Origins and chromosome differentiation of Thinopyrum elongatum revealed by PepC, Pgk1 genes and ND-FISH

<i>Thinopyrum elongatum</i> is an important gene pool for wheat genetic improvement. However, the origins of the <i>Thinopyrum</i> genomes and the nature of the genus’ intraspecific relationships are still controversial. In this study, we used single-copy nuclear genes and non-denaturing fluorescence <i>in situ</i> hybridization (ND-FISH) to characterize genome constitution and chromosome differentiation in <i>Th. elongatum</i>. According to phylogenetic analyses based on <i>PepC</i> and <i>Pgk1</i> genes, there was an E genome with three versions (E^e, E^b, E^x) and St genomes in the polyploid <i>Th. elongatum</i>. The ND-FISH results of pSc119.2 and pAs1 revealed that the karyotypes of diploid <i>Th. elongatum</i> and <i>Th. bessarabicum</i> were different and the chromosome differentiation occurred among accessions of the diploid <i>Th. elongatum</i>. In addition, the tetraploid <i>Th. elongatum</i> has two groups of ND-FISH karyotype, indicating that the tetraploid <i>Th. elongatum</i> might be a segmental allotetraploid. In summary, our results suggested that the diploid <i>Th. elongatum</i>, <i>Th. bessarabicum</i> and <i>Pseudoroegneria</i> were the donors of the E^e, E^b and St genome to polyploid <i>Th. elongatum</i> species, respectively.

Roegneria alashanica Keng: a species with the StStStYStY genome constitution

The genome constitution of tetraploid Roegneria alashanica Keng has been in question for a long time. Most scientific studies have suggested that R. alashanica had two versions of the St genome, St1St2, similar to that of Pseudoroegneria elytrigioides (C. Yen & J.L. Yang) B.R. Lu. A study, however, concluded that R. alashanica had the StY genome formula typical for tetraploid species of Roegneria. For the present study, R. alashanica, Elymus longearistatus (Bioss.) Tzvelev (StY genomes), Pseudoroegneria strigosa (M. Bieb.) Á. Löve (St), Pseudoroegneria libanoctica (Hackel) D.R. Dewey (St), and Pseudoroegneria spicata (Pursh) Á. Löve (St) were screened for the Y-genome specific marker B14(F+R)269. All E. longearistatus plants expressed intense bands specific to the Y genome. Only 6 of 10 R. alashanica plants exhibited relatively faint bands for the STS marker. Previously, the genome in species of Pseudoroegneria exhibiting such faint Y-genome specific marker was designated as StY. Based on these results, R. alashanica lacks the Y genome in E. longearistatus but likely possess two remotely related St genomes, St and StY. According to its genome constitution, R. alashanica should be classified in the genus Pseudoroenera and given the new name Pseudoroegneria alashanica (Keng) R.R.-C. Wang and K.B. Jensen.