The S-LOCUS CYSTEINE-RICH PROTEIN (SCR): A Small Peptide with A High Impact on the Evolution of Flowering Plants
Self-incompatibility (SI) is an archetypal cell-to-cell communication system in which self-pollen is rejected to prevent inbreeding. In crucifers (or Brassicaceae family), the pollen SI determinant is a small peptide, the S-LOCUS CYSTEINE-RICH PROTEIN (SCR, also known as SP11). During self-pollination, SCR binds to the extracellular domain of its cognate stigmatic receptor, the S-LOCUS RECEPTOR KINASE (SRK). This initiates a signaling cascade leading to self-pollen inhibition. The genes encoding both SI determinants are tightly linked in a multiallelic genomic region defined as the S-locus. Among S alleles, SCR shows extreme variability, and few residues in the protein have been reported to be critical for its specificity. In a heterozygous situation, SCR alleles display complex dominance relationships based on the silencing of certain SCR genes. This chapter provides a summary of the role of SCR in SI, the relationships between SCR alleles, and the role SCR loss played in the model plant Arabidopsis thaliana.
KeywordsPollen Tube Tapetal Cell Dominance Relationship Anther Development Pollen Coat
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