Universal resistance mechanism discovered in plants
Plants have a natural defense system with which they can protect themselves against pathogens such as fungi, bacteria or viruses. A particularly effective resistance mechanism against the powdery mildew fungus has long been known in barley plants. Scientists led by Ralph Panstruga from the Max Planck Institute for Plant Breeding Research in Cologne, together with colleagues from the USA, have discovered that this so-called mlo resistance also works in other plant species. In principle, this should make it possible in the future to combat crop damage caused by powdery mildew in a more targeted manner and with fewer chemicals.
Despite intensive plant protection measures, around 30 percent of the world harvest is lost to plant diseases. Immense harvest losses are caused annually, among other things, by the powdery mildew fungus. In barley, the so-called mlo mutants have been known for about sixty years, which very efficiently block all attempts by the powdery mildew fungus to attack these cereal plants at a very early stage. In agriculture, the mlo -related powdery mildew resistance in barley has been used intensively for 25 years. In Central Europe, about fifty percent of the barley cultivars currently grown have this form of resistance. However, until recently, no other plant species was known to have a similarly effective immunity to powdery mildew. It was therefore assumed that mlo resistance is a barley-specific phenomenon. The special feature of mlo resistance is that it is not caused by the presence of a resistance protein, but by the absence of a protein that is probably used by the fungal pathogen as a portal of entry.
However, recent genetic studies with thale cress (Arabidopsis thaliana), a dicotyledonous plant as opposed to monocotyledonous barley, revealed that this model plant also possesses the traits of natural powdery mildew resistance. However, the formation of three Mlo proteins must fail in Arabidopsis in order to ensure full protection against the pathogen. Also known as "genetic redundancy", this phenomenon may explain why mlo resistance has not yet been found in more plant species.
The fact that Mlo protein-depleted immunity works in both monocots (barley) and dicots (Arabidopsis) suggests that the pathogenetic mechanism of the respective powdery mildew fungi has evolved at least since of the phylogenetic splitting of monocotyledonous and dicotyledonous plants from about 200 million years ago. This finding further shows that it should in principle be possible to generate mlo -resistant mutants in any higher plant species. Against the background of around 500 powdery mildew species distributed worldwide and the high agronomic relevance of these pathogens, this is an extremely important finding. © Max Planck Society
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