserreger verursachen bei Kulturpflanzen weltweit grosse Ernteverluste. Im Genpool von Weizen gibt es vererbbare (genetische) Resistenz gegen gewisse Krankheitserreger. In dem Projekt sollen die molekularen und biochemischen Grundlagen dieser Resistenz erforscht werden.Die natürliche, genetisch bedingte Krankheitsresistenz in Kulturpflanzen ist in der Pflanzenzüchtung von grosser Bedeutung. Sie erlaubt es, Ernteverluste zu reduzieren und den Einsatz von chemischen Fungiziden zu reduzieren. Oft können sich aber Krankheitserreger an Resistenzen anpassen und Resistenzgene damit nutzlos machen. Es ist deshalb wichtig, die Mechanismen besser zu verstehen, wie Krankheitserreger Resistenzen überwinden können. Andererseits gibt es einige wenige Resistenzgene, die seit vielen Jahren genutzt werden und für die bisher keine Anpassung der Pilzpathogene gefunden wurde. Die molekulare Grundlage dieser dauerhaften Resistenz ist noch wenig verstanden. Wir haben in den letzten Jahren ein in Weizen seit mehr als 40 Jahren wirksames Resistenzgen (Lr34 genannt) gegen Braunrost isoliert. Es kodiert für ein Transportprotein in der pflanzlichen Membran. Ebenfalls haben wir ein spezifisches Resistenzgen gegen Mehltau isoliert, das in vielen Formen vorkommt, aber als einzelnes Gen jeweils nur gegen einige, nie aber alle, Rassen des Mehltaupilzes Resistenz vermittelt.In diesem Projekt soll der genaue molekulare und biochemische Mechanismus der Lr34-vermittelten, dauerhaften Resistenz charakterisiert werden. Zudem soll, aufbauend auf einem zu erarbeitenden, detaillierten molekularen Verständnis der Interaktion zwischen Weizen und dem Mehltaupathogen, die Möglichkeiten einer Verbesserung der spezifischen Krankheitsresistenz geprüft werden. Dazu soll auch das gesamte Erbgut des Mehltaupilzes entschlüsselt werden.Die Resultate dieser Arbeit führen zu einem besseren Verständnis der Interaktion von Weizen und pathogenen Pilzen. Dieses Wissen kann in der Pflanzenzüchtung auf vielfältige Weise genutzt werden. Das Projekt bietet Doktorierenden und Postdocs eine ideale Basis für eigene Forschungsarbeiten und zur Qualifikation für eine weitere wissenschaftliche Laufbahn im Gebiet der pflanzlichen und agronomischen Molekularbiologie. Schliesslich tragen diese molekularen Arbeiten an der Kulturpflanze Weizen bei zur Diskussion von Nutzen und Risiken gentechnisch veränderter Nutzpflanzen.

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Last update: 21.02.2013

Self-organised

Number	Title	Start	Funding scheme

Bread wheat (Triticum aestivum L.) is an allohexaploid plant (2n=6x=42) containing the three closely related homoeologous A, B and D genomes. Wheat is grown on more than 200 million hectares worldwide, with a production of more than 600 million tons annually, representing together with rice the most important crop for human nutrition. Wheat is attacked by a large number of pathogens, mostly of fungal origin. The decades of modern resistance breeding, and the selection by farmers during the millennia before, have produced a rich resource of resistance traits. These traits are genetically well characterized, and most importantly, their function has been studied in agricultural systems for many years. The available data, e.g. on durability or environmental dependence, are highly valuable and represent an important advantage compared to model plants where no long term data are available. The mildew and the three rust diseases of wheat are among the 8-10 most relevant wheat diseases at the global level. The molecular analysis and biology of resistance traits against these diseases is the focus of this proposal. We have recently cloned the Lr34 resistance gene which has provided durable, partial resistance against leaf rust, stripe rust and powdery mildew for more than 50 years in wheat cultivars grown on very large acreage. We found that Lr34 resistance is conferred by a single gene encoding a PDR protein belonging to the ABC transporters. To understand the molecular basis of the Lr34 based durable resistance we want to study its function at the genetic and biochemical level. The three molecular polymorphisms between the susceptible and resistant allele will be separately tested for functional importance by transformation into wheat and possibly barley. In rice, Lr34 function will be studied in a knock-out mutant of the closely related Lr34 homolog. Lr34 function will be studied as far as possible in diploid systems, but work in bread wheat is also essential as a Lr34-type of resistance has only been described in hexaploid wheat so far. A putative dominant negative effect of a Lr34 mutant might be caused by direct or indirect interaction with proteins derived from homoeologous loci on the A and B genomes, possibly contributing to basal resistance. By tilling of these genes and subsequent mutant combination, we will test if the triple mutants are affected in basal resistance to host and non-host pathogens. The Arabidopsis protein PEN3 functions in non-host resistance and is homologous to LR34. Therefore, we hypothesize, in analogy to the putative function in Arabidopsis, that Lr34 is involved in the transport of an antimicrobial compound. Candidate molecules will be tested in a yeast system. The cloning of an allelic series of functional Pm3 powdery mildew resistance genes in our lab has resulted in a better understanding of function and specificity. Based on the recent finding that a susceptible allele of Pm3 (Pm3CS) is a potential suppressor of the rye Pm8 resistance gene, we want to clone Pm8. Pm8 is a putative Pm3 ortholog in rye and we want to study its evolutionary and functional relatedness to Pm3. In addition, we will analyze at the molecular level the suppression mechanism of a resistance gene, a phenomen observed quite frequently in wheat. Finally, the localization of the PM3 proteins will be studied in view of later experiments with the AVRPM3 interactors where we will also profit from using the molecular diversity of Pm3 alleles.In a third set of experiments, we want to clone AvrPm3 from wheat mildew to understand Pm3-based resistance by molecular interaction studies of R and AVR proteins. A cross of two mildew isolates has already been established and sequencing of the wheat powdery mildew genome is in progress. We have also made a high quality BAC library, and, thus, all the tools are now available for a map-based cloning approach. The genomic sequence of the pathogen that will be established during the project will also be used for a number of approaches in pathogenomics to better understand the molecular basis of the biotrophic lifestyle of this pathogen.The proposed work in the three topics is expected to significantly contribute to an improved molecular understanding of both broad-spectrum, durable resistance as well as specific fungal disease resistance in wheat.