title: Specificity determinants and diversification of the Brassica self-incompatibility pollen ligand.
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.
authors.affiliation: Department of Plant Biology, Cornell Theory Center, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Thanat
authors.initials: T
authors.lastname: Chookajorn
authors.forename: Aardra
authors.initials: A
authors.lastname: Kachroo
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Ripoll
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Clark
authors.forename: June B
authors.initials: JB
authors.lastname: Nasrallah
mesh_terms: D000595:Amino Acid Sequence; D001937:Brassica / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010940:Plant Proteins; D011058:Pollen / Q000378:metabolism*; D011487:Protein Conformation; D011494:Protein Kinases / Q000737:chemistry / Q000235:genetics*; D017386:Sequence Homology, Amino Acid
chemical_list: D010940:Plant Proteins; D011494:Protein Kinases; C079832:S-receptor kinase