Induced and spontaneous self-compatible mutants as tools for the study of self-incompatibility systems and as genetic resources for breeding in fruit crops of Rosaceae

Abstract

Most of the important fruit crops in Rosaceae exhibit S-RNase-based self-incompatibility （SI） that is gametophytically controlled by a multigene complex, the S-locus.　The S haplotype-specific recognition systems of the Rosaceae were investigated through genetic and molecular characterization of self-compatible （SC） mutants.　These analyses revealed that S-RNase genes were indispensable for a stylar self-incompatible response in all members of the Rosaceae studied to date.　In contrast, the pollen factors are currently classified into two different types.　In Prunus, such as apricot and sweet cherry, there is a single functional F-box protein called SLF or SFB that is predicted to recognize self S-RNase, because almost all pollen-part self-compatible mutants （PPMs） analyzed had lost SLF/SFB.　In the Pyrinae, including apple and pear, there are multiple S-related F-box proteins that are postulated to recognize non-self S-RNase, whereas no PPMs with an altered S haplotype had been discovered.　Recently, our group developed a PPM of Japanese pear, which was identified from among male-derived progeny of a gamma-irradiated tree.　Here, I summarize the theoretical and practical contributions of known SC mutants and introduce the genetic and phenotypic basis of self-compatibility in the newly obtained mutant that will be valuable for the breeding of SC cultivars and further investigation of the mechanisms of regulation and function of SI in Rosaceae.