Fungal transporters involved in efflux of natural toxic compounds and fungicides

Survival of microorganisms in natural environments is favored by the capaci ty to produce compounds toxic to competing organisms and the ability to res ist the effects of such toxic compounds. Both factors contribute to a compe titive advantage of organisms in ecosystems. All organisms have evolved act ive transport mechanisms by which endogenous and exogenous toxicants can be secreted. Two major classes of transporter proteins are the ATP-binding ca ssette (ABC) and the major facilitator superfamily (MFS) transporters, Memb ers of both classes can have broad and overlapping substrate specificities for natural toxic compounds and can be regarded as a "first-line defense ba rrier" in survival mechanisms, In plant pathogens, these transporters can p lay an essential role in protection against plant defense compounds during pathogenesis, Also, some transporters actively secrete host-specific and no nhost-specific toxins, Remarkably, ABC and MFS transporters can also play a major role in fungicide sensitivity and resistance. Their role in multidru g resistance of Aspergillus nidulans, Candida albicans, and Saccharomyces c erevisiae to azoles and other fungitoxic compounds is well established. Kno wledge of ABC and MFS transporters opens possibilities of developing novel strategies for controlling plant diseases, either by modulation of transpor ter activity or by transgenic expression of transporter genes in plants. (C ) 2000 Academic Press.