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Infection Structure-Specific Reductive Iron Assimilation Is Required for Cell Wall Integrity and Full Virulence of the Maize Pathogen Colletotrichum graminicola

June 2013 , Volume 26 , Number  6
Pages  695 - 708

Emad Albarouki1 and Holger B. Deising1,2

1Interdisziplinäres Zentrum für Nutzpflanzenforschung and 2Institut für Agrar- und Ernährungswissenschaften, Phytopathologie und Pflanzenschutz, Martin-Luther-Universität Halle-Wittenberg, Betty-Heimann-Str. 3, D-06120 Halle (Saale), Germany

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Accepted 20 February 2013.

Ferroxidases are essential components of the high-affinity reductive iron assimilation pathway in fungi. Two ferroxidase genes, FET3-1 and FET3-2, have been identified in the genome of the maize anthracnose fungus Colletotrichum graminicola. Complementation of growth defects of the ferroxidase-deficient Saccharomyces cerevisiae strain Δfet3fet4 showed that both Fet3-1 and Fet3-2 of C. graminicola represent functional ferroxidases. Expression of enhanced green fluorescent protein fusions in yeast and C. graminicola indicated that both ferroxidase proteins localize to the plasma membrane. Transcript abundance of FET3-1 increased dramatically under iron-limiting conditions but those of FET3-2 were hardly detectable. Δfet3-1 and Δfet3-2 single as well as Δfet3-1/2 double-deletion strains were generated. Under iron-sufficient or deficient conditions, vegetative growth rates of these strains did not significantly differ from that of the wild type but Δfet3-1 and Δfet3-1/2 strains showed increased sensitivity to reactive oxygen species. Furthermore, under iron-limiting conditions, appressoria of Δfet3-1 and Δfet3-1/2 strains showed significantly reduced transcript abundance of a class V chitin synthase and exhibited severe cell wall defects. Infection assays on intact and wounded maize leaves, quantitative data of infection structure differentiation, and infection stage-specific expression of FET3-1 showed that reductive iron assimilation is required for appressorial penetration, biotrophic development, and full virulence.

© 2013 The American Phytopathological Society