Location: Sunflower and Plant Biology Research2013 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. Leafy spurge is continuing to be developed as a model for understanding seasonal bud dormancy in vegetative propagules of herbaceous plants. We collaborated with UC Riverside Plant Transformation Research Center to develop an efficient DNA transformation system for leafy spurge. UC Riverside lab has completed transformation experiments and shipped potential transgenic plants to Fargo, ND. Transformation will be verified using genomic DNA Blot analysis and the overall protocol verified in Fargo. We have completed Illumina sequencing of four of the eight leafy spurge genomic libraries giving us a current depth of coverage of about 20X. We are currently testing various assembly programs and protocols using this preliminary data to construct genomic contigs containing promoter sequences for expressed and or conserved genes. We have also obtained transgenic poplar clones expressing splice variants of the leafy spurge and a putative poplar DORMANCY ASSOCIATED MADS BOX (DAM) gene. Preliminary results indicate unexpected phenotypes resulting from DAM gene expression, and we are in the process of investigating the changes in gene expression resulting from the transformed constructs. We have also completed experiments and initial analysis of the diurnal regulation of both DAM and FLOWERING LOCUS T (FT) in leafy spurge and the impact of dormancy-inducing conditions on the expression of this diurnal pattern of expression. We completed various experiments including ethylene measurement, ACC oxidase activities, immunoblot analysis, and imunolocalization. A manuscript is in preparation on the results which showed that ACC oxidase levels and activities increase during paradormancy release, and ethylene appears to be synthesized in young cells of growing buds. We are comparing transcriptomes between leafy spurge buds and seeds during dormancy development and release to gain new insights on molecular mechanisms of dormancy by examining the expression levels of over 200 growth-related genes using qRT-PCR. The same gene set and techniques are being used to examine the effect of glyphosate on gene expression in crown buds of leafy spurge before and after decapitation. Associated with these glyphosate studies, we are examining the level of selected hormone in shoots and buds. A manuscript is in preparation that reports an impact of dehydration on induction of endodormancy as determined by exposure of leafy spurge plants to severe dehydration. A final manuscript was prepared and published on the population genetics of Canada thistle. We completed analysis of BAC clones containing DAM, FT, and DREB genes, and identified conserved sequences that likely play a role in expression of these genes. A final manuscript has been published. Finally, collaborative studies are underway to determine 1) temperature effects on afterripening in wild and domesticated sunflower seeds, 2) genomic and physiological aspects blackleg and sclerotinia disease of sunflower and canola, 3) the basis for seed shattering in canola, and 4) to investigate crop-weed interactions.
1. Population genetics of Canada thistle. Canada thistle is a noxious perennial weed that invades natural- and agro-ecosystems. Biological control efforts languish because there is insufficient information on the origin and relatedness of this weed to native and endangered thistles. ARS scientists in Fargo, ND, and Montpellier, France and university partners in British Columbia, Canada, collected populations of thistles across the North America, Europe, and parts of Asia and examined the genetic diversity and phylogeny of Canada thistle and native thistles in the U.S. They showed that insect biological control agents do not associate with host phylogenetic lines within the Cirsium-Cardueae clade, demonstrated that Canada thistle has not yet interbred with any closely-related species in the U.S, and established the invasion pathways of Canada thistle from Eurasia to the U.S. This research provides a comprehensive framework to rationally evaluate the potential for biological control of Canada thistle in relation to its genetic variability across the native and introduced ranges.
2. Mechanisms of weed-induced yield losses identified. Weeds reduce crop yields and quality. Studies have consistently demonstrated that yield reductions are not due to direct competition for environmental resources in modern, high-input, agricultural systems. Instead, weeds appear to induce developmental programs such as shade avoidance in the crop that result in reduced yield. Shade avoidance is advantageous in nature where plants compete for limited resources, but is detrimental in agricultural settings where resources are rarely limiting. ARS scientists in Fargo, ND, and Stoneville, MS, in collaboration with university partners in South Dakota, have demonstrated that weeds cause reduced expression of photosynthesis genes in corn rather than genes associated with shade avoidance. Additionally, they identified some specific genes in the crop that respond to weed pressure, which helps identify specific signals from weeds that cause the negative developmental changes in crops.
Guggisberg, A., Welk, E., Sforza, R., Horvath, D.P., Anderson, J.V., Foley, M.E., Rieseberg, L.H. 2012. Invasion history of North American Canada thistle, Cirsium arvense. Journal of Biogeography. 39:1919-1931.