A Plant Immune Receptor Adopts a Two-Step Recognition Mechanism to Enhance Viral Effector Perception

Mol Plant. 2019 Feb 4;12(2):248-262. doi: 10.1016/j.molp.2019.01.005. Epub 2019 Jan 11.

Abstract

Plant intracellular nucleotide binding leucine-rich repeat (NLR) immune receptors play critical roles in pathogen surveillance. Most plant NLRs characterized so far were found to use a single domain/sensor to recognize pathogen effectors. Here we report that the Sw-5b NLR immune receptor uses two distinct domains to detect the viral movement protein NSm encoded by tospovirus. In addition to its leucine-rich repeat (LRR) domain that has been previously reported, the N-terminal Solanaceae domain (SD) of Sw-5b also interacts with NSm and a conserved 21-amino-acid region of NSm (NSm21). The specific interaction between Sw-5b SD and NSm is required for releasing the inhibitory effect of coiled-coil domain on the NB-ARC-LRR region. Furthermore, we found that the binding of NSm affects the nucleotide binding activity of the NB-ARC-LRR in vitro, while Sw-5b NB-ARC-LRR is activated only when NSm and NSm21 levels are high. Interestingly, Sw-5b SD could significantly enhance the ability of the NB-ARC-LRR to detect low levels of NSm effector and facilitate its activation and induction of defense response. An Sw-5b SD mutant that is disrupted in NSm recognition failed to enhance the ability of the NB-ARC-LRR to sense low levels of NSm and NSm21. Taken together, our results suggest that Sw-5b SD functions as an extra sensor and the NB-ARC-LRR as an activator, and that Sw-5b NLR adopts a two-step recognition mechanism to enhance viral effector perception.

Keywords: Solanaceae domain (SD); defense response; nucleotide binding leucine-rich repeat (NLR) immune receptors; pathogen perception; plant innate immunity; two-step recognition.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Lycopersicon esculentum / immunology
  • Lycopersicon esculentum / metabolism*
  • Lycopersicon esculentum / virology*
  • Plant Immunity*
  • Plant Proteins / chemistry*
  • Plant Proteins / metabolism*
  • Protein Binding
  • Protein Domains
  • Substrate Specificity
  • Tospovirus / physiology*
  • Viral Proteins / metabolism

Substances

  • Plant Proteins
  • Viral Proteins