Stowaway MITEs in Hordeum (Poaceae): evolutionary history, ancestral elements and classification

Given the lack of direct observational data relating to transposition of Stowaway miniature inverted repeat transposable elements, phylogenetic methods may provide a means of generating data that adds to our knowledge of these elements. In a phylogenetic framework the evolutionary history of homologous elements may be traced, and the nucleotide sequence of elements at or close to the time of insertion can be reconstructed. Based on a phylogeny of the diploid species of the genus Hordeum we explore evolutionary aspects of four non-homologous groups of Stowaway elements inserted into three nuclear genes: nucellin, xylose isomerase, and barley leucine zipper 1. The data illustrate how elements starting from a high degree of sequence similarity between terminal inverted repeat regions gradually degrade, and confirm previous notions about preferential insertion at particular TA target sites. It is shown how creation of consensus sequences as estimates of ancestral elements may be positively misleading. The Stowaway family of transposable elements is often further divided into subfamilies based on sequence similarity between elements. Sequence similarity data from the elements discovered in the xylose isomerase gene, and other elements found through BLAST searches in GenBank, reveal inconsistency in the rules used for classification. In order to reflect natural groups, a classification of transposable elements must be based on phylogenetic evidence rather than raw similarity. © The Willi Hennig Society 2009.