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Identification and characterization of host-specifically-induced effectors

The general term “effector” in plant-microbe interactions is applied to proteins which are secreted by the microbe and have a crucial role in host colonization by interfering with the plant defense system or metabolism. Effector-proteins are often referred to as small secreted proteins (SSPs < 300 aa). Indeed many of the functionally characterized effector proteins fall in this category. In general the majority of the in planta-induced SSPs from P. indica were either Arabidopsis or barley responsive, suggesting that colonization of different hosts may require exploitation of distinct effectors that can interact with elements characteristic to each host. We could show that one effector, Dld1, expressed during colonization of barley, belongs to a large paralogous family (named DELD) whose members show a regular distribution of histidines. In cooperation with Prof. Andrei Lupas and Dr. Jörg Martin (MPI for Developmental Biology, Tübingen) the crystal structure of Dld1 has been solved. This small protein proved to be a novel histidine- zipper with an antiparallel helical hairpin with coiled-coil packing and histidine residues along one face of the hairpin.