Establishment of biotrophy by parasitic fungi and reprogramming of host cells for disease resistance.

Parasitic biotrophs such as mildews and rusts evolved specific mechanisms that keep host cells alive during infection. These fungi appear to absorb nutrients mainly by proton-symport-driven transporter proteins that reside in specialized feeding structures. Accumulating evidence suggests that biotrophic fungi both suppress induction of plant defense responses in physical proximity to infection sites and induce specific host genes for the establishment of biotrophy. The peculiarities of biotrophic pathogenesis likely reflect diverse types of plant disease-resistance responses. The cloning of race-specific resistance genes to powdery mildew infection and of genes required for their function provides first insights into molecular mechanisms enabling the host to recognize mildew effector components and suggests candidate mechanisms of resistance signaling. Resistance to powdery mildew fungi that result from mutations in host genes promises to shed light on mechanisms that are required for the establishment of disease susceptibility.