Gene expression polymorphisms and ESTs associated with gravitropic response of subterranean branch meristems and growth habit in Leymus wildryes

Negatively orthogeotropic (NOGT) tiller and diageotropic (DGT) rhizome meristems develop from the same type of lateral axillary meristems and phytomer structure. Although subterranean NOGT and DGT buds appear similar, they display different responses to gravity and perhaps other cues governing branch angle and overall growth habit (GH). Leymus wildryes show remarkable variation in GH and include some of the largest native grasses in western North America. Previous studies detected GH QTLs on homoeologous regions of LG3a and LG3b controlling differences between caespitose Leymus cinereus and rhizomatous Leymus triticoides allotetraploids. Heterologous barley and wheat microarrays in conjunction with bulk segregate analysis were used to find gene expression polymorphisms associated with GH QTLs. Approximately 34% and 25% of the probe sets showed detectable signals on the barley and wheat arrays, respectively. Overall gene expression patterns of NOGT and DGT meristems were remarkably similar, consistent with the assertion that Leymus NOGT and DGT buds develop from homologous meristems. Only 28 and 27 genes on barley and wheat gene chips, respectively, showed more than twofold differential expressions between NOGT and DGT tissues. One expression polymorphism genetically mapped in the Leymus LG3 rhizome QTL region.