Molecular Plant-Microbe Interactions (2014) 27, 315-327

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Nancy Ludwig, Marco Löhrer, Marcus Hempel, Sebastian Mathea, Ivo Schliebner, Matthias Menzel, Andreas Kiesow, Ulrich Schaffrath, Holger B. Deising and Ralf Horbach (2014)
Melanin is not required for turgor generation but enhances cell-wall rigidity in appressoria of the corn pathogen Colletotrichum graminicola
Molecular Plant-Microbe Interactions 27 (4), 315-327
Abstract: The ascomycete and causative agent of maize anthracnose and stem rot, Colletotrichum graminicola, differentiates melanized infection cells called appressoria that are indispensable for breaching the plant cell wall. High concentrations of osmolytes accumulate within the appressorium, and the internal turgor pressure of up to 5.4 MPa provides sufficient force to penetrate the leaf epidermis directly. In order to assess the function of melanin in C. graminicola appressoria, we identified and characterized the polyketide synthase 1 (CgPKS1) gene which displayed high similarity to fungal polyketide synthases (PKS) involved in synthesis of 1,3,6,8-tetrahydronaphthalene, the first intermediate in melanin biosynthesis. Cgpks1 albino mutants created by targeted gene disruption were unable to penetrate intact leaves and ruptured frequently but, surprisingly, were able to penetrate ultrathin polytetrafluoroethylene membranes mimicking the plant surface. Nonmelanized Cgpks1 appressoria were sensitive to externally applied cell-wall-degrading enzymes whereas melanized appressoria were not affected. Expression studies using a truncated CgPKS1 fused to green fluorescent protein revealed fluorescence in immature appressoria and in setae, which is in agreement with transcript data obtained by RNA-Seq and quantitative polymerase chain reaction. Unexpectedly, surface scans of mutant and wild-type appressoria revealed considerable differences in cell-wall morphology. Melanization of appressoria is indispensable for successful infection of intact leaves. However, cell collapse experiments and analysis of the appressorial osmolyte content by Mach-Zehnder interferometry convincingly showed that melanin is not required for solute accumulation and turgor generation, thus questioning the role of melanin as a barrier for osmolytes in appressoria of C. graminicola.
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Link to article at publishers website
Database assignments for author(s): Ulrich Schaffrath

Research topic(s) for pests/diseases/weeds:
molecular biology - genes

Pest and/or beneficial records:

Beneficial Pest/Disease/Weed Crop/Product Country Quarant.

Colletotrichum graminicola Maize/corn (Zea mays)