International Symposium on Cereal Leaf Blights 2019 | University College Dublin, Ireland | 22-24 May 2019

Structure analysis uncovers a novel effector family related to Ustilago killer proteins in Zymoseptoria tritici

Karine de Guillen
CNRS UMR5048, CBS, Montpellier, France

Thomas Kroj
UMR BGPI, INRA, Baillarguet, Montpellier, France

Anne Genissel
UMR BIOGER INRA Campus AgroParisTech Thiverval-Grignon France

Barthe Philippe
CNRS UMR5048, CBS, Montpellier, France

Hoh François
CNRS UMR5048, CBS, Montpellier, France

Marc-Henri LeBrun*
UMR BIOGER INRA Campus AgroParisTech Thiverval-Grignon France

Padilla André
CNRS UMR5048, CBS, Montpellier, France

Poster Presentation
Pathogen Functional Genetics and Genomics

Atrium, UCD O'Brien centre for Science
Poster 25

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Zymoseptoria tritici has a large number of secreted protein effectors coding genes, most of which are expressed during infection of wheat leaves. We determined the 3-dimensional structure of Z. tritici effector Mycgr3-91409. Previous structure-based HMM pattern searches suggested that Mycgr3-91409 is the only representative of the MAX (Magnaporthe AVRs and ToxB) effector family in Z. tritici. MAX effectors have a conserved β-sandwich fold and highly diverse primary protein sequences. Mycgr3-91409 was expressed in E. coli without its signal peptide and the purified protein was analysed for its 3D structure by NMR spectroscopy, and X-ray crystallography. Mycgr3-91409 had a α/β-sandwich structure completely different from MAX effector, but similar to KP6 killer proteins from Ustilago maydis. KP6α and KP6β are forming a protein complex toxic to non-producing fungi. Accordingly, Mycgr3-91409 was named Zt-KP6-1. Zt-KP6-1 orthologs were identified in Z tritici populations and in closely related species Z. brevis, but not in other fungi. Survey of Zt-KP6-1 genetic diversity, indicated that it was subjected to purifying selection, suggesting a functional role for this protein. A paralog of Zt-KP6-1, Mycgr3-96389, was identified in Z. tritici and in related species Z. pseudotritici and Z. ardabiliae, but not in other fungi. Structure modeling suggested that Mycgr3-96389 had the same protein fold as KP6α and Zt-KP6-1, and it was named Zt-KP6-2. RNAseq data indicated that Zt-KP6-1 and Zt-KP6-2 were not expressed during fungal growth in vitro, but they were highly expressed during the asymptomatic phase of wheat leaf infection. Therefore, these two proteins are interesting candidate effectors, expressed specifically during infection. It will be interesting to determine whether these effectors have a toxic activity on fungi and/or plants. These experiments also clearly showed that determining the 3D structure of effectors, is a powerful method to assign these proteins to families.