Abstract
Powdery mildew fungi are obligate biotrophic pathogens that only grow on living hosts and cause damage in thousands of plant species. Despite their agronomical importance, little direct functional evidence for genes of pathogenicity and virulence is currently available because mutagenesis and transformation protocols are lacking. Here, we show that the accumulation in barley (Hordeum vulgare) and wheat (Triticum aestivum) of double-stranded or antisense RNA targeting fungal transcripts affects the development of the powdery mildew fungus Blumeria graminis. Proof of concept for host-induced gene silencing was obtained by silencing the effector gene Avra10, which resulted in reduced fungal development in the absence, but not in the presence, of the matching resistance gene Mla10. The fungus could be rescued from the silencing of Avra10 by the transient expression of a synthetic gene that was resistant to RNA interference (RNAi) due to silent point mutations. The results suggest traffic of RNA molecules from host plants into B. graminis and may lead to an RNAi-based crop protection strategy against fungal pathogens.
Highlights
Obligate biotrophic plant pathogens, such as powdery mildew and rust fungi, represent a large group of organisms that together cause diseases on thousands of plant species (Schulze-Lefert and Vogel, 2000; Zhang et al, 2005)
The uptake of doublestranded RNA or small interfering RNA into these animals occurs by sucking or chewing of plant material, followed by resorption in thegut system. Biotrophic fungal pathogens such as B. graminis interact with their corresponding host intimately via a highly specialized cell called a haustorium, which is surrounded by the extrahaustorial matrix bordered by plant and fungal membranes on either side and that represents the interface for signal exchange as well as nutrient uptake (Panstruga, 2003)
Screening for Fungal RNA interference (RNAi) Target Genes To determine whether the accumulation in barley (Hordeum vulgare) cells of doublestranded RNA (dsRNA) or small interfering RNA (siRNA) targeting fungal transcripts could affect the outcome of the interaction with B. graminis, we used RNAi in the host cell to target fungal transcripts and examined the progression of the fungal infection
Summary
Obligate biotrophic plant pathogens, such as powdery mildew and rust fungi, represent a large group of organisms that together cause diseases on thousands of plant species (Schulze-Lefert and Vogel, 2000; Zhang et al, 2005). Biotrophic fungal pathogens such as B. graminis interact with their corresponding host intimately via a highly specialized cell called a haustorium, which is surrounded by the extrahaustorial matrix bordered by plant and fungal membranes on either side and that represents the interface for signal exchange as well as nutrient uptake (Panstruga, 2003) (see Supplemental Figure 1 online). This close contact of the interaction partners might facilitate the exchange of proteins and of RNA as a carrier of biological information affecting the outcome of the interaction. This hypothesis would have far-reaching implications for our understanding of plant–pathogen interactions and disease control
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