Rapid evolution of genes in linked to multiple transitions from self-incompatibility to self-compatibility.

The gene family is widespread in eukaryotes, and particular members of this family play critical roles in the gametophytic self-incompatibility (GSI) system in plants. Wild diploid strawberry () species have diversified their sexual systems via self-incompatible and self-compatible traits, yet how these traits evolved in remains elusive. By integrating the published and assembled genomes and the newly generated RNA-seq data, members of the gene family were systematically identified in six species, including three self-incompatible species (, , and ) and three self-compatible species (, , and ). In total, 115 genes were identified in the six genomes and can be classified into three classes (I-III) according to phylogenetic analysis. The identified genes could be divided into 22 homologous gene sets according to amino acid sequence similarity and phylogenetic and syntenic relationships. We found that extensive gene loss and pseudogenization coupled with small-scale duplications mainly accounted for variations in the gene numbers in . Multiple copies of homologous genes were mainly generated from tandem and segmental duplication events. Furthermore, we newly identified five genes in three self-incompatible genomes, including two in , two in , and one in , which fit for typical features of a pistil determinant, including highly pistil-specific expression, highly polymorphic proteins and alkaline isoelectric point (pI), while no genes were found in all three self-compatible species. Surprisingly, these / genes contain at least one large intron (>10 kb). This study revealed that the rapid evolution of / genes within the genus could be associated with its sexual mode, and repeated evolution of the self-compatible traits in was convergent via losses of .