Abstract
Author SummaryThe plant parasitic fungus Ustilago maydis is a biotrophic pathogen that depends on live plant tissue for development. It is highly adapted to maize (Zea mays), where it causes the corn smut disease. Fungal cells growing within the plant apoplast are surrounded by the host plasma membrane at all growth stages, thereby establishing tight interaction zones with the host cells that assure optimal access to host-derived nutrients, including organic carbon sources. Here, we focus on the previously unknown feeding mechanisms of this plant pathogen within its host plant. We identified a fungal plasma membrane transporter, Srt1, that is expressed exclusively after plant infection and that turns out to be essential for virulence development of Ustilago in infected plants. Srt1 is the first characterized fungal transporter that allows direct utilization of sucrose without extracellular hydrolysis into monosaccharides, the carbon form more commonly taken up by pathogenic fungi. It is highly specific for sucrose, and its affinity largely exceeds that of equivalent plant transporters. This not only provides advantages for the carbon acquisition by the pathogen, but quite likely also offers a mechanism to prevent induction of plant defense responses known to occur upon apoplastic sucrose hydrolysis.
Highlights
Plant pathogenic fungi cause major yield losses and affect the quality and safety of food and feed produced from infected plant material
The plant parasitic fungus Ustilago maydis is a biotrophic pathogen that depends on live plant tissue for development
Fungal cells growing within the plant apoplast are surrounded by the host plasma membrane at all growth stages, thereby establishing tight interaction zones with the host cells that assure optimal access to host-derived nutrients, including organic carbon sources
Summary
Plant pathogenic fungi cause major yield losses and affect the quality and safety of food and feed produced from infected plant material. Different fungi have developed different strategies to deal with their hosts. Other fungi start with a biotrophic infection and switch to necrotrophic behavior at later stages of infection or under certain environmental conditions (hemibiotrophic fungi). Recognition of such pathogens by infected plants typically results in the production of reactive oxygen species and in hypersensitive cell death [1]. The most important challenge for all pathogens is, the development of strategies allowing the avoidance of signals potentially recognized by the host
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