Molecular analysis of PRP8 inteins in the Botrytis genus illustrates a complex evolutionary history

Inteins are rare protein elements that are removed post-translationally from a host protein. This is an autocatalytic splicing process necessary for the maturation of the host protein. In addition to the essential splicing domains, most inteins encode a homing endonuclease (HEG). The HEG enables the intein to spread through the gene pool of a species and potentially to also undergo horizontal transmission to other species. The HEG introduces a highly specific double-stranded DNA break, which triggers the host’s recombinational repair system. During this repair process, the host copies the intein with some of its flanking regions into the previously unoccupied target site. The current model of intein evolution proposes a cycle involving intein invasion, degeneration, loss and re- invasion. We have investigated the evolution of the PRP8 intein within the Botrytis genus. The PRP8 gene sequences of 22 Botrytis species and several closely related genera were investigated. The PRP8 gene of 15 species was occupied by an intein, 6 species carried an empty target allele, and once species was polymorphic for the presence/absence of the intein. Analysis of the intein sequences, their flanking regions and the sequences of the empty target alleles suggest that Botrytis has acquired the intein by horizontal ransmission. We found no evidence of intein degeneration or loss in this genus.