The evolutionary dynamics of self-incompatibility systems.
Self-incompatible flowering plants reject pollen that expresses the same mating specificity as the pistil (female reproductive tract). In most plant families, pollen and pistil mating specificities segregate as a single locus, the S locus. In at least two self-incompatibility systems, distinct pollen and pistil specificity genes are embedded in an extensive nonrecombining tract. To facilitate consideration of how new S locus specificities arise in systems with distinct pollen and pistil genes, we present a graphical model for the generation of hypotheses. It incorporates the evolutionary principle that nonreciprocal siring success (cross-pollinations between two plants produce seeds in only one direction) tends to favor the rejecting partner. This model suggests that selection within S-allele specificity classes could accelerate the rate of nonsynonymous (amino acid-changing) substitutions, with periodic selective sweeps removing segregating variation within classes. Accelerated substitution within specificity classes could also promote the origin of new S-allele specificities.
Newbigin
Ed
E
School of Botany, University of Melbourne, Victoria 3010, Australia.
Uyenoyama
Marcy K
MK
D000483:Alleles; D019143:Evolution, Molecular; D035264:Flowers / Q000235:genetics; D008957:Models, Genetic; D010944:Plants / Q000235:genetics*; D011058:Pollen / Q000235:genetics; D012098:Reproduction; D015398:Signal Transduction