Direct ligand-receptor complex interaction controls Brassica self-incompatibility.
Many higher plants have evolved self-incompatibility mechanisms to prevent self-fertilization. In Brassica self-incompatibility, recognition between pollen and the stigma is controlled by the S locus, which contains three highly polymorphic genes: S-receptor kinase (SRK), S-locus protein 11 (SP11) (also called S-locus cysteine-rich protein; SCR) and S-locus glycoprotein (SLG). SRK encodes a membrane-spanning serine/threonine kinase that determines the S-haplotype specificity of the stigma, and SP11 encodes a small cysteine-rich protein that determines the S-haplotype specificity of pollen. SP11 is localized in the pollen coat. It is thought that, during self-pollination, SP11 is secreted from the pollen coat and interacts with its cognate SRK in the papilla cell of the stigma to elicit the self-incompatibility response. SLG is a secreted stigma protein that is highly homologous to the SRK extracellular domain. Although it is not required for S-haplotype specificity of the stigma, SLG enhances the self-incompatibility response; however, how this is accomplished remains controversial. Here we show that a single form of SP11 of the S8 haplotype (S8-SP11) stabilized with four intramolecular disulphide bonds specifically binds the stigma membrane of the S8 haplotype to induce autophosphorylation of SRK8, and that SRK8 and SLG8 together form a high-affinity receptor complex for S8-SP11 on the stigma membrane.
Takayama
S
S
Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma 630-0101, Japan.
Shimosato
H
H
Shiba
H
H
Funato
M
M
Che
F S
FS
Watanabe
M
M
Iwano
M
M
Isogai
A
A
D000595:Amino Acid Sequence; D001937:Brassica / Q000235:genetics / Q000502:physiology*; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008024:Ligands; D008861:Microsomes / Q000378:metabolism; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010766:Phosphorylation; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018514:Plant Structures / Q000378:metabolism / Q000502:physiology; D011058:Pollen / Q000502:physiology; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012098:Reproduction
D006023:Glycoproteins; D008024:Ligands; D010940:Plant Proteins; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins; C431526:SP11 protein, Brassica; C064156:self-incompatibility locus specific glycoprotein, Brassica; D011494:Protein Kinases; C079832:S-receptor kinase