Identification of the pollen determinant in the gametophytic self-incompatibility system through the analysis of self-compatible mutants in Prunus

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This study identifies the pollen determinant (pollen S) of the S-RNase based gametophytic self-incompatibility system utilizing the mutated S haplotypes. Based on the results obtained we have developed the working model for the molecular basis of self-(in)compatibility in Prunus. The summary of the results obtained is as follows.(1)Analysis of the mutated S haplotype in almondComparisons of the S locus region of a mutated Sc-hapotype with the original one identifies S haplotype-specific F-box progein gene (SFB). SFB shows the S haplotype-specific sequence polymorphism and pollen-specific expression, indicating that SFB is a very good candidate for the pollen Sin Prunus.(2)Analysis of self-compatible S haplotypes of cherry and Japanese apricotSf of Japanese apricot and S4' of sweet cherry are known to be the pollen part mutant S haplotypes. Analysis of their S locus regions revealed insertion mutations in SFBs of these S haplotypes. The insertions lead to frame shift to produce truncated transcripts for SFB, which could be the cause of self-compatibility in Sf and S4' haplotypes.(3)Self-(in)compatibility in tetraploid sour cherryIn Solanaceae, which shows the same type of gametophytic self-incompatibility as Prunus, polyploidization generally leads to self-compatibility through the so-called phenomenon, "the competitive interaction". We have analyzed self-(in)compatibility in the progeny of several crosses between several sour cherry cultivars. It appeared that the segregation of self-(in)compatibility is determined by the number of functional and non-functional S haplotypes present in the progeny, suggesting that "the competitive interaction" is absent in Prunus.(4)Working model for the molecular basis of self-(in)compatibility in PrunusBased on the above-described results, we have developed and published the working model for the genetic and molecular basis of self-(in)compatibility in Prunus.