Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2008
Publication Date: 6/15/2008
Citation: Kaur, P., Mott, I.W., Larson, S.R., Bushman, B.S., Kim, R.W., Hernandez, A.G., Liu, L., Mikel, M.A. 2008. Gene Expression Polymorphisms and ESTs Associated With Gravitropic Response of Subterranean Branch Meristems and Growth Habit in Leymus Wildryes. Plant Science 175:330-338 Interpretive Summary: Growth habit (GH) in grasses ranges from vigorous rhizomatous spreaders to compact bunch-type. The degree of rhizomatous growth contributes to a plant's ability to establish, persist, and produce biomass. Aggressive rhizome spreading is also an enabling attribute of weedy species such as quackgrass. Previous genetic mapping studies in Basin Wildrye detected Quantitative Trait Loci (QTLs) on Leymus chromosome 3 that control bunch-type and rhizomatous growth. The direction of actively growing underground shoot buds or meristems ultimately determines whether the plant spreads out away from the crown or remains tightly bunched. Both lateral and upward growing underground meristems appear nearly identical, but rely on environmental cues such as gravity to determine which direction to grow. We have used microarray GeneChips designed for wheat and barley to measure differences in gene expression between lateral and upward growing underground stem meristems in Basin Wildrye. These GeneChips have proven valuable in detecting gene expression in this distantly related species. Of the approximately 20,000 genes detected, only 28 and 27 genes on barley and wheat gene chips, respectively, showed more than two fold differential expressions between the two types of meristems. Several of the differentially expressed genes identified have been previously implicated in plant gravitropism. This gene expression study has confirmed that lateral and upward growing underground meristems arise from homologous tissues that have minimal differences in gene expression that in response to gravity regulate the direction of growth.
Technical Abstract: 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 L. cinereus and rhizomatous L. 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 two fold differential expressions between NOGT and DGT tissues. One expression polymorphism genetically mapped in the Leymus LG3 rhizome QTL region.