Four previously identified Petunia inflata S-locus F-box genes are involved in pollen specificity in self-incompatibility.

Dear Editor, Petunia possesses self-incompatibility (SI), by which pistils reject self-pollen but accept non-self pollen for fertilization (de Nettancourt, 2001; Iwano and Takayama, 2012). Genes that regulate self/non-self recognition between pollen and pistil are located at the highly polymorphic S-locus. An S-haplotype contains the pistil-specific S-RNase gene that regulates pistil specificity (Lee et al., 1994). The first S-locus F-box (SLF) gene was identified in Antirrhinum hispanicum by Lai et al. (2002), and subsequently Sijacic et al. (2004) showed that an SLF gene in P. inflata is involved in pollen specificity. Recently, Kubo et al. (2010) found that multiple, but as yet unknown number of, SLF genes collectively regulate pollen specificity. The collaborative non-self recognition model predicts that for pollen of a given S-haplotype, each SLF interacts with a subset of non-self S-RNases in the cytoplasm of a pollen tube to mediate their ubiquitination and degradation by the 26S proteasome, and that all SLF proteins are required to detoxify a complete suite of non-self S-RNases (Kubo et al., 2010). That pollen specificity is regulated by more than the first SLF gene identified has raised a number of questions concerning the evolution, operation and maintenance of the system (Wang and Kao, 2011). To address these questions, it is essential that all the SLF genes involved in pollen specificity be identified.