Horizontal Gene Transfer and Recombination in Histone 3 Gene Evolution of Alternaria

Abstract

Evolution of H3 gene was analyzed by comparing H3 gene phylogeny with reference phylogeny constructed by alt a 1, gpd, and ITS sequences in Alternaria and related species. Several H3 gene types defined by intron presence and absence were recovered and distribution of each gene type on the phylogeny was very complex. We postulated four alternative hypotheses to explain the findings: 1) maintenance of different types of H3 gene in a strain with one of them as a major copy and the others as minor copies

2) repeated insertion and deletion of introns during evolution of H3 genes

3) maintenance of multiple copy of the gene in the ancestral species and independent loss of different type of genes in each descendent

4) exchange of genetic materials among strains leading to horizontal transfer of the gene and recombination between different copies of the gene to achieve concerted evolution. Among them, the fourth hypothesis of horizontal gene transfer and recombination was chosen as the most plausible explanation for the evolution of H3 gene in Alternaria and related species. The first hypothesis of maintaining multiple types of H3 gene could explain the multiple PCR bands of radicina species-group and Stemphylium group.