Characterization of an antimicrobial and phytotoxic ribonuclease secreted by the fungal wheat pathogen Zymoseptoria tritici

Graeme Kettles, Carlos Bayon, Caroline A Sparks, Gail Canning, Kostya Kanyuka, Jason J. Rudd

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18 Citations (Scopus)
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The fungus Zymoseptoria tritici is the causal agent of Septoria Tritici Blotch (STB) disease of wheat leaves. Zymoseptoria tritici secretes many functionally uncharacterized effector proteins during infection. Here, we characterized a secreted ribonuclease (Zt6) with an unusual biphasic expression pattern. Transient expression systems were used to characterize Zt6, and mutants thereof, in both host and non-host plants. Cell-free protein expression systems monitored the impact of Zt6 protein on functional ribosomes, and in vitro assays of cells treated with recombinant Zt6 determined toxicity against bacteria, yeasts and filamentous fungi. We demonstrated that Zt6 is a functional ribonuclease and that phytotoxicity is dependent on both the presence of a 22-amino-acid N-terminal 'loop' region and its catalytic activity. Zt6 selectively cleaves both plant and animal rRNA species, and is toxic to wheat, tobacco, bacterial and yeast cells, but not to Z. tritici itself. Zt6 is the first Z. tritici effector demonstrated to have a likely dual functionality. The expression pattern of Zt6 and potent toxicity towards microorganisms suggest that, although it may contribute to the execution of wheat cell death, it is also likely to have an important secondary function in antimicrobial competition and niche protection.

Original languageEnglish
Pages (from-to)320-331
Number of pages12
JournalNew Phytologist
Issue number1
Early online date12 Sept 2017
Publication statusPublished - Jan 2018


  • Anti-Infective Agents/isolation & purification
  • Ascomycota/enzymology
  • Cell Death/drug effects
  • Fungal Proteins/genetics
  • Microbiota/drug effects
  • Mycotoxins/genetics
  • Plant Diseases/microbiology
  • Plant Leaves/microbiology
  • Ribonucleases/genetics
  • Triticum/microbiology


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