Structure Analysis Uncovers a Highly Diverse but Structurally Conserved Effector Family in Phytopathogenic Fungi

PLoS Pathog. 2015 Oct 27;11(10):e1005228. doi: 10.1371/journal.ppat.1005228. eCollection 2015 Oct.

Abstract

Phytopathogenic ascomycete fungi possess huge effector repertoires that are dominated by hundreds of sequence-unrelated small secreted proteins. The molecular function of these effectors and the evolutionary mechanisms that generate this tremendous number of singleton genes are largely unknown. To get a deeper understanding of fungal effectors, we determined by NMR spectroscopy the 3-dimensional structures of the Magnaporthe oryzae effectors AVR1-CO39 and AVR-Pia. Despite a lack of sequence similarity, both proteins have very similar 6 β-sandwich structures that are stabilized in both cases by a disulfide bridge between 2 conserved cysteins located in similar positions of the proteins. Structural similarity searches revealed that AvrPiz-t, another effector from M. oryzae, and ToxB, an effector of the wheat tan spot pathogen Pyrenophora tritici-repentis have the same structures suggesting the existence of a family of sequence-unrelated but structurally conserved fungal effectors that we named MAX-effectors (Magnaporthe Avrs and ToxB like). Structure-informed pattern searches strengthened this hypothesis by identifying MAX-effector candidates in a broad range of ascomycete phytopathogens. Strong expansion of the MAX-effector family was detected in M. oryzae and M. grisea where they seem to be particularly important since they account for 5-10% of the effector repertoire and 50% of the cloned avirulence effectors. Expression analysis indicated that the majority of M. oryzae MAX-effectors are expressed specifically during early infection suggesting important functions during biotrophic host colonization. We hypothesize that the scenario observed for MAX-effectors can serve as a paradigm for ascomycete effector diversity and that the enormous number of sequence-unrelated ascomycete effectors may in fact belong to a restricted set of structurally conserved effector families.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Ascomycota / chemistry*
  • Ascomycota / pathogenicity
  • Fungal Proteins / chemistry
  • Magnetic Resonance Spectroscopy
  • Molecular Sequence Data
  • Protein Structure, Secondary

Substances

  • Fungal Proteins

Grant support

This work was supported by a PhD grant for DO from the Colombian National Agency for the Science and Technology COLCIENCIAS, COLFUTURO (call 528) and by grants from the “Agence nationale de la recherche” of France ANR-10-INSB-05-0 (French Infrastructure for Integrated Structural Biology—FRISBI) to AP, KG and JG, ANR-09-GENM-029 (Analysis and comparison of genomes of the fungal pathogen Magnaporthe oryzae—GEMO) to EF and TK and ANR-07-GPLA-0007 (Molecular bases of disease and resistance in the Interaction of Rice and Magnaporthe grisea – IRMA) to TK. This work benefited from interactions promoted by COST Action FA 1208. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.