Ustilago maydis attacks and reproduces in the aerial parts of the corn plant. Huge tumor-like tissue growth often form at the site of infection. These galls can reach the size of a child's head. The growths are triggered by molecules released by the fungus, called effectors. They manipulate the plant's metabolism and suppress its immune system. They also promote cell growth and division in corn. To do this, they interfere with a plant signaling pathway regulated by the plant hormone auxin.
"The fungus uses this auxin signaling pathway for its own purposes," explains Prof. Dr. Armin Djamei, who heads the Plant Pathology Department at the INRES Institute of the University of Bonn. "This is because the huge growth of the tissue devours energy and resources that are then lacking for defense against Ustilago maydis. In addition, the fungus finds an ideal supply of nutrients in the growths and can multiply well there." The formation of the characteristic galls is thus definitely in the interest of the pathogen.
"We therefore wanted to find out how the fungus promotes these proliferation processes," says Djamei. "To do this, we searched for genetic material in the fungus that enables it to control the auxin signaling pathway of its host plant and thus its cell growth." The complex search began seven years ago at the Gregor Mendel Institute in Vienna. Later, the crop researcher continued the work at the Leibniz Institute in Gatersleben and later at the University of Bonn.
Pathogen reprograms its host