Remodeling of cytokinin metabolism at infection sites of Colletotrichum graminicola on maize leaves

Behr M.*, Motyka V.*, Weihmann F., Malbeck J., Deising H.B., Wirsel S.G.R. (*contributed equally)

Klíčová slova: Colletotrichum graminicola, maize, cytokinin, green islands, senescence, infection, zeatin
Abstrakt: 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 HPLC/MS/MS methodology, we analyzed changes in the patterns and levels of cytokinins (CKs) at high spatial and analytical resolution. Twenty individual CKs were detected in green islands. Levels of cis-zeatin-9-riboside and cis-zeatin-9-riboside-5´-monophosphate increased drastically, whereas those of the most prominent CK, cis-zeatin-O-glucoside, decreased. The fungus likely performed these conversions since corresponding activities were also detected in in vitro cultures amended with CKs. We found no evidence that C. graminicola is able to synthesize CKs 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, were formed. After applying CKs onto uninfected leaves, transcripts of marker genes for senescence, photosynthesis, and assimilate distribution were measured by qRT-PCR, and furthermore PAM (Pulse-Amplitude-Modulation) chlorophyll fluorometry and SPAD (Single-Photon Avalanche Diode) analyses were conducted. These experiments suggested that modulation of CK metabolism at the infection site affects host physiology.
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Autoři z ÚEB: Jiří Malbeck, Václav Motyka