Leymus EST linkage maps identify 4NsL-5NsL reciprocal translocation, wheat-Leymus chromosome introgressions, and functionally important gene loci

Allotetraploid (2n = 4x = 28) Leymus triticoides and Leymus cinereus are divergent perennial grasses, which form fertile hybrids. Genetic maps with n = 14 linkage groups (LG) comprised with 1,583 AFLP and 67 heterologous anchor markers were previously used for mapping quantitative trait loci (QTLs) in these hybrids, and chromosomes of other Leymus wildryes have been transferred to wheat. However, identifications of the x = 7 homoeologous groups were tenuous and genetic research has been encumbered by a lack of functional, conserved gene marker sequences. Herein, we mapped 350 simple sequence repeats and 26 putative lignin biosynthesis genes from a new Leymus EST library and constructed one integrated consensus map with 799 markers, including 375 AFLPs and 48 heterologous markers, spanning 2,381 centiMorgans. LG1b and LG6b were reassigned as LG6b* and LG1b*, respectively, and LG4Ns and LG4Xm were inverted so that all 14 linkage groups are aligned to the x = 7 Triticeae chromosomes based on EST alignments to barley and other reference genomes. Amplification of 146 mapped Leymus ESTs representing six of the seven homoeologous groups was shown for 17 wheat-Leymus chromosome introgression lines. Reciprocal translocations between 4L and 5L in both Leymus and Triticum monococcum were aligned to the same regions of Brachypodium chromosome 1. A caffeic acid O-methyltransferase locus aligned to fiber QTL peaks on Leymus LG7a and brown midrib mutations of maize and sorghum. Glaucousness genes on Leymus and wheat chromosome 2 were aligned to the same region of Brachypodium chromosome 5. Markers linked to the S self-incompatibility gene on Leymus LG1a cosegregated with markers on LG2b, possibly cross-linked by gametophytic selection. Homoeologous chromosomes 1 and 2 harbor the S and Z gametophytic self-incompatibility genes of Phalaris, Secale, and Lolium, but the Leymus chromosome-2 self-incompatibility gene aligns to a different region on Brachypodium chromosome 5. Nevertheless, cosegregation of self-incompatibility genes on Leymus presents a powerful system for mapping these loci.