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Specificity determinants and diversification of the Brassica self-incompatibility pollen ligand
- Thanat Chookajorn†,‡,
- Aardra Kachroo†,‡,§,
- Daniel R. Ripoll¶,
- Andrew G. Clark∥, and
- June B. Nasrallah†,††
- †Department of Plant Biology, ¶Computational Biology Service Unit, Cornell Theory Center, and ∥Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853
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Contributed by June B. Nasrallah, October 31, 2003
Abstract
Self-incompatibility in crucifers is effected by allele-specific interactions between the highly polymorphic stigmatic S locus receptor kinase (SRK) and its pollen ligand, the S locus cysteine-rich protein (SCR). Here we show that specificity in SCR function is determined by four contiguous amino acids in one variant, indicating that the minimum sequence requirement for gaining a new specificity can be low. We also provide evidence for an extraordinarily high degree of evolutionary flexibility in SCR, whereby SCR can tolerate extensive amino acid changes within the limits of maintaining the same predicted overall structure. This remarkable adaptability suggests a hypothesis for generation of new self-incompatibility specificities by gradual modification of SRK-SCR affinities and, more generally, for functional specialization within families of homologous ligands and receptors.
Footnotes
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↵ †† To whom correspondence should be addressed. E-mail: jbn2{at}cornell.edu.
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↵ ‡ T.C. and A.K. contributed equally to this work.
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↵ § Present address: Department of Plant Pathology, University of Kentucky, Lexington, KY 40517.
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Abbreviations: SI, self-incompatibility; SRK, S locus receptor kinase; SCR, S locus cysteine-rich protein; eSRK, SRK ectodomain.
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See accompanying Biography on page 909.
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This contribution is part of the special series of Inaugural Articles by members of the National Academy of Sciences elected on April 29, 2003.
- Copyright © 2004, The National Academy of Sciences
