Multiple variants of the fungal effector AVR-Pik bind the HMA domain of the rice protein OsHIPP19, providing a foundation to engineer plant defense

J Biol Chem. 2021 Jan-Jun:296:100371. doi: 10.1016/j.jbc.2021.100371. Epub 2021 Feb 4.


Microbial plant pathogens secrete effector proteins, which manipulate the host to promote infection. Effectors can be recognized by plant intracellular nucleotide-binding leucine-rich repeat (NLR) receptors, initiating an immune response. The AVR-Pik effector from the rice blast fungus Magnaporthe oryzae is recognized by a pair of rice NLR receptors, Pik-1 and Pik-2. Pik-1 contains a noncanonical integrated heavy-metal-associated (HMA) domain, which directly binds AVR-Pik to activate plant defenses. The host targets of AVR-Pik are also HMA-domain-containing proteins, namely heavy-metal-associated isoprenylated plant proteins (HIPPs) and heavy-metal-associated plant proteins (HPPs). Here, we demonstrate that one of these targets interacts with a wider set of AVR-Pik variants compared with the Pik-1 HMA domains. We define the biochemical and structural basis of the interaction between AVR-Pik and OsHIPP19 and compare the interaction to that formed with the HMA domain of Pik-1. Using analytical gel filtration and surface plasmon resonance, we show that multiple AVR-Pik variants, including the stealthy variants AVR-PikC and AVR-PikF, which do not interact with any characterized Pik-1 alleles, bind to OsHIPP19 with nanomolar affinity. The crystal structure of OsHIPP19 in complex with AVR-PikF reveals differences at the interface that underpin high-affinity binding of OsHIPP19-HMA to a wider set of AVR-Pik variants than achieved by the integrated HMA domain of Pik-1. Our results provide a foundation for engineering the HMA domain of Pik-1 to extend binding to currently unrecognized AVR-Pik variants and expand disease resistance in rice to divergent pathogen strains.

Keywords: (NLR); nucleotide-binding leucine-rich repeat protein; plant biochemistry; plant defense; protein structure; protein–protein interaction; receptor structure–function; virulence factor.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alleles
  • Ascomycota / genetics*
  • Ascomycota / metabolism
  • Ascomycota / pathogenicity
  • Disease Resistance / genetics
  • Disease Resistance / immunology*
  • Host-Pathogen Interactions / immunology
  • Magnaporthe / immunology
  • Models, Molecular
  • NLR Proteins / metabolism
  • Oryza / genetics
  • Oryza / metabolism
  • Plant Diseases / microbiology
  • Plant Proteins / metabolism


  • NLR Proteins
  • Plant Proteins

Supplementary concepts

  • Pyricularia oryzae