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Remodeling of Cytokinin Metabolism at Infection Sites of Colletotrichum graminicola on Maize Leaves

August 2012 , Volume 25 , Number  8
Pages  1,073 - 1,082

Michael Behr,1 Václav Motyka,2 Fabian Weihmann,1 Jiří Malbeck,2 Holger B. Deising,1,3 and Stefan G. R. Wirsel1,3

1Institute of Agricultural and Nutritional Sciences, Faculty of Natural Sciences III, Martin-Luther-University Halle-Wittenberg, Betty-Heimann-Str. 3, D-06120 Halle (Saale), Germany; 2Institute of Experimental Botany, Academy of Sciences of the Czech Republic, Rozvojová 263, CZ-165 02 Prague 6, Czech Republic; 3Interdisziplinäres Zentrum für Nutzpflanzenforschung (IZN), Martin-Luther-Universität Halle-Wittenberg, Betty-Heimann-Str. 3, D-06120 Halle (Saale), Germany

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Accepted 10 April 2012.

When inoculated onto maize leaves at the onset of senescence, the hemibiotroph Colletotrichum graminicola causes green islands that are surrounded by senescing tissue. Taking advantage of green islands as indicators of sites of the establishment of successful infection and of advanced high-performance liquid chromatography tandem mass spectrometry methodology, we analyzed changes in the patterns and levels of cytokinins (CK) at high spatial and analytical resolution. Twenty individual CK were detected in green islands. Levels of cis-zeatin-9-riboside and cis-zeatin-9-riboside-5′-monophosphate increased drastically, whereas that of the most prominent CK, cis-zeatin-O-glucoside, decreased. The fungus likely performed these conversions because corresponding activities were also detected in in vitro cultures amended with CK. We found no evidence that C. graminicola is able to synthesize CK entirely de novo in minimal medium but, after adding dimethylallyl diphosphate, a precursor of CK biosynthesis occurring in plants, a series of trans-zeatin isoforms (i.e., trans-zeatin-9-riboside-5′-monophosphate, trans-zeatin-9-riboside, and trans-zeatin) was formed. After applying CK onto uninfected leaves, transcripts of marker genes for senescence, photosynthesis, and assimilate distribution were measured by quantitative reverse-transcribed polymerase chain reaction; furthermore, pulse-amplitude modulation chlorophyll fluorometry and single-photon avalanche diode analyses were conducted. These experiments suggested that modulation of CK metabolism at the infection site affects host physiology.

© 2012 The American Phytopathological Society