Poster: Reproductive Development

Abs # 458: Molecular characterization of the solanaceous self-incompatibility (S-) locus

Presenter:	Wang, Yan , yxw130@psu.edu
Authors	Wang, Yan  (A)   Tsukamoto, Tatsuya  (A)   Wang, Xi  (A)   Sijacic, Paja  (A)   McCubbin, Andrew G (B)   Huang, Shihshieh  (C)   Yi, Ki-wan  (A)   Kao, Teh-hui  (A)
Affiliations:	(A): The Pennsylvania State University (B): Washington State University (C): Monsanto Company

The Solanaceae, Rosaceae and Scrophulariaceae possess an RNase-mediated self-incompatibility (SI) mechanism. Two genes at the polymorphic S-locus, the S-RNase gene and the yet unidentified pollen S-gene, control the specificity of the pistil and pollen, respectively, in the SI interaction. To identify the pollen S-gene and characterize the S-locus of Petunia inflata (Solanaceae), we used 13 pollen-expressed S-linked genes as markers to map the S-locus and as probes to isolate BAC clones. From the analysis of 1205 segregating F₂ plants, nine of the markers were found to be tightly linked to the S-locus, and the remaining four were found to show various degrees of recombination. Among the latter four markers, G221 and 3.16 delimit the maximum size of the S-locus. Allelic sequence analysis for 7 of the marker genes revealed that they, unlike the S-RNase gene, exhibited a very low degree of allelic sequence diversity. Chromosome walking from multiple points of the S-locus, as defined by the nine tightly linked markers, has so far resulted in 9 separate contigs, which collectively span more than 4 Mb, suggesting that the solanaceous S-locus is a huge multi-gene complex. A 328-kb region containing the S₂-RNase gene was completely sequenced. Sequence analysis revealed the existence of highly repetitive sequences and retroposons. Among the predicted genes in this region was SLF (for S-Locus F-box Protein), which is located ~160 kb downstream of the S₂-RNase gene. Similar genes have been found in the S-loci of Antirrhinum Hispanicum (Scrophulariaceae) and Prunus dulcis (Rosaceae). The characteristics of SLF suggest that it is a potential candidate for the pollen S-gene, and its function in SI is being examined by a transgenic approach.