Abstract: Self-incompatibility (SI) is a genetic mechanism of self/non-self pollen recognition to prevent self-fertilization in many flowering plants and, in most cases, this is controlled by a multi-allelic S-locus. S-RNase and S-locus F box (SLF) proteins have been shown to be the female and male determinants of gametophytic self-incompatibility (GSI), respectively, in the Solanaceae, Scrophulariaceae and Rosaceae. Nevertheless, it is thought that additional factors are required for the SI response. Herein, we constructed a mature anther cDNA library from a self-incompatible Petunia hybrida Vilm. line of the S3S3 haplotype. Using AhS2-RNase from Antirrhinum hispanicum as a bait for yeast two-hybrid screening, we found that petunia germinating pollen (PGP) S/D3 was capable of interacting physically with the bait. However, the interaction lacked haplotype specificity. The PGPS/D3 gene is a single copy gene that is expressed in tissues such as the style, ovary, pollen, and leaf. The PGPS/D3::GFP (green fluorescence protein) construct was detected in both the membrane and cytoplasm. The implications of these findings in the operation of S-RNase-based SI are discussed.(Author for correspondence.Tel: 0(10) 6255 2880；Fax: 0(10) 6253 7814； E-mail:ybxue@genetics.ac.cn)

Key words: petunia germinating pollen (PGP) S/D3, Petunia hybrida, self-incompatibility, S-RNase.