Evolutionary diversification of satellite DNA sequences from Leymus (Poaceae: Triticeae)

The genus Leymus (lymegrass) comprises about 30 polyploid, perennial, temperate grass species in the tribe Triticeae (family Poaceae). Previous studies indicated a large diversity in the Leymus genome, and therefore, the aim of this study was to isolate new repetitive DNA sequences that can be used for differentiating Leymus species and elucidating their genomic relationships. A C0t-1 DNA plasmid library was generated from genomic DNA of American tetraploid species Leymus triticoides . A family of highly repetitive satellite DNA sequences, designated Lt1, was obtained from this library. The Lt1 family consisted of 380 bp SacI repeating units arranging in tandem arrays. A 120 bp MspI subfamily was discovered within this family, indicating that cytosine methylation may have played an important role in the evolution of satellite sequences. The Lt1 satellite was localized in the subtelomeric heterochromatic blocks of L. triticoides chromosomes, which are present on all chromosomes and often on both arms. The Lt1 sequences are abundant in L. triticoides but absent in its closely related species Leymus racemosus . Significant homology was found between the Lt1 family and numerous repetitive sequences from Poaceae species, indicating that the Lt1 is an ancient family of tandemly repeated sequences in grasses.

Molecular genetic linkage maps for allotetraploid Leymus wildryes (Gramineae: Triticeae)

Molecular genetic maps were constructed for two full-sib populations, TTC1 and TTC2, derived from two Leymus triticoides × Leymus cinereus hybrids and one common Leymus triticoides tester. Informative DNA markers were detected using 21 EcoRI–MseI and 17 PstI–MseI AFLP primer combinations, 36 anchored SSR or STS primer pairs, and 9 anchored RFLP probes. The 164-sib TTC1 map includes 1069 AFLP markers and 38 anchor loci in 14 linkage groups spanning 2001 cM. The 170-sib TTC2 map contains 1002 AFLP markers and 36 anchor loci in 14 linkage groups spanning 2066 cM. Some 488 homologous AFLP loci and 24 anchor markers detected in both populations showed similar map order. Thus, 1583 AFLP markers and 50 anchor loci were mapped into 14 linkage groups, which evidently correspond to the 14 chromosomes of allotetraploid Leymus (2n = 4x = 28). Synteny of two or more anchor markers from each of the seven homoeologous wheat and barley chromosomes was detected for 12 of the 14 Leymus linkage groups. Moreover, two distinct sets of genome-specific STS markers were identified in these allotetraploid Leymus species. These Leymus genetic maps and populations will provide a useful system to evaluate the inheritance of functionally important traits of two divergent perennial grass species.Key words: AFLP, perennial grasses, RFLP, STS, SSR.