Structure and function of rust haustoria
K. Mendgen, C. Struck, M. Hahn, and R. T. Voegele
Lehrstuhl für Phytopathologie, Fachbereich Biologie der Universität
Konstanz, 78434 Konstanz, Germany
Fachbereich Biologie, Phytopathologie, Universität Kaiserslautern,
Rust fungi are among the most common plant diseases infecting more then
8000 monocot and over 40 000 dicot species. These parasites are obligate
biotrophs. They differentiate infection structures such as appressoria
over stomatal openings to enter the leaf and develop haustoria within
host cells. High-pressure freezing and freeze substitution of haustoria
revealed a matrix between the plasma membranes of host and parasite that
serves as apoplastic space probably used for nutrient transfer. Gene expression
in haustoria of Uromyces fabae, the broad bean rust fungus, is differentially
regulated. Some 20 % of the mRNA population is found mainly in haustoria,
and not at all or only at very low levels in spores and the other early
infection structures, respectively.
Highly expressed genes were sequenced and the function of the most abundant
proteins was elucidated. Immunolabelling showed that the fungus secretes
invertase into the extrahaustorial matrix. An H+-ATPase is located in
the fungal plasma membrane and pumps protons into this fungus-plant interface.
A proton-hexose cotransporter pumps glucose and fructose into the haustoria.
Within the haustorium, hexoses are metabolized, but are also converted
to mannitol and other hexitols. These compounds are likely to serve as
storage metabolites, in osmoprotection and/or protection from free radicals.
We characterized several amino acid transporters active in haustoria by
heterologous expression in yeast and Xenopus oocytes. These transporters
are specific for amino acids exhibiting only low concentrations in the
Our data indicate that the rust haustorium is one, if not the main source
and distributor of amino acids and carbohydrates for the rust fungus.
Its specific role makes it a target to control rust diseases.
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haustoria in sugar supply during infection of Vicia faba by the rust fungus
Uromyces fabae. Proc. Natl. Acad. Sci. U.S.A. 98, 8133 - 8138
2. Hahn, M, Mendgen, K. (2001) Signal and nutrient exchange at biotrophic
plant-fungus interfaces. Curr. Op. in Plant Biol. 4, 322-327
3. Struck, C., Ernst, M., Hahn, M. (2002) Characterization of a developmentally
regulated amino acid transporter (AAT1p) of the rust fungus Uromyces fabae.
Mol. Plant Pathol. 3, 23-30