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Plant Cell. 2001 Jan;13(1):163-78.

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.

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  • 1Commonwealth Scientific and Industrial Research Organisation, Plant Industry, GPO Box 1600, Canberra ACT 2601, Australia.

Abstract

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.

PMID:
11158537
[PubMed - indexed for MEDLINE]
PMCID:
PMC102207
Free PMC Article

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