Location: Sunflower and Plant Biology Research2011 Annual Report
1a. Objectives (from AD-416)
The specific objectives are 1) to define and clarify biological factors, mechanisms, and pathways that regulate reproduction and dormancy in vegetative propagules of perennial weeds, including, but not limited to leafy spurge (Euphorbia esula) and Canada thistle (Cirsium arvense); and 2) to define and clarify biological factors, mechanisms, and pathways that regulate seed dormancy and germination in weeds, including, but not limited to leafy spurge (Euphorbia esula).
1b. Approach (from AD-416)
Weeds are a major pest leading to reduced production of the nation’s food and fiber crops. They also negatively impact natural ecosystems. Certain characteristics of weeds, such as dormancy of reproductive structures account for their persistence, survival, and ability to escape control methods. Leafy spurge (Euphorbia esula) is a noxious perennial weed in the Northern Great Plains due to its negative impacts in rangeland and natural lands. Similarly, Canada thistle is a serious perennial weed worldwide in many natural and agroecosystems. Leafy spurge displays para-, endo-, and eco-dormancy in underground adventitious crown and root bud, as well as seed dormancy. This project will focus on leafy spurge and utilize Canada thistle for comparative purposes for the investigation of paradormancy. Thus, the project will employ physiological, biochemical, molecular, and genomic approaches to elucidate regulatory mechanisms, signals, and pathways related to dormancy. The long-term goal of this project is to increase fundamental knowledge about dormancy in leafy spurge and other perennial weeds to facilitate development of improved and new weed management strategies.
3. Progress Report
Leafy spurge and Canada thistle are noxious perennial weeds used to investigate dormancy in buds and seeds. We developed a method to investigate vegetative reproduction in Canada thistle and conducted transcriptomic analysis of paradormancy breaking using pyrosequencing, which indicated a role for ABA and auxin in dormancy breaking and stress associated with root sectioning. Canada thistle root sections treated with ABA showed reduced shoot growth and ABA levels peaked about 48 h after sectioning of roots. We have collected Canada thistle tissues for further hormone analyses. Additionally, we have completed the population genetic analysis of Canada thistle collected across North America and Europe. We determined that short-term dehydration-stress and extended cold treatments break endodormancy of leafy spurge crown buds. Microarray analyses identified gene expression patterns common to both treatments and allowed us to separate potential genes and molecular processes specific to endodormancy-break and flowering of leafy spurge. We also continued investigations of the effect of light and temperature on endodormancy induction and flowering, and determined that ramp-down of both was required for endodormancy induction. However, ramp-down in temperature alone was sufficient for plants to respond to a flower-inducing vernalization treatment. These experiments highlighted the importance of AP2/ERF-type transcription factors in endodormancy induction and release. Follow-up on the regulation of these genes during dormancy transitions is being done using RT-qPCR. We are investigating mechanisms through which DORMANCY ASSOCIATED MADS-BOX (DAM) genes regulate dormancy in leafy spurge. The probable target of DAM, FLOWERING LOCUS T (FT), has been cloned and we are investigating direct binding of DAM to the FT promoter. We analyzed microarray data related to the effects of constant and alternating temperature on germinability of leafy spurge seeds and are preparing manuscripts. Transformation of leafy spurge using Agrobacterium and kanamycin selection was unsuccessful; thus, we have initiated research using hygromycin selection. Other experiments in progress relate to the effect of ethylene on dormancy induction and regulation of genes of interest. Pilot studies have been initiated on glyphosate-induced paradormancy release of leafy spurge crown and root buds. We also continued collaboration with university scientists to elucidate global patterns of gene expression related to crop/weed competition and bud dormancy in poplar. Additionally, we prepared a manuscript on map-based cloning of a seed dormancy quantitative trait locus from weedy rice.
1. Cell division regulates dormancy in root buds of leafy spurge. Conventional and organic farmers and ranchers are plagued by perennial weeds. Leafy spurge is a noxious and invasive perennial weed in rangeland, which reproduces and spreads from hundreds of buds on the underground root system. Most of the time root buds are in a quiescent state called dormancy. Dormancy makes control very difficult, because after control measures are applied, regrowth occurs from dormant buds. It is known that dormancy is ultimately caused by blockage of cell division. ARS researchers in Fargo, ND, investigated an important plant cell division protein called CDKF in bud of leafy spurge. They discovered a site in this protein where it can add a phosphate molecule to itself and determined that self-addition of phosphate is crucial for forming complexes with other cell division proteins to ultimately reactivate dormant buds. New knowledge on bud dormancy is critical to improve control of perennial weeds. This research provides new insight into proteins and pathway for cell division and could provide a target for developing next generation weed management strategies.
Fuerst, E.P., Anderson, J.V., Kennedy, A.C., Gallagher, R.S. 2011. Induction of polyphenol oxidase activity in dormant wild oat (Avena fatua) seeds and caryopses: a defense response to seed decay fungi. Weed Science. 59(2):137-144.