Characterization of the ABC transporter genes MgAtr1 and MgAtr2 from the wheat pathogen Mycosphaerella graminicola

ATP-binding cassette (ABC) transporters are membrane-bound transporters involved in various physiological processes. In this paper we describe the cloning of the ABC transporter encoding genes MgAtr1 and MgAtr2 from the wheat pathogen Mycosphaerella graminicola (anamorph Septoria tritici). Both deduced proteins MgAtr1 and MgAtr2 are highly homologous to other fungal ABC transporters. RT-PCR revealed that the MgAtr2 mRNA population consists of partially and fully spliced transcripts. Putative substrates of ABC transporters, modulators of ABC transporter activity, and inducers of ABC transporter gene transcription were analyzed for their potential to induce expression of MgAtr1 and MgAtr2 in m. graminicola. The genes are differently upregulated by compounds such as the plant secondary metabolites eugenol and reserpine. Similar results are obtained for several antibiotics and the azole fungicides cyproconazole and imazalil. Moreover, a different expression pattern between yeast-like cells and mycelium of this dimorphic fungus was observed. These results indicate that MgAtr1 and MgAtr2 play a role in protection of m. graminicola against natural toxic compounds and xenobiotics. A putative role in protection against plant defense compounds during pathogenesis is suggested.