Self-incompatibility (SI) is a major obstacle for stable fruit production in fruit trees of Rosaceae. SI of Rosaceae is controlled by the
S locus on which at least two genes, pistil
S and pollen
S, are located. The product of the pistil
S gene is a polymorphic and extracellular ribonuclease, called S-RNase, while that of the pollen
S gene is a protein containing the F-box motif, SFB (
S haplotype-specific F-box protein)/SFBB (
S locus F-box brothers). Recent studies suggested that SI of Rosaceae includes two different systems, i.e.,
Prunus of tribe Amygdaleae exhibits a self-recognition system in which its SFB recognizes self-S-RNase, while tribe Pyreae (
Pyrus and
Malus) shows a non-self-recognition system in which many SFBB proteins are involved in SI, each recognizing subset of non-self-S-RNases. Further biochemical and biological characterization of the
S locus genes, as well as other genes required for SI not located at the
S locus, will help our understanding of the molecular mechanisms, origin, and evolution of SI of Rosaceae, and may provide the basis for breeding of self-compatible fruit tree cultivars.
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