We previously identified both self-incompatible and self-compatible plants in a natural population of self-incompatible Petunia axillaris subsp. axillaris, and found that all the self-compatible plants studied carried either S C1- or S C2-haplotype. Genetic crosses showed that S C2 was identical to S 17 identified from another natural population of P. axillaris, except that its pollen function was defective, and that the pollen-part mutation in S C2 was tightly linked to the S-locus. Recent identification of the S-locus F-box gene (SLF) as the gene that controls pollen specificity in S-RNase-based self-incompatibility has prompted us to examine the molecular basis of this pollen-part mutation. We cloned and sequenced the S 17-allele of SLF of P.axillaris, named PaSLF 17, and found that S C2 S C2 plants contained extra restriction fragments that hybridized to PaSLF 17 in addition to all of those observed in S 17 S 17 plants. Moreover, these additional fragments co-segregated with S C2. We used the S C2-specific restriction fragments as templates to clone an allele of PaSLF by PCR. To determine the identity of this allele, named PaSLF x , primers based on its sequence were used to amplify PaSLFalleles from genomic DNA of 40 S-homozygotes of P. axillaris, S 1 S 1 through S 40 S 40. Sequence comparison revealed that PaSLF x was completely identical with PaSLF 19 obtained from S 19 S 19. We conclude that the S-locus of S C2 contained both S 17-allele and the duplicated S 19-allele of PaSLF. S C2 is the first naturally occurring pollen-part mutation of a solanaceous species that was shown to be associated with duplication of the pollen S. This finding lends support to the proposal, based on studies of irradiation-generated pollen-part mutants of solanaceous species, that duplication, but not deletion, of the pollen S, causes breakdown of pollen function.
- Duplication of S-locus F-box gene
- Petunia axillaris
- Pollen-part self-compatible mutant