Six amino acid changes confined to the leucine-rich repeat beta-strand/beta-turn motif determine the difference between the P and P2 rust resistance specificities in flax.
At least six rust resistance specificities (P and P1 to P5) map to the complex P locus in flax. The P2 resistance gene was identified by transposon tagging and transgenic expression. P2 is a member of a small multigene family and encodes a protein with nucleotide binding site (NBS) and leucine-rich repeat (LRR) domains and an N-terminal Toll/interleukin-1 receptor (TIR) homology domain, as well as a C-terminal non-LRR (CNL) domain of approximately 150 amino acids. A related CNL domain was detected in almost half of the predicted Arabidopsis TIR-NBS-LRR sequences, including the RPS4 and RPP1 resistance proteins, and in the tobacco N protein, but not in the flax L and M proteins. Presence or absence of this domain defines two subclasses of TIR-NBS-LRR resistance genes. Truncations of the P2 CNL domain cause loss of function, and evidence for diversifying selection was detected in this domain, suggesting a possible role in specificity determination. A spontaneous rust-susceptible mutant of P2 contained a G-->E amino acid substitution in the GLPL motif, which is conserved in the NBS domains of plant resistance proteins and the animal cell death control proteins APAF-1 and CED4, providing direct evidence for the importance of this motif in resistance gene function. A P2 homologous gene isolated from a flax line expressing the P resistance specificity encodes a protein with only 10 amino acid differences from the P2 protein. Chimeric gene constructs indicate that just six of these amino acid changes, all located within the predicted beta-strand/beta-turn motif of four LRR units, are sufficient to alter P2 to the P specificity.
Dodds
P N
PN
Commonwealth Scientific and Industrial Research Organisation, Plant Industry, GPO Box 1600, Canberra ACT 2601, Australia.
Lawrence
G J
GJ
Ellis
J G
JG
D000483:Alleles; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001483:Base Sequence; D018744:DNA, Plant; D019597:Flax / Q000235:genetics* / Q000382:microbiology; D005658:Fungi / Q000502:physiology*; D020440:Gene Duplication; D006239:Haplotypes; D000090263:Leucine-Rich Repeat Proteins; D008969:Molecular Sequence Data; D009154:Mutation; D030821:Plants, Genetically Modified / Q000235:genetics / Q000382:microbiology; D011506:Proteins / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid
D018744:DNA, Plant; D000090263:Leucine-Rich Repeat Proteins; D011506:Proteins