13 ERA-CAP: Functional characterisation and validation of nonhost components in Triticeae species for durable resistance against fungal diseases

Nonhost resistance (NHR) is the most durable and broadly acting form of resistance plants posses to ward off the majority of pathogen attacks regularly occurring within the environment they are living in. In order to exploit NHR in future crop protection concepts we need to understand why the minority of adapted host pathogens can circumvent or suppress NHR and what defense- or accommodation-related proteins, signalling pathways or structural components of their host plants are targeted in order to establish disease. A major obstacle to the rapid exploitation of NHR in crop breeding is related to the fact that NHR is operating at the species level, and only in exceptional cases corresponding sources of resistance can be crossed with related crop plants. Therefore, gene technological approaches to transfer nonhost-resistance components across species barriers are an attractive alternative to traditional or molecular breeding.

In the ERA-NET consortium TritNONHOST, plus a number of related projects e.g. funded within the German GABI program (BMBF), we identified a number of genes and genetic loci in barley and wheat that are associated or correlated with NHR to three major fungal pathogens including powdery mildews. A limited set of those belonging to the group of receptor-like kinases were successfully validated in functional transient assays in barley and wheat and will provide an important source for the proposed work in the DURESTrit consortium, in addition to resistance loci derived from the wild barley species Hordeum bulbosum or from experimental barley populations segregating for NHR strength. In DURESTrit, we propose to functionally validate receptor-like kinase genes plus a limited number of genes with outstanding regulation behaviour in host- versus nonhost interactions both in barley and wheat by generating and characterizing stable transgenic and backcross lines from wild barley introgressions, respectively. These materials will either carry transgenes or genome fragments from NHR donors, or have potentially important resistance components silenced by RNAi or genetically modified using TALEN technology.

The project will result in the validation of previously identified strong NHR candidates , with a special emphasis on receptor-like kinases, and in the identification of new NHR components introduced into barley or wheat by wide crosses or genetic engineering. This will deepen our understanding of NHR in cereals and provide materials and know-how for the exploitation of NHR by translational research.

DURESTrit will address the objectives within six scientific work packages (WP) that are organized along a gradual shift from the validation and potential use of previously identified NHR genes and loci to the discovery of additional NHR components and study of molecular interactions between pathogen-derived effector-, host target and corresponding nonhost (non)target molecules.

In WP 1 and 2 the focus will be on the identification and validation of genes in barley that underlie NHR to Bgh, along with three barley receptor-like kinase genes already shown to confer nonhost-like resistance in wheat upon transient expression.

In WP 3, the receptor-like kinase genes will be knocked down by RNAi and knocked out by TALEN-mediated, targeted mutagenesis in order to undertake comparative analyses of their role in host basal resistance to Bgh and NHR to Bgt.

In WP4 novel candidate genes for NHR, derived from a large-scale transcript profiling and gene-mapping approachs in wheat and barley, will be functionally tested by virus-induced gene silencing (VIGS) leading to the validation of additional NHR genes.

In WP5 and WP6 the link between gene function in barley for NHR or fungal accommodation and effector-gene function in Bgh will be made by a systematic protein-protein interaction screen and by functional assays such as host-induced gene silencing of interacting candidates in Bgh and CSEP delivery /expression (transient and stable transgenics).

DURESTrit addresses the strategic, international priorities of Global Food Security through sustainable agricultural practises with low environmental impact. The research underpins the effective and sustainable exploitation of disease resistance in our cereal crops, namely wheat and barley, providing knowledge, genetic resources and tools to deliver durable broad-spectrum resistance. While numerous studies have dissected the genetic pathways conferring disease resistance in non-crop model plants, we know very little about how these findings relate to disease resistance in our major crops. This project addresses this serious gap in our knowledge, looking at the roles of candidate NHR genes, including three RLK in plant-pathogen interactions in wheat and barley, and the fungal effectors responsible for disease in the barley powdery mildew pathogen. The barley RLKs in the focus of the DURESTrit consortium have been identified in previous projects at IPK as being implicated in NHR in barley and wheat, and now need to be functionally characterised more precisely and tested for their potential value in conferring NHR-like disease control. Thus, the research outputs from DURESTrit will strongly capitalize on previous achievements of partners and may impact on agricultural production by providing novel resistant cereal varieties, lowering chemical inputs and providing positive outcomes for the European economy, environment and society.

The completion of the genomic sequence of barley and wheat will revolutionise research on Europe's major cereal crops. It is therefore imperative that the European science base ensures that the necessary scientific expertise, tools and resources are in place to take maximum advantage of these invaluable resources. This project will provide advanced training for 4 PhD students and 4 early-stage researchers (post-docs), providing them with the knowledge and skill base to undertake functional genomics and advanced genetic studies in cereals, besides offering scientific exchanges between European and US partners, e.g. by secondments.