Molecular evolution and origin of tetraploid Elymus species

It is well known that Elymus arose through hybridization between representatives of different genera and several different polyhaplomic genomes have been described. Cytogenetically, five basic genomes (St, H, Y, P and W) in different combinations have been found in the genus. The vast majority of species are tetraploids and they are characterized by having the StY genome or the StH genome. It is not known where the Y genome originated, although it is a common in Elymus from Central and East Asia. It has been hypothesized from isozymic and cytological studies of Elymus species that the Old and New World taxa may be of separate origin of the H genome in the StH genome species. Data from single copy of nuclear gene RPB2 indicated that the Eurasian and American StH genome species have independent alloploid origins with different H-genome donors. This hypothesis is needed to be tested by using more molecular data. Sequences from single copy of nuclear genes (RPB2, beta-amylase gene and EF-G) indicated that StY genome species is allopolyploid origin. This paper presents a briefly review on current status of molecular evolution and origin of tetraploid Elymus species.