Structural Characterization and Evolutionary Relationship of High-Molecular-Weight Glutenin Subunit Genes in Roegneria nakaii and Roegneria alashanica

The Roegneria of Triticeae is a large genus including about 130 allopolyploid species. Little is known about its high-molecular-weight glutenin subunits (HMW-GSs). Here, we reported six novel HMW-GS genes from R. nakaii and R. alashanica. Sequencing indicated that Rny1, Rny3, and Ray1 possessed intact open reading frames (ORFs), whereas Rny2, Rny4, and Ray2 harbored in-frame stop codons. All of the six genes possessed a similar primary structure to known HMW-GS, while showing some unique characteristics. Their coding regions were significantly shorter than Glu-1 genes in wheat. The amino acid sequences revealed that all of the six genes were intermediate towards the y-type. The phylogenetic analysis showed that the HMW-GSs from species with St, StY, or StH genome(s) clustered in an independent clade, varying from the typical x- and y-type clusters. Thus, the Glu-1 locus in R. nakaii and R. alashanica is a very primitive glutenin locus across evolution. The six genes were phylogenetically split into two groups clustered to different clades, respectively, each of the two clades included the HMW-GSs from species with St (diploid and tetraploid species), StY, and StH genomes. Hence, it is concluded that the six Roegneria HMW-GS genes are from two St genomes undergoing slight differentiation.