Molecular phylogeny and reticulate origins of several American polyploid Hordeum species

Abstract

The phylogeny of diploid species in the genus Hordeum has been studied intensively. Although the origin of American polyploid species has been analyzed using multiple-copy internal transcribed spacer sequences, the origins of these species in Hordeum remain unclear. The objectives of our study were to elucidate the origins of American polyploid species and to explore phylogenetic relationships of these polyploids to diploid Hordeum and other diploid species in Triticeae using a single copy of a nuclear gene, disrupted meiotic cDNA1 (DMC1). DMC1 sequences from nine Hordeum polyploid species were analyzed. Sequence comparisons revealed that one copy of sequences from polyploid species Hordeum fuegianum , Hordeum jubatum , and Hordeum tetraploidum showed a 82 bp miniature inverted-repeat terminal element (MITE) (Stowaway) insertion, which was also detected in the Triticeae diploid species Australopyrum species (W genome) and Taeniatherum caput-medusae (Ta genome). Maximum parsimony and Bayesian analysis suggested that diploid Hordeum brachyantherum subsp. californicum is one ancestor of polyploids Hordeum arizonicum , H. brachyantherum subsp. brachyantherum , Hordeum depressum , and Hordeum procerum . The other ancestor of tetraploid H. depressum is probably Hordeum euclaston . Hordeum cordobense was suggested to be one of the genome donors to hexaploid H. procerum. The diploid Hordeum flexuosum and tetraploid H. tetraploidum were suggested as the parents to hexaploid species Hordeum parodii . The result is that one sequence from each of three Hordeum tetrapolyploids, including H. fuegianum, H. jubatum, and H. tetraploidum, and one from Hordeum hexaploid H. arizonicum fall outside the Hordeum clade of the DMC1 phylogenetic tree, therefore representing another example of complex evolutionary history. Our data may shed light on future phylogenetic studies in Triticeae, especially for the polyploids, by broadening the scope of investigations through sampling more genome types in Poaceae, not only from the tribe Triticeae.