Genetic control of rhizomes and genomic localization of a major-effect growth habit QTL in perennial wildrye

Authors: YUN, LAN - Inner Mongolian Agriculture University; Larson, Steven; Mott, Ivan; Jensen, Kevin; Staub, Jack

Submitted to: Molecular Genetics and Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2014
Publication Date: 6/10/2014
Citation: Yun, L., Larson, S.R., Mott, I.W., Jensen, K.B., Staub, J.E. 2014. Genetic control of rhizomes and genomic localization of a major-effect growth habit QTL in perennial wildrye. Molecular Genetics and Genomics. 289:383-397.

Interpretive Summary: Underground rhizome stems facilitate vegetative dispersal, survival, and regrowth of perennial grasses. Developmental differences between upright, prostrate, and subterranean stems probably involve hormone-mediated responses to gravity or light, but genetic mechanisms controlling these differences have not been elucidated. The chromosome location of genes controlling rhizome spreading were analyzed in experimental families derived from hybrids between rhizomatous creeping wildrye and non-rhizomatous basin wildrye, which are perennial relatives of wheat, barley, and cereal rye. Two recessive genes, one dominant gene, and one very strong additive-effect gene were detected. The dominant wildrye rhizome gene was located in the same chromosome region as the "Rhz3" rhizome gene of perennial rice and perennial sorghum. The most prominent rhizome gene of perennial wildrye was mapped to a chromosome region containing no more than 106 genes in the Brachypodium grass genome DNA reference sequence, including one particularly important hormone signal factor gene, "IAA10". This "IAA10" hormone signaling gene was expressed in the rhizomes of perennial wildrye and provides a theoretical link to the subterranean growth pattern grass rhizomes. These experimental materials and results provide a useful genetic model for rhizome development in grasses including valuable forage, range, and turf grasses and problematic weeds such as quackgrass.

Technical Abstract: Subterranean rhizome branches facilitate vegetative dispersal, survival, and regrowth of perennial grasses. Developmental differences between upright, prostrate, and subterranean stem branching patterns may involve auxin-mediated responses to gravity or light, but genetic mechanisms controlling these differences have not been elucidated. Quantitative trait loci (QTLs) controlling rhizome spreading were compared in reciprocal pseudo-backcross populations derived from hybrids of rhizomatous creeping wildrye (Leymus triticoides) and caespitose basin wildrye (Leymus cinereus), which are perennial relatives of wheat, barley, and cereal rye. Two recessive rhizome QTLs were unique to the creeping wildrye backcross, one dominant rhizome QTL was unique to the basin wildrye backcross, and one major-effect QTL was detectable in both reciprocal backcrosses with high log odds (LOD=33.6) in the basin wildrye background. A dominant rhizome QTL (LOD=11.1) located on Leymus linkage group (LG) 2a was aligned to the Rhz3 orthogene of perennial rice (Oryza longistamina) and perennial sorghum (Sorghum propinquum). The 3-LOD peak interval for the major-effect additive QTL was mapped to a 3.8-cM interval on the disal end of Leymus LG 6aL, which aligned to a 0.7-Mb region of Brachypodium Chromosome 3 containing 106 genes. Six markers cosegregated with the QTL peak, including an Aux/IAA auxin signal factor gene that was expressed in Leymus rhizome meristems and provides a plausible link to the gravitropic and aphototropic behavior of subterranean rhizomes. These experimental materials and results provide a useful genetic model for rhizome development in temperate grasses including valuable forage, range, and turf grasses and problematic weeds such as quackgrass (Elymus repens).