Predicting Specificities Under the Non-self Gametophytic Self-Incompatibility Recognition Model.

Non-self gametophytic self-incompatibility (GSI) recognition system is characterized by the presence of multiple F-box genes tandemly located in the -locus, that regulate pollen specificity. This reproductive barrier is present in Solanaceae, Plantaginacea and Maleae (Rosaceae), but only in functional assays have been performed to get insight on how this recognition mechanism works. In this system, each of the encoded -pollen proteins (called SLFs in Solanaceae and Plantaginaceae /SFBBs in Maleae) recognizes and interacts with a sub-set of non-self -pistil proteins, called S-RNases, mediating their ubiquitination and degradation. In there are 17 genes per -haplotype, making impossible to determine experimentally each SLF specificity. Moreover, domain -swapping experiments are unlikely to be performed in large scale to determine -pollen and -pistil specificities. Phylogenetic analyses of the Petunia SLFs and those from two genomes, suggest that diversification of s predate the two genera separation. Here we first identify putative genes from nine and 10 genomes to determine how many gene lineages are present in the three genera, and the rate of origin of new gene lineages. The use of multiple genomes per genera precludes the effect of incompleteness of the genome at the -locus. The similar number of gene lineages in the three genera implies a comparable effective population size for these species, and number of specificities. The rate of origin of new specificities is one per 10 million years. Moreover, here we determine the amino acids positions under positive selection, those involved in SLF specificity recognition, using 10 -haplotypes with more than 11 genes. These 16 amino acid positions account for the differences of self-incompatible (SI) behavior described in the literature. When SLF and S-RNase proteins are divided according to the SI behavior, and the positively selected amino acids classified according to hydrophobicity, charge, polarity and size, we identified fixed differences between SI groups. According to the 3D structure of the two proteins these amino acid positions interact. Therefore, this methodology can be used to infer SLF/S-RNase specificity recognition.