Comparative analysis of the self-incompatibility (S-) locus region of Prunus mume: identification of a pollen-expressed F-box gene with allelic diversity.
BACKGROUND
Self-incompatibility (SI) in the Solanaceae, Rosaceae and Scrophulariaceae is gametophytically controlled by a single polymorphic locus, termed the S-locus. To date, the only known S-locus product is a polymorphic ribonuclease, termed S-RNase, which is secreted by stylar tissue and thought to act as a cytotoxin that degrades the RNA of incompatible pollen tubes. However, understanding how S-RNase causes S-haplotype specific inhibition of pollen tubes has been hampered by the lack of a cloned pollen S-determinant gene.


RESULTS
To identify the pollen S-determinant gene, we investigated the genomic structure of the S-locus region of the S1- and S7-haplotypes of Prunus mume (Japanese apricot), and identified 13 genes around the S-RNase gene. Among them, only one F-box gene, termed SLF (S-locus F-box), fulfilled the conditions for a pollen S-determinant gene: (i) together with the S-RNase gene, it is located within the highly divergent genomic region of the S-locus, (ii) it exhibits S-haplotype specific diversity among three analysed S-haplotypes, and (iii) it is specifically expressed in pollen, but not in the styles or leaves.


CONCLUSIONS
The results indicate that SLF is a prime candidate for the pollen S-determinant gene of SI.
Entani
Tetsuyuki
T
Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma 630-0101, Japan.
Iwano
Megumi
M
Shiba
Hiroshi
H
Che
Fang-Sik
FS
Isogai
Akira
A
Takayama
Seiji
S
D000595:Amino Acid Sequence; D014644:Genetic Variation; D008969:Molecular Sequence Data; D011058:Pollen / Q000235:genetics; D027861:Prunus / Q000201:enzymology / Q000235:genetics*; D012260:Ribonucleases / Q000235:genetics; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
D012260:Ribonucleases