Leucine-rich repeat-mediated intramolecular interactions in nematode recognition and cell death signaling by the tomato resistance protein Mi

Plant J. 2003 Jun;34(5):585-93. doi: 10.1046/j.1365-313x.2003.01749.x.

Abstract

The root-knot nematode resistance gene Mi from tomato encodes a nucleotide-binding/leucine-rich repeat (NB/LRR) protein with a novel amino-terminal domain compared to related disease-resistance genes. The closely linked paralog Mi-1.1, which does not confer nematode resistance, encodes a protein 91% identical to the functional copy, Mi-1.2. The chimeric construct Mi-DS3, which encodes the 161 amino-terminal residues from Mi-1.1 fused to the remainder of Mi-1.2, induces localized necrosis when transiently expressed in Nicotiana benthamiana leaves. We produced mutant constructs that exchanged sequences encoding each of the 40 amino acid differences from the Mi-1.1 LRR region into Mi-DS3 and into Mi-1.2. For 23 of the substitutions, necrosis was lost upon transient expression of the mutated Mi-DS3 in N. benthamiana, and nematode resistance was lost when the altered Mi-1.2 was expressed in the tomato roots. One substitution, R961D, failed to give Mi-DS3-induced necrosis, but produced a dominant lethal phenotype when introduced into Mi-1.2. This gain-of-function phenotype was suppressed by co-expression with the amino-terminal region of Mi-1.1, suggesting that residue 961 is critical for negative regulation by the corresponding N-terminal region. Substitutions of Mi-1.1 residues 984-986 retained the ability to cause necrosis in Mi-DS3, but resulted in loss-of-nematode resistance in Mi-1.2, suggesting that these residues are essential for nematode recognition. None of the loss-of-function mutations in Mi-1.2 had a dominant negative phenotype. These results indicate that the Mi-1.2 LRR is involved in regulation of the transmission of the resistance response as well as in recognition of the nematode.

Publication types

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

MeSH terms

  • Amino Acid Motifs
  • Amino Acid Substitution
  • Animals
  • Cell Death
  • Disease Susceptibility
  • Genes, Dominant / genetics
  • Leucine / metabolism*
  • Lycopersicon esculentum / cytology
  • Lycopersicon esculentum / metabolism*
  • Lycopersicon esculentum / parasitology*
  • Mutation
  • Nematoda / physiology*
  • Phenotype
  • Plant Proteins / chemistry*
  • Plant Proteins / genetics
  • Plant Proteins / metabolism*
  • Plant Roots / cytology
  • Plant Roots / metabolism
  • Plant Roots / parasitology
  • Signal Transduction

Substances

  • Plant Proteins
  • Leucine